Federal Register, Volume 81 Issue 157 (Monday, August 15, 2016)

[Federal Register Volume 81, Number 157 (Monday, August 15, 2016)]
[Rules and Regulations]
[Pages 54422-54475]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-18399]

[[Page 54421]]

Vol. 81

Monday,

No. 157

August 15, 2016

Part V

Environmental Protection Agency

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40 CFR Parts 87 and 1068

Finding That Greenhouse Gas Emissions From Aircraft Cause or Contribute
to Air Pollution That May Reasonably Be Anticipated To Endanger Public
Health and Welfare; Final Rule

Federal Register / Vol. 81 , No. 157 / Monday, August 15, 2016 /
Rules and Regulations

[[Page 54422]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 87 and 1068

[EPA-HQ-OAR-2014-0828; FRL-9950-15-OAR]
RIN 2060-AS31

Finding That Greenhouse Gas Emissions From Aircraft Cause or
Contribute to Air Pollution That May Reasonably Be Anticipated To
Endanger Public Health and Welfare

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: In this action, the Administrator finds that elevated
concentrations of greenhouse gases in the atmosphere endanger the
public health and welfare of current and future generations within the
meaning of section 231(a)(2)(A) of the Clean Air Act (CAA, or Act). She
makes this finding specifically with respect to the same six well-mixed
greenhouse gases--carbon dioxide (CO2), methane, nitrous
oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride--
that together were defined as the air pollution in the 2009
Endangerment Finding under section 202(a) of the CAA and that together
constitute the primary cause of the climate change problem. The
Administrator also finds that emissions of those six well-mixed
greenhouse gases from certain classes of engines used in certain
aircraft are contributing to the air pollution--the aggregate group of
the same six greenhouse gases--that endangers public health and welfare
under CAA section 231(a)(2)(A).

DATES: These findings are effective on September 14, 2016.

ADDRESSES: The EPA has established a docket for this rulemaking under
Docket ID No. EPA-HQ-OAR-2014-0828. All documents in the docket are
listed in the www.regulations.gov Web site. Although listed in the
index, some information is not publicly available, e.g., confidential
business information (CBI) or other information whose disclosure is
restricted by statute. Certain other material, such as copyrighted
material, is not placed on the Internet and will be publicly available
only in hard copy in the EPA's docket. Publicly available docket
materials are available either electronically in www.regulations.gov or
in hard copy at the Air and Radiation Docket and Information Center,
EPA/DC, EPA WJC West, Room 3334, 1301 Constitution Ave. NW.,
Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30
p.m., Monday through Friday, excluding legal holidays. The telephone
number for the Public Reading Room is (202) 566-1744, and the telephone
number for the Air Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Lesley Jantarasami, Office of
Atmospheric Programs, Climate Change Division, Environmental Protection
Agency, 1200 Pennsylvania Ave. NW., Mail Code 6207-A, Washington, DC
20460; Telephone number: (202) 343-9990; Email address:
ghgendangerment@epa.gov. For additional information regarding these
final findings, please go to the Web site http://www3.epa.gov/otaq/climate/regs-aviation.htm.

SUPPLEMENTARY INFORMATION:

Judicial Review

Under CAA section 307(b)(1), judicial review of this final action
is available only by filing a petition for review in the U.S. Court of
Appeals for the District of Columbia Circuit by October 14, 2016. This
final action is a nationally applicable action because it triggers the
EPA's statutory duty to promulgate aircraft engine emission standards
under CAA section 231, which are nationally applicable regulations and
for which judicial review will be available only in the U.S. Court of
Appeals for the District of Columbia Circuit. In the alternative, even
if this action were considered to be only locally or regionally
applicable, the Administrator determines that it has nationwide scope
and effect within the meaning of CAA section 307(b)(1) both because of
the obligation to establish standards under CAA section 231 that it
triggers and because it concerns risks from GHG pollution and
contributions to such pollution that occur across the nation. Under CAA
section 307(d)(7)(B), only an objection to this final action that was
raised with reasonable specificity during the period for public comment
can be raised during judicial review. This section also provides a
mechanism for us to convene a proceeding for reconsideration, ``[i]f
the person raising an objection can demonstrate to [EPA] that it was
impracticable to raise such objection within [the period for public
comment] or if the grounds for such objection arose after the period
for public comment (but within the time specified for judicial review)
and if such objection is of central relevance to the outcome of this
rule.'' Any person seeking to make such a demonstration to us should
submit a Petition for Reconsideration to the Office of the
Administrator, Environmental Protection Agency, Room 3000, William
Jefferson Clinton Building, 1200 Pennsylvania Ave. NW., Washington, DC
20460, with a copy to the person listed in the preceding FOR FURTHER
INFORMATION CONTACT section, and the Associate General Counsel for the
Air and Radiation Law Office, Office of General Counsel (Mail Code
2344-A) Environmental Protection Agency, 1200 Pennsylvania Ave. NW.,
Washington, DC 20460.

Table of Contents

I. General Information
A. Does this action apply to me?
II. Introduction: Overview and Context for This Final Action
A. Summary
B. Background Information Helpful To Understanding This Final
Action
C. The EPA's Responsibilities Under the Clean Air Act
D. U.S. Aircraft Regulations and the International Community
III. Legal Framework for This Action
A. Section 231(a)(2)(A)--Endangerment and Cause or Contribute
B. Air Pollutant, Public Health and Welfare
IV. The Administrator's Finding Under CAA Section 231 That
Greenhouse Gases Endanger Public Health and Welfare
A. The Science Upon Which the Agency Relied
B. The Air Pollution Consists of Six Key Well-Mixed Greenhouse
Gases
C. The Air Pollution Is Reasonably Anticipated To Endanger Both
Public Health and Welfare
D. Summary of the Administrator's Endangerment Finding Under CAA
Section 231
V. The Administrator's Cause or Contribute Finding for Greenhouse
Gases Emitted by Certain Classes of Engines Used by Covered Aircraft
Under CAA Section 231
A. The Air Pollutant
B. The Administrator's Finding Under CAA Section 231(a)(2)(A)
That Greenhouse Gas Emissions From Certain Classes of Aircraft
Engines Used in Certain Aircraft Cause or Contribute to Air
Pollution That May Be Reasonably Anticipated To Endanger Public
Health and Welfare
C. Response to Key Comments on the Administrator's Cause or
Contribute Finding
VI. Statutory Authority and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
B. Paperwork Reduction Act (PRA)
C. Regulatory Flexibility Act (RFA)
D. Unfunded Mandates Reform Act (UMRA)
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks

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H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
I. National Technology Transfer and Advancement Act (NTTAA)
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
K. Congressional Review Act (CRA)
L. Determination Under Section 307(d)
VII. Statutory Provisions and Legal Authority

I. General Information

A. Does this action apply to me?

These final findings trigger new duties that apply to the EPA but
do not themselves apply new requirements to other entities outside the
federal government. Specifically, in issuing these final findings that
emissions of the six well-mixed GHGs from certain classes of engines
used in certain aircraft cause or contribute to air pollution which may
reasonably be anticipated to endanger public health or welfare, the EPA
becomes subject to a duty under CAA section 231 to propose and
promulgate aircraft engine emission standards applicable to emissions
of that air pollutant from those classes of engines. We are
anticipating indicating an expected timeline for proposed GHG emission
standards for the classes of aircraft engines included in the
contribution finding in EPA's Unified Agenda of Federal Regulatory and
Deregulatory Actions. Only those future standards will apply to and
have an effect on other entities outside the federal government.
Entities potentially interested in this final action include those that
manufacture and sell aircraft engines and aircraft in the United
States. Categories that may be regulated in a future regulatory action
include:
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\1\ Manufacturers of new aircraft engines refers to
manufacturers of new type engines and in-production engines, and
manufacturers of new aircraft refers to manufacturers of new type
aircraft and in-production aircraft.

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Examples of Potentially Affected
Category NAICS \a\ Code SIC \b\ Code Entities \1\
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Industry................................... 3364412 3724 Manufacturers of new aircraft
engines.
Industry................................... 336411 3721 Manufacturers of new aircraft.
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\a\ North American Industry Classification System (NAICS).
\b\ Standard Industrial Classification (SIC) code.

This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be interested in this
final action. This table lists the types of entities that the EPA is
now aware could potentially have an interest in this final action. By
issuing these final findings under CAA section 231(a)(2)(A) regarding
emissions of greenhouse gases from aircraft engines, the EPA is now
required to undertake a separate notice and comment rulemaking to
propose and issue emission standards applicable to greenhouse gas
emissions from the classes of aircraft engines subject to the findings,
and the Federal Aviation Administration (FAA) is to prescribe
regulations to ensure compliance with EPA's future emissions standards
pursuant to CAA section 232. Other types of entities not listed in the
table could also be interested and potentially affected by subsequent
actions at some future time. If you have any questions regarding the
scope of this final action, consult the person listed in the preceding
FOR FURTHER INFORMATION CONTACT section.

II. Introduction: Overview and Context for This Final Action

A. Summary

Pursuant to CAA section 231(a)(2)(A), the Administrator finds that
emissions of the six well-mixed \2\ greenhouse gases (GHGs) from
certain classes of aircraft engines used in certain types of aircraft
(referred to interchangeably as ``covered aircraft'' or ``US covered
aircraft'' throughout this document) contribute to air pollution that
may reasonably be anticipated to endanger the public health and welfare
of current and future generations. This final action follows the
Administrator's proposed findings,\3\ and responds to public comments
submitted to the EPA following that proposal. It is based on careful
consideration of the scientific evidence, as well as a thorough review
of the public comments. In light of the large number of comments
received and overlap between many comments, EPA has not responded to
each comment individually. Instead, EPA has summarized and provided
responses to each significant argument, assertion and question
contained within the totality of these comments. Covered aircraft are
those aircraft to which the International Civil Aviation Organization
(ICAO) has agreed the recently recommended international CO2
standard will apply \4\: Subsonic jet aircraft with a maximum takeoff
mass (MTOM) greater than 5,700 kilograms and subsonic propeller-driven
(e.g., turboprop) aircraft with a MTOM greater than 8,618 kilograms.
Examples of covered aircraft include smaller jet aircraft such as the
Cessna Citation CJ3+ and the Embraer E170, up to and including the
largest commercial jet aircraft--the Airbus A380 and the Boeing 747.
Other examples of covered aircraft include larger turboprop aircraft,
such as the ATR 72 and the Bombardier Q400.
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\2\ The term ``well-mixed GHGs''--used both in the definition of
``air pollution'' in the endangerment finding and in the definition
of ``air pollutant'' in the cause or contribute finding--is based on
the fact that these gases are sufficiently long lived in the
atmosphere such that, once emitted, concentrations of each gas
become well mixed throughout the entire global atmosphere. These
shared attributes are one of five primary reasons that the EPA
considers the six gases as an aggregate group rather than as
individual gases. See section IV.B for more information on the
definition of ``air pollution'' and section V.A for more information
on the definition of the ``air pollutant.''
\3\ U.S. EPA, 2015: Proposed Finding That Greenhouse Gas
Emissions From Aircraft Cause or Contribute To Air Pollution That
May Reasonably Be Anticipated To Endanger Public Health and Welfare
and Advance Notice of Proposed Rulemaking; Proposed Rule, 80 Federal
Register (FR) 37758 (July 1, 2015).
\4\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for the
Aeroplane CO2 Emissions Standards, Circular (Cir) 337, 40 pp, AN/
192, Available at: http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed May 9, 2016). The ICAO Circular 337
is found on page 87 of the catalog and is copyright protected; Order
No. CIR337.
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In this final action, the EPA is informed by and places
considerable weight on the extensive scientific and technical evidence
in the record supporting the 2009 Endangerment and Cause or Contribute
Findings under CAA section 202(a) (hereafter, collectively referred to
as the 2009 Endangerment Finding).\5\ This includes the major, peer-
reviewed scientific assessments that were used to address the question
of whether elevated concentrations of GHGs in the

[[Page 54424]]

atmosphere endanger public health and welfare under CAA section 202(a),
as well as the analytical framework and conclusions upon which the EPA
relied in making that finding. The Administrator's view is that the
body of scientific evidence amassed in the record for the 2009
Endangerment Finding also compellingly supports an endangerment finding
under CAA section 231(a)(2)(A). Furthermore, this finding under section
231(a)(2)(A) reflects the EPA's careful consideration not only of the
scientific and technical record for the 2009 Endangerment Finding, but
also of science assessments released since 2009, which, as illustrated
below, strengthen and further support the judgment that GHGs in the
atmosphere may reasonably be anticipated to endanger the public health
and welfare of current and future generations. No information or
assessments published since late 2009 suggest that it would be
reasonable for the EPA to now reach a different or contrary conclusion
for purposes of CAA section 231(a)(2)(A) than the Agency reached for
purposes of section 202(a).
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\5\ U.S. EPA, 2009: Endangerment and Cause or Contribute
Findings for Greenhouse Gases Under Section 202(a) of the Clean Air
Act; Final Rule, 74 FR 66496 (December 15, 2009).
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The Administrator defines the ``air pollution'' referred to in
section 231(a)(2)(A) of the CAA to be the combined mix of
CO2, methane, nitrous oxide, hydrofluorocarbons,
perfluorocarbons, and sulfur hexafluoride (henceforth the six ``well-
mixed GHGs''). This is the same definition that was used for the
finding for purposes of section 202(a). It is the Administrator's
judgment that the total body of scientific evidence compellingly
supports a positive endangerment finding that elevated concentrations
of the six well-mixed GHGs constitute air pollution that endangers both
the public health and welfare of current and future generations within
the meaning of CAA section 231(a)(2)(A). The Administrator is not at
this time making a finding regarding whether other substances emitted
from aircraft engines cause or contribute to air pollution which may
reasonably be anticipated to endanger public health or welfare.
Under CAA section 231(a)(2)(A), the Administrator must also
determine whether emissions of any air pollutant from a class or
classes of aircraft engines cause or contribute to the air pollution
that may reasonably be anticipated to endanger public health or
welfare. Following the rationale outlined in the 2009 Endangerment
Finding, the Administrator in this action is using the same definition
of the air pollutant as was used for purposes of section 202(a) for
purposes of making the cause or contribute determination under section
231(a)(2)(A)--that is, the aggregate group of the same six well-mixed
GHGs. With respect to this pollutant, based on the data summarized in
section V.B, the Administrator finds that emissions of the six well-
mixed GHGs from aircraft engines used in covered aircraft contribute to
the air pollution that endangers public health and welfare under
section 231(a)(2)(A). The Administrator is not at this time making a
cause or contribute finding regarding GHG emissions, or emissions of
other substances, from engines used in non-covered aircraft.
The Administrator's final findings come in response to a citizen
petition submitted by Friends of the Earth, Oceana, the Center for
Biological Diversity, and Earthjustice (Petitioners) requesting that
the EPA issue an endangerment finding and standards under CAA section
231(a)(2)(A) for the GHG emissions from aircraft. Further, the EPA
anticipates that the 39th ICAO Assembly will approve a final
CO2 emissions standard in October 2016, and that
subsequently, ICAO will formally adopt the final CO2
emissions standard in March 2017. These final endangerment and cause or
contribute findings for aircraft engine GHG emissions are also part of
preparing for a subsequent domestic rulemaking process under CAA
section 231. If an international standard is approved and finalized by
ICAO, member states that wish to use aircraft in international
transportation will then be required under the Chicago Convention \6\
to adopt standards that are of at least equivalent stringency to those
set by ICAO. Section II.D provides additional discussion of the
international aircraft standard-setting process. This document does not
take action or respond to comments on the 2015 U.S. EPA Aircraft
Greenhouse Gas Emissions Advance Notice of Proposed Rulemaking
(henceforth the ``2015 ANPR''),\7\ which discussed such standards.
Technical issues and comments for the 2015 ANPR would be addressed in a
future notice of proposed rulemaking related to such standards.
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\6\ ICAO, 2006: Convention on International Civil Aviation,
Ninth Edition, Document 7300/9, 114 pp. Available at: http://www.icao.int/publications/Documents/7300_9ed.pdf (last accessed May
9, 2016).
\7\ 80 FR 37758 (July 1, 2015).
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B. Background Information Helpful to Understanding This Final Action

1. Greenhouse Gases and Their Effects
GHGs in the atmosphere have the effect of trapping some of the
Earth's heat that would otherwise escape to space. GHGs are both
naturally occurring and anthropogenic. The primary GHGs directly
emitted by human activities include CO2, methane, nitrous
oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
Of these six gases, two (CO2 and nitrous oxide) are emitted
by aircraft engines.
These six gases, once emitted, remain in the atmosphere for decades
to centuries. Thus, they become well mixed globally in the atmosphere,
and their concentrations accumulate when emissions exceed the rate at
which natural processes remove them from the atmosphere. Observations
of the Earth's globally averaged combined land and ocean surface
temperature over the period 1880 to 2012 show a warming of 0.85 degrees
Celsius or 1.53 degrees Fahrenheit.\8\ The Intergovernmental Panel on
Climate Change's (IPCC) 2013-2014 Fifth Assessment Report concluded
that heating effect caused by the human-induced buildup of these and
other GHGs in the atmosphere, plus other human activities (e.g., land
use change and aerosol emissions), is extremely likely (>95 percent
likelihood) to be the cause of most of the observed global warming
since the mid-20th century.\9\ Further information about climate change
and its impact on health, society, and the environment is included in
the record for the 2009 Endangerment Finding. The relevant scientific
information from that record has also been included in the docket for
this determination under CAA section 231(a)(2)(A) (EPA-HQ-OAR-2014-
0828). Section IV of this preamble discusses this information, as well
as information from the most recent scientific assessments, in the
context of the Administrator's endangerment finding under CAA section
231.
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\8\ IPCC, 2013: Summary for Policymakers. In: Climate Change
2013: The Physical Science Basis. Contribution of Working Group I to
the Fifth Assessment Report of the Intergovernmental Panel on
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor,
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley
(eds.)]. Cambridge University Press, 29 pp.
\9\ Ibid.
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The U.S. transportation sector constitutes a meaningful part of
total U.S. and global anthropogenic GHG emissions. In 2014, aircraft
remained the single largest GHG-emitting transportation source not yet
subject to any GHG standards. Aircraft clearly contribute to U.S.
transportation emissions, accounting for 12 percent of all U.S.
transportation GHG emissions and representing more than 3 percent of
total U.S. GHG emissions in 2014.\10\

[[Page 54425]]

Globally, U.S. aircraft GHG emissions represent 29 percent of all
global aircraft GHG emissions and 0.5 percent of total global GHG
emissions. Section V of this preamble provides detailed information on
aircraft GHG emissions in the context of the Administrator's cause or
contribute finding under CAA section 231(a)(2)(A).
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\10\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
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2. Statutory Basis for This Final Action
Section 231(a)(2)(A) of the CAA states that ``The Administrator
shall, from time to time, issue proposed emission standards applicable
to the emission of any air pollutant from any class or classes of
aircraft engines which in [her] judgment causes, or contributes to, air
pollution which may reasonably be anticipated to endanger public health
or welfare.''
Before the Administrator may propose and issue final standards
addressing emissions of an air pollutant under section 231, the
Administrator must satisfy a two-step test. First, the Administrator
must decide whether, in her judgment, the air pollution under
consideration may reasonably be anticipated to endanger public health
or welfare. Second, the Administrator must decide whether, in her
judgment, emissions of an air pollutant from certain classes of
aircraft engines cause or contribute to this air pollution.\11\ If the
Administrator answers both questions in the affirmative, she must
propose and issue final standards under section 231. See Massachusetts
v. EPA, 549 U.S. 497, 533 (2007) (interpreting analogous provision in
CAA section 202). Section III of this document summarizes the legal
framework for this final action under CAA section 231. Typically, past
endangerment and cause or contribute findings have been proposed and
promulgated concurrently with proposed and promulgated standards under
various sections of the CAA, including section 231. In those actions,
public comment was taken on the proposed findings as part of the notice
and comment process for the proposed emission standards. See, e.g.,
Rulemaking for non-road compression-ignition engines under section
213(a)(4) of the CAA, Proposed Rule at 58 FR 28809, 28813-14 (May 17,
1993), Final Rule at 59 FR 31306, 31318 (June 17, 1994); Rulemaking for
highway heavy-duty diesel engines and diesel sulfur fuel under sections
202(a) and 211(c) of the CAA, Proposed Rule at 65 FR 35430 (June 2,
2000), and Final Rule at 66 FR 5002 (January 18, 2001). However, there
is no requirement that the Administrator propose or finalize the
endangerment and cause or contribute findings concurrently with the
related standards. See 74 FR 66502 (December 15, 2009). As explained in
the 2009 Endangerment Finding, nothing in section 202(a) requires the
EPA to propose or issue endangerment and cause or contribute findings
in the same rulemaking, and Congress left the EPA discretion to choose
an approach that satisfied the requirements of section 202(a). See id.
The same analysis applies to section 231, which is analogous to section
202(a). The EPA is choosing to finalize these findings at this time for
a number of reasons, including its previous commitment to issue such
findings in response to a 2007 citizens' petition.\12\
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\11\ To clarify the distinction between air pollution and air
pollutant, in the context of GHGs, the air pollution is the
atmospheric concentrations and can be thought of as the total,
cumulative stock of GHGs in the atmosphere. The air pollutant, on
the other hand, is the emissions of GHGs and can be thought of as
the flow that changes the size of the total stock.
\12\ Center for Biological Diversity, Center for Food Safety,
Friends of the Earth, International Center for Technology
Assessment, and Oceana, 2007: Petition for Rulemaking Under the
Clean Air Act to Reduce the Emissions of Air Pollutants from
Aircraft the Contribute to Global Climate Change, December 31, 2007.
Available at http://www3.epa.gov/otaq/aviation.htm (last accessed
April 8, 2016). EPA, 2012: Response to the Petition for Rulemaking
Under the Clean Air Act to Reduce the Emission of Air Pollutants
from Aircraft that Contribute to Global Climate Change, June 14,
2012. Available at http://www3.epa.gov/otaq/aviation.htm (last
accessed April 8, 2016).
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The Administrator has applied the rulemaking provisions of CAA
section 307(d) to this action, pursuant to CAA section 307(d)(1)(V),
which provides that the provisions of 307(d) apply to ``such other
actions as the Administrator may determine.'' \13\ CAA section 307(d)
provides specific procedural requirements for the EPA to follow in
taking certain rulemaking actions under the CAA, that apply in lieu of
the otherwise applicable provisions of the Administrative Procedure
Act, 5 U.S.C. 553-557, and 706. See, CAA section 307(d)(1). Any
standard-setting rulemaking under section 231 will also be subject to
the notice and comment rulemaking procedures under 307(d), as provided
in CAA section 307(d)(1)(F) (applying the provisions of 307(d) to the
promulgation or revision of any aircraft emission standard under
section 231). Thus, these findings were subject to the same rulemaking
procedures and requirements, as applicable, as would have applied if
they had been part of a standard-setting rulemaking.
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\13\ As the Administrator is applying the provisions of section
307(d) to this rulemaking under section 307(d)(1)(V), we need not
determine whether those provisions would apply to this action under
section 307(d)(1)(F).
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C. The EPA's Responsibilities Under the Clean Air Act

The CAA provides broad authority to combat air pollution to protect
public health and welfare and the environment. Cars, trucks,
construction equipment, airplanes, and ships, as well as a broad range
of electricity generation, industrial, commercial and other facilities,
are subject to various CAA programs. Many of these programs are
targeted at ensuring protection of public health and welfare with a
margin of safety, others are directed at encouraging improved
industrial emissions performance and use of lesser polluting
technologies and processes, and some address the prevention of adverse
environmental effects. Implementation of the Act over the past four
decades has resulted in significant reductions in air pollution that
have benefited human health and the environment. The EPA's duties
regarding aircraft air pollution emissions under CAA section 231
reflect a combination of the CAA's goals to protect public health and
welfare and encourage improved emissions performance. This is shown by
section 231(a)(2)(A)'s directive that EPA first identify whether
emissions of aircraft engine air pollutants cause or contribute to air
pollution that may reasonably be anticipated to endanger public health
or welfare (which is broadly defined in section 302(h) of the CAA).\14\
This is also shown by section 231(b)'s subsequent requirement that
EPA's standards, which may require improved emissions performance over
the status quo, provide sufficient time for the development and
application of requisite technology to meet emission standards, after
consideration of costs.
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\14\ Previously the EPA has made the prerequisite endangerment
and cause or contribute findings under CAA section 231(A) that
formed the basis to begin addressing the issue of various aircraft
pollutants including NOX aircraft pollution. U.S. EPA,
``Control of Air Pollution from Aircraft and Aircraft Engines,
Emission Standards and Test Procedures for Aircraft.'' Final Rule,
38 FR 19088 (July 17, 1973). See also section IV.B.7.d of this
preamble for a discussion of previous NOX section 231(A)
findings.
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1. The EPA's Regulation of Greenhouse Gases
In Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court
found that GHGs are air pollutants that can be regulated under the CAA.
The Court held that the Administrator must determine whether emissions
of GHGs from new motor vehicles cause or contribute to air pollution
which may

[[Page 54426]]

reasonably be anticipated to endanger public health and/or welfare, or
whether the science is too uncertain to make a reasoned decision. In
making these decisions, the Administrator was bound by the provisions
of section 202(a) of the CAA. The Supreme Court decision resulted from
a petition for rulemaking under section 202(a) filed by more than a
dozen environmental, renewable energy, and other organizations.
Following the Supreme Court decision, the EPA proposed (74 FR
18886, April 24, 2009) and then finalized (74 FR 66496, December 15,
2009) the 2009 Endangerment Finding, which can be summarized as
follows:
Endangerment Finding: The Administrator found that the
then-current and projected concentrations of the combined mix in the
atmosphere of the six well-mixed GHGs--CO2, methane, nitrous
oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride--
endanger the public health and welfare of current and future
generations.
Cause or Contribute Finding: The Administrator found that
the combined emissions of the six well-mixed GHGs from new motor
vehicles and new motor vehicle engines contribute to the GHG pollution
which threatens public health and welfare.
The Administrator made both of these findings with respect to the
six well-mixed GHGs, recognizing that CAA section 202(a) sources emit
only four of the six substances. The findings did not themselves impose
any requirements on industry or other entities. However, these findings
compelled the EPA to promulgate GHG emission standards for new motor
vehicles under section 202(a). Subsequently, in May 2010 the EPA, in
collaboration with the National Highway Traffic Safety Administration
(NHTSA), finalized Phase 1 GHG emission standards for light-duty
vehicles (2012-2016 model years).\15\ This was followed in August 2011
by adoption of the first-ever GHG emission standards for heavy-duty
engines and vehicles (2014-2018 model years).\16\ On August 29, 2012,
the EPA finalized the second phase of the GHG emission standards for
light-duty vehicles (2017-2025 model years), further reducing GHG
emissions from light-duty vehicles.\17\ In 2014, the President directed
the EPA and the Department of Transportation to set standards in 2016
that further increase fuel efficiency and reduce GHG emissions from
medium- and heavy-duty vehicles.\18\
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\15\ U.S. EPA, 2010: Light-Duty Vehicle Greenhouse Gas Emission
Standards and Corporate Average Fuel Economy Standards; Final Rule,
75 FR 25324 (May 7, 2010).
\16\ U.S. EPA, 2011: Greenhouse Gas Emissions Standards and Fuel
Efficiency Standards for Medium- and Heavy-Duty Engines and
Vehicles; Final Rule, 76 FR 57106 (September 15, 2011).
\17\ U.S. EPA, 2012: 2017 and Later Model Year Light-Duty
Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy
Standards; Final Rule, 77 FR 62623 (October 15, 2012).
\18\ Executive Office of the President, 2014: Remarks by the
President on Fuel Efficiency Standards of Medium and Heavy-Duty
Vehicles, Office of the Press Secretary, February 18. Available at:
https://www.whitehouse.gov/the-press-office/2014/02/18/remarks-president-fuel-efficiency-standards-medium-and-heavy-duty-vehicl
(last accessed April 27, 2016).
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The GHG rules for cars and trucks have been supported by a broad
range of stakeholders, including states, major automobile and truck
manufacturers, and environmental and labor organizations. Together
these new standards for cars and trucks are resulting in significant
reductions in GHG emissions, and over the lifetime of these vehicles
GHG emissions will have been reduced more than 6.25 billion metric
tons.^{19 20}
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\19\ U.S. EPA, 2012: EPA and NHTSA Set Standards to Reduce
Greenhouse Gases and Improve Fuel Economy for Model Years 2017-2025
Cars and Light Trucks. Document No. EPA-420-F-12-051, 10 pp.
Available at http://www.epa.gov/otaq/climate/documents/420f12051.pdf
(last accessed April 27, 2016). See also Table 7.4-2 in U.S. EPA,
2012: Regulatory Impact Analysis: Final Rulemaking for 2017-2025
Light-Duty Vehicle Greenhouse Gas Emissions Standards and
Corporation Average Fuel Economy Standards, EPA-420-R-12-016, 555
pp. Available at: https://www3.epa.gov/otaq/climate/documents/420r12016.pdf (last accessed April 27, 2016).
\20\ U.S. EPA, 2011: Greenhouse Gas Emissions Standards and Fuel
Efficiency Standards for Medium-and Heavy-Duty Engines and Vehicles;
Final Rule, 76 FR 57106 (September 15, 2011).
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On June 25, 2013, President Obama announced a Climate Action Plan
that set forth a series of executive actions to further reduce GHGs,
prepare the U.S. for the impacts of climate change, and lead
international efforts to address global climate change.\21\ As part of
the Climate Action Plan, the President issued a Presidential Memorandum
directing the EPA to work expeditiously to complete carbon pollution
standards for the power sector.\22\ In August 2015, after notice and
comment rulemaking, the EPA finalized two carbon pollution rulemakings:
One for new, modified, and reconstructed electric utility generating
units \23\ and another for existing power plants.\24\
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\21\ Executive Office of the President, 2013: The President's
Climate Action Plan, June 25, 21 pp. Available at: http://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf (last accessed April 8, 2016).
\22\ Executive Office of the President, 2013: Presidential
Memorandum--Power Sector Carbon Pollution Standards, Office of the
Press Secretary, June 25. Available at: http://www.whitehouse.gov/the-press-office/2013/06/25/presidential-memorandum-power-sector-carbon-pollution-standards (last accessed April 8, 2016).
\23\ U.S. EPA, 2015: Standards of Performance for Greenhouse Gas
Emissions From New, Modified, and Reconstructed Stationary Sources:
Electric Utility Generating Units; Final Rule, 80 FR 64510 (October
23, 2015).
\24\ U.S. EPA, 2014: Carbon Pollution Emission Guidelines for
Existing Stationary Sources: Electric Utility Generating Units;
Final Rule, 80 FR 64661 (October 23, 2015). On February 9, 2016 the
Supreme Court stayed this rule pending judicial review. The Court's
stay order does not articulate a basis for the stay and does not
address the merits of the rule.
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In the Climate Action Plan, the President also indicated that the
United States was working internationally to make progress in a variety
of areas and specifically noted the progress being made by ICAO to
develop global CO2 emission standards for aircraft.\25\ The
final endangerment and cause or contribute findings for aircraft GHG
emissions under section 231(a)(2)(A) of the CAA are a preliminary but
necessary first step to begin to address GHG emissions from the
aviation sector, the highest-emitting category of transportation
sources that the EPA has not yet addressed. As presented in more detail
in Section V of this document, total U.S. aircraft GHG emissions in
2014 represented 12 percent of GHG emissions from the U.S.
transportation sector,\26\ and in 2010, the latest year with complete
global emissions data, U.S. aircraft GHG emissions represented 29
percent of global aircraft GHG emissions.^{27 28} U.S. aircraft
GHG emissions are projected to increase by 43 percent over the next two
decades.\29\

[[Page 54427]]

See section V of this preamble for more information about the data
sources that comprise the aircraft GHG emissions inventory.
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\25\ Executive Office of the President, 2013: The President's
Climate Action Plan, June 25, 21 pp. Available at http://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf (last accessed April 8, 2016).
\26\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\27\ Ibid.
\28\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, pp. 599-670.
\29\ As discussed in section V.B.4.c, fuel burn growth rates for
air carriers and general aviation aircraft operating on jet fuel are
projected to grow by 43 percent from 2010 to 2036, and this provides
a scaling factor for growth in GHG emissions which would increase at
a similar rate as the fuel burn by 2030, 2036, and 2040. FAA, 2016:
FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp. Available at
https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last accessed April 8,
2016).
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2. Background on the Aircraft Petition, the 2008 Advance Notice of
Proposed Rulemaking, and the D.C. District Court Decision
Section 231(a)(2)(A) of the CAA directs the Administrator of the
EPA to, from time to time, propose aircraft engine emissions standards
applicable to the emission of any air pollutant from any classes of
aircraft engines which in her judgment causes or contributes to air
pollution which may reasonably be anticipated to endanger public health
or welfare.
On December 5, 2007, Friends of the Earth, Oceana, the Center for
Biological Diversity, Earthjustice, and others (Petitioners) sent a
letter to the EPA petitioning the Agency to undertake rulemaking
regarding GHG emissions from aircraft.\30\ Specifically, Petitioners
requested that the EPA make a finding that GHG emissions from aircraft
engines ``may reasonably be anticipated to endanger public health and
welfare'' and that the EPA promulgate standards for GHG emissions from
aircraft.
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\30\ Center for Biological Diversity, Center for Food Safety,
Friends of the Earth, International Center for Technology
Assessment, and Oceana, 2007: Petition for Rulemaking Under the
Clean Air Act to Reduce the Emissions of Air Pollutants from
Aircraft the Contribute to Global Climate Change, December 5, 26 pp.
Available at http://www.epa.gov/otaq/aviation.htm (last accessed
April 8, 2016) and Docket EPA-HQ-OAR-2014-0828.
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Following the Supreme Court's decision in Massachusetts v. EPA in
2007, the EPA issued an advance notice of proposed rulemaking (ANPR) in
2008 presenting information relevant to potentially regulating GHGs
under the Act and soliciting public comment on how to respond to the
Court's ruling and the potential ramifications of the Agency's decision
to regulate GHGs under the CAA. This ANPR described and solicited
comment on numerous petitions the Agency had received to regulate GHG
emissions from both stationary and mobile sources, including aircraft.
73 FR 44354, 44468-73 (July 30, 2008). With regard to aircraft, the
Agency sought comment on the impact of aircraft operations on GHG
emissions and the potential for reductions in GHG emissions from these
operations.
On July 31, 2008, Earthjustice, on behalf of Petitioners, notified
the EPA of its intent to file suit under CAA section 304(a) against the
EPA for the Agency's alleged unreasonable delay in responding to its
aircraft petition and in making an endangerment finding under section
231. On June 11, 2010, Petitioners filed a complaint against the EPA in
the U.S. District Court for the District of Columbia claiming that,
among other things, the EPA had unreasonably delayed because it had
failed to answer the 2007 Petition and to determine whether GHG
emissions from aircraft cause or contribute to air pollution which may
reasonably be anticipated to endanger public health and/or welfare.
The District Court found that while CAA section 231 generally
confers broad discretion to the EPA in determining what standards to
promulgate, section 231(a)(2)(A) imposed a nondiscretionary duty on the
EPA to make a finding with respect to endangerment from aircraft GHG
emissions. Center for Biological Diversity, et al. v. EPA, 794 F. Supp.
2d 151 (D.D.C. 2011). This ruling was issued in response to the EPA's
motion to dismiss the case on jurisdictional grounds and did not
address the merits of the Plaintiffs' claims regarding the Agency's
alleged unreasonable delay. Therefore, it did not include an order for
the EPA to make such a finding by a certain date. In a subsequent
ruling on the merits, the Court found that the Plaintiffs had not shown
that the EPA had unreasonably delayed in making an endangerment
determination regarding GHG emissions from aircraft. Center for
Biological Diversity, et al. v. EPA, No. 1:10-985 (D.D.C. March, 20,
2012). Thus, the Court did not find the EPA to be liable based on the
Plaintiffs' claims and did not place the Agency under a remedial order
to make an endangerment finding or to issue standards. The Plaintiffs
did not appeal this ruling to the U.S. Court of Appeals for the
District of Columbia Circuit (also called the ``D.C. Circuit'' in this
document).
The EPA issued a Response to the Aircraft Petition \31\ on June 27,
2012, stating our intention to move forward with a proposed
endangerment finding for aircraft GHG emissions under section 231,
while explaining that it would take the Agency significant time to
complete this action. The EPA explained that the Agency would not begin
this effort until after the U.S. Court of Appeals completed its then-
pending review of the previous section 202 Endangerment Finding, since
the then-awaited ruling might provide important guidance for the EPA in
conducting future GHG endangerment findings. The EPA further explained
that after receiving the Court of Appeal's ruling, it would take at
least 22 months from that point for the Agency to conduct an additional
finding regarding aircraft GHG emissions.
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\31\ U.S. EPA, 2012: Memorandum in Response to Petition
Regarding Greenhouse Gas Emissions from Aircraft, June 14, 11 pp.
Available at http://www.epa.gov/otaq/aviation.htm (last accessed
April 8, 2016) and Docket EPA-HQ-OAR-2014-0828.
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Meanwhile, the Court of Appeals upheld the EPA's section 202
findings in a decision of a three-judge panel on June 26, 2012, and
denied petitions for rehearing of that decision on December 20, 2012.
Coalition for Responsible Regulation, Inc., v. EPA, 684 F.3d 102 (D.C.
Cir. 2012), reh'g denied 2012 U.S. App. LEXIS 26315, 25997 (D.C. Cir
2012).\32\ Given these rulings, we are proceeding with these findings
regarding aircraft engine GHG emissions as a further step toward
responding to the 2007 Petition for Rulemaking.
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\32\ Petitions for certiorari were filed in the Supreme Court,
and the Supreme Court granted six of those petitions but ``agreed to
decide only one question: `Whether EPA permissibly determined that
its regulation of greenhouse gas emissions from new motor vehicles
triggered permitting requirements under the Clean Air Act for
stationary sources that emit greenhouse gases.' '' Utility Air Reg.
Group v. EPA, 134 S. Ct. 2427, 2438 (2014); see also Virginia v.
EPA, 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA, 134 S. Ct. 418
(2013), and CRR, 134 S. Ct. 468 (2013) (all denying cert.). Thus,
the Supreme Court did not disturb the D.C. Circuit's holding that
affirmed the 2009 Endangerment Finding.
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D. U.S. Aircraft Regulations and the International Community

The EPA and the FAA traditionally work within the standard-setting
process of ICAO's Committee on Aviation Environmental Protection (CAEP
or the Committee) to establish international emission standards and
related requirements, which individual nations later adopt into
domestic law in fulfillment of their obligations under the Convention
on International Civil Aviation (Chicago Convention). Historically,
under this approach, international emission standards have first been
adopted by ICAO, and subsequently the EPA has initiated rulemakings
under CAA section 231 to establish domestic standards that are at least
as stringent as ICAO's standards. This approach has been affirmed as a
reasonable way to implement the Agency's duties under CAA section 231
by the U.S. Court of Appeals for the D.C. Circuit. Nat'l Ass'n of Clean
Air Agencies (NACAA) v. EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007).
After EPA promulgates aircraft engine emissions standards, CAA section
232 requires the FAA to issue regulations to ensure compliance with
these standards when issuing certificates under its authority under
Title 49 of the United

[[Page 54428]]

States Code. These final endangerment and cause or contribute findings
for aircraft GHG emissions are in preparation for this domestic
emissions standards rulemaking process.
1. International Regulations and U.S. Obligations
The EPA has worked with the FAA since 1973, and later with ICAO, to
develop domestic and international standards and other recommended
practices pertaining to aircraft engine emissions. ICAO is a United
Nations (UN) specialized agency, established in 1944 by the Chicago
Convention, ``in order that international civil aviation may be
developed in a safe and orderly manner and that international air
transport services may be established on the basis of equality of
opportunity and operated soundly and economically.'' \33\ ICAO sets
international standards and regulations for aviation safety, security,
efficiency, capacity, and environmental protection and serves as the
forum for cooperation in all fields of international civil aviation.
ICAO works with the Chicago Convention's member states and global
aviation organizations to develop international Standards and
Recommended Practices (SARPs), which member states reference when
developing their legally enforceable national civil aviation
regulations. The United States is currently one of 191 participating
ICAO member states.^{34 35}
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\33\ ICAO, 2006: Convention on International Civil Aviation,
Ninth Edition, Document 7300/9, 114 pp. Available at: http://www.icao.int/publications/Documents/7300_9ed.pdf (last accessed
April 20, 2016).
\34\ Members of ICAO's Assembly are generally termed member
states or contracting states. These terms are used interchangeably
throughout this preamble.
\35\ There are currently 191 contracting states according to
ICAO's Web site: www.icao.int (last accessed April 8, 2016).
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In the interest of global harmonization and international air
commerce, the Chicago Convention urges its member states to collaborate
in securing the highest practicable degree of uniformity in
regulations, standards, procedures and organization. The Chicago
Convention also recognizes that member states may adopt standards that
are more stringent than those agreed upon by ICAO. Any member state
which finds it impracticable to comply in all respects with any
international standard or procedure, or that deems it necessary to
adopt regulations or practices differing in any particular respect from
those established by an international standard, is required to give
immediate notification to ICAO of the differences between its own
practice and that established by the international standard.\36\
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\36\ ICAO, 2006: Doc 7300-Convention on International Civil
Aviation, Ninth Edition, Document 7300/9, 114 pp. Available at
http://www.icao.int/publications/Documents/7300_9ed.pdf (last
accessed April 8, 2016).
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ICAO's work on the environment focuses primarily on those problems
that benefit most from a common and coordinated approach on a worldwide
basis, namely aircraft noise and engine emissions. SARPs for the
certification of aircraft noise and aircraft engine emissions are
covered by Annex 16 of the Chicago Convention. To continue to address
aviation environmental issues, in 2004, ICAO established three
environmental goals: (1) Limit or reduce the number of people affected
by significant aircraft noise; (2) limit or reduce the impact of
aviation emissions on local air quality; and (3) limit or reduce the
impact of aviation GHG emissions on the global climate.
The Chicago Convention has a number of other features that govern
international commerce. First, member states that wish to use aircraft
in international transportation must adopt emissions standards and
other recommended practices that are at least as stringent as ICAO's
standards. Member states may ban the use of any aircraft within their
airspace that does not meet ICAO standards.\37\ Second, the Chicago
Convention indicates that member states are required to recognize the
airworthiness certificates of any state whose standards are at least as
stringent as ICAO's standards.\38\ Third, to ensure that international
commerce is not unreasonably constrained, a member state which elects
to adopt more stringent domestic emission standards is obligated to
notify ICAO of the differences between its standards and ICAO
standards.\39\
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\37\ ICAO, 2006: Convention on International Civil Aviation,
Article 87, Ninth Edition, Document 7300/9, 114 pp. Available at
http://www.icao.int/publications/Documents/7300_9ed.pdf (last
accessed April 8, 2016).
\38\ ICAO, 2006: Convention on International Civil Aviation,
Article 33, Ninth Edition, Document 7300/9, 114 pp. Available at
http://www.icao.int/publications/Documents/7300_9ed.pdf (last
accessed April 8, 2016).
\39\ ICAO, 2006: Convention on International Civil Aviation,
Article 38, Ninth Edition, Document 7300/9, 114 pp. Available at
http://www.icao.int/publications/Documents/7300_9ed.pdf (last
accessed April 8, 2016).
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ICAO's CAEP, which consists of members and observers from states,
intergovernmental and non-governmental organizations representing
aviation industry and environmental interests, undertakes ICAO's
technical work in the environmental field. The Committee is responsible
for evaluating, researching, and recommending measures to the ICAO
Council that address the environmental impacts of international civil
aviation. CAEP's terms of reference indicate that ``CAEP's assessments
and proposals are pursued taking into account: Technical feasibility;
environmental benefit; economic reasonableness; interdependencies of
measures (for example, among others, measures taken to minimize noise
and emissions); developments in other fields; and international and
national programs.'' \40\ The ICAO Council reviews and adopts the
recommendations made by CAEP. It then reports to the ICAO Assembly, the
highest body of the Organization, where the main policies on aviation
environmental protection are adopted and translated into Assembly
Resolutions. If ICAO adopts a CAEP proposal for a new environmental
standard, it then becomes part of ICAO standards and recommended
practices (Annex 16 to the Chicago Convention).^{41 42}
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\40\ ICAO: CAEP Terms of Reference. Available at http://www.icao.int/environmental-protection/Pages/Caep.aspx#ToR (last
accessed April 27, 2016).
\41\ ICAO, 2008: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Third Edition, July, 110 pp. Available at http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed
April 8, 2016). The ICAO Annex 16 Volume II is found on page 19 of
the ICAO Products & Services 2016 catalog and is copyright
protected; Order No. AN16-2.
\42\ CAEP develops new emission standards based on an assessment
of the technical feasibility, cost, and environmental benefit of
potential requirements.
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At CAEP meetings, the United States is represented by the FAA and
plays an active role.\43\ The EPA has historically been a principal
participant in various ICAO/CAEP working groups and other international
venues, assisting and advising FAA on aviation emissions, technology,
and environmental policy matters. In turn, the FAA assists and advises
the EPA on aviation environmental issues, technology and certification
matters.
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\43\ Pursuant to the President's memorandum of August 11, 1960
(and related Executive Order No. 10883 from 1960), the Interagency
Group on International Aviation (IGIA) was established to facilitate
coordinated recommendations to the Secretary of State on issues
pertaining to international aviation. The DOT/FAA is the chair of
IGIA, and as such, the FAA represents the U.S. on environmental
matters at CAEP.
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The first international standards and recommended practices for
aircraft engine emissions were recommended by CAEP's predecessor, the
Committee on Aircraft Engine Emissions (CAEE), and

[[Page 54429]]

adopted by ICAO in 1981.\44\ These standards limited aircraft engine
emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of
nitrogen (NOX). The 1981 standards applied to newly
manufactured engines, which are those engines built after the effective
date of the regulations--also referred to as in-production engines. In
1993, ICAO adopted a CAEP/2 proposal to tighten the original
NOX standard by 20 percent and amend the test
procedures.\45\ These 1993 standards applied both to newly certified
turbofan engines, which are those engine models that received their
initial type certificate after the effective date of the regulations--
also referred to as newly certified engines or new engine designs--and
to in-production engines, but with different effective dates for newly
certified engines and in-production engines. In 1995, CAEP/3
recommended a further tightening of the NOX standards by 16
percent and additional test procedure amendments, but in 1997 the ICAO
Council rejected this stringency proposal and approved only the test
procedure amendments. At the CAEP/4 meeting in 1998, the Committee
adopted a similar 16 percent NOX reduction proposal, which
ICAO approved in 1998. The CAEP/4 standards applied only to new engine
designs certified (or newly certified engines) after December 31, 2003
(i.e., unlike the CAEP/2 standards, the CAEP/4 requirements did not
apply to in-production engines). In 2004, CAEP/6 recommended a 12
percent NOX reduction, which ICAO approved in
2005.^{46 47} The CAEP/6 standards applied to new engine
designs certified after December 31, 2007. In 2010, CAEP/8 recommended
a further tightening of the NOX standards by 15 percent for
new engine designs certified after December 31, 2013.^{48 49}
The Committee also recommended that the CAEP/6 standards be applied to
in-production engines (eliminating the production of CAEP/4 compliant
engines with the exception of spare engines), and ICAO approved these
recommendations in 2011.\50\
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\44\ ICAO, 2008: Aircraft Engine Emissions: Foreword,
International Standards and Recommended Practices, Environmental
Protection, Annex 16, Volume II, Third Edition, July, 110 pp.
Available at http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Annex 16
Volume II is found on page 19 of the ICAO Products & Services 2016
catalog and is copyright protected; Order No. AN16-2.
\45\ CAEP conducts its work over a period of years. Each work
cycle is numbered sequentially and that identifier is used to
differentiate the results from one CAEP to another by convention.
The first technical meeting on aircraft emission standards was
CAEP's successor, i.e., CAEE. The first meeting of CAEP, therefore,
is referred to as CAEP/2.
\46\ CAEP/5 did not address new aircraft engine emission
standards.
\47\ ICAO, 2008: Aircraft Engine Emissions, Annex 16, Volume II,
Third Edition, July 2008, Amendment 5 effective on July 11, 2005,
110 pp. Available at http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Annex 16
Volume II is found on page 19 of the ICAO Products & Services 2016
catalog and is copyright protected; Order No. AN16-2.
\48\ CAEP/7 did not address new aircraft engine emission
standards.
\49\ ICAO, 2010: Committee on Aviation Environmental Protection
(CAEP), Report of the Eighth Meeting, Montreal, February 1-12, 2010,
CAEP/8-WP/80 Available in Docket EPA-HQ-OAR-2010-0687.
\50\ ICAO, 2014: Aircraft Engine Emissions, Annex 16, Volume II,
Third Edition, July 2008, Amendment 8, 108 pp. CAEP/8 corresponds to
Amendment 7 effective on July 18, 2011. Available at http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed
April 8, 2016). The ICAO Annex 16 Volume II is found on page 19 of
the ICAO Products & Services 2016 catalog and is copyright
protected; Order No. AN16-2/E/11.
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2. The International Civil Aviation Organization's Reasons for
Addressing Aircraft GHG Emissions
In October 2010, the 37th Assembly (Resolution A37-19) of ICAO
requested the development of an ICAO CO2 emissions
standard.\51\ The Resolution provided a framework towards the
achievement of an environmentally sustainable future for international
aviation. With this Resolution, the ICAO Assembly agreed to a global
aspirational goal for international aviation of improving annual fuel
efficiency by two percent up to the year 2050, and stabilizing
CO2 emissions at 2020 levels.\52\ Reducing climate impacts
of international aviation is a critical element of ICAO's strategic
objective of achieving environmental protection and sustainable
development of air transport. ICAO is currently pursuing a
comprehensive set of measures to reduce aviation's climate impact,
including lower-carbon alternative fuels, CO2 emissions
technology-based standards, operational improvements, and market based
measures. The development and adoption of a CO2 emissions
standard is an important part of ICAO's comprehensive set of measures.
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\51\ A consolidated statement of continuing policies and
practices related to environmental protection (known as Assembly
Resolutions) is revised and updated by the Council every three years
for adoption by the ICAO Assembly. ICAO, 2010: Resolutions Adopted
by the Assembly, 37th Session, Montreal, September 29-October 8,
2010, Provisional Edition, November 2010.
\52\ The global aspirational goal for international aviation of
improving annual fuel efficiency by 2 percent is for the annual
international civil aviation in-service fleet. Fuel efficiency is
measured on the basis of the volume of fuel used per revenue tonne
kilometer performed. ICAO CAEP, 2009: Aspirational Goals and
Implementation Options, Working Paper HLM-ENV/09-WP/5, 5 pp.
Available at http://www.icao.int/Meetings/AMC/MA/High%20Level%202009/hlmenv_wp005_en.pdf (last accessed April 8,
2015).
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3. EPA's Regulation of Aircraft Emissions and the Relationship of the
Final Endangerment and Cause or Contribute Findings to International
Aircraft Standards
As required by the CAA, the EPA has been engaged in reducing
harmful air pollution from aircraft engines for over 40 years,
regulating gaseous exhaust emissions, smoke, and fuel venting from
aircraft engines.\53\ We have periodically revised these regulations.
In a 1997 rulemaking, for example, we made our emission standards and
test procedures more consistent with those of ICAO's CAEP for turbofan
engines used in commercial aviation with rated thrusts greater than
26.7 kilonewtons.\54\ These ICAO requirements are generally referred to
as CAEP/2 standards.\55\ The 1997 rulemaking included new
NOX emission standards for newly manufactured commercial
turbofan engines (as described earlier, those engines built after the
effective date of the regulations that were already certified to pre-
existing standards--also referred to as in-production engines) \56\ and
for newly certified commercial turbofan engines (as described earlier,
those engine models that received their initial type certificate after
the effective date of the regulations--also referred to as new engine
designs).\57\ It also included a CO emission standard for in-production
commercial turbofan engines.\58\ In 2005, we promulgated more stringent
NOX emission standards for newly certified commercial
turbofan
---------------------------------------------------------------------------

\53\ U.S. EPA, 1973: Emission Standards and Test Procedures for
Aircraft; Final Rule, 38 FR 19088 (July 17, 1973).
\54\ U.S. EPA, 1997: Control of Air Pollution from Aircraft and
Aircraft Engines; Emission Standards and Test rocedures; Final Rule,
62 FR 25355 (May 8, 1997).
\55\ The full CAEP membership meets every three years and each
session is denoted by a numerical identifier. For example, the
second meeting of CAEP is referred to as CAEP/2, and CAEP/2 occurred
in 1994.
\56\ This does not mean that in 1997 we promulgated requirements
for the re-certification or retrofit of existing in-use engines.
\57\ In the existing EPA regulations, 40 CFR part 87, newly
certified aircraft engines are described as engines of a type or
model of which the date of manufacture of the first individual
production model was after the implementation date. Newly
manufactured aircraft engines are characterized as engines of a type
or model for which the date of manufacturer of the individual engine
was after the implementation date.
\58\ U.S. EPA, 1997: Control of Air Pollution from Aircraft and
Aircraft Engines; Emission Standards and Test Procedures; Final
Rule, 62 FR 25355 (May 8, 1997).

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[[Page 54430]]

engines.\59\ That final rule brought the U.S. standards closer to
alignment with ICAO CAEP/4 requirements that became effective in 2004.
In 2012, we issued more stringent two-tiered NOX emission
standards for newly certified and in-production commercial and non-
commercial turbofan aircraft engines, and these NOX
standards align with ICAO's CAEP/6 and CAEP/8 requirements that became
effective in 2013 and 2014, respectively.^{60 61} The EPA's
actions to regulate certain pollutants emitted from aircraft engines
come directly from the authority in section 231 of the CAA, and we have
aligned the U.S. emissions requirements with those promulgated by ICAO.
All of these previous emission standards have generally been considered
anti-backsliding standards (most aircraft engines meet the standards),
which are technology-following.
---------------------------------------------------------------------------

\59\ U.S. EPA, 2005: Control of Air Pollution from Aircraft and
Aircraft Engines; Emission Standards and Test Procedures; Final
Rule, 70 FR 69664 (November 17, 2005).
\60\ U.S. EPA, 2012: Control of Air Pollution from Aircraft and
Aircraft Engines; Emission Standards and Test Procedures; Final
Rule, 77 FR 36342 (June 18, 2012).
\61\ While ICAO's standards were not limited to ``commercial''
aircraft engines, our 1997 standards were explicitly limited to
commercial engines, as our finding that NOX and carbon
monoxide emissions from aircraft engines cause or contribute to air
pollution which may reasonably be anticipated to endanger public
health or welfare was so limited. See 62 FR 25358 (May 8, 1997). In
the 2012 rulemaking, we expanded the scope of that finding and of
our standards pursuant to CAA section 231(a)(2)(A) to include such
emissions from both commercial and non-commercial aircraft engines
based on the physical and operational similarities between
commercial and noncommercial civilian aircraft and to bring our
standards into full alignment with ICAO's.
---------------------------------------------------------------------------

In addressing CO2 emissions, ICAO has moved to
regulating a whole aircraft. ICAO explained its decision to regulate
pollutant emissions from the whole aircraft in a 2013 ICAO
circular.\62\ Several factors are considered when addressing whole-
aircraft CO2 emissions, as CO2 emissions are
influenced by aerodynamics, weight, and engine technology. Since the
aircraft-specific characteristics of aerodynamics and weight affect
fuel consumption, they ultimately affect CO2 engine exhaust
emissions. Rather than viewing CO2 as a measurable emission
from the engine alone, ICAO addresses CO2 emissions as an
aircraft-specific characteristic based on fuel consumption.
---------------------------------------------------------------------------

\62\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for the
Aeroplane CO2 Emissions Standard, Circular (Cir) 337, 40 pp, AN/192.
Available at http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Circular 337
is found on page 87 of the ICAO Products & Services 2016 catalog and
is copyright protected; Order No. CIR337.
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The EPA has worked diligently over the past six years within the
ICAO/CAEP process on a range of technical issues regarding aircraft
CO2 emission standards. The 2015 ANPR discussed the issues
arising from those international proceedings and requested public
comment on a variety of issues to assist the Agency in developing its
position with regard to these issues, to help ensure transparency and
obtain views on aircraft engine GHG emission standards that it might
potentially adopt under the CAA.
As described in the 2015 ANPR, in 2013 CAEP agreed on a metric \63\
to compare CO2 emissions from aircraft. The CO2
metric value is a comparative metric meant to differentiate between
generations of aircraft and to equitably capture improvements in
aerospace technology that contribute to a reduction in the airplane
CO2 emissions. The CO2 metric is not intended for
use as a direct measure of CO2 emissions rates or
operational fuel burn, rather it is a comparative measure of technology
on different aircraft.
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\63\ The CO2 metric is the average of three cruise
test points normalized by a dimensionless parameter representing
aircraft fuselage size. The units of the metric value are kilograms
of fuel burned per kilometer flown. However, because the metric is a
normalized value it cannot be used to estimate operational fuel burn
or emission rates of aircraft. The metric value is described in
detail in both ICAO Circular 337 and in section D of the 2015 ANPR.
ICAO, 2013: CAEP/9 Agreed Certification Requirement for the
Aeroplane CO2 Emissions Standard, Circular (Cir) 337, 40 pp., AN/
192, Available at http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 27, 2016). The ICAO Circular
337 is found on page 87 of the catalog and is copyright protected;
Order No. CIR337.
---------------------------------------------------------------------------

Using this metric, CAEP considered and analyzed 10 different
stringency levels for both in-production and new type standards,
comparing aircraft with a similar level of technology on the same
stringency level. These levels were generically referred to numerically
from ``1'' as the least stringent to ``10'' as the most stringent,
which correspond to the upper and lower lines of constant technology,
respectively, from the 2015 ANPR. The 2015 ANPR described the range of
stringency levels under consideration at CAEP as falling into three
categories as follows: (1) CO2 stringency levels that could
impact \64\ only the oldest, least efficient aircraft in-production
around the world, (2) middle range CO2 stringency levels
that could impact many aircraft currently in-production and comprising
much of the current operational fleet, and (3) CO2
stringency levels that could impact aircraft that have either just
entered production or are in final design phase but will be in-
production by the time the international CO2 standards
becomes effective.\65\
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\64\ As described in the 2015 ANPR, the aircraft shown in
[Figure II.1 and II.2] are in-production and current in-development.
These aircraft could be impacted by an in-production standard in
that, if they were above the standard, they would need to either
implement a technology response or go out of production. For a new
type only standard there will be no regulatory requirement for these
aircraft to respond.
\65\ 80 FR at 37797.
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At its meeting in February of 2016, CAEP agreed on an initial set
of international standards to regulate CO2 emissions from
aircraft.\66\ It was agreed that these international standards should
apply to both new type and in-production aircraft. The applicability
date for the in-production standard was agreed to be later than for the
new type standard. CAEP explained that this will allow manufacturers
and certification authorities additional preparation time to
accommodate the standards. The new type and in-production stringency
levels for smaller and larger aircraft were agreed to be set at
different levels to reflect the range of technology being used and the
availability of new fuel burn reduction technologies that vary across
aircraft of differing size and weight. Table II.1 provides a brief
overview of the applicability dates and stringency levels of the
standards agreed to at ICAO/CAEP. As described earlier, CAEP considered
and analyzed 10 different stringency levels for both in-production and
new type standards (from 1 as the least stringent to 10 as the most
stringent).
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\66\ Further, the EPA anticipates that the 39th ICAO Assembly
will approve these CO2 emissions standards in October
2016, and that subsequently, ICAO will formally adopt these
CO2 emissions standards in March 2017.

[[Page 54431]]

Table II.1--Stringency Levels and Applicability Dates for ICAO/CAEP CO2 Emission Standards
----------------------------------------------------------------------------------------------------------------
In-production
aircraft
Aircraft MTOM thresholds New type aircraft \67\ maximum
(kg) maximum permitted CO2 permitted CO2
metric value metric value

----------------------------------------------------------------------------------------------------------------
Stringency Level........................ >5,700 to <60,000......... \A\ 5..................... \B\ 3
Horizontal Transition \68\ \C\....................... \D\
60,000 to ~70,000.........
> ~70,000................. \E\ 8.5................... \F\ 7
Applicability Date...................... Application for a new type 2020...................... 2023
certificate or a change (2023 for planes with less
to an existing type than 19 seats).
certificate.
Production Cut Off........ n/a....................... 2028
----------------------------------------------------------------------------------------------------------------
\A\ Equation of ICAO Stringency Option #5: MV = 10-2.73780+(0.681310*\l\\o\\g\ 10(\M\\T\\O\\M\))+(-
0.0277861*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)
\B\ Equation of ICAO Stringency Option #3: MV = 10-2.57535+(0.609766*\l\\o\\g\ 10(\M\\T\\O\\M\))+(-
0.0191302*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)
\C\ Equation of New Type transition--60,000 to 70,395 kg: MV = 0.764
\D\ Equation of In-production transition--60,000 to 70,107 kg: MV = 0.797
\E\ Equation of ICAO Stringency Option #8.5: MV = 10-2.57535+(0.609766*\l\\o\\g\ 10(\M\\T\\O\\M\))+(-
0.0191302*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)
\F\ Equation of ICAO Stringency Option #7: MV = 10-1.39353+(-0.020517*\l\\o\\g\
10(\M\\T\\O\\M\))+(0.0593831*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)

Figures II.1 and II.2 show a graphical depiction of both the new
type and in-production standards compared against the lines of constant
technology described in the 2015 ANPR and CO2 metric value
levels of current (as of February 2016) in-production and in-
development \69\ aircraft. The aircraft data shown were generated by
the EPA using a commercially available aircraft modeling tool called
PIANO.\70\ It should be noted that a number of the aircraft currently
shown as in-production are expected to go out of production and be
replaced by known in-development aircraft prior to both the new type
and the in-production CO2 standards going into effect
internationally.
---------------------------------------------------------------------------

\67\ ``In Development'' aircraft shown in Figures II.1 and II.2
are the aircraft that were in development by manufacturers at the
time the 2015 ANPR was published.
\68\ Stringency lines above and below 60,000 kilograms (MTOM)
are connected by a horizontal transition starting at 60,000
kilograms (MTOM) and continuing right (increasing mass) until it
intersects with the next level.
\69\ Aircraft that are currently in-development but will be in
production by the applicability dates. These could be new types or
significant partial redesigned aircraft.
\70\ PIANO (Project Interactive Analysis and Optimization),
Aircraft Design and Analysis Software by Dr. Dimitri Simos, Lissys
Limited, UK, 1990-present; Available at www.piano.aero (last
accessed April 8, 2016). This is a commercially available aircraft
design and performance software suite used across the industry and
academia. This model contains non-manufacturer provided estimates of
performance of various aircraft.
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BILLING CODE 6560-50-P

[[Page 54432]]

[GRAPHIC] [TIFF OMITTED] TR15AU16.000

[[Page 54433]]

[GRAPHIC] [TIFF OMITTED] TR15AU16.001

BILLING CODE 6560-50-C
In this final action, the EPA is promulgating findings under
section 231(a)(2) that emissions of the six well-mixed GHGs from
certain classes of engines used in covered aircraft cause or contribute
to endangering air pollution. The EPA is not yet issuing proposed or
final emission standards, nor is the EPA taking final action that
prejudges what future standards will be. Instead, the EPA's final
endangerment and cause or contribute findings for aircraft GHG
emissions are in preparation for a subsequent, expected domestic

[[Page 54434]]

rulemaking process to adopt future GHG emissions standards. If the ICAO
Assembly, in October 2016, approves the final CO2 standards
and subsequently ICAO formally adopts the final CO2
standards in March 2017, the EPA's standards will need to be at least
as stringent as the ICAO CO2 aircraft standards for the
United States to meet its treaty obligations under the Chicago
Convention. As a result of these positive findings, the EPA is
obligated under section 231 of the CAA to set emission standards
applicable to GHG emissions from the classes of aircraft engines
included in the contribution finding, no matter the outcome of ICAO's
future actions in October 2016 and March 2017.

III. Legal Framework for This Action

The EPA has previously made an endangerment finding for GHGs under
Title II of the CAA, in the 2009 Endangerment Finding for section
202(a) source categories. In the 2009 Endangerment Finding, the EPA
explained its legal framework for making an endangerment finding under
section 202(a) of the CAA (74 FR 18886, 18890-94 (April 24, 2009), and
74 FR 66496, 66505-10 (December 15, 2009)). The text in section 202(a)
that was the basis for the 2009 Endangerment Finding addresses ``the
emission of any air pollutant from any class or classes of new motor
vehicles or new motor vehicle engines, which in [the Administrator's]
judgment cause, or contribute to, air pollution which may reasonably be
anticipated to endanger public health or welfare.'' Similarly, section
231(a)(2)(A) concerns ``the emission of any air pollutant from any
class or classes of aircraft engines which in [the Administrator's]
judgment causes, or contributes to, air pollution which may reasonably
be anticipated to endanger public health or welfare.'' Thus, the text
of the CAA section concerning aircraft emissions in section
231(a)(2)(A) mirrors the text of CAA section 202(a) that was the basis
for the 2009 Endangerment Finding.
The EPA's approach in the 2009 Endangerment Finding (described
below in sections III.A and III.B) was affirmed by the U.S. Court of
Appeals for the D.C. Circuit in Coalition for Responsible Regulation,
Inc. v. EPA, 684 F.3d 102 (D.C. Cir. 2012), reh'g denied 2012 U.S. App.
LEXIS 26313, 26315, 25997 (D.C. Cir. 2012) (CRR). In particular, the
D.C. Circuit ruled that the 2009 Endangerment Finding (including the
Agency's denial of petitions for reconsideration of that Finding) was
not arbitrary or capricious, was consistent with the U.S. Supreme
Court's decision in Massachusetts v. EPA and the text and structure of
the CAA, and was adequately supported by the administrative record.
CRR, 684 F.3d at 116-128. The D.C. Circuit found that the EPA had based
its decision on ``substantial scientific evidence'' and noted that the
EPA's reliance on major scientific assessments was consistent with the
methods that decision-makers often use to make a science-based
judgment. Id. at 120-121. Petitions for certiorari were filed in the
Supreme Court, and the Supreme Court granted six of those petitions but
``agreed to decide only one question: `Whether EPA permissibly
determined that its regulation of greenhouse gas emissions from new
motor vehicles triggered permitting requirements under the Clean Air
Act for stationary sources that emit greenhouse gases.' '' Utility Air
Reg. Group v. EPA, 134 S. Ct. 2427, 2438 (2014); see also Virginia v.
EPA, 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA, 134 S. Ct. 418
(2013), and CRR, 134 S. Ct. 468 (2013) (all denying cert.). Thus, the
Supreme Court did not disturb the D.C. Circuit's holding that affirmed
the 2009 Endangerment Finding. Accordingly, the Agency finds that it is
reasonable to use that same approach under section 231(a)(2)(A)'s
similar endangerment text, and as explained in the following
discussion, is acting consistently with that judicially sanctioned
framework for purposes of this final section 231 finding.
Two provisions of the CAA govern this final action. Section
231(a)(2)(A) sets forth a two-part predicate for regulatory action
under that provision: Endangerment and cause or contribute. Section 302
of the Act contains definitions of the terms ``air pollutant'' and
``welfare'' used in section 231(a)(2)(A). These statutory provisions
are discussed below.

A. Section 231(a)(2)(A)--Endangerment and Cause or Contribute

As noted above, section 231(a)(2)(A) of the CAA (like section
202(a)) calls for the Administrator to exercise her judgment and make
two separate determinations: first, whether the relevant kind of air
pollution--here, the six well-mixed GHGs--may reasonably be anticipated
to endanger public health or welfare, and second, whether emissions of
any air pollutant from classes of the sources in question (aircraft
engines under section 231 and new motor vehicles or engines under
section 202) cause or contribute to this air pollution.\71\
---------------------------------------------------------------------------

\71\ See CRR, 684 F.3d at 117 (explaining two-part analysis
under section 202(a)).
---------------------------------------------------------------------------

The Administrator interprets the two-part test required under
section 231(a)(2)(A) as being the same as that explained in the 2009
Endangerment Finding. See 74 FR 66505-06. As in the section 202(a)
context, this analysis entails a scientific judgment by the
Administrator about the potential risks posed by GHG emissions to
public health and welfare. See CRR, 684 F.3d at 117-118.\72\
---------------------------------------------------------------------------

\72\ When agencies such as the EPA make determinations based on
review of scientific data within their technical expertise, those
decisions are given an ``extreme degree of deference'' by the
courts. As the D.C. Circuit noted in reviewing the 2009 Endangerment
Finding, ``although we perform a searching and careful inquiry into
the facts underlying the agency's decisions, we will presume the
validity of the agency action as long as a rational basis for it is
presented.'' CRR, 684 F.3d at 120 (internal citations and marks
omitted).
---------------------------------------------------------------------------

In making this scientific judgment, the Administrator is guided by
five principles. First, the Administrator is required to protect public
health and welfare. She is not asked to wait until harm has occurred
but instead must be ready to take regulatory action to prevent harm
before it occurs.\73\ The Administrator is thus to consider both
current and future risks.
---------------------------------------------------------------------------

\73\ See id. at 121-122.
---------------------------------------------------------------------------

Second, the Administrator is to exercise judgment by weighing
risks, assessing potential harms, and making reasonable projections of
future trends and possibilities. It follows that when exercising her
judgment the Administrator balances the likelihood and severity of
effects. This balance involves a sliding scale: on one end the severity
of the effects may be significant, but the likelihood low, while on the
other end the severity may be less significant, but the likelihood
high.\74\ At different points along this scale, the Administrator is
permitted to find endangerment. Accordingly, the Administrator need not
set a precise or minimum threshold of risk or harm as part of making an
endangerment finding, but rather may base her determination on `` `a
lesser risk of greater harm . . . or a greater risk of lesser harm' or
any combination in between.'' CRR, 684 F.3d at 123 (quoting Ethyl Corp.
v. EPA, 541 F.2d, 1, 18 (D.C. Cir. 1976)).
---------------------------------------------------------------------------

\74\ See id. at 122-123 (noting that the Sec. 202(a)(1) inquiry
``necessarily entails a case-by-case, sliding scale approach''
because endangerment is `` `composed of reciprocal elements of risk
and harm, or probability and severity' '' (quoting Ethyl Corp. v.
EPA, 541 F.2d, 1, 18 (D.C. Cir. 1976)).
---------------------------------------------------------------------------

Third, because scientific knowledge is constantly evolving, the
Administrator may be called upon to make decisions while recognizing
the uncertainties and limitations of the data or information available,
as risks to public health or

[[Page 54435]]

welfare may involve the frontiers of scientific or medical
knowledge.\75\ At the same time, the Administrator must exercise
reasoned decision making, and avoid speculative inquiries.
---------------------------------------------------------------------------

\75\ See id. at 121-122.
---------------------------------------------------------------------------

Fourth, the Administrator is to consider the cumulative impact of
sources of a pollutant in assessing the risks from air pollution, and
is not to look only at the risks attributable to a single source or
class of sources. We additionally note that in making an endangerment
finding, the Administrator is not limited to considering only those
impacts that can be traced to the amount of air pollution directly
attributable to the subject source classes. Such an approach would
collapse the two prongs of the test by requiring that any climate
change impacts upon which an endangerment determination is made result
solely from the GHG emissions of aircraft. See 74 FR at 66542
(explaining the same point in the context of analogous language in
section 202(a)). Similarly, the Administrator is not, in making the
endangerment and cause or contribute findings, to consider the effect
of emissions reductions from the resulting standards.\76\ The threshold
endangerment and cause or contribute criteria are separate and distinct
from the standard setting criteria that apply if the threshold findings
are met, and they serve a different purpose. Indeed, the more serious
the endangerment to public health and welfare, the more important it
may be that action be taken to address the actual or potential harm
even if no one action alone can solve the problem, and a series of
actions is called for.
---------------------------------------------------------------------------

\76\ As the D.C. Circuit explained in reviewing the 2009
Endangerment Finding under analogous language in section 202(a):
``At bottom, Sec. 202(a)(1) requires EPA to answer only two
questions: whether particular `air pollution'--here, greenhouse
gases--`may reasonably be anticipated to endanger public health or
welfare,' and whether motor-vehicle emissions `cause, or contribute
to' that endangerment.'' CRR, 648 F.3d at 117.
---------------------------------------------------------------------------

Fifth, the Administrator is to consider the risks to all parts of
our population, including those who are at greater risk for reasons
such as increased susceptibility to adverse health and welfare effects.
If vulnerable subpopulations are especially at risk, the Administrator
is entitled to take that point into account in deciding the question of
endangerment. Here too, both likelihood and severity of adverse effects
are relevant. As explained previously in the 2009 Endangerment Finding
and as reiterated below for this section 231 finding, vulnerable
subpopulations face serious health and welfare risks as a result of
climate change.
As the Supreme Court recognized in Massachusetts v. EPA, 549 U.S.
at 534, the EPA may make an endangerment finding despite the existence
of ``some residual uncertainty'' in the scientific record. See also
CRR, 684 F. 2d at 122. Thus, this framework recognizes that regulatory
agencies such as the EPA must be able to deal with the reality that
``[m]an's ability to alter his environment has developed far more
rapidly than his ability to foresee with certainty the effects of his
alterations.'' Ethyl Corp v. EPA, 541 F.2d 1, 6 (D.C. Cir.), cert.
denied 426 U.S. 941 (1976). Both ``the Clean Air Act `and common sense
. . . demand regulatory action to prevent harm, even if the regulator
is less than certain that harm is otherwise inevitable.' ''
Massachusetts v. EPA, 549 U.S. at 506, n.7 (citing Ethyl Corp.); see
also CRR, 684 F.3d at 121-122.
In the 2009 Endangerment Finding, the Administrator recognized that
the scientific context for an action addressing climate change was
unique at that time because there was a very large and comprehensive
base of scientific information that had been developed over many years
through a global consensus process involving numerous scientists from
many countries and representing many disciplines. 74 FR at 66506. That
informational base has since grown. The Administrator also previously
recognized that there are varying degrees of uncertainty across many of
these scientific issues, which remains true. It is in this context that
she is exercising her judgment and applying the statutory framework in
this final section 231 finding. Further discussion of the language in
section 231(a)(2)(A), and parallel language in 202(a), is provided
below to explain more fully the basis for this interpretation, which
the D.C. Circuit upheld in the 202(a) context.
1. The Statutory Language
The interpretation described above flows from the statutory
language itself. The phrase ``may reasonably be anticipated'' and the
term ``endanger'' in section 231(a)(2)(A) (as in section 202(a))
authorize, if not require, the Administrator to act to prevent harm and
to act in conditions of uncertainty. They do not limit her to merely
reacting to harm or to acting only when certainty has been achieved;
indeed, the references to anticipation and to endangerment imply that
to fail to look to the future or to less than certain risks would be to
abjure the Administrator's statutory responsibilities. As the D.C.
Circuit explained, the language ``may reasonably be anticipated to
endanger public health or welfare'' in CAA section 202(a) requires a
``precautionary, forward-looking scientific judgment about the risks of
a particular air pollutant, consistent with the CAA's precautionary and
preventive orientation.'' CRR, 684 F.3d at 122 (internal citations
omitted). The court determined that ``[r]equiring that EPA find
`certain' endangerment of public health or welfare before regulating
GHGs would effectively prevent EPA from doing the job that Congress
gave it in [section] 202(a)--utilizing emission standards to prevent
reasonably anticipated endangerment from maturing into concrete harm.''
Id. The same language appears in section 231(a)(2)(A), and the same
interpretation applies in that context.
Moreover, by instructing the Administrator to consider whether
emissions of an air pollutant cause or contribute to air pollution in
the second part of the two-part test, the Act makes clear that she need
not find that emissions from any one sector or class of sources are the
sole or even the major part of an air pollution problem. The use of the
term ``contribute'' clearly indicates that such emissions need not be
the sole or major cause of the pollution. In addition, the absence of
the term ``significantly'' or any other word that modifies
``contribute'' shows that the EPA need not find that contributing
emissions cross a minimum percentage- or mass-based threshold to be
cognizable. The phrase ``in [her] judgment'' authorizes the
Administrator to weigh risks and to consider projections of future
possibilities, while also recognizing uncertainties and extrapolating
from existing data. Finally, when exercising her judgment in making
both the endangerment and cause or contribute findings, the
Administrator balances the likelihood and severity of effects. Notably,
the phrase ``in [her] judgment'' modifies both ``may reasonably be
anticipated'' and ``cause or contribute.''
2. How the Origin of the Current Statutory Language Informs the EPA's
Interpretation of Section 231(a)(2)(A)
In the proposed and final 2009 Endangerment Finding, the EPA
explained that when Congress revised the section 202(a) language that
governed that finding, along with other provisions, as part of the 1977
amendments to the CAA, it was responding to decisions issued by the
D.C. Circuit in Ethyl Corp. v. EPA regarding the pre-1977 version of
section 211(c) of the Act. 74 FR at

[[Page 54436]]

18891; see also 74 FR at 66506. The legislative history of those
amendments, particularly the report by the House Committee on
Interstate and Foreign Commerce, demonstrates that the EPA's
interpretation of the section 231(a)(2)(A) language as set forth here
in support of the Agency's section 231 finding is fully consistent with
Congress' intention in crafting these provisions. See H.R. Rep. 95-294
(1977), as reprinted in 4 A Legislative History of the Clean Air Act
Amendments of 1977 (1978) at 2465 (hereinafter LH). The committee
explained that its action addressed not only section 211(c)(1)(A) but
rather the entirety of the proposed legislative amendments, and stated
that the committee's bill would thus apply the interpretation of
section 211(c)(1)(A) in the en banc decision in Ethyl Corp. to all
other sections of the Act relating to public health protection. 4 LH at
2516. It also noted that it had used the same basic formulation in
section 202 and section 231, as well as in other sections. Id. at 2517.
As both CAA sections 231 and 202 were included in the 1977 amendments,
the Agency's discussion for the 2009 Endangerment Finding regarding the
history of section 202 and how it supports the EPA's approach is also
relevant for section 231. EPA's interpretation of section 231 is the
same as its interpretation of the parallel language in section 202(a),
which is explained in the 2009 Endangerment Finding. See 74 FR at
18891; see also 74 FR at 66506.
The legislative history clearly indicates that the House Committee
believed the Ethyl Corp. decisions posed several ``crucial policy
questions'' regarding the protection of public health and welfare. H.R.
Rep. 95-294 at 48, 4 LH at 2515.\77\ The following paragraphs summarize
the en banc decision in Ethyl Corp. v. EPA and describe how the House
Committee revised the endangerment language in the 1977 amendments to
the CAA to serve several purposes consistent with that decision. In
particular, the language: (1) Emphasizes the preventive or
precautionary nature of the CAA;\78\ (2) authorizes the Administrator
to reasonably project into the future and weigh risks; (3) assures the
consideration of the cumulative impact of all sources; (4) instructs
that the health of susceptible individuals, as well as healthy adults,
should be part of the analysis; and (5) indicates an awareness of the
uncertainties and limitations in information available to the
Administrator. H.R. rep. 95-294 at 49-50, 4 LH 2516-17.\79\
---------------------------------------------------------------------------

\77\ The Supreme Court recognized that the current language in
section 202(a)(1), which uses the same formulation as that in
section 231(a)(2)(A), is ``more protective'' than the 1970 version
that was similar to the section 211 language before the D.C. Circuit
in Ethyl Corp. Massachusetts v. EPA, 549 U.S. at 506, fn 7.
\78\ See H.R. Rep. 95-294 at 49, 4 LH at 2516 (``To emphasize
the preventive or precautionary nature of the Act, i.e. to assure
that regulatory action can effectively prevent harm before it
occurs'').
\79\ Congress also standardized this language across the various
sections of the CAA which address emissions from both stationary and
mobile sources. H.R. Rep. 95-294 at 50, 4 LH at 2517; section 401 of
the CAA Amendments of 1977.
---------------------------------------------------------------------------

In revising the statutory language, Congress relied heavily on the
en banc decision in Ethyl Corp. v. EPA, which reversed a three-judge
panel opinion regarding an EPA rule restricting the content of lead in
leaded gasoline.\80\ After reviewing the relevant facts and law, the
full court evaluated the statutory language at issue to see what level
of ``certainty [was] required by the Clean Air Act before EPA may
act.'' 541 F.2d at 7.
---------------------------------------------------------------------------

\80\ At the time of the 1973 rules requiring the reduction of
lead in leaded gasoline, section 211(c)(1)(A) of the CAA stated that
the Administrator may promulgate regulations that: ``control or
prohibit the manufacture, introduction into commerce, offering for
sale, or sale of any fuel or fuel additive for use in a motor
vehicle or motor vehicle engine (A) if any emissions product of such
fuel or fuel additive will endanger the public health or welfare . .
.'' CAA section 211(c)(1)(A) (1970).
---------------------------------------------------------------------------

The petitioners argued that the statutory language ``will
endanger'' required proof of actual harm, and that the actual harm had
to come from emissions from the fuels in and of themselves. Id. at 12,
29. The en banc court rejected this approach, finding that the term
``endanger'' allowed the Administrator to act when harm is threatened,
and did not require proof of actual harm. Id. at 13. ``A statute
allowing for regulation in the face of danger is, necessarily, a
precautionary statute.'' Id. Optimally, the court found, regulatory
action would not only precede, but prevent, a perceived threat. Id.
The court also rejected petitioners' argument that any threatened
harm must be ``probable'' before regulation was authorized.
Specifically, the court recognized that danger ``is set not by a fixed
probability of harm, but rather is composed of reciprocal elements of
risk and harm, or probability and severity.'' Id. at 18. Next, the
court held that the EPA's evaluation of risk is necessarily an exercise
of judgment, and that the statute did not require a factual finding.
Id. at 24. Thus, ultimately, the Administrator must ``act, in part on
`factual issues,' but largely `on choices of policy, on an assessment
of risks, [and] on predictions dealing with matters on the frontiers of
scientific knowledge . . .'' Id. at 29 (citations omitted). Finally,
the en banc court agreed with the EPA that even without the language in
section 202(a) (which is also in section 231(a)(2)(A)) regarding
``cause or contribute to,'' it was appropriate for the EPA to consider
the cumulative impact of lead from numerous sources, not just the fuels
being regulated under section 211(c). Id. at 29-31.
The dissent in the original Ethyl Corp. decision and the en banc
opinion were of ``critical importance'' to the House Committee which
proposed the revisions to the endangerment language in the 1977
amendments to the CAA. H.R. Rep. 95-294 at 48, 4 LH at 2515. The
Committee addressed those questions with the language that now appears
in section 231(a)(2)(A) and several other CAA provisions--``emission of
any air pollutant . . . which in [the Administrator's] judgment causes,
or contributes to, air pollution which may reasonably be anticipated to
endanger public health or welfare.''
As noted above in section III.A.1, the phrase ``in [her] judgment''
calls for the Administrator to make a comparative assessment of risks
and projections of future possibilities, consider uncertainties, and
extrapolate from limited data. Thus, the Administrator must balance the
likelihood of effects with the severity of the effects in reaching her
judgment. The Committee emphasized that the Administrator's exercise of
``judgment'' \81\ may include making projections, assessments and
estimates that are reasonable, as opposed to a speculative or ``
`crystal ball' inquiry.'' Moreover, procedural safeguards apply to the
exercise of judgment, and final decisions are subject to judicial
review. Also, the phrase ``in [her] judgment'' modifies both the
phrases ``cause and contribute'' and ``may reasonably be anticipated,''
as discussed above. H.R. Rep. 95-294 at 50-51, 4 LH at 2517-18.
---------------------------------------------------------------------------

\81\ Throughout this document under CAA section 231, as
throughout the previous notices concerning the 2009 Endangerment
Finding under section 202, the judgments on endangerment and cause
or contribute are described as a finding or findings. This is for
ease of reference only, and is not intended to imply that the
Administrator's judgment is solely a fact finding exercise; rather,
the Administrator's exercise of judgment is to consider and weigh
multiple factors when applying the scientific information to the
statutory criteria.
---------------------------------------------------------------------------

As the Committee further explained, the phrase ``may reasonably be
anticipated'' points the Administrator in the direction of assessing
current and future risks rather than waiting for proof of actual harm.
This phrase is also intended to instruct the Administrator to consider
the limitations and

[[Page 54437]]

difficulties inherent in information on public health and welfare. H.R.
Rep. 95-294 at 51, 4 LH at 2518.\82\
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\82\ Thus, the statutory language does not require that the EPA
prove the effects of climate change ``beyond a reasonable doubt.''
Indeed, such an approach is inconsistent with the concepts of
reasonable anticipation and endangerment embedded in the statute.
See also CRR, 684 F.3d at 121-122.
---------------------------------------------------------------------------

Finally, the phrase ``cause or contribute'' ensures that all
sources of the contaminant which contribute to air pollution are
considered in the endangerment analysis (e.g., not a single source or
category of sources). It is also intended to require the Administrator
to consider all sources of exposure to a pollutant (for example, food,
water, and air) when determining risk. Id.
3. Additional Considerations for the Cause or Contribute Analysis
By instructing the Administrator to consider whether emissions of
an air pollutant cause or contribute to air pollution, the statute is
clear that she need not find that emissions from any one sector or
class of sources are the sole or even the major part of an air
pollution problem. The use of the term ``contribute'' clearly indicates
a lower threshold than the sole or major cause.
Moreover, like the section 202(a) language that governed the 2009
Endangerment Finding, the statutory language in section 231(a)(2)(A)
does not contain a modifier on its use of the term ``contribute.'' This
contrasts with other CAA provisions that expressly require
``significant'' contribution. Compare, e.g., CAA sections
110(a)(2)(D)(i)(I); 111(b); 213(a)(2), (4). In the absence of specific
language regarding the degree of contribution, the Administrator is to
exercise her judgment in determining contribution. Congress clearly
authorized regulatory controls to address air pollution even if the air
pollution problem results from a wide variety of sources. While the
endangerment test looks at the entire air pollution problem and the
risks it poses, the cause or contribute test is designed to authorize
the EPA to identify and then address what may well be many different
sectors, classes, or groups of sources that are each part of the
problem.
As explained for the 2009 Endangerment Finding, the D.C. Circuit
has discussed the concept of contribution in the CAA, and its case law
supports the EPA's interpretation that the level of contribution in
this context need not be significant. 74 FR at 66542. In Catawba County
v. EPA, 571 F.3d 20 (D.C. Cir. 2009), the court upheld EPA's
PM2.5 attainment and nonattainment designation decisions,
analyzing CAA section 107(d), which requires EPA to designate an area
as nonattainment if it ``contributes to ambient air quality in a nearby
area'' that does not meet the national ambient air quality standards.
Id. at 35. The court noted that it had previously held that the term
``contributes'' is ambiguous in the context of CAA language. See EDF v.
EPA, 82 F.3d 451, 459 (D.C. Cir. 1996). ``[A]mbiguities in statutes
within an agency's jurisdiction to administer are delegations of
authority to the agency to fill the statutory gap in reasonable
fashion.'' 571 F.3d at 35 (citing Nat'l Cable & Telecomms. Ass'c v.
Brand X Internet Servs, 545 U.S. 967, 980 (2005)). The court then
proceeded to consider and reject petitioners' argument that the verb
``contributes'' in CAA section 107(d) necessarily connotes a
significant causal relationship. Specifically, the D.C. Circuit again
noted that the term is ambiguous, leaving it to EPA to interpret in a
reasonable manner. In the context of this discussion, the court noted
that ``a contribution may simply exacerbate a problem rather than cause
it . . .'' 571 F.3d at 39.
This is consistent with the D.C. Circuit's discussion of the
concept of contribution in the context of CAA section 213 and rules for
nonroad vehicles in Bluewater Network v. EPA, 370 F.3d 1 (D.C. Cir.
2004). In that case, industry argued that section 213(a)(3) requires a
finding of a significant contribution from classes of new nonroad
engines or vehicles to ozone or carbon monoxide concentrations before
the EPA can regulate those engines or vehicles, while the EPA's view
was that the CAA requires a finding only of contribution. Id. at 13.
Section 213(a)(3)'s regulatory authority for specific classes of
nonroad engines or vehicles, like that of section 231(a)(2)(A) for
classes of aircraft engines, is triggered by a finding that certain
sources ``cause, or contribute to,'' air pollution, whereas an adjacent
provision, section 213(a)(2), is triggered by a finding of a
``significant'' contribution from all new and existing nonroad engines
and vehicles. The court looked at the ``ordinary meaning of
`contribute' '' when upholding the EPA's reading of section 213(a)(3).
After referencing dictionary definitions of ``contribute,'' the court
also noted that ``[s]tanding alone, the term has no inherent
connotation as to the magnitude or importance of the relevant `share'
in the effect; certainly it does not incorporate any `significance'
requirement.'' 370 F.3d at 13.\83\ The court found that the bare
``contribute'' language in section 213(a)(3) invests the Administrator
with discretion to exercise judgment regarding what constitutes a
sufficient contribution for the purpose of making a cause or contribute
finding. Id. at 14.\84\
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\83\ Specifically, the decision noted that `` `contribute' means
simply `to have a share in any act or effect,' Webster's Third New
International Dictionary 496 (1993), or `to have a part or share in
producing,' 3 Oxford English Dictionary 849 (2d ed. 1989).'' Id. at
13.
\84\ The court explained, ``[t]he repeated use of the term
`significant' to modify the contribution required for all nonroad
vehicles, coupled with the omission of this modifier from the
`cause, or contribute to' finding required for individual categories
of new nonroad vehicles, indicates that Congress did not intend to
require a finding of `significant contribution' for individual
vehicle categories.'' Id. at 13.
---------------------------------------------------------------------------

Like the statutory language considered in Catawba County and
Bluewater Network, as well as the section 202(a) language that governed
the Agency's previous findings for GHGs emitted by other types of
mobile sources, section 231(a)(2)(A) refers to contribution and does
not specify that the contribution must be significant before an
affirmative finding can be made. To be sure, any finding of a
``contribution'' requires some measureable amount of pollutant
emissions to be resulting from the analyzed source category; a truly
trivial or de minimis ``contribution'' might not count as such
(although such a small level is not presented by the facts of today's
findings). The Administrator therefore has ample discretion in
exercising her reasonable judgment and determining whether, under the
circumstances presented, the cause or contribute criterion has been
met.\85\ As noted above, in addressing provisions in section 202(a),
the D.C. Circuit has explained that the Act at the endangerment finding
step did not require the EPA to identify a precise numerical value or
``a minimum threshold of risk or harm before determining whether an air
pollutant endangers.'' CRR, 684 F.3d at 122-123. Accordingly, EPA ``may
base an endangerment finding on `a lesser risk of greater harm . . . or
a greater risk of lesser harm' or any combination in between.'' Id.
(quoting Ethyl Corp., 541 F.2d at 18). Recognizing the substantial
record of empirical data and scientific evidence that the EPA relied
upon in the 2009 Endangerment Finding, the court determined that its
``failure to

[[Page 54438]]

distill this ocean of evidence into a specific number at which
greenhouse gases cause `dangerous' climate change is a function of the
precautionary thrust of the CAA and the multivariate and sometimes
uncertain nature of climate science, not a sign of arbitrary or
capricious decision-making.'' Id. at 123. As the language in section
231(a)(2)(A) is analogous to that in section 202(a), it is clearly
reasonable to apply this interpretation to the endangerment
determination under section 231(a)(2)(A). Moreover, the logic
underlying this interpretation supports the general principle that
under CAA section 231 the EPA is not required to identify a specific
minimum threshold of contribution from potentially subject source
categories in determining whether their emissions ``cause or
contribute'' to the endangering air pollution. The reasonableness of
this principle is further supported by the fact that section 231 does
not impose on the EPA a requirement to find that such contribution is
``significant,'' let alone the sole or major cause of the endangering
air pollution. This context further supports the EPA's interpretation
that section 231(a)(2)(A) does not require some level of contribution
that rises to a pre-determined numerical level or percentage- or mass-
based portion of the overall endangering air pollution.
---------------------------------------------------------------------------

\85\ Section V discusses the evidence in this case that supports
the finding of contribution. The EPA need not determine at this time
the circumstances in which emissions would be trivial or de minimis
and would not warrant a finding of contribution.
---------------------------------------------------------------------------

In addition, when exercising her judgment in making a cause or
contribute determination, the Administrator not only considers the
cumulative impact, but also looks at the totality of the circumstances
and weight of evidence (e.g., the air pollutant, the air pollution, the
nature of the endangerment, the type or classes of sources at issue,
the number of sources in the source sector or class, and the number and
type of other source sectors or categories that may emit the air
pollutant) when determining whether the emissions ``justify
regulation'' under the CAA. See Catawba County, 571 F.3d at 39
(discussing EPA's interpretation of the term ``contribute'' under CAA
section 107(d) and finding it reasonable for the agency to apply a
totality of the circumstances approach); see also 74 FR at 66542.
Further discussion of this issue can be found in sections IV and V of
this preamble.
4. Summary of Responses to Key Legal Comments on the Interpretation of
the CAA Section 231(a) Endangerment and Cause or Contribute Test
Here we summarize key public comments regarding the legal
interpretation of CAA section 231(a)(2)(A) that supports this finding
and the Agency's response. The Response to Comments document contains
the Agency's full response to comments on this topic.
Some commenters strongly supported the proposed findings. These
comments stated, for example, that the proposed findings were clearly
authorized under CAA section 231(a)(2)(A) and further noted that the
U.S. Supreme Court had upheld EPA's authority under section 202(a) of
the CAA to make an endangerment finding with regard to GHG emissions
from motor vehicles and that the findings required under section
202(a)(1) are the same as the findings required under section
231(a)(2)(A). Another commenter, however, questioned the EPA's
authority to make endangerment and cause or contribute findings for
GHGs, stating that the EPA had not sufficiently explained its authority
to address pollutants other than NAAQS under CAA section 231. This
commenter made the following points in support of this view. First, the
comment pointed to the use of the term ``air quality control regions''
in CAA sections 231(a)(1)(A) and 231(a)(3) as suggesting that Congress
intended to authorize EPA to issue standards only for pollutants for
which a NAAQS has been established. Second, the comment stated that the
EPA should address this issue in light of a recent Supreme Court case,
Utility Air Regulatory Grp. v. EPA, 134 S.Ct. 2427 (2014).
After consideration of these comments, we disagree with the
argument that Congress intended to only authorize the EPA to address
NAAQS pollutants under section 231(a)(2)(A). That provision of the Act
requires the EPA to issue standards ``applicable to the emission of any
air pollutant from any class or classes of aircraft engines which in
[her] judgment causes, or contributes to, air pollution which may
reasonably be anticipated to endanger public health or welfare.'' CAA
section 231(a)(2)(A) (emphasis added). Looking to that plain language,
there is nothing that limits the scope of the air pollutants that can
be found to contribute to possible endangerment, and therefore which
the EPA may be required to regulate, under that section to NAAQS
pollutants. To the contrary, the language is clear that the EPA would
be required to regulate aircraft engine emissions of ``any air
pollutant'' as long the pre-requisite endangerment and cause or
contribute findings are made. ``Air pollutant'' is not defined in
section 231; instead, the definition under CAA section 302(g) applies,
which states in relevant part that `` `air pollutant' means any air
pollutant agent or combination of such agents, including any physical,
chemical . . . substance or matter which is emitted into or otherwise
enters ambient air.'' CAA section 302(g) (emphasis added). Interpreting
this provision in Massachusetts v. EPA, the U.S. Supreme Court observed
that ``[o]n its face, the definition embraces all airborne compounds of
whatever stripe, and underscores that intent through the repeated use
of the word `any.' '' 549 U.S. 497, 529 (2007). It further stated that
``[b]ecause greenhouse gases fit well within'' this ``capacious
definition of `air pollutant' '' the EPA has the statutory authority to
regulate the emission of such gases from new motor vehicles under CAA
section 202(a)(2). Id. at 532. As noted above, sections 231(a)(2)(A)
and 202(a)(1) have parallel structures, use substantially the same
language, and use the same definition of air pollutant. As that
definition is ``unambiguous'' in its inclusion of GHGs, Massachusetts,
549 U.S. at 529, the Act clearly authorizes the EPA to make these
findings for GHGs under CAA section 231(a)(2)(A). Moreover, one U.S.
District Court has also ruled that the EPA has a duty to determine
whether aircraft engine emissions of GHGs cause or contribute to
endangerment, and that ruling was not appealed to the D.C. Circuit.
Center for Biological Diversity, et al. v. EPA, 794 F. Supp. 2d 151
(D.D.C. 2011). Consequently, the statutory language imposing the EPA's
duties under section 231(a)(2)(A), and relevant case law in the GHG
context, do not support the commenter's limited reading of the EPA's
authority under that language.
The commenter points to the use of the term ``air quality control
regions'' in nearby paragraphs of CAA sections 231(a)(1)(A) and (a)(3)
to support its suggestion that Congress intended to limit the EPA's
analysis and regulatory authority to NAAQS pollutants in section
231(a)(2)(A). That argument is flawed for several reasons. The
commenter points to section 231(a)(1), which relates to a study the EPA
was to conduct of emissions of air pollutants from aircraft, and to
section 231(a)(3), which requires the EPA to hold public hearings with
respect to proposed standards under section 231(a)(2) in ``air quality
control regions . . . most seriously affected by aircraft emissions''
to the extent practicable. These obligations are imposed in addition to
those imposed by section 231(a)(2)(A), and their separate establishment
does not by that fact narrow the EPA's scope of authority regarding its
obligations imposed under section 231(a)(2)(A). They are additive, not
subtractive, duties. Moreover, one of those added

[[Page 54439]]

duties, to investigate the extent to which aircraft emissions affect
air quality in air quality control regions under section 231(a)(1)(A),
was a one-time duty that corresponded to NAAQS that have long-since
been revised, whereas the EPA's duty to propose and promulgate aircraft
emission standards is a continuing one to be conducted ``from time to
time'' under section 231(a)(2)(A). The commenter provides no reasoning
to explain why these provisions imposing additional duties should be
read to limit the scope of section 231(a)(2) beyond their proximity.
Sections 231(a)(1) and (a)(3) do not speak to what pollutants may be
addressed under section 231(a)(2). Further, there is no incompatibility
between the use of the term ``air quality control regions'' in those
provisions to identify geographic areas where certain activities are to
occur and making the endangerment and cause or contribute findings for
GHGs that are finalized in this action. In fact, the EPA long ago
discharged its one-time duty under CAA section 231(a)(1)(A) \86\ and,
after proposing new aircraft engine emission standards, could also meet
its obligations to hold public hearings in the air quality control
regions most seriously affected by aircraft emissions, to the extent
practicable, all while meeting its obligations under section
231(a)(2)(A). Accordingly, the EPA does not interpret sections
231(a)(1) and (a)(3) to limit the scope of the duties and authority
established by section 231(a)(2) to NAAQS pollutants. Further, the EPA
has previously implemented section 231(a)(2) to reach air pollutants
for which no NAAQS exists and has applied that provision to establish
standards for non-NAAQS pollutants, such as smoke. See, e.g., 40 CFR
87.21(a)-(c), (e), 87.23(a)-(c), and 87.31(a)-(c) emission standards
for smoke. The EPA's regulation of non-NAAQS smoke emissions from
aircraft engines has never been judicially challenged. Finally, even if
the Act were ambiguous, which it is not, the EPA's interpretation of
section 231(a)(2) to include authority to address GHGs, is reasonable
for the reasons described above.
---------------------------------------------------------------------------

\86\ USEPA, 1973: Aircraft Emissions: Impact On Air Quality And
Feasibility Of Control. U.S. Environmental Protection Agency, 102
pp. Available at http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=2000T6Z0.txt (last accessed April 26, 2016).
---------------------------------------------------------------------------

The U.S. Supreme Court's opinion in UARG cited by the commenter
does not change this analysis. The commenter misinterprets the UARG
decision to mean that for purposes of determining applicability of the
CAA's Prevention of Significant Deterioration (PSD) preconstruction
permitting program, ``air pollutant'' meant only pollutants for which
NAAQS had been established. The UARG decision, however, does not limit
PSD applicability to only NAAQS pollutants. In fact, the Court
recognized that such theories had been advanced during the course of
that litigation but expressly declined to consider them in its
decision. See 134 S.Ct. 2427, 2442 n.6 (2014). Rather, in UARG, the
Court's holding pertained only to GHGs. More specifically, the Court
held that the EPA may not treat GHGs as an air pollutant for the
specific purpose of determining whether a source is a major source (or
a modification thereof) and thus required to obtain a PSD permit or an
operating permit under title V of the CAA. Id. at 2449.
Further, the regulatory context that was addressed in UARG is
distinguishable from that of this action. In UARG, the Court explained
that Massachusetts does not prevent an Agency from using statutory
context to infer that in some provisions ``air pollutant'' refers only
to those airborne substances that ``may sensibly be encompassed within
the particular regulatory program.'' 134 S.Ct. at 2441. However, the
commenter offers no reason why GHG emissions from U.S. covered aircraft
could not ``sensibly be encompassed'' under CAA section 231; nor is the
EPA aware of any such reasons. In fact, UARG itself recognizes a
distinction between the statutory scheme of the CAA permitting programs
at issue in that case and the mobile source programs under Title II of
the Act which were at issue in Massachusetts. Namely, the UARG opinion
notes that part of the Court's reasoning in Massachusetts was based on
its understanding that ``nothing in the Act suggested that regulating
greenhouse gases under [Title II] would conflict with the statutory
design. Title II would not compel EPA to regulate in any way that would
be `extreme,' `counterintuitive,' or contrary to `common sense.' . . .
At most, it would require EPA to take the modest step of adding
greenhouse-gas standards to the roster of new-motor-vehicle emission
regulations.'' 134 S.Ct. at 2441 (quoting Massachusetts, 549 U.S. at
531). Like Massachusetts, the statutory provisions for this action are
found in Title II, and closely parallel the structure and language of
the statutory program at issue in Massachusetts.\87\ Compare CAA
section 231(a)(2)(A) with 202(a)(1). Nor will reading the Title II
provision section 231(a)(2)(A) to extend to GHGs result in a regulatory
outcome that would be extreme, counterintuitive or contrary to common
sense. Instead, as the D.C. Circuit has previously ruled, the EPA's
discretion when establishing reasonable standards under section 231 is
exceptionally broad. See NACAA, 489 F.3d at 1230-32. In short, the UARG
opinion in no way precludes the EPA's interpretation that ``air
pollutant'' as used in CAA section 231(a)(2)(A) includes GHGs, but
rather supports that interpretation.
---------------------------------------------------------------------------

\87\ Although this comment asserts that section 202(a) does not
include mention of ``air quality control region'' as other
provisions of section 231(a) do, that distinction is immaterial. As
described above, the use of that term in other paragraphs imposing
additional duties beyond those established by section 231(a)(2)(A)
does not affect what pollutants may be addressed under section
231(a)(2)(A).
---------------------------------------------------------------------------

To the extent that the commenter is suggesting that the EPA should
exercise its discretion to interpret CAA section 231(a)(2)(A) to
exclude GHGs, the EPA declines to do so. The commenter has provided no
persuasive reason for such an exclusion. Moreover, to make the
threshold findings in this action, the EPA must, fundamentally, answer
only two questions: Whether the particular ``air pollution''--here, the
six well-mixed GHGs--``may reasonably be anticipated to endanger public
health or welfare,'' and whether emissions of those six well-mixed GHGs
from U.S. covered aircraft engines ``cause, or contribute to'' that
endangerment. See CRR, 648 F.3d at 117 (interpreting analogous
provisions in CAA section 202(a)). Because the EPA answers both of
these questions in the affirmative for emissions of the six well-mixed
GHGs from U.S. covered aircraft engines--based on extensive scientific
evidence and emissions information, as explained in detail in sections
IV and V below--it is appropriate and reasonable to make both
endangerment and cause or contribute findings under section
231(a)(2)(A) in this action.
In sum, after considering all of the relevant information,
including that in public comments, the EPA interprets section
231(a)(2)(A) to include authority to address GHGs from U.S. covered
aircraft engines. This interpretation is consistent with both its own
and with judicial interpretations that the EPA's authority under the
analogous section 202(a) unambiguously extends to GHGs.

B. Air Pollutant, Public Health and Welfare

The CAA defines both ``air pollutant'' and ``welfare.'' Air
pollutant is defined as: ``any air pollution agent or combination of
such agents, including any physical, chemical, biological,

[[Page 54440]]

radioactive (including source material, special nuclear material, and
byproduct material) substance or matter which is emitted into or
otherwise enters the ambient air. Such term includes any precursors to
the formation of any air pollutant, to the extent the Administrator has
identified such precursor or precursors for the particular purpose for
which the term `air pollutant' is used.'' CAA section 302(g). GHGs fit
well within this capacious definition. See Massachusetts v. EPA, 549
U.S. at 532. They are ``without a doubt'' physical chemical substances
emitted into the ambient air. Id. at 529. Section V below contains
further discussion of the term ``air pollutant'' for purposes of this
section 231(a)(2)(A) contribution finding, which uses the same
definition of air pollutant as the one the EPA adopted for purposes of
the 2009 Endangerment Finding.
Regarding ``welfare,'' the CAA states that ``[a]ll language
referring to effects on welfare includes, but is not limited to,
effects on soils, water, crops, vegetation, manmade materials, animals,
wildlife, weather, visibility, and climate, damage to and deterioration
of property, and hazards to transportation, as well as effects on
economic values and on personal comfort and well-being, whether caused
by transformation, conversion, or combination with other air
pollutants.'' CAA section 302(h). This definition is quite broad.
Importantly, it is not an exclusive list due to the use of the term
``includes, but is not limited to . . .'' Effects other than those
listed here may also be considered effects on welfare.
Moreover, the terms contained within the definition are themselves
expansive. For example, deterioration to property could include damage
caused by extreme weather events. Effects on vegetation could include
impacts from changes in temperature and precipitation as well as from
the spreading of invasive species or insects. Prior welfare effects
evaluated by the EPA in other contexts include impacts on vegetation,
as well as reduced visibility, changes in nutrient balance and acidity
of the environment, soiling of buildings and statues, and erosion of
building materials. See, e.g., Final Secondary National Ambient Air
Quality Standards for Oxides of Nitrogen and Sulfur, 77 FR 20218 (April
3, 2012); Control of Emissions from Nonroad Large Spark Ignition
Engines and Recreational Engines (Marine and Land-Based), 67 FR 68242
(November 8, 2002); Final Heavy-Duty Engine and Vehicle Standards and
Highway Diesel Sulfur Control Requirements, 66 FR 5002 (January 18,
2001).
Although the CAA defines ``effects on welfare'' as discussed above,
there is no definition of ``public health'' in the Clean Air Act. The
Supreme Court has discussed the concept of ``public health'' in the
context of whether costs can be considered when setting NAAQS. Whitman
v. American Trucking Ass'n, 531 U.S. 457 (2001). In Whitman, the Court
imbued the term with its most natural meaning: ``the health of the
public.'' Id. at 466. When considering public health, the EPA has
looked at morbidity, such as impairment of lung function, aggravation
of respiratory and cardiovascular disease, and other acute and chronic
health effects, as well as mortality. See, e.g., Final National Ambient
Air Quality Standard for Ozone, 73 FR 16436 (March 27, 2008).

IV. The Administrator's Finding Under CAA Section 231 That Greenhouse
Gases Endanger Public Health and Welfare

The Administrator finds, for purposes of CAA section 231(a)(2)(A),
that elevated concentrations of the six well-mixed GHGs constitute air
pollution that may reasonably be anticipated to endanger both the
public health and welfare of current and future generations. The
Administrator is making this finding specifically with regard to the
same definition of the ``air pollution'' under CAA section 231(a)(2) as
that used under CAA section 202(a)(1), namely the combined mix of
CO2, methane, nitrous oxide, hydrofluorocarbons,
perfluorocarbons, and sulfur hexafluoride, which together are the root
cause and best understood drivers of human-induced climate change and
the resulting impacts on public health and welfare. The EPA received
public comments on this definition of air pollution from the proposed
findings, and summarizes responses to some of those key comments below;
fuller responses to public comments can be found in EPA's Response to
Comments document included in the docket. The Administrator addresses
other climate-forcing agents both in the 2009 Endangerment Finding \88\
and in this action; however, these substances are not included in the
air pollution definition used in this action for the reasons discussed
below in section IV.B.7.
---------------------------------------------------------------------------

\88\ 74 FR at 66519-21.
---------------------------------------------------------------------------

Section IV.A below discusses the EPA's approach to evaluating the
scientific evidence before it. Section IV.B discusses the scope and
nature of the relevant air pollution for the endangerment finding under
CAA section 231(a)(2)(A), including a discussion of other substances
with climate effects that were addressed but not included in the
definition of air pollution. Section IV.C summarizes the scientific
evidence that the air pollution is reasonably anticipated to endanger
both public health and welfare. Section IV.D summarizes the
Administrator's conclusion for purposes of section 231(a)(2)(A), in
light of the evidence, analysis, and conclusions that led to the 2009
Endangerment Finding as well as more recent evidence and consideration
of public comments, that emissions of the six well-mixed GHGs in the
atmosphere may reasonably be anticipated to endanger public health and
welfare.

A. The Science Upon Which the Agency Relied

This finding under section 231(a)(2)(A) reflects the EPA's careful
consideration not only of the scientific and technical record for the
2009 Endangerment Finding, but also of science assessments released
since 2009, which, as illustrated below, strengthen and further support
the judgment that the six well-mixed GHGs in the atmosphere may
reasonably be anticipated to endanger public health and welfare. The
Administrator's view is that the body of scientific evidence amassed in
the record for the 2009 Endangerment Finding compellingly supports an
endangerment finding for the six well-mixed GHGs under CAA section
231(a)(2)(A). While the EPA is providing a summary of newer scientific
assessments below, the EPA is also relying on the same scientific and
technical evidence discussed in the notices for the 2009 Endangerment
Finding in these final findings for purposes of CAA section
231(a)(2)(A).\89\
---------------------------------------------------------------------------

\89\ See sections III of the 2009 Proposed Endangerment Finding
and sections III and IV of the 2009 Endangerment Finding. 74 FR at
18894-18904 and 74 FR at 66510-36.
---------------------------------------------------------------------------

The EPA is following the same approach toward technical and
scientific information in this finding under section 231(a)(2)(A) as it
used in the 2009 Endangerment Finding. More specifically, in the 2009
Endangerment Finding the EPA's approach to providing the technical and
scientific information to inform the Administrator's judgment regarding
the question of whether GHGs endanger public health and welfare was to
consider the recent, major assessments by the U.S. Global Change
Research Program (USGCRP), the IPCC, and the National Research Council
of the

[[Page 54441]]

National Academies of Sciences, Engineering, and Medicine (referred to
interchangeably as NRC or NAS) as the primary scientific and technical
basis informing the endangerment finding. These assessments draw
synthesis conclusions across thousands of individual peer-reviewed
studies that appear in scientific journals, and the reports themselves
undergo additional peer review. The EPA has considered the processes
and procedures employed by the USGCRP, IPCC, and the NRC in terms of
factors such as their objectivity, integrity, utility, and
transparency, including how they have employed rigorous peer review
processes. The EPA considers these assessments to represent the best
available science that maintains the highest level of adherence to
Agency guidelines for information quality.\90\ These assessments have
been adequately peer reviewed in a manner commensurate with the EPA's
Peer Review Policy \91\ and guidance in the EPA's Peer Review
Handbook.\92\
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\90\ Applicable guidance includes U.S. EPA 2012: Addendum to A
Summary of General Assessment Factors for Evaluating the Quality of
Scientific and Technical Information, 9 pp. Available at https://www.epa.gov/risk/guidance-evaluating-and-documenting-quality-existing-scientific-and-technical-information (last accessed July
11, 2016) and U.S. EPA, 2002: Guidelines for Ensuring and Maximizing
the Quality, Objectivity, Utility, and Integrity of Information
Disseminated by the EPA, 61 pp. Available at https://www.epa.gov/quality/guidelines-ensuring-and-maximizing-quality-objectivity-utility-and-integrity-information (last accessed July 11, 2016).
\91\ U.S. EPA, 2006: Memorandum on Peer Review and Peer
Involvement at the U.S. EPA, 4 pp. Available at https://www.epa.gov/osa/memorandum-peer-review-and-peer-involvement-epa (last accessed
April 12, 2016).
\92\ U.S. EPA, 2015: EPA Peer Review Handbook, Fourth Edition,
248 pp. Available at https://www.epa.gov/osa/peer-review-handbook-4th-edition-2015-0 (last accessed April 12, 2016). Also, the EPA
Science Advisory Board reviewed this approach to the underlying
technical and scientific information supporting this action, and
concluded that the approach had precedent and the action will be
based on well-reviewed information. A copy of this letter and all
other relevant EPA peer review documentation is located in the
docket for today's final action (EPA-HQ-OAR-2014-0828).
---------------------------------------------------------------------------

The EPA is giving careful consideration to all of the scientific
and technical information in the record. However, the Administrator
considers the major scientific assessments as the primary scientific
and technical basis of her endangerment decision. This provides
assurance that the Administrator is basing her judgment on the best
available, well-vetted science that reflects the consensus of the
climate science research community. These assessments addressed the
scientific issues that the EPA was required to examine, were
comprehensive in their coverage of the GHG and climate change issues,
and underwent rigorous and exacting peer review by the expert
community, as well as rigorous levels of U.S. government review, in
which the EPA took part. The major findings of the USGCRP, IPCC, and
NRC assessments support the Administrator's determination that elevated
concentrations of GHGs in the atmosphere may reasonably be anticipated
to endanger the public health and welfare of current and future
generations. The EPA presented this scientific support at length in the
comprehensive record for the 2009 Endangerment Finding.
The EPA reviewed ten administrative petitions for reconsideration
of the 2009 Endangerment Finding in 2010.\93\ In the Reconsideration
Denial, the Administrator denied those petitions on the basis of the
Petitioners' failure to provide substantial support for their argument
that the EPA should revise the 2009 Endangerment Finding and their
objections' lack of ``central relevance'' to the Finding.\94\ The EPA
prepared an accompanying three-volume Response to Petitions document to
provide additional information, often more technical in nature, in
response to the arguments, claims, and assertions by the Petitioners to
reconsider the Endangerment Finding.\95\
---------------------------------------------------------------------------

\93\ Administrative petitions are available from www3.epa.gov/climatechange/endangerment/petitions.html (last accessed June 21,
2016), and in the docket for the 2009 Endangerment Finding: EPA-HQ-
OAR-2009-0171.
\94\ U.S. EPA, 2010: Denial of the Petitions to Reconsider the
Endangerment and Cause or Contribute Findings for Greenhouse Gases
Under section 202(a) of the Clean Air Act, 75 FR 49557 (August 13,
2010) (``Reconsideration Denial''). In that notice, the EPA
thoroughly considered the scientific and technical information
relevant to the petitions. In addition to the other information
discussed in the present notice, the EPA is also relying on the
scientific and technical evidence discussed in that prior notice for
purposes of its proposed determination under CAA section 231. See
section III of the Reconsideration Denial.
\95\ The Response to Petitions document is available from
www3.epa.gov/climatechange/endangerment/petitions.html (last
accessed June 21, 2016), and in the docket for the 2009 Endangerment
Finding: EPA-HQ-OAR-2009-0171.
---------------------------------------------------------------------------

The 2009 Endangerment Finding and the 2010 Reconsideration Denial
were challenged in a lawsuit before the D.C. Circuit.\96\ On June 26,
2012, the D.C. Circuit upheld the Endangerment Finding and the
Reconsideration Denial, ruling that the Finding (including the
Reconsideration Denial) was not arbitrary or capricious, was consistent
with the U.S. Supreme Court's decision in Massachusetts v. EPA (which
affirmed the EPA's authority to regulate GHGs) \97\ and the text and
structure of the CAA, and was adequately supported by the
administrative record.\98\ The D.C. Circuit also agreed with the EPA
that the Petitioners had ``not provided substantial support for their
argument that the Endangerment Finding should be revised.'' \99\ It
found that the EPA had based its decision on ``substantial scientific
evidence,'' observing that ``EPA's scientific evidence of record
included support for the proposition that greenhouse gases trap heat on
earth that would otherwise dissipate into space; that this `greenhouse
effect' warms the climate; that human activity is contributing to
increased atmospheric levels of greenhouse gases; and that the climate
system is warming,'' as well as providing extensive scientific evidence
for EPA's determination that anthropogenically induced climate change
threatens both public health and welfare.\100\ The D.C. Circuit further
noted that the EPA's reliance on assessments was consistent with the
methods decision-makers often use to make a science-based
judgment.\101\ Moreover, it supported the EPA's reliance on the major
scientific assessment reports conducted by USGCRP, IPCC, and NRC and
found:
---------------------------------------------------------------------------

\96\ Coalition for Responsible Regulation, Inc. v. Environmental
Protection Agency, 684 F.3d 102 (D.C. Cir. 2012), reh'g en banc
denied, 2012 U.S. App. LEXIS 25997, 26313, 26315 (D.C. Cir. 2012)
(CRR).
\97\ 549 U.S. 497 (2007).
\98\ CRR, 684 F.3d at 117-27.
\99\ Id. at 125.
\100\ Id. at 120-121.
\101\ Id. at 121.

The EPA evaluated the processes used to develop the various
assessment reports, reviewed their contents, and considered the
depth of the scientific consensus the reports represented. Based on
these evaluations, the EPA determined the assessments represented
the best source material to use in deciding whether GHG emissions
may be reasonably anticipated to endanger public health or welfare .
. . It makes no difference that much of the scientific evidence in
large part consisted of ``syntheses'' of individual studies and
research. Even individual studies and research papers often
synthesize past work in an area and then build upon it. This is how
science works. The EPA is not required to re-prove the existence of
the atom every time it approaches a scientific question.\102\
---------------------------------------------------------------------------

\102\ Id. at 120.

In addition, the EPA's consideration of the major assessments to
inform the Administrator's judgment allowed for full and explicit
recognition of scientific uncertainty regarding the endangerment posed
by the atmospheric buildup of GHGs. The Administrator considered the
fact that ``some aspects of climate change science and the projected
impacts are more certain than others.'' \103\ The D.C. Circuit

[[Page 54442]]

subsequently noted that ``the existence of some uncertainty does not,
without more, warrant invalidation of an endangerment finding.'' \104\
---------------------------------------------------------------------------

\103\ 74 FR at 66524.
\104\ CRR, 684 F.3d at 121.
---------------------------------------------------------------------------

As noted above, the Supreme Court granted some of the petitions for
certiorari that were filed, while denying others, but agreed to decide
only the question: ``Whether EPA permissibly determined that its
regulation of greenhouse gas emissions from new motor vehicles
triggered permitting requirements under the Clean Air Act for
stationary sources that emit greenhouse gases.'' \105\ Thus, the
Supreme Court did not disturb the D.C. Circuit's holding that affirmed
the 2009 Endangerment Finding.
---------------------------------------------------------------------------

\105\ Utility Air Reg. Group v. EPA, 134 S. Ct. 2427, 2438
(2014) (internal marks and citations omitted). See also Virginia v.
EPA, 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA, 134 S. Ct. 418
(2013), and CRR, 134 S. Ct. 468 (2013) (all denying cert.).
---------------------------------------------------------------------------

Since the closure of the administrative record concerning the 2009
Endangerment Finding (including the denial of petitions for
reconsideration), a number of new major, peer-reviewed scientific
assessments have been released. The EPA carefully reviewed the updated
scientific conclusions in these assessments, largely to evaluate
whether they would lead the EPA in this CAA section 231(a)(2)(A)
finding to use a different interpretation of, or place more or less
weight on, the major findings reflected in the previous assessment
reports that underpinned the Administrator's judgment that the six
well-mixed GHGs endanger public health and welfare. The EPA reviewed
the following new major peer-reviewed scientific assessments:

IPCC's 2013-2014 Fifth Assessment Report (AR5) \106\
---------------------------------------------------------------------------

\106\ IPCC, 2013: Climate Change 2013: The Physical Science
Basis. Contribution of Working Group I to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Stocker,
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A.
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University
Press, 1535 pp, doi:10.1017/CBO9781107415324; IPCC, 2014: Climate
Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global
and Sectoral Aspects. Contribution of Working Group II to the Fifth
Assessment Report of the Intergovernmental Panel on Climate Change
[Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea,
T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B.
Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and
L.L. White (eds.)]. Cambridge University Press, 1132 pp; IPCC, 2014:
Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B:
Regional Aspects. Contribution of Working Group II to the Fifth
Assessment Report of the Intergovernmental Panel on Climate Change
[Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach,
T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B.
Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and
L.L. White (eds.)]. Cambridge University Press, 688 pp; and IPCC,
2014: Climate Change 2014: Mitigation of Climate Change.
Contribution of Working Group III to the Fifth Assessment Report of
the Intergovernmental Panel on Climate Change [Edenhofer, O., R.
Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A.
Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, 1435 pp.
---------------------------------------------------------------------------

IPCC's 2012 ``Special Report on Managing the Risks of Extreme
Events and Disasters to Advance Climate Change Adaptation'' (SREX)
\107\
---------------------------------------------------------------------------

\107\ IPCC, 2012: Managing the Risks of Extreme Events and
Disasters to Advance Climate Change Adaptation. A Special Report of
Working Groups I and II of the Intergovernmental Panel on Climate
Change [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken,
K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen,
M. Tignor, and P.M. Midgley (eds.)]. Cambridge University Press, 582
pp.
---------------------------------------------------------------------------

USGCRP's 2014 ``Climate Change Impacts in the United States:
the Third National Climate Assessment'' (NCA3) \108\
---------------------------------------------------------------------------

\108\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, 841 pp.
---------------------------------------------------------------------------

NRC's 2010 ``Ocean Acidification: A National Strategy to Meet
the Challenges of a Changing Ocean'' (Ocean Acidification) \109\
---------------------------------------------------------------------------

\109\ NRC, 2010: Ocean Acidification: A National Strategy to
Meet the Challenges of a Changing Ocean. The National Academies
Press, 188 pp.
---------------------------------------------------------------------------

NRC's 2011 ``Climate Change, the Indoor Environment, and
Health'' (Indoor Environment) \110\
---------------------------------------------------------------------------

\110\ NRC Institute of Medicine, 2011: Climate Change, the
Indoor Environment, and Health. Washington, DC: The National
Academies Press, 272 pp.
---------------------------------------------------------------------------

NRC's 2011 ``Report on Climate Stabilization Targets:
Emissions, Concentrations, and Impacts over Decades to Millennia''
(Climate Stabilization Targets) \111\
---------------------------------------------------------------------------

\111\ NRC 2011: Climate Stabilization Targets: Emissions,
Concentrations, and Impacts over Decades to Millennia. The National
Academies Press, 298 pp.
---------------------------------------------------------------------------

NRC's 2011 ``National Security Implications for U.S. Naval
Forces'' (National Security Implications) \112\
---------------------------------------------------------------------------

\112\ NRC, 2011: National Security Implications of Climate
Change for U.S. Naval Forces. The National Academies Press, 226 pp.
---------------------------------------------------------------------------

NRC's 2011 ``Understanding Earth's Deep Past: Lessons for Our
Climate Future'' (Understanding Earth's Deep Past) \113\
---------------------------------------------------------------------------

\113\ NRC, 2011: Understanding Earth's Deep Past: Lessons for
Our Climate Future. The National Academies Press, 212 pp.
---------------------------------------------------------------------------

NRC's 2012 ``Sea-Level Rise for the Coasts of California,
Oregon, and Washington: Past, Present, and Future'' (Sea Level Rise)
\114\
---------------------------------------------------------------------------

\114\ NRC, 2012: Sea-Level Rise for the Coasts of California,
Oregon, and Washington: Past, Present, and Future. The National
Academies Press, 201 pp.
---------------------------------------------------------------------------

NRC's 2013 ``Climate and Social Stress: Implications for
Security Analysis'' (Climate and Social Stress) \115\
---------------------------------------------------------------------------

\115\ NRC, 2013: Climate and Social Stress: Implications for
Security Analysis. The National Academies Press, 280 pp.
---------------------------------------------------------------------------

NRC's 2013 ``Abrupt Impacts of Climate Change'' (Abrupt
Impacts) \116\
---------------------------------------------------------------------------

\116\ NRC, 2013: Abrupt Impacts of Climate Change: Anticipating
Surprises. The National Academies Press, 250 pp.
---------------------------------------------------------------------------

NRC's 2014 ``The Arctic in the Anthropocene: Emerging Research
Questions'' (Arctic) \117\.
---------------------------------------------------------------------------

\117\ NRC, 2014: The Arctic in the Anthropocene: Emerging
Research Questions. The National Academies Press, 220 pp.

From its review, the EPA finds that these new assessments are
largely consistent with, and in many cases strengthen and add to, the
already compelling and comprehensive scientific evidence detailing the
role of the six well-mixed GHGs in driving climate change, explained in
the 2009 Endangerment Finding.
1. Response to Key Comments on the EPA's Approach to the Science
Here we summarize key public comments regarding the approach to the
science--see the Response to Comments document for the Agency's full
responses to comments. Several commenters agreed and no commenters
disagreed with the EPA's approach to the science for making an
endangerment decision specifically with respect to the six well-mixed
GHGs (see section IV.B.7 for a summary of key public comments and our
responses to commenters who argued that the science supports expanding
the scope of the endangerment finding to include other climate forcers
beyond the six well-mixed GHGs). They specifically mentioned their
support for the EPA's approach to considering the scientific and
technical information in the record of the 2009 Endangerment Finding--
primarily the recent, major assessments by the USGCRP, the IPCC, and
the NRC--as well as the most recent scientific assessments for
additional support and justification. For the reasons stated in section
IV.A above, the EPA agrees with the commenters that this approach
ensures that the Administrator considers the best available scientific
and technical information.

B. The Air Pollution Consists of Six Key Well-Mixed Greenhouse Gases

The Administrator must define the scope and nature of the relevant
air pollution for the endangerment finding under CAA section
231(a)(2)(A). In this

[[Page 54443]]

final action, the Administrator finds that the air pollution is the
combined mix of six well-mixed GHGs, which together are the root cause
and best understood drivers of human-induced climate change and the
resulting impacts on public health and welfare. These six GHGs--
CO2, methane, nitrous oxide, hydrofluorocarbons,
perfluorocarbons, and sulfur hexafluoride--are considered an aggregate
group for purposes of this finding. The Administrator's definition of
air pollution for purposes of section 231(a)(2)(A) is made in light of
(1) the evidence, analysis, and conclusions that led to the 2009
Endangerment Finding; (2) more recent evidence from scientific
assessments published since 2009; and (3) consideration of public
comments, for which key comments and responses are summarized in
sections IV.B.6 and 7 below. The Administrator considered five primary
reasons in the 2009 Endangerment Finding for focusing on this aggregate
group as the air pollution: (1) They share common physical properties
that influence their climate effects; (2) on the basis of these common
physical properties, they have been determined to be the root cause of
human-induced climate change, are the best-understood driver of climate
change, and are expected to remain the primary driver of future climate
change; (3) they are the common focus of climate change science
research and policy analyses and discussions; (4) using the combined
mix of these gases as the definition (versus an individual gas-by-gas
approach) is consistent with the science, because risks and impacts
associated with GHG-induced climate change are not assessed on an
individual gas-by-gas basis; and (5) using the combined mix of these
gases is consistent with past EPA practice, where separate substances
from different sources, but with common properties, may be treated as a
class (e.g., oxides of nitrogen, particulate matter, volatile organic
compounds).\118\ After consideration of all information before her,
including public comments, as explained below, the Administrator
maintains her view that these five reasons for defining the scope and
nature of the air pollution to be these six well-mixed GHGs remain
valid and well supported by the current science and are therefore
reasonable bases for adopting the same definition of ``air pollution''
in this section 231(a)(2)(A) finding as that under section 202(a)(1).
The following subsections summarize the five reasons detailed in the
2009 Endangerment Finding and as appropriate, summarize additional
supporting information from the recent scientific assessments published
since 2009.
---------------------------------------------------------------------------

\118\ 74 FR at 66517-19.
---------------------------------------------------------------------------

1. Common Physical Properties of the Six Greenhouse Gases
The six GHGs share common physical properties that are relevant to
the climate change problem. They all are sufficiently long lived in the
atmosphere such that, once emitted, concentrations of each gas become
globally well mixed in the atmosphere.\119\ A well-mixed gas has
relatively uniform concentrations in the atmosphere anywhere around the
globe, with little local or regional variation except immediately next
to sources or sinks. A given amount of a well-mixed gas emitted
anywhere will have similar impacts on global concentrations regardless
of the geographic location of emission. All six GHGs trap outgoing heat
that would otherwise escape to space, and all are directly emitted from
a source as a GHG rather than becoming a GHG in the atmosphere after
emission of a precursor gas. This fundamental scientific understanding
of the intrinsic physical, chemical, and atmospheric properties of the
six GHGs has not changed and remains supported by the more recent
climate change assessments.
---------------------------------------------------------------------------

\119\ The properties ``long lived'' and ``well mixed'' used in
this document mean that the gas has a lifetime in the atmosphere
sufficient to become globally well mixed throughout the entire
atmosphere, which requires a minimum atmospheric lifetime of about
one year. Atmospheric lifetime is a measure of how long a type of
molecule is likely to remain in the atmosphere before it breaks
down, reacts with other gases, or is absorbed by Earth's surface.
The IPCC often refers interchangeably to the six well-mixed GHGs as
long-lived GHGs; however, the IPCC and others in the international
climate change community, such as the United Nations Environment
Programme, also refer to methane and some HFCs as ``near-term
climate forcers,'' ``short-lived climate forcers,'' or ``short-lived
climate pollutants.'' These terms refer to those compounds whose
impacts on Earth's climate occurs primarily with the first decade
after their emission. According to the IPCC AR5 (2014), methane has
an atmospheric lifetime of about 12 years. One of the most commonly
used hydrofluorocarbons (HFC-134a) has a lifetime of about 13 years.
Thus, methane and some HFCs are both short- and long-lived GHGs--
i.e., they have lifetimes long enough to become globally well mixed
in the atmosphere, but short enough to primarily affect Earth's
climate within a decade after their emission. For comparison,
nitrous oxide has a lifetime of around 130 years; sulfur
hexafluoride over 3,000 years; and some perfluorocarbons up to
10,000 to 50,000 years. CO2 is sometimes approximated as
having a lifetime of roughly 100 years, but for a given amount of
CO2 emitted, a better description is that some fraction
of the atmospheric increase in concentration is quickly absorbed by
the oceans and terrestrial vegetation, some fraction of the
atmospheric increase will only slowly decrease over a number of
years, and a small portion of the increase will remain for many
centuries or more.
---------------------------------------------------------------------------

2. The Six Well-Mixed Greenhouse Gases Are the Primary and Best
Understood Driver of Current and Projected Climate Change
The Administrator judges that the scientific evidence is compelling
that together the six well-mixed GHGs constitute the largest
anthropogenic driver of climate change. In addition, the six well-mixed
GHGs are the best-understood driver of climate change because they have
well-understood physical properties as described above that govern
their climate effect (e.g., their radiative forcing, a measure of their
total net effect on the global energy balance). As explained in more
detail in the 2009 Endangerment Finding,\120\ the Administrator made
the judgment that the scientific evidence is compelling that elevated
concentrations of heat-trapping GHGs are the root cause of recently
observed climate change and that the scientific record showed that most
of the observed increase in global average temperatures since the mid-
20th century is very likely due to the observed increase in
anthropogenic GHG concentrations. The attribution of observed climate
change to anthropogenic activities was based on multiple lines of
evidence. The first line of evidence arises from our basic physical
understanding of the effects of changing concentrations of GHGs,
natural factors, and other human impacts on the climate system. The
second line of evidence arises from indirect, historical estimates of
past climate changes that suggest that the changes in global surface
temperature over the last several decades are unusual. The third line
of evidence arises from the use of computer-based climate models to
simulate the likely patterns of response of the climate system to
different forcing mechanisms (both natural and anthropogenic). Observed
increases in global average air temperatures are driving observed
climate impacts like widespread melting of snow and ice and rising
global average sea level. The Administrator also considered these
observed changes as additional evidence of the unequivocal warming of
the climate system driven primarily by elevated atmospheric GHG
concentrations because the consistency of these observed changes in
physical and biological systems and the observed significant warming
cannot be explained entirely due to natural variability or other
confounding non-climate factors.
---------------------------------------------------------------------------

\120\ 74 FR at 66517-18.

---------------------------------------------------------------------------

[[Page 54444]]

In addition, as described in more detail in the 2009 Endangerment
Finding,\121\ the Administrator made the judgment that the scientific
evidence is compelling that six GHGs are expected to remain the primary
driver of future climate change and that, without substantial and near-
term efforts to significantly reduce emissions, it can be expected that
atmospheric concentrations of the six GHGs will continue to climb and
thus lead to ever greater rates of climate change. Given the long
atmospheric lifetime of the six well-mixed GHGs, which range from
roughly a decade to centuries, future atmospheric GHG concentrations
for the remainder of this century and beyond will be influenced not
only by future emissions but indeed by present-day and near-term
emissions. Consideration of future plausible scenarios, and how our
current GHG emissions essentially commit present and future generations
to cope with an altered atmosphere and climate, reinforces the
Administrator's judgment that it is appropriate to define the
combination of the six key greenhouse gases as the air pollution. Most
future scenarios that assume no explicit GHG mitigation actions (beyond
those already enacted) project increasing global GHG emissions over the
century, which in turn result in climbing GHG concentrations.
Concentrations of the six well-mixed GHGs increase even for those
scenarios where annual emissions toward the end of the century are
assumed to be lower than current annual emissions.
---------------------------------------------------------------------------

\121\ 74 FR at 66518-19.
---------------------------------------------------------------------------

The EPA has also carefully reviewed the recent assessments of the
IPCC, USGCRP, and NRC. The EPA finds that these recent assessments
support and strengthen the evidence cited in the 2009 Endangerment
Finding that current atmospheric GHG concentrations are now at elevated
and essentially unprecedented levels primarily as a result of both
historic and current anthropogenic emissions. The 2014 USGCRP NCA3
states, ``Atmospheric levels measured at Mauna Loa in Hawai`i and at
other sites around the world reached 400 parts per million in 2013,
higher than the Earth has experienced in over a million years.'' \122\
Such concentrations are the primary driver of observed changes in
Earth's climate system, namely increased global average temperatures
that drive climate impacts like widespread melting of snow and ice and
rising global average sea level (discussed in more detail in section
IV.C). The recent assessments of the IPCC, USGCRP, and NRC also
describe how these six well-mixed GHGs play a dominant role in future
warming of the climate system. The USGCRP NCA3 makes the following
finding with very high confidence: ``The magnitude of climate change
beyond the next few decades depends primarily on the amount of heat-
trapping gases emitted globally, and how sensitive the Earth's climate
is to those emissions.'' \123\ Key findings from the recent assessments
regarding global and U.S. trends are described briefly below.
---------------------------------------------------------------------------

\122\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 739.
\123\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p.20. See also p. 736: ``Past emissions of heat-trapping
gases have already committed the world to a certain amount of future
climate change. How much more the climate will change depends on
future emissions and the sensitivity of the climate system to those
emissions.''
---------------------------------------------------------------------------

a. Key Observed Trends Driven Primarily by the Six Well-Mixed GHGs
According to the IPCC AR5, observations of the Earth's globally
averaged combined land and ocean surface temperature over the period
1880 to 2012 show a warming of 0.85 [0.65 to 1.06] degrees Celsius or
1.53 [1.17 to 1.91] degrees Fahrenheit.\124\ The IPCC AR5 concludes
that the increase in atmospheric GHG concentrations since 1750, plus
other human activities (e.g., land use change and aerosol emissions),
has had a radiative forcing effect estimated to be 2.3 Watts per square
meter (W/m\2\) in 2011.\125\ Radiative forcing is a measure of a
substance's total net effect on the global energy balance for which a
positive number represents a warming effect and a negative number
represents a cooling effect. The IPCC's estimate is an increase from
the previous 2007 IPCC Fourth Assessment Report (AR4) total net
estimate of 1.6 W/m\2\ that was referred to in the record for the 2009
Endangerment Finding. The reasons for this increase include continued
increases in GHG concentrations, as well as reductions in the estimated
negative forcing due to aerosol particles. The IPCC AR5 rates the level
of confidence \126\ in their radiative forcing estimates as ``high''
for methane and ``very high'' for CO2 and nitrous oxide.
---------------------------------------------------------------------------

\124\ ``IPCC, 2013: Summary for Policymakers. In: Climate Change
2013: The Physical Science Basis. Contribution of Working Group I to
the Fifth Assessment Report of the Intergovernmental Panel on
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor,
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley
(eds.)]. Cambridge University Press, 29 pp.
\125\ Ibid.
\126\ The IPCC expresses levels of confidence using five
qualifiers: Very low, low, medium, high, and very high. These levels
are based on a qualitative evaluation of the robustness of the
evidence (considering the type, amount, quality, and consistency of
evidence such as data, mechanistic understanding, theory, models,
and expert judgment) and the degree of agreement among the findings.
---------------------------------------------------------------------------

The new assessments also have greater confidence since the 2009
Endangerment Finding in attributing recent warming to human causes. The
IPCC AR5 stated that it is extremely likely (>95 percent likelihood)
that human influences have been the dominant cause of warming since the
mid-20th century, which is an even stronger statement than the AR4
conclusion that it is very likely (>90 percent likelihood) that most of
the increase in temperature since the mid-20th century was due to the
observed increase in anthropogenic GHG concentrations. The AR4
conclusion was referred to in the record for the 2009 Endangerment
Finding. In addition, the IPCC AR5 found that concentrations of
CO2 and several other of the major GHGs are higher than they
have been in at least 800,000 years. This is an increase from what was
reported in IPCC AR4, which found higher concentrations than in at
least 650,000 years.
The USGCRP NCA3 states that there is very high confidence \127\
that the global climate change of the past 50 years is primarily due to
human activities. Human activities are affecting climate through
increasing atmospheric levels of heat-trapping GHGs, through changing
levels of various particles that can have either a heating or cooling
influence on the atmosphere, and through activities such as land use
changes that alter the reflectivity of the Earth's surface and cause
climatic warming and cooling effects. The USGCRP concludes that
``considering all known natural and human drivers of climate since
1750, a strong net warming from long-lived greenhouse gases produced by
human activities dominates the recent climate record.'' \128\
---------------------------------------------------------------------------

\127\ The NCA expresses levels of confidence using four
qualifiers: low, medium, high, and very high. These levels are based
on the strength and consistency of the observed evidence; the skill,
range, and consistency of model projections; and insights from peer-
reviewed sources.
\128\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 741.
---------------------------------------------------------------------------

These recent and strong conclusions attributing recent observed
global warming to human influence have been made despite what some have
termed a

[[Page 54445]]

warming slowdown or ``hiatus'' over the past 15 years or so. The IPCC
AR5 notes that global mean surface temperature exhibits substantial
natural decadal and interannual variability. Short-term variability
does not alter conclusions about the long-term climate trend that the
IPCC AR5 finds after its review of independently verified observational
records: ``Each of the past three decades has been successively warmer
at the Earth's surface than all the previous decades in the
instrumental record, and the first decade of the 21st century has been
the warmest.'' ^{129 130}
---------------------------------------------------------------------------

\129\ IPCC, 2013: Climate Change 2013: The Physical Science
Basis. Contribution of Working Group I to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Stocker,
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A.
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University
Press, p. 161.
\130\ Furthermore, we note that according to both NOAA and NASA,
2015 was the warmest year in the modern instrumental record for
globally averaged surface temperature, breaking the record
previously held by 2014. This now means that the last fifteen years
have been fifteen of the sixteen warmest years on record. Available
at http://www.ncdc.noaa.gov/sotc/global/201513 (last accessed April
11, 2016).
---------------------------------------------------------------------------

Temperature trends at the global level have also been observed
regionally and in the United States. In the Northern Hemisphere, the
IPCC AR5 finds that the last 30 years were likely the warmest 30-year
period of the last 1400 years. The USGCRP NCA3 states with very high
confidence that ``U.S. average temperature has increased by 1.3 [deg]F
to 1.9 [deg]F since record keeping began in 1895; most of this increase
has occurred since about 1970. The most recent decade was the nation's
warmest on record.'' \131\ The USGCRP also notes that the rate of U.S.
temperature increase over the past 4 to 5 decades has been greater than
the rate observed in earlier decades.
---------------------------------------------------------------------------

\131\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 28.
---------------------------------------------------------------------------

b. Key Projections Based Primarily on Future Scenarios of the Six Well-
Mixed GHGs
Future temperature changes will depend on what path the world
follows with respect to GHG emissions and associated levels of GHG
concentrations in the atmosphere. The NRC Climate Stabilization Targets
assessment concludes that CO2 emissions are currently
altering the atmosphere's composition and will continue to alter
Earth's climate for thousands of years. The NRC Understanding Earth's
Deep Past assessment finds that ``the magnitude and rate of the present
greenhouse gas increase place the climate system in what could be one
of the most severe increases in radiative forcing of the global climate
system in Earth history.'' \132\ A key future projection of this
assessment is that by the end of the century, if no emissions
reductions are made, CO2 concentrations are projected to
increase to levels that Earth has not experienced for more than 30
million years. In its high emission scenario, the IPCC AR5 projects
that global temperatures by the end of the century will likely be 2.6
to 4.8 degrees Celsius (4.7 to 8.6 degrees Fahrenheit) warmer than
today. Temperatures on land and in northern latitudes will likely warm
even faster than the global average.
---------------------------------------------------------------------------

\132\ NRC, 2011: Understanding Earth's Deep Past: Lessons for
Our Climate Future. The National Academies Press, p. 138.
---------------------------------------------------------------------------

For the United States, the USGCRP NCA3 concludes, ``Warming is
ultimately projected for all parts of the nation during this century.
In the next few decades, this warming will be roughly 2 [deg]F to 4
[deg]F in most areas. By the end of the century, U.S. warming is
projected to correspond closely to the level of global emissions:
roughly 3 [deg]F to 5 [deg]F under lower emissions scenarios (B1 or RCP
4.5) involving substantial reductions in emissions, and 5 [deg]F to 10
[deg]F for higher emissions scenarios (A2 or RCP 8.5) that assume
continued increases in emissions; the largest temperature increases are
projected for the upper Midwest and Alaska.'' \133\
---------------------------------------------------------------------------

\133\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 29.
---------------------------------------------------------------------------

3. The Six Well-Mixed GHGs Are Currently the Common Focus of the
Climate Change Science and Policy Communities
The six well-mixed GHGs are currently the common focus of climate
science and policy analyses and discussions. Grouping them is
consistent with the focus of international and domestic climate science
research enterprises like the IPCC and USGCRP. The IPCC and USGCRP
assessment reports assess the climate change effects on health,
society, and the environment as a result of human-induced climate
change driven primarily by the group of six gases.
Grouping them is also consistent with the focus of climate policy.
The United Nations Framework Convention on Climate Change (UNFCCC),
signed and ratified by the United States in 1992, requires its
signatories to ``develop, periodically update, publish and make
available . . . national inventories of anthropogenic emissions by
sources and removals by sinks of all greenhouse gases not controlled by
the Montreal Protocol, using comparable methodologies . . .'' \134\ To
date, the primary focus of UNFCCC actions and discussions has been on
the six well-mixed GHGs, including the recent Paris Agreement in which
Parties agreed to undertake nationally determined contributions to
achieving the goal of ``global peaking of GHG emissions as soon as
possible'' in order to reach a long-term global temperature
target.\135\ Domestically, the EPA has been developing standards for
GHG emissions from mobile and stationary sources under the Clean Air
Act since finalizing the 2009 Endangerment Finding.
---------------------------------------------------------------------------

\134\ United Nations Framework Convention on Climate Change,
1992: Article 4(1)(a) of the United Nations Framework Convention on
Climate Change, p. 10. Available at https://unfccc.int/files/essential_background/background_publications_htmlpdf/application/pdf/conveng.pdf (last accessed April 11, 2016).
\135\ United Nations Framework Convention on Climate Change,
2015: Adoption of the Paris Agreement Conference of the Parties
Twenty-first session Paris, FCCC/CP/2015/L.9/Rev.1, 12 December
2015, Available at: https://unfccc.int/resource/docs/2015/cop21/eng/l09r01.pdf (last accessed April 8, 2016).
---------------------------------------------------------------------------

4. Defining Air Pollution as the Aggregate Group of Six GHGs Is
Consistent With Evaluation of Risks and Impacts Due to Human-Induced
Climate Change
Based on her review of the science described in detail above in
section IV.B.2, the Administrator judges that the six well-mixed GHGs
constitute the largest anthropogenic driver of climate change and play
a dominant role in observed and projected changes in Earth's climate
system. Thus, the Administrator finds, as she did in the 2009
Endangerment Finding, that because the six well-mixed GHGs are
collectively the primary driver of current and projected human-induced
climate change, the current and future risks (here described in section
IV.C below) due to human-induced climate change--whether these risks
are associated with increases in temperature, changes in precipitation,
a rise in sea levels, changes in the frequency and intensity of weather
events, or more directly with the elevated GHG concentrations
themselves--can be associated with this definition of air pollution.
Due to the cumulative purpose of the statutory language, even if the
Administrator were to look at the atmospheric

[[Page 54446]]

concentration of each GHG individually, she would still consider the
impact of the concentration of a single GHG in combination with that
caused by the other GHGs.
5. Defining Air Pollution as the Aggregate Group of Six GHGs Is
Consistent With Past EPA Practice
Treating the air pollution as the aggregate of the well-mixed GHGs
is consistent with other provisions of the CAA and previous EPA
practice under the CAA, where separate emissions from different sources
but with common properties may be treated as a class (e.g., particulate
matter (PM)). This approach addresses the total, cumulative effect that
the elevated concentrations of the six well-mixed GHGs have on climate
and, thus, on different elements of health, society, and the
environment. The EPA treats, for example, PM as a common class of air
pollution; PM is a complex mixture of extremely small particles and
liquid droplets. Particle pollution is made up of a number of
components, including acids (such as nitrates and sulfates), organic
chemicals, metals, and soil or dust particles.
6. Response to Key Comments on Defining the Air Pollution as the
Aggregate Group of the Six Well-Mixed Greenhouse Gases
Many commenters agreed with the EPA that the ``air pollution'' for
purposes of the endangerment finding under section 231(a)(2)(A) of the
CAA should be defined as the six well-mixed GHGs. Several commenters
discussed the fact that aircraft engines emit only two of the six well-
mixed GHGs. Commenters pointed out that the majority of aircraft
emissions are CO2, while nitrous oxide emissions are
described as ``nominal (<1%)'' or ``trace.'' Some commenters ultimately
concluded that the EPA's approach to defining the air pollution as an
aggregate group of six gases is acceptable, but that the scope of
future regulations should be limited to CO2. One commenter
agreed with the Agency's evaluation of the six GHGs based on their
common attributes, but questioned the EPA's decision to aggregate the
six gases rather than considering them individually for purposes of
making the findings. Other commenters disagreed with the EPA and
requested limiting the definition of air pollution in this action to
CO2 or to CO2 and nitrous oxide.
The EPA disagrees with comments regarding changing the definition
of the air pollution to limit it to only those GHGs that are emitted
from aircraft or to CO2 only. The EPA has explained both in
the 2009 Endangerment Finding and in the proposed findings under CAA
section 231(a)(2)(A) that the definition of the air pollution is based
on shared characteristics and common attributes relevant to climate
change science and policy \136\--which is not affected by the identity
of the source(s) of the emissions contributing to the air pollution.
The EPA recognized in the proposed findings that aircraft emit two of
the six well-mixed GHGs but stated that nonetheless it is entirely
reasonable and appropriate, and in keeping with the 2009 Endangerment
Finding and past EPA practice, for the Administrator to group into a
single class those substances that possess shared relevant properties,
even though they are not all emitted from the classes of sources before
her.\137\ After considering all the comments, this continues to be the
EPA's view. Moreover, this approach to defining air pollution (and air
pollutant, as described below) as a grouping of many substances is not
unique to GHGs but rather is common practice under the CAA, for example
for particulate matter and volatile organic compounds.
---------------------------------------------------------------------------

\137\ 80 FR at 37774, 37785 and 37787.
---------------------------------------------------------------------------

The five primary reasons for grouping the six well-mixed GHGs are
explained in detail above in sections IV.B.1 through IV.B.5. Because
the well-mixed GHGs are collectively the primary driver of current and
projected human-induced climate change, all current and future risks
due to human-induced climate change can be associated with this
definition of air pollution. Thus, this grouping is consistent with
evaluation of the scientific issues that the EPA is required to examine
in this endangerment finding, namely the risks and impacts due to
human-induced climate change. As discussed above, the key scientific
evidence and observations that are the basis of this finding focus on
the combined six well-mixed GHGs, and did not assess risks and impacts
associated with greenhouse gas-induced climate change using an
individual gas approach. Accordingly, we are not undertaking a separate
endangerment analysis for each of the six well-mixed gases
individually.
The question of limits to the scope of future regulations is
outside of the scope of this action because the EPA has neither
proposed nor is finalizing in this action any such regulatory
standards. This final action does not itself impose any requirements on
source categories under CAA section 231. Thus, the EPA anticipates that
this question could be raised and considered, as needed, in the
standard-setting phase of the regulatory process, and the EPA will
consider comments submitted on the issue of the appropriate form of
emission standards in response to EPA's anticipated future notice of
proposed rulemaking on standards. Although this final action
establishes a duty for the EPA to promulgate standards for the GHG
emissions from engines used by covered aircraft, the findings do not
pre-judge the form that such standards may take.
Another commenter expressed concern about EPA's proposed
endangerment finding because it does not differentiate between
CO2 emissions that result from combustion of fossil fuels
and those that result from ``combustion of biomass or biofuels derived
from herbaceous crops or crop residues, as well as biogenic
CO2 emissions associated with the production, gathering and
processing of crops or crop residues used in bio-based products
including fuels.'' \138\ The commenter argues that such crop-related
biogenic CO2 emissions should be excluded from the
endangerment finding because the CO2 released back to the
atmosphere when emitted from crop-derived biogenic sources contains the
same carbon that was previously removed or sequestered from
CO2 in the atmosphere and thus does not contribute to
elevated atmospheric concentrations of the six well-mixed GHGs.
---------------------------------------------------------------------------

\138\ Biogenic CO2 Coalition, 2015: Comments on EPA's
Proposed Finding That Greenhouse Gas Emissions From Aircraft Cause
or Contribute to Air Pollution That May Reasonably Be Anticipated To
Endanger Public Health and Welfare, 80 FR 37757 (July 1, 2015).
Docket ID number EPA-HQ-OAR-2014-0828-0916. Available at
www.regulations.gov (last accessed April 11, 2016).
---------------------------------------------------------------------------

The EPA reiterates that the Administrator defines the relevant air
pollution considered in the endangerment finding as the aggregate group
of the six well-mixed GHGs based on shared physical characteristics and
common attributes relevant to climate change science and policy, which
is not affected by consideration of the sources of the emissions
contributing to the air pollution. In the record for the 2009
Endangerment Finding, the Agency stated that ``all CO2
emissions, regardless of source, influence radiative forcing equally
once it reaches the atmosphere and therefore there is no distinction
between biogenic and non-biogenic CO2 regarding the
CO2 and the other well-mixed GHGs within the definition of
air pollution that is reasonably anticipated to endanger public health
and welfare.'' \139\ The EPA continues to hold that position in these

[[Page 54447]]

findings, which is supported by the evidence before it. First, the fact
that these CO2 emissions originate from combustion of
carbon-based fuels created through different processes is not relevant
to defining the air pollution that is reasonably anticipated to
endanger public health and welfare. The origin and constitution of a
fuel prior to its combustion and subsequent emission into the
atmosphere has no bearing on the fact that CO2 and the other
well-mixed GHGs are all sufficiently long lived to become well mixed in
the atmosphere, directly emitted, of well-known radiative forcing, and
generally grouped and considered together in climate change scientific
and policy forums as the primary driver of climate change. Moreover, as
explained in section IV.C of this document, the endangerment arises
from the elevated concentrations of the six well-mixed GHGs in the
atmosphere. A molecule of biogenic CO2 has the same
radiative forcing effect as a molecule of fossil-fuel derived
CO2. In other words, no matter the original source of the
CO2, the behavior of the CO2 molecules in the
atmosphere in terms of radiative forcing, chemical reactivity, and
atmospheric lifetime is effectively the same. Any differential
treatment of biogenic CO2 in the context of the endangerment
finding would be inconsistent with the primary scientific basis for the
grouping of the six well-mixed GHGs as a single class for purposes of
identifying the air pollution (and air pollutant, as explained below).
A more detailed response to the issues raised in this comment can be
found in the Response to Comments document in the docket.
---------------------------------------------------------------------------

\139\ EPA, 2009. Response to Comments document, Volume 9: The
Endangerment Finding, EPA-HQ-OAR-2009-0171-11676. Available at
www.regulations.gov (last accessed April 11, 2016).
---------------------------------------------------------------------------

7. Other Climate Forcers Not Being Included in the Definition of Air
Pollution for This Finding
Both in the 2009 Endangerment Finding and in this action, the
Administrator recognizes that there are other substances in addition to
the six well-mixed GHGs that are emitted from human activities and that
affect Earth's climate (referred to as climate forcers). However, as
described in more detail in the 2009 Endangerment Finding and in the
proposed findings under CAA section 231(a)(2)(A),\140\ these substances
do not fit within one or more of the five primary reasons for focusing
on this aggregate group as the air pollution. As described in the
following subsections, we received comments on the omission of water
vapor, NOX, and aerosol particles emitted from aircraft from
the proposed definition of air pollution for this finding, but not on
the omission of other climate forcers. After considering public
comments and additional information in the new assessments regarding
the climate-relevant substances outside the group of the six well-mixed
GHGs, it is the Administrator's view that the reasons stated in the
2009 Endangerment Finding \141\ for not including these substances in
the scope of the GHG air pollution still apply at this time.
---------------------------------------------------------------------------

\140\ 74 FR at 66519-21 and 80 FR at 37781-84.
\141\ 74 FR at 66519-21.
---------------------------------------------------------------------------

As the EPA acknowledged in the proposed findings,\142\ some short-
lived substances--namely water vapor, NOX emitted at high
altitude, and aerosol particles including black carbon--have physical
properties that result in their having different, and often larger,
climate effects when emitted at high altitudes. For example, the
assessment literature indicates that aerosol particles, including black
carbon, emitted at high altitudes have more interactions with clouds
and therefore have different effects on the global energy balance than
do particles emitted at the surface. However, the very properties that
lead to differential climate effects depending on the altitude of
emission--properties that are different from those of the six well-
mixed GHGs--lead to more uncertainty in the scientific understanding of
these short-lived substances' total effect on Earth's climate. The
short-lived nature of these substances means that, unlike GHGs that are
sufficiently long lived to become well mixed in the atmosphere, the
climatic impact of the substance is dependent on a number of factors
such as the location and time of its emission. The magnitude, and often
the direction (positive/warming or negative/cooling), of the globally
averaged climate impact will differ depending on the location of the
emission due to the local atmospheric conditions (e.g., due to
differing concentrations of other compounds with which the emissions
can react, background humidity levels, or the presence or absence of
clouds). In addition, for emissions at any given location, the spatial
and temporal pattern of the climate forcing will be heterogeneous,
again often differing in direction (for example, in the case of
NOX emissions, the near-term effect in the hemisphere in
which the emissions occur is usually warming due to increased ozone
concentrations, but the longer term effects, and effects in the other
hemisphere, are often cooling due to increased destruction of methane).
More detail on the uncertainties relating to the climate effects of
these short-lived substances is provided in the subsections below in
response to public comments and in the Response to Comments document.
---------------------------------------------------------------------------

\142\ 80 FR at 37781-84.
---------------------------------------------------------------------------

Overall, the state of the science as represented in the assessment
literature at present continues to highlight significant scientific
uncertainties regarding the total net forcing effect of water vapor,
NOX, and aerosol particles when emitted at high altitudes.
The dependence of the effects on where the substance is emitted, and
the complex temporal and spatial patterns that result, mean that the
current level of understanding regarding these short-lived substances
is much lower than for the six well-mixed GHGs. Given the
aforementioned scientific uncertainties at present, the Agency is not
including these constituents in the definition of air pollution for
purposes of the endangerment finding under section 231(a)(2)(A) of the
CAA.
Many public comments either supported or opposed inclusion of other
substances in addition to the six well-mixed GHGs in the definition of
air pollution, and some specifically suggested water vapor,
NOX, and aerosol particles as additional substances to
include in that definition. The Agency's full responses to those
comments can be found in the Response to Comments document; key
comments and responses are summarized below.
a. Response to Key Comments on Including Other Climate Forcers in the
Definition of Air Pollution
Some commenters argued that the proposed findings under CAA section
231(a)(2)(A) did not demonstrate careful examination of the scientific
issues with regard to those short-lived substances that have different
climate effects when emitted at high altitudes, and that a more
thorough analysis should lead the EPA to conclude that water vapor,
NOX, and black carbon also drive climate change in addition
to the six well-mixed GHGs. These comments stated that the EPA should
have quantified and included the effect of high-altitude water vapor,
NOX, and black carbon in the Agency's discussion of drivers
of climate change. Another commenter argued that the EPA should include
metal particulates (specifically lead, barium, and aluminum) in the
definition of air pollution for this finding because of their role in
aviation-induced cloudiness, which the commenter argues has a larger
effect on climate change than the six well-mixed GHGs.
Although the EPA is not at this time taking final action to
determine whether these other climate forcers should be found to
represent air pollution within

[[Page 54448]]

the meaning of CAA section 231(a)(2)(A), the EPA disagrees with these
comments suggesting that the Agency did not carefully examine the
scientific issues and information supporting its current endangerment
finding in regard to these substances. Consistent with the approach
described in the proposed findings and for the reasons discussed above,
the Administrator considers the major peer-reviewed scientific
assessments of the IPCC and NRC as the primary scientific and technical
basis informing the endangerment finding and providing the current
state of scientific understanding of the differential climate effects
that water vapor, NOX, and aerosols such as black carbon
have when emitted at high altitudes. The EPA has considered the
following assessment reports to obtain the best estimates of these
substances' net impact on the climate system, which is generally
discussed in terms of radiative forcing: The IPCC AR5, the IPCC 2007
Fourth Assessment Report (AR4),\143\ the IPCC Special Report: Aviation
and the Global Atmosphere (IPCC 1999),\144\ the NRC's Advancing the
Science of Climate Change (NRC 2010),\145\ and the NRC's Atmospheric
Effects of Aviation: A Review of NASA's Subsonic Assessment Project
(NRC 1999).\146\ The USGCRP assessments have not dealt specifically
with emissions at high altitude.
---------------------------------------------------------------------------

\143\ IPCC, 2007: Climate Change 2007: The Physical Scientific
Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change [Solomon,
S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor
and H.L. Miller (eds.)] Cambridge University Press, 996 pp.
\144\ IPCC, 1999: Aviation and the Global Atmosphere, Special
Report to the Intergovernmental Panel on Climate Change [Penner,
J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)]
Cambridge University Press, 373 pp.
\145\ NRC, 2010: Advancing the Science of Climate Change. The
National Academies Press, 528 pp.
\146\ NRC, 1999: Atmospheric Effects of Aviation: A Review of
NASA's Subsonic Assessment Project. The National Academies Press, 54
pp.
---------------------------------------------------------------------------

As described previously in section IV.A of this document, the
Administrator's consideration of the major scientific assessments
provides assurance that the Administrator is basing her judgment on the
best available, well-vetted science that reflected the consensus of the
climate science research community. These scientific assessments
addressed the scientific issues that the EPA was required to examine,
were comprehensive in their coverage of the GHG and climate change
issues, and underwent rigorous and exacting peer review by the expert
community, as well as rigorous levels of U.S. government review, in
which the EPA took part. The commenters provide no compelling arguments
against this approach, which underwent judicial review and was upheld
as described in section IV.A of this document. The assessments
synthesize literally thousands of individual studies to convey the
consensus conclusions on what the body of scientific literature tells
us, and the commenters did not provide evidence that we had missed or
mischaracterized conclusions of the assessments regarding aviation
impacts.
The state of the science as represented in the assessment
literature supports the EPA's reasons for defining the air pollution as
the aggregate group of the six well-mixed GHGs, which include their
common physical properties relevant to climate change (i.e., directly
emitted and sufficiently long lived to become well mixed in the
atmosphere), the fact that these gases are considered the primary
drivers of climate change, and the fact that these gases remain the
best understood drivers of anthropogenic climate change. Water vapor,
NOX, aerosol particles, or aviation-induced cloudiness
associated with metal particulates do not share these common
attributes, and are each associated with substantial scientific
uncertainty. Accordingly, although the EPA is not making a final
determination on whether these additional substances should be found to
be air pollution within the meaning of CAA section 231(a)(2)(A), the
EPA is not at this time changing or expanding the definition of the air
pollution to include these additional substances. The following
subsections provide additional discussion of the state of the science
as represented in the assessment literature regarding the climatic
effects of these substances when emitted at high altitudes.
b. Responses to Key Comments on Changes in Clouds From High Altitude
Emissions of Water Vapor and Particles
Some commenters supported the EPA's summary of the scientific
assessment literature and agreed that there are substantial scientific
uncertainties regarding net climate effects of aviation-induced
cloudiness from high altitude emissions of water vapor and particles.
Other commenters disagreed and argued that there is clear scientific
evidence that aviation-induced cloudiness associated with high altitude
emissions of water vapor drives climate change and should be included
in the definition of air pollution. One commenter disagrees and argues
that, due to their effect on aviation-induced cloudiness and climate
change, metal particulates should be included in the definition of air
pollution.
The EPA disagrees with the comments regarding changing or expanding
the definition of the air pollution employed in this endangerment
finding to include these additional substances. For the reasons stated
above, the Administrator considers the scientific assessment literature
as the primary scientific and technical basis informing the
endangerment finding and providing the state of climate science on
aviation-induced cloudiness. Section IV.B.4 of the proposed findings
under CAA section 231(a)(2)(A) \147\ explained that aviation-induced
cloudiness (sometimes called AIC) refers to all changes in cloudiness
associated with aviation operations, which are primarily due to the
effects of high altitude emissions of water vapor and particles
(primarily sulfates and black carbon). Changes in cloudiness affect the
climate by both reflecting solar radiation (cooling) and trapping
outgoing longwave radiation (warming). Unlike the warming effects
associated with GHGs that are sufficiently long lived to become well
mixed in the atmosphere, the climate effects associated with changes in
cloud cover are more regional and temporal in nature. The assessment
literature describes three main components of aviation-induced
cloudiness--persistent contrails, contrail-induced cirrus, and induced
cirrus. Aircraft engine emissions of water vapor at high altitudes
during flight can lead to the formation of condensation trails, or
contrails, under certain conditions such as ice-supersaturated air
masses with specific humidity levels and temperature.
---------------------------------------------------------------------------

\147\ 80 FR at 37782-83.
---------------------------------------------------------------------------

The NRC estimated that persistent contrails increased cloudiness
above the United States by two percent between 1950 and 1988, with
similar results reported over Europe.\148\ As stated above, clouds can
have both warming and cooling effects, and persistent contrails were
once considered to have significant net warming effects. However, more
recent estimates suggest a smaller overall climate forcing effect of
persistent contrails. The IPCC AR5 best estimate for the global mean
radiative forcing from contrails is 0.01 W/m\2\ (medium confidence and
with an uncertainty range of 0.005 to 0.03 W/m\2\). \149\ To put both
the magnitude and

[[Page 54449]]

large uncertainty range of this number for the first of the three
components of aviation-induced cloudiness into context, some examples
of other IPCC AR5 best estimates for global mean radiative forcing
include: 1.68 W/m\2\ for CO2 (very high confidence and with
an uncertainty range of 1.33 to 2.03 W/m\2\), 0.97 W/m\2\ for methane
(high confidence and with an uncertainty range of 0.74 to 1.20 W/m\2\),
and 0.17 W/m\2\ for nitrous oxide (very high confidence and with an
uncertainty range of .013 to 0.21 W/m\2\).\150\ In addition, the NRC
(2010) assessment suggested that contrails may affect regional diurnal
temperature differences, but this has been called into question by the
recent findings presented in the IPCC AR5, which suggests that aviation
contrails do not have an effect on mean or diurnal range of surface
temperatures (medium confidence).
---------------------------------------------------------------------------

\148\ NRC, 1999: Atmospheric Effects of Aviation: A Review of
NASA's Subsonic Assessment Project. The National Academies Press, 54
pp.
\149\ IPCC, 2013: Climate Change 2013: The Physical Science
Basis. Contribution of Working Group I to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Stocker,
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A.
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University
Press, 1535 pp.
\150\ IPCC, 2013: Summary for Policymakers. In: Climate Change
2013: The Physical Science Basis. Contribution of Working Group I to
the Fifth Assessment Report of the Intergovernmental Panel on
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor,
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley
(eds.)]. Cambridge University Press, 29 pp.
---------------------------------------------------------------------------

Persistent contrails also sometimes lose their linear form and
develop into cirrus clouds, an effect referred to as contrail-induced
cirrus. Studies to date have been unable to isolate this second of
three main climate forcing components of aviation-induced cloudiness,
but the IPCC AR5 provides a combined contrail and contrail-induced
cirrus best estimate of 0.05 W/m\2\ (low confidence and with an
uncertainty range of 0.02 and 0.15 W/m\2\).\151\
---------------------------------------------------------------------------

\151\ IPCC, 2013: Climate Change 2013: The Physical Science
Basis. Contribution of Working Group I to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Stocker,
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A.
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University
Press, 1535 pp.
---------------------------------------------------------------------------

Particles emitted or formed in the atmosphere as a result of
aircraft emissions (primarily sulfates and black carbon) may also act
as ice nuclei and modify naturally forming cirrus clouds, an effect
referred to as ``induced cirrus.'' This third of three main climate
forcing components of aviation-induced cloudiness is an area of active
research, and there are significant challenges in estimating the
climatic impacts of cirrus cloud modification. Neither IPCC AR4 nor AR5
provided global or regional estimates related to this forcing, with the
AR5 stating that ``it is deemed too uncertain to be further assessed
here.''\152\ The 2007 IPCC AR4 characterizes our knowledge of the
natural freezing modes in cirrus conditions as ``poor'' and notes that
cirrus cloud processes are not well represented in global models.\153\
---------------------------------------------------------------------------

\152\ Ibid.
\153\ IPCC, 2007: Climate Change 2007: The Physical Scientific
Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change [Solomon,
S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor
and H.L. Miller (eds.)] Cambridge University Press, 996 pp.
---------------------------------------------------------------------------

Given differences in scientific understanding of the three main
components of aviation-induced cloudiness, the more recent assessments
have not provided quantitative estimates of the overall net climate
forcing effect of changes in clouds from high altitude emissions of
water vapor and particles. Going back to the 1999 IPCC assessment's
quantitative estimates, the science is characterized as ``very
uncertain'' with a range for the best estimate between 0 to 0.040 W/
m\2\.\154\ Thus, based on its consideration of the scientific evidence
and all the comments on this issue, the EPA agrees with those
commenters that indicate there are substantial scientific uncertainties
regarding net effects of the three components of aviation-induced
cloudiness on the climate system. These uncertainties result in the
Agency's not being prepared at this time to determine whether these
additional substances are air pollution within the meaning of CAA
section 231(a)(2)(A) and not including them within the definition of
``air pollution'' being employed in this endangerment finding.
---------------------------------------------------------------------------

\154\ IPCC, 1999: Aviation and the Global Atmosphere, Special
Report to the Intergovernmental Panel on Climate Change [Penner,
J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)]
Cambridge University Press, 373 pp.
---------------------------------------------------------------------------

c. Responses to Key Comments on Direct Radiative Forcing Effects of
High Altitude Particle Emissions
Some commenters supported the EPA's summary of the scientific
uncertainties regarding the net direct radiative forcing effects of
aviation-induced particles including black carbon. Other commenters
disagreed and argued that there is clear scientific evidence that black
carbon in particular drives climate change and should be included in
the definition of air pollution.
The EPA disagrees with comments regarding changing or expanding the
definition of the air pollution employed in this endangerment finding
to include aviation-induced particles like black carbon. For the
reasons stated above, the Administrator considers the scientific
assessment literature as the primary scientific and technical basis
informing the endangerment finding and providing the state of climate
science regarding the direct radiative forcing effects of high altitude
emissions of the two primary aviation-induced particles, sulfates and
black carbon. Section IV.B.4 of the proposed findings under CAA section
231(a)(2)(A) \155\ explained that aircraft emit precursor gases that
convert to sulfate particles in the atmosphere, such as sulfur dioxide.
Sulfate particles have direct effects on the climate by scattering
solar radiation, which is a negative radiative forcing that ultimately
results in cooling. The more recent assessments have not identified a
quantitative best estimate for this negative radiative forcing effect
specifically from aviation, as it is an active area of scientific study
with large uncertainties. Going back to the 1999 IPCC assessment's
quantitative estimates, the direct radiative forcing effect of sulfate
aerosols from aviation for the year 1992 is estimated at -0.003 W/m\2\
with an uncertainty range between -0.001 and -0.009 W/m\2\.\156\
---------------------------------------------------------------------------

\155\ 80 FR at 37783.
\156\ IPCC, 1999: Aviation and the Global Atmosphere, Special
Report to the Intergovernmental Panel on Climate Change [Penner,
J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)]
Cambridge University Press, 373 pp.
---------------------------------------------------------------------------

Similarly, the proposed findings under CAA section 231(a)(2)(A)
explained that black carbon emissions from aviation, which are produced
by the incomplete combustion of jet fuel, primarily absorb solar
radiation and heat the surrounding air, resulting in a warming effect
(positive radiative forcing). The more recent assessments have not
identified a quantitative best estimate for this effect specifically
from aviation, as it is an area of active scientific study with large
uncertainties. Going back to the 1999 IPCC assessment's quantitative
estimates, the global mean radiative forcing of black carbon emissions
from aircraft is estimated to be 0.003 W/m\2\ with uncertainty spanning
0.001 to 0.009 W/m\2\.\157\ The IPCC 1999 assessment suggests that
because the contribution of black carbon in the stratosphere (which
actually contributes to cooling of the Earth's surface rather than
warming) was not included in its calculations, its estimates of
radiative forcing were likely to be too high.
---------------------------------------------------------------------------

\157\ Ibid.
---------------------------------------------------------------------------

In addition, the 2009 Endangerment Finding did not include aerosols
in the

[[Page 54450]]

definition of air pollution, noting that much of the uncertainty range
surrounding the best estimate of total net forcing due to all human
activities was due to uncertainties about the cooling and warming
effects of aerosols \158\ (though from all sources, not just aircraft).
The 2009 Endangerment Finding also stated that the magnitude of aerosol
effects can vary immensely with location and season of emissions,
noting that estimates of its total climate forcing effect have a large
uncertainty range.\159\ Regarding black carbon specifically, the 2009
Endangerment Finding noted that it does not share common physical and
chemical attributes with the six well-mixed GHGs because it is an
aerosol particle (not a gas) that has different physical, chemical, and
atmospheric properties. Black carbon affects the climate differently
than GHGs that are sufficiently long lived to become well mixed in the
atmosphere. In contrast to its indirect warming and cooling effects via
clouds, black carbon causes a direct warming effect primarily by
absorbing incoming and reflected sunlight (whereas GHGs that are
sufficiently long lived to become well mixed in the atmosphere cause
warming by trapping outgoing, infrared heat), and by darkening bright
surfaces such as snow and ice, which reduces reflectivity. Black carbon
is short-lived, remaining in the atmosphere for only about a week, and
does not become well-mixed in the atmosphere. There are also concerns
in the international climate science and policy communities about how
to treat the short-lived black carbon emissions alongside GHGs--for
example, what are the appropriate metrics to compare the warming and/or
climate effects of the different substances, given that, unlike GHGs
that are sufficiently long lived to become well mixed in the
atmosphere, the magnitude of aerosol effects can vary immensely with
location and season of emissions.
---------------------------------------------------------------------------

\158\ 74 FR at 66517.
\159\ 74 FR at 66520.
---------------------------------------------------------------------------

Thus, although the EPA is not at this time prepared to make a final
determination on whether black carbon should be found to be air
pollution within the meaning of CAA section 231(a)(2)(A), based on its
consideration of the scientific evidence and all the comments on this
issue, and consistent with its conclusion in the 2009 Endangerment
Finding, the EPA disagrees with commenters that ask for black carbon to
be included in the definition of the air pollution as part of this
endangerment finding. Because aerosols such as black carbon and
sulfates are fundamentally different from and do not share the relevant
properties that support grouping the six well-mixed GHGs together as a
class, and scientific uncertainties remain regarding the net radiative
forcing effects of these substances (whether in general or when emitted
at high altitudes), the EPA is not at this time including them in the
definition of air pollution employed in this finding. However, because
of these uncertainties the Agency is not at this time taking final
action to determine whether these additional substances should be found
to represent air pollution within the meaning of CAA section
231(a)(2)(A).
d. Responses to Key Comments on Changes in Atmospheric Chemistry From
High Altitude Nitrogen Oxides Emissions
Most commenters supported the EPA's summary of the scientific
uncertainties regarding the changes in atmospheric chemistry from high
altitude NOX emissions. At least one commenter disagreed and
argued that there is clear scientific evidence that the effects of
NOX emissions on ozone production have a significant climate
forcing effect. They concluded that NOX should therefore be
included in an endangerment finding.
The EPA disagrees with comments to the extent that they suggest
including NOX in this endangerment finding by changing or
expanding the definition of the air pollution. NOX emissions
have different, and potentially larger, climate effects when emitted at
high altitudes and about 90 percent of aircraft NOX is
emitted in flight (not during landing and takeoff),\160\ meaning its
relevance for climate change is primarily in relation to emissions at
high altitude. The atmospheric lifetime of NOX emitted near
the surface is on the order of a few hours, while in the upper
troposphere, or roughly the cruise altitude for jet aircraft, it is on
the order of several days.
---------------------------------------------------------------------------

\160\ FAA, System for Assessing Aviation's Global Emissions,
Version 1.5, Global Aviation Emissions Inventories for 2000 through
2004, FAA-EE-2005-02, September 2005, revised March 2008, available
at http://www.faa.gov/about/office_org/headquarters_offices/apl/researc/models/sage/ (Last accessed April 14, 2016).
---------------------------------------------------------------------------

Section IV.B.4 of the proposed findings under CAA section
231(a)(2)(A) \161\ explained that emissions of NOX do not
themselves have warming or cooling effects, but affect the climate
through catalyzing changes in the chemical equilibrium of the
atmosphere. High altitude emissions of NOX increase the
concentration of ozone, which has a warming effect in the short term.
Elevated NOX concentrations also lead to an increased rate
of destruction of methane, which has a cooling effect in the long-term.
The reduced methane concentrations eventually contribute to decreases
in ozone, which also decreases the long-term net warming effect. Thus,
the net radiative impact of NOX emissions depends on the
balance between the reductions in methane versus the production of
ozone, which in turn depends on the time scale under consideration.
---------------------------------------------------------------------------

\161\ 80 FR at 37783-84.
---------------------------------------------------------------------------

For the reasons stated above, the Administrator considers the
scientific assessment literature as the primary scientific and
technical basis informing the endangerment finding and providing the
state of climate science regarding how emissions of NOX
affect the climate system. Quantifying these impacts is an area of
active scientific study with large uncertainties. The quantification of
the net global effect of NOX is difficult because the
atmospheric chemistry effects are heavily dependent on highly localized
atmospheric properties and mixing ratios. Because the background
atmospheric concentration of NOX is important for
quantifying the impact of NOX emissions on ozone and methane
concentrations, the location of aircraft emissions is an important
additional factor. Going back to the IPCC 1999 assessment since no more
recent quantitative estimates are available, the globally averaged
radiative forcing estimates for high-altitude aircraft emissions of
NOX in 1992 were 0.023 W/m\2\ for ozone-induced changes
(uncertainty range of 0.011 to 0.046 W/m\2\), and -0.014 W/m\2\ for
methane-induced changes (uncertainty range of -0.005 to -0.042 W/
m\2\).\162\
---------------------------------------------------------------------------

\162\ IPCC, 1999: Aviation and the Global Atmosphere, Special
Report to the Intergovernmental Panel on Climate Change [Penner,
J.E., D.H. Lister, D.J. Griggs, D.J. Dokken, M. McFarland (eds.)]
Cambridge University Press, 373 pp.
---------------------------------------------------------------------------

The IPCC AR5 presents the impact of aviation high-altitude
NOX emissions using a different metric, global warming
potential (GWP), which is a measure of the warming impact of a pulse of
emissions of a given substance over 100 years relative to the same mass
of CO2. The AR5 presents a range from -21 to +75 for GWP of
aviation NOX.\163\ The uncertainty in sign indicates
uncertainty

[[Page 54451]]

whether the net effect is one of warming or cooling. This report
further suggests that at cruise altitude there is strong regional
sensitivity of ozone and methane to NOX, particularly
notable at low latitudes.
---------------------------------------------------------------------------

\163\ IPCC, 2013: Climate Change 2013: The Physical Science
Basis. Contribution of Working Group I to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Stocker,
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A.
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge
University Press, 1535 pp.
---------------------------------------------------------------------------

Thus, although the EPA is not prepared to determine whether
NOX emissions at high altitude should be found to be air
pollution within the meaning of CAA section 231(a)(2)(A), based on its
consideration of the scientific evidence and all the comments on this
issue, and consistent with its conclusion in the 2009 Endangerment
Finding, the EPA disagrees with commenters that assert that
NOX should be included at this time in the definition of the
air pollution for this finding. NOX does not share the
relevant properties that support grouping the six well-mixed GHGs
together as a class. NOX is not classified as a GHG because
it influences the climate system indirectly through production of ozone
rather than directly through trapping outgoing heat. In addition,
NOX does not have a sufficiently long atmospheric lifetime
to become well-mixed in the atmosphere and significant scientific
uncertainties remain regarding its net radiative forcing effects.
The Administrator notes that NOX emissions are already
regulated under the EPA's rules implementing CAA section 231, at 40 CFR
part 87, due to their impacts during landing and take-off operations
(LTO). The prerequisite endangerment and cause or contribute findings
that formed the basis for these standards, however, did not rely upon
any conclusions regarding the climate forcing impacts of
NOX, but rather the role of LTO NOX emissions as
a precursor to ozone formation in areas that did not meet the NAAQS for
ozone.\164\ The continuing significant uncertainties regarding high
altitude NOX emissions, which are emitted during cruise
operations rather than during LTO, as a climate forcer do not undermine
the Agency's prior conclusion under CAA section 231(a)(2)(A) that
emissions of NOX from aircraft engines cause or contribute
to air pollution which may reasonably be anticipated to endanger public
health or welfare due to their contribution to ozone concentrations
that exceed the NAAQS. This final finding does not revise or reopen the
Agency's prior findings under CAA section 231(a)(2)(A) that emissions
of NOX from aircraft engines cause or contribute to air
pollution which may reasonably be anticipated to endanger public health
or welfare due to their contribution to ozone concentrations that
exceed the NAAQS.
---------------------------------------------------------------------------

\164\ U.S. EPA, ``Control of Air Pollution from Aircraft and
Aircraft Engines, Emission Standards and Test Procedures for
Aircraft.'' Final Rule, 38 FR 19088 (July 17, 1973).
---------------------------------------------------------------------------

C. The Air Pollution is Reasonably Anticipated To Endanger Both Public
Health and Welfare

The Administrator finds that elevated atmospheric concentrations of
the six well-mixed GHGs may reasonably be anticipated to endanger the
public health and welfare of current and future generations within the
meaning of CAA section 231(a)(2)(A). This section describes the major
pieces of scientific evidence supporting the Administrator's
endangerment finding, discusses both the public health and welfare
aspects of the endangerment finding, and addresses a number of key
issues the Administrator considered when evaluating the state of the
science.
The EPA is informed by and places considerable weight on the
extensive scientific and technical evidence in the record supporting
the 2009 Endangerment Finding, including the major, peer-reviewed
scientific assessments used to address the question of whether GHGs in
the atmosphere endanger public health and welfare, and on the
analytical framework and conclusions upon which the EPA relied in
making that finding. This final finding under CAA section 231(a)(2)(A)
accounts for the EPA's careful consideration of the scientific and
technical record for the 2009 Endangerment Finding, of the new, major
scientific assessments issued since closing the administrative record
for the 2009 Endangerment Finding, and of public comments. No recent
information or assessments published since late 2009 or provided by
commenters suggest that it would be reasonable for the EPA to now reach
a different or contrary conclusion for purposes of CAA section
231(a)(2)(A) than the one the EPA reached in 2009 under CAA section
202(a). Rather, they provide further support for this final finding
under section 231(a)(2)(A). In particular, the new assessments
discussed in this document provide additional detail regarding public
health impacts, particularly on groups and people especially vulnerable
to climate change, including children, the elderly, low-income
communities and individuals, indigenous groups, and communities of
color.
Following the same decision framework and analysis that we followed
for the 2009 Endangerment Finding, as detailed in section IV.B of that
finding,\165\ here we summarize the general approach used by the
Administrator in reaching the judgment that a positive endangerment
finding should be made for purposes of CAA section 231(a)(2)(A), as
well as the specific rationale for finding that the GHG air pollution
may reasonably be anticipated to endanger both public health and
welfare. First, the Administrator finds the scientific evidence linking
anthropogenic emissions and resulting elevated atmospheric
concentrations of the six well-mixed GHGs to observed global and
regional temperature increases and other climate changes to be
sufficiently robust and compelling. The Administrator is basing her
finding on the total weight of scientific evidence and what the science
has to say regarding the nature and potential magnitude of the risks
and impacts across all climate-sensitive elements of public health and
welfare, now and projected out into the foreseeable future. The
Administrator has considered the state of the science on how
anthropogenic emissions and the resulting elevated atmospheric
concentrations of the six well-mixed GHGs may affect each of the major
risk categories, include human health, air quality, food production and
agriculture, forestry, water resources, sea level rise and coastal
areas, the energy sector, infrastructure and settlements, and
ecosystems and wildlife. The Administrator understands that the nature
and potential severity of impacts can vary across these different
elements of public health and welfare, and that they can vary by
region, as well as over time.
---------------------------------------------------------------------------

\165\ 74 FR at 66523-36.
---------------------------------------------------------------------------

The Administrator is therefore aware that, because human-induced
climate change has the potential to be far-reaching and multi-
dimensional, not all risks and potential impacts can be characterized
with a uniform level of quantification or understanding, nor can they
be characterized with uniform metrics. Thus, the Administrator is not
necessarily placing the greatest weight on those risks and impacts
which have been the subject of the most study or quantification.
Rather, given this variety in not only the nature and potential
magnitude of risks and impacts, but also in our ability to
characterize, quantify and project into the future such impacts, the
Administrator must use her judgment to weigh the threat in each of the
risk categories, weigh the potential benefits where relevant, and
ultimately to judge whether these risks and

[[Page 54452]]

benefits, when viewed in total, endanger public health and/or welfare.
First, the Administrator has not established a specific threshold
metric for the different categories of risk and impacts, which are
referred to as impact sectors. The potential for both adverse and
beneficial effects is considered, as well as the relative magnitude of
such effects, to the extent that the relative magnitudes can be
quantified or characterized. Furthermore, given the multiple ways in
which the buildup of anthropogenic GHG emissions in the atmosphere can
cause effects (e.g., via elevated CO2 concentrations,
temperature increases, precipitation increases, sea level rise, and
changes in extreme events), these multiple pathways are considered. The
Administrator has balanced and weighed the varying risks and effects
for each impact sector. She has judged whether there is a pattern
across the sector that supports or does not support an endangerment
finding, and if so whether the support is of more or less weight. In
cases where there is a potential for both benefits and risks of harm,
the Administrator has balanced these factors by determining whether
there appears to be any directional trend in the overall evidence that
would support placing more weight on one than the other, taking into
consideration all that is known about the likelihood of the various
risks and effects and their seriousness. In all of these cases, the
judgment is largely qualitative in nature and is not reducible to
precise metrics or quantification.
Regarding the timeframe for the endangerment test, it is the
Administrator's view that both current and future conditions must be
considered. The Administrator is thus taking the view that the
endangerment period of analysis extend from the current time to the
next several decades and in some cases to the end of this century. This
consideration is also consistent with the timeframes used in the
underlying scientific assessments. The future timeframe under
consideration is consistent with the atmospheric lifetime and climate
effects of the six well-mixed GHGs and also with our ability to make
reasonable and plausible projections of future conditions. The
Administrator acknowledges that some aspects of climate change science
and the projected impacts are more certain than others. Our state of
knowledge is strongest for recently observed, large-scale changes.
Uncertainty tends to increase in characterizing changes at smaller
(regional) scales relative to large (global) scales. Uncertainty also
increases as the temporal scales move away from the present, either
backward or more importantly forward in time. Nonetheless, the current
state of knowledge of observed and past climate changes and their
causes enables projections of plausible future changes under different
scenarios of anthropogenic forcing for a range of spatial and temporal
scales. The subsections below summarize the scientific information on
climate change impacts to public health and welfare that inform the
Administrator's judgment, as well as the key public comments and Agency
responses. The Agency's full responses to public comments can be found
in the Response to Comments document.
1. The Air Pollution is Reasonably Anticipated To Endanger Public
Health
The Administrator finds under CAA section 231(a)(2)(A) that the
well-mixed GHG air pollution is reasonably anticipated to endanger
public health, for both current and future generations. The
Administrator finds that the public health of current generations is
endangered and that the threat to public health for both current and
future generations will mount over time as GHGs continue to accumulate
in the atmosphere and result in ever greater rates of climate change.
The Administrator continues to find robust scientific evidence in the
assessment literature that climate change can increase the risk of
morbidity and mortality and believes that these public health impacts
can and should be considered when determining endangerment to public
health under CAA section 231(a)(2)(A). As described in section IV.B.1
of the 2009 Endangerment Finding, the Administrator is not limited to
only considering whether there are any direct health effects such as
respiratory or toxic effects associated with exposure to GHGs.
Here we summarize information from the scientific assessment
literature cited in the 2009 Endangerment Finding showing that climate
change resulting from anthropogenic GHG emissions threatens multiple
aspects of public health.\166\ In determining that the well-mixed GHG
air pollution is reasonably anticipated to endanger public health for
current and future generations under CAA section 202(a), the
Administrator noted her view that climate change can increase the risk
of morbidity and mortality. In making that public health determination,
the Administrator considered direct temperature effects, air quality
effects, the potential for changes in vector-borne diseases, and the
potential for changes in the severity and frequency of extreme weather
events. In addition, the Administrator considered whether and how
susceptible populations may be particularly at risk. As explained in
more detail in the 2009 Endangerment Finding, with respect to direct
temperature effects, by raising average temperatures, climate change
increases the likelihood of heat waves, which are associated with
increased deaths and illnesses. Climate change is also expected to lead
to reductions in cold-related mortality. The 2009 Endangerment Finding,
while noting uncertainty about how heat and cold related mortality
would change in the future, also pointed to a USGCRP assessment report
discussion that increases in heat-related mortality due to global
warming in the United States were unlikely to be compensated for by
decreases in cold-related mortality. With regard to air quality
effects, climate change is expected to increase ozone pollution over
broad areas of the country, including large metropolitan population
centers, and thereby increase the risks of respiratory infection,
aggravation of asthma, and premature death. Other public health threats
stem from the potential for increased deaths, injuries, infectious and
waterborne diseases, stress-related disorders, and other adverse
effects associated with increased hurricane intensity and increased
frequency of intense storms and heavy precipitation associated with
climate change. In addition, climate change is expected to be
associated with an increased risk of food-, water-, and vector-borne
diseases in susceptible populations. Climate change also has the
potential to change aeroallergen production (for example, through
lengthening the growing season for allergen-producing plants), and
subsequent human exposures could increase allergenic illnesses.
Children, the elderly, and the poor are among the most vulnerable to
climate-related health risks and impacts. The Administrator placed
weight on the fact that these certain groups are most vulnerable to
these climate-related health effects.
---------------------------------------------------------------------------

\166\ 74 FR at 66524-30.
---------------------------------------------------------------------------

The EPA concludes that the 2009 Endangerment Finding's discussion
under CAA section 202(a) is equally persuasive for purposes of CAA
section 231(a)(2)(A). In addition, the EPA has carefully reviewed the
key conclusions in the recent assessments regarding public health risks
and the current and projected health impacts from human-

[[Page 54453]]

induced climate change. The EPA finds that the new assessments are
consistent with or strengthen the underlying science considered in the
2009 Endangerment Finding regarding public health effects from changes
in temperature, air quality, extreme weather, and climate-sensitive
diseases and aeroallergens, further supporting an endangerment finding
under CAA section 231(a)(2)(A). These key findings are described
briefly here.
The USGCRP NCA3 finds that, ``Climate change threatens human health
and well-being in many ways, including impacts from increased extreme
weather events, wildfire, decreased air quality, threats to mental
health, and illnesses transmitted by food, water, and diseases carriers
such as mosquitoes and ticks. Some of these health impacts are already
underway in the United States.'' \167\ Regarding temperature effects,
the USGCRP NCA3 states, ``The effects of temperature extremes on human
health have been well documented for increased heat waves, which cause
more deaths, hospital admissions and population vulnerability.'' \168\
The conclusions of the assessment literature cited in the 2009
Endangerment Finding were uncertain with respect to the balance of
future heat- versus cold-related mortality associated with climate
change, but they noted that the available evidence suggested that the
increased risk from heat would exceed the decreased risk from cold in a
warming climate. The most recent assessments now have greater
confidence that increases in heat-related mortality likely will be
larger than the decreases in cold-related mortality, further supporting
this endangerment finding under CAA section 231(a)(2)(A). The USGCRP
NCA3 concludes, ``While deaths and injuries related to extreme cold
events are projected to decline due to climate change, these reductions
are not expected to compensate for the increase in heat-related
deaths.'' \169\ The IPCC AR5 also notes a potential benefit of climate
change could include ``modest reductions in cold-related mortality and
morbidity in some areas due to fewer cold extremes (low confidence),''
\170\ but that, ``[o]verall, we conclude that the increase in heat-
related mortality by mid-century will outweigh gains due to fewer cold
periods.'' \171\
---------------------------------------------------------------------------

\167\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 221.
\168\ Ibid at p. 252.
\169\ Ibid at p. 224.
\170\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and
Vulnerability. Part A: Global and Sectoral Aspects. Contribution of
Working Group II to the Fifth Assessment Report of the
Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros,
D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee,
K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N.
Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)].
Cambridge University Press, p. 713.
\171\ Ibid. at p. 721.
---------------------------------------------------------------------------

Regarding air quality effects, the assessment literature cited in
the 2009 Endangerment Finding concluded that climate change is expected
to increase regional ozone pollution, with associated risks in
respiratory illnesses and premature death, but that the directional
effect of climate change on ambient particulate matter levels was less
certain. One of the more recent assessments, the USGCRP NCA3, similarly
concludes, ``Climate change is projected to harm human health by
increasing ground-level ozone and/or particulate matter air pollution
in some locations. . . . There is less certainty in the responses of
airborne particles to climate change than there is about the response
of ozone.'' \172\ The IPCC AR5 finds that ozone and particulate matter
have been associated with adverse health effects in many locations in
North America, and that ozone concentrations could increase under
future climate change scenarios if emissions of precursors were held
constant. For particulate matter, both the USGCRP NCA3 and IPCC AR5
discuss increasing wildfire risk under climate change and explain that
wildfire smoke exposure can lead to various respiratory and
cardiovascular impacts. The USGCRP NCA3 states, ``The effects of
wildfire on human health have been well documented with increases in
wildfire frequency, leading to decreased air quality and negative
health impacts.'' \173\ The NRC Indoor Environment assessment
identifies potential adverse health risks associated with climate
change-induced alterations in the indoor environment, including
possible exposure to air pollutants due to changes in outdoor air
quality. Other risks include potential for alterations in indoor
allergens due to climate change-related increases in outdoor pollen
levels, potential chemical exposures due to greater use of pesticides
to address changes in geographic ranges of pest species, and dampness/
mold associated symptoms and illness due to potential flooding and
water damage in buildings from projected climate change-related
increases in storm intensity and extreme precipitation events in some
regions of the United States. Each of these assessments further
supports finding endangerment under CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

\172\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 222.
\173\ Ibid at p. 252.
---------------------------------------------------------------------------

Regarding extreme weather events (e.g., storms, heavy
precipitation, and, in some regions of the United States, floods and
droughts), the conclusions of the assessment literature cited in the
2009 Endangerment Finding found potential for increased deaths,
injuries, infectious and waterborne diseases, and stress-related
disorders. The more recent assessments further support this conclusion
for purposes of CAA section 231(a)(2)(A). The USGCRP NCA3 finds that
``Heavy downpours are increasing nationally, especially over the last
three to five decades. Largest increases are in the Midwest and
Northeast. Increases in the frequency and intensity of extreme
precipitation events are projected for all U.S. regions.'' \174\ The
USGCRP NCA3 identifies that: ``Elevated waterborne disease outbreaks
have been reported in the weeks following heavy rainfall, although
other variables may affect these associations. Water intrusion into
buildings can result in mold contamination that manifests later,
leading to indoor air quality problems.'' \175\ Other risks include
mortality associated with flooding and impacts on mental health, such
as anxiety and post-traumatic stress disorder. The IPCC AR5 also
discusses increased risk of death and injury in coastal zones and
regions vulnerable to inland flooding. The USGCRP NCA3 and the IPCC AR5
both find that climate change may increase exposure to health risks
associated with drought conditions, which includes impacts from
wildfires, dust storms, extreme heat events, and flash flooding.
Droughts can lead to reduced water quantity and degraded water quality,
thereby increasing the risk of water-related diseases. The IPCC SREX
assessment projects further increases in some extreme weather and
climate events during this century, and it specifically notes that
changes in extreme weather events have implications for disaster risk
in the health sector.
---------------------------------------------------------------------------

\174\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 36.
\175\ Ibid at p. 224-225.
---------------------------------------------------------------------------

The potential for changes in climate-sensitive diseases was also
cited in the 2009 Endangerment Finding. This included an increase in
the spread of several food and water-borne pathogens,

[[Page 54454]]

which can affect susceptible populations. Also noted was the potential
for range expansion of some zoonotic disease carriers such as the Lyme
disease-carrying tick. The new assessment literature similarly focuses
on increased exposure risk for some diseases under climate change,
finding that increasing temperatures may expand or shift the ranges of
some disease vectors like mosquitoes, ticks, and rodents. The IPCC AR5
notes that climate change may influence the ``growth, survival,
persistence, transmission, or virulence of pathogens'' \176\ that cause
food and water-borne disease. The USGCRP NCA3 notes that uncertainty
remains regarding future projections of increased human burden of
vector-borne disease, given complex interacting factors such as
``local, small-scale differences in weather, human modification of the
landscape, the diversity of animal hosts, and human behavior that
affects vector-human contact, among other factors.'' \177\ This new
assessment literature further supports finding endangerment under CAA
section 231(a)(2)(A).
---------------------------------------------------------------------------

\176\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and
Vulnerability. Part A: Global and Sectoral Aspects. Contribution of
Working Group II to the Fifth Assessment Report of the
Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros,
D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee,
K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N.
Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)].
Cambridge University Press, p. 726.
\177\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 225.
---------------------------------------------------------------------------

Regarding aeroallergens, the assessment literature cited in the
2009 Endangerment Finding found potential for climate change to affect
the prevalence and severity of allergy symptoms, but definitive data or
conclusions were lacking on how climate change might impact
aeroallergens in the United States. Further supporting an endangerment
finding under CAA section 231(a)(2)(A), the most recent assessments now
express greater confidence that climate change influences the
production of pollen, which in turn could affect the incidence of
asthma and other allergic respiratory illnesses such as allergic
rhinitis, as well as effects on conjunctivitis and dermatitis. Both the
USGCRP NCA3 and the IPCC AR5 found that increasing temperature has
lengthened the allergenic pollen season for ragweed, and that increased
CO2 by itself can elevate production of plant-based
allergens. The IPCC AR5 concludes that in North America, there is high
confidence that ``warming will lead to further changes in the seasonal
timing of pollen release.'' \178\
---------------------------------------------------------------------------

\178\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and
Vulnerability. Part B: Regional Aspects. Contribution of Working
Group II to the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D.
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O.
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S.
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge
University Press, Cambridge, pp. 1465-1466.
---------------------------------------------------------------------------

a. Health Impacts of Climate Change on Vulnerable Populations
In the 2009 Endangerment Finding, the EPA cited the assessment
literature's conclusions regarding the fact that certain populations,
including children, the elderly, and the poor, are most vulnerable to
climate change-related health effects. The 2009 Endangerment Finding
also described climate change impacts facing indigenous peoples in the
United States, particularly Alaska Natives. The new assessment
literature strengthens these conclusions and further supports an
endangerment finding under CAA section 231(a)(2)(A) by providing more
detailed findings regarding these populations' vulnerabilities and the
projected impacts they may experience. In addition, the most recent
assessment reports provide new analysis about how some populations
defined jointly by ethnic/racial characteristics and geographic
location may be vulnerable to certain climate change health impacts.
The following paragraphs summarize information from the most recent
assessment reports on these vulnerable populations.
The USGCRP NCA3 finds, ``Climate change will, absent other changes,
amplify some of the existing health threats the nation now faces.
Certain people and communities are especially vulnerable, including
children, the elderly, the sick, the poor, and some communities of
color.'' \179\ Limited resources make low-income populations more
vulnerable to ongoing climate-related threats, less able to adapt to
anticipated changes, and less able to recover from climate change
impacts. Low-income populations also face higher prevalence of chronic
health conditions than higher income groups, which increases their
vulnerability to the health effects of climate change.
---------------------------------------------------------------------------

\179\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 221.
---------------------------------------------------------------------------

According to the USGCRP NCA3 and IPCC AR5, some populations defined
jointly by ethnic/racial characteristics and geographic location are
more vulnerable to certain health effects of climate change due to
factors such as existing health disparities (e.g., higher prevalence of
chronic health conditions), increased exposure to health stresses, and
social factors that affect local resilience and ability to recover from
impacts.
The USGCRP NCA3 also finds that climate change, in addition to
chronic stresses such as extreme poverty, is affecting indigenous
peoples' health in the United States through impacts such as reduced
access to traditional foods, decreased water quality, and increasing
exposure to health and safety hazards. The IPCC AR5 finds that climate
change-induced warming in the Arctic and resultant changes in
environment (e.g., permafrost thaw, effects on traditional food
sources) have significant observed and projected impacts on the health
and well-being of Arctic residents, especially indigenous peoples.
Small, remote, predominantly indigenous communities are especially
vulnerable given their ``strong dependence on the environment for food,
culture, and way of life; their political and economic marginalization;
existing social, health, and poverty disparities; as well as their
frequent close proximity to exposed locations along ocean, lake, or
river shorelines.'' \180\ In addition, increasing temperatures and loss
of Arctic sea ice increases the risk of drowning for those engaged in
traditional hunting and fishing.
---------------------------------------------------------------------------

\180\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and
Vulnerability. Part B: Regional Aspects. Contribution of Working
Group II to the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D.
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O.
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S.
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge
University Press, Cambridge, p. 1581.
---------------------------------------------------------------------------

The USGCRP NCA3 concludes that ``Children, primarily because of
physiological and developmental factors, will disproportionately suffer
from the effects of heat waves, air pollution, infectious illness, and
trauma resulting from extreme weather events.'' \181\ As noted above,
the IPCC AR5 finds that in North America, climate change will influence
production of pollen, and that this affects asthma and other allergic
respiratory diseases to which children are among those especially
susceptible.

[[Page 54455]]

The IPCC AR5 also identifies children as a susceptible population to
health effects associated with heat waves, storms, and floods.
---------------------------------------------------------------------------

\181\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p.228.
---------------------------------------------------------------------------

Both the USGCRP and IPCC conclude that climate change increases
health risks facing the elderly. Older people are at much higher risk
of mortality during extreme heat events. Pre-existing health conditions
also make older adults susceptible to cardiac and respiratory impacts
of air pollution and to more severe consequences from infectious and
waterborne diseases. Limited mobility among older adults can also
increase health risks associated with extreme weather and floods.
Accordingly, as discussed above, all of these recent assessments
further support finding endangerment under CAA section 231(a)(2)(A).
b. Responses to Key Comments on Endangerment to Public Health
Public comments supported the EPA's summary of the scientific
information and finding that the well-mixed GHG air pollution is
reasonably anticipated to endanger public health of current and future
generations under CAA section 231(a)(2)(A). Commenters cited a number
of examples of climate impacts relevant to public health including
changes in outdoor and indoor air quality, extreme temperatures,
floods, fires, and hurricanes. Some commenters also agreed with the
EPA's summary of health impacts to certain vulnerable populations and
emphasized that certain populations like the elderly, poor, very young,
and indigenous groups are more vulnerable to the health impacts of
climate change for various reasons. No commenters disagreed with the
EPA's summary of the scientific information or with its conclusion on
endangerment to public health. The EPA agrees with the commenters that
this endangerment finding is well supported by the scientific
assessment literature; that it covers a range of health risks
associated with climate change-induced changes in air quality,
increases in temperatures, changes in extreme weather events, increases
in food and water borne pathogens, and changes in aeroallergens; and
that certain populations are more vulnerable to climate change health
risks and impacts.
2. The Air Pollution Is Reasonably Anticipated To Endanger Welfare
The Administrator finds under CAA section 231(a)(2)(A) that the air
pollution comprised of the six well-mixed GHGs is reasonably
anticipated to endanger welfare, for both current and future
generations. As with public health, the Administrator considered the
multiple pathways in which the GHG air pollution and resultant climate
change affect climate-sensitive sectors and the impact this may have on
welfare. These sectors include food production and agriculture;
forestry; water resources; sea level rise and coastal areas; energy,
infrastructure, and settlements; and ecosystems and wildlife. The
Administrator examined each climate-sensitive sector individually,
informed by the scientific information in the major assessments
contained in the administrative record for the 2009 Endangerment
Finding as well as the newer assessments in the record for this action,
and weighed the extent to which the risks and impacts within each
sector support or do not support a positive endangerment finding in her
judgment. The Administrator then viewed the full weight of evidence
looking across all sectors to reach her decision regarding endangerment
to welfare. For each of these sectors, the evidence indicates that the
risk and the severity of adverse impacts on welfare are expected to
increase over time, providing compelling support for a finding of
endangerment to welfare. The Administrator also considered impacts on
the U.S. population from climate change effects occurring outside of
the United States, such as national security concerns for the United
States that may arise as a result of climate change impacts in other
regions of the world, and finds that this provides additional support
to the finding of endangerment to welfare of current and future
generations of the United States population.
The 2009 Endangerment Finding summarized information from the
scientific assessment literature showing that climate change resulting
from anthropogenic GHG emissions also threatens multiple aspects of
welfare under CAA section 202(a).\182\ In determining that the well-
mixed GHG air pollution is reasonably anticipated to endanger welfare
for current and future generations, the Administrator considered the
multiple pathways by which GHG air pollution and resultant climate
change affect welfare by evaluating the numerous and far-ranging risks
and impacts associated with food production and agriculture; forestry;
water resources; widespread snow and ice melt, sea level rise and
coastal areas; energy, infrastructure, and settlements; and ocean
acidification, ecosystems, and wildlife. The Administrator also
considered observed and projected risks and impacts on the U.S.
population from climate change effects occurring outside of the United
States. As explained in more detail in the 2009 Endangerment Finding,
the potential serious adverse impacts of extreme events, such as
wildfires, flooding, drought, and extreme weather conditions provided
strong support for the determination. Water resources across large
areas of the country are at serious risk from climate change, with
effects on water supplies, water quality, and adverse effects from
extreme events such as floods and droughts. The severity of risks and
impacts is likely to increase over time with accumulating GHG
concentrations and associated temperature increases and precipitation
changes. Coastal areas are expected to face increased risks from storm
and flooding damage to property, as well as adverse impacts from rising
sea level such as land loss due to inundation, erosion, wetland
submergence and habitat loss. Climate change is expected to result in
an increase in electricity production for peak electricity demand, and
extreme weather from climate change threatens energy, transportation,
and water resource infrastructure. Climate change may exacerbate
existing environmental pressures in certain settlements. In Alaska,
indigenous communities are likely to experience disruptive impacts.
Climate change is also very likely to fundamentally change U.S.
ecosystems over the 21st century and to lead to predominantly negative
consequences for biodiversity, ecosystem goods and services, and
wildlife. Though there may be some benefits for agriculture and
forestry in the next few decades, the body of evidence points towards
increasing risks of net adverse impacts on U.S. food production,
agriculture and forest productivity as average temperature continues to
rise. Looking across all sectors discussed above, the risk and the
severity of adverse impacts on welfare are expected to increase over
time. Lastly, these impacts are global and may exacerbate problems
outside the United States that raise humanitarian, trade, and national
security issues for the United States.
---------------------------------------------------------------------------

\182\ 74 FR at 66530-36.
---------------------------------------------------------------------------

The Administrator concludes that the discussion in the 2009
Endangerment Finding under CAA section 202(a) is equally compelling to
support an endangerment finding under CAA section 231(a)(2)(A). In
addition, the EPA has carefully reviewed the recent scientific
conclusions in the assessments regarding human-induced

[[Page 54456]]

climate change impacts on welfare.\183\ The EPA finds that they further
support finding endangerment under CAA section 231(a)(2)(A), as they
are largely consistent with or strengthen the underlying science
supporting the 2009 Endangerment Finding regarding observed and
projected climate change risks and impacts to food production and
agriculture; forestry; water resources; widespread snow and ice melt,
sea level rise, and coastal areas; energy, infrastructure, and
settlements; ocean acidification, ecosystems, and wildlife; and impacts
on the U.S. population from climate change effects occurring outside of
the United States. These key findings are described briefly here.
---------------------------------------------------------------------------

\183\ The CAA states that ``[a]ll language referring to effects
on welfare includes, but is not limited to, effects on soils, water,
crops, vegetation, man-made materials, animals, wildlife, weather,
visibility, and climate, damage to and deterioration of property,
and hazards to transportation, as well as effects on economic values
and on personal comfort and well-being, whether caused by
transformation, conversion, or combination with other air
pollutants.'' CAA section 302(h). This language is quite broad.
Importantly, it is not an exclusive list due to the use of the term
``includes, but is not limited to . . .'' Effects other than those
listed here may also be considered effects on welfare.
---------------------------------------------------------------------------

Regarding agriculture, the assessment literature cited in the 2009
Endangerment Finding found potential for increased CO2
levels to benefit yields of certain crops in the short term, but with
considerable uncertainty. The body of evidence pointed towards
increasing risk of net adverse impacts on U.S. food production and
agriculture over time, with the potential for significant disruptions
and crop failure in the future. The most recent assessments now have
greater confidence that climate change will negatively affect U.S.
agriculture over this century, and support finding endangerment under
CAA section 231(a)(2)(A). Specifically, the USGCRP NCA3 concludes,
``While some U.S. regions and some types of agricultural production
will be relatively resilient to climate change over the next 25 years
or so, others will increasingly suffer from stresses due to extreme
heat, drought, disease, and heavy downpours. From mid-century on,
climate change is projected to have more negative impacts on crops and
livestock across the country.'' \184\ The IPCC AR5 concludes, ``Overall
yields of major crops in North America are projected to decline
modestly by mid-century and more steeply by 2100 among studies that do
not consider adaptation (very high confidence).'' \185\ The IPCC AR5
notes that in the absence of extreme events, climate change may benefit
certain regions and crops, but that in North America significant
harvest losses have been observed due to recent extreme weather events.
In addition, the IPCC SREX assessment specifically notes that projected
changes in extreme weather events will increase disaster risk in the
agriculture sector.
---------------------------------------------------------------------------

\184\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 16.
\185\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and
Vulnerability. Part B: Regional Aspects. Contribution of Working
Group II to the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D.
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O.
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S.
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge
University Press, Cambridge, p. 1462.
---------------------------------------------------------------------------

Regarding forestry, the assessment literature cited in the 2009
Endangerment Finding found that near-term benefits to forest growth and
productivity in certain parts of the country from elevated
CO2 concentrations and temperature increases to date are
offset by longer-term risks from wildfires and the spread of
destructive pests and disease that present serious adverse risks for
forest productivity. The most recent assessments provide further
support for finding endangerment under CAA section 231(a)(2)(A). Both
the USGCRP NCA3 and the IPCC AR5 conclude that climate change is
increasing risks to forest health from fire, tree disease and insect
infestations, and drought. The IPCC AR5 also notes risks to forested
ecosystems associated with changes in temperature, precipitation
amount, and CO2 concentrations, which can affect species and
ecological communities, leading to ecosystem disruption,
reorganization, movement or loss. The NRC Arctic assessment states that
climate change is likely to have a large negative impact on forested
ecosystems in the high northern latitudes due to the effects of
permafrost thaw and greater wildfire frequency, extent, and severity.
The NRC Climate Stabilization Targets assessment found that for an
increase in global average temperature of 1 to 2 [deg]C above pre-
industrial levels, the area burnt by wildfires in western North America
will likely more than double.
Regarding water resources, the assessment literature cited in the
2009 Endangerment Finding concluded that increasing temperatures and
increased variability in precipitation associated with climate change
is expected to have adverse impacts on water quality and is likely to
further constrain water quantity through changes in snowpack, increased
risk of floods, drought, and other concerns such as water pollution.
Similarly, the new assessments further support projections of water
resource impacts associated with increased floods and short-term
drought in most U.S. regions, and therefore support an endangerment
finding under CAA section 231(a)(2)(A). The USGCRP NCA3 also finds
that, ``[c]limate change is expected to affect water demand,
groundwater withdrawals, and aquifer recharge, reducing groundwater
availability in some areas.'' \186\ The IPCC AR5 finds that in part of
the western United States, ``water supplies are projected to be further
stressed by climate change, resulting in less water availability and
increased drought conditions.'' \187\ The IPCC AR5 states, ``Throughout
the eastern USA, water supply systems will be negatively impacted by
lost snowpack storage, rising sea levels contributing to increased
storm intensities and saltwater intrusion, possibly lower streamflows,
land use and population changes, and other stresses.'' \188\ The IPCC
AR5 also synthesizes recent studies that project a range of adverse
climate impacts in North America to surface water quality (including to
the Great Lakes), drinking water treatment/distribution, and sewage
collection systems.
---------------------------------------------------------------------------

\186\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 70.
\187\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and
Vulnerability. Part B: Regional Aspects. Contribution of Working
Group II to the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D.
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O.
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S.
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge
University Press, Cambridge, pp. 1456-1457.
\188\ Ibid at p. 1457.
---------------------------------------------------------------------------

The assessment literature cited in the 2009 Endangerment Finding
found that the most serious potential adverse effects to coastal areas
are the increased risk of storm surge and flooding in coastal areas
from current and projected rates of sea level rise and more intense
storms. Coastal areas also face other adverse impacts from sea level
rise such as land loss due to inundation, erosion, wetland submergence,
and habitat loss. The most recent assessments provide further evidence
in line with the science supporting the 2009 Endangerment Finding, and
support finding endangerment under CAA section 231(a)(2)(A). The USGCRP
NCA3 finds, ``Sea level rise, combined with coastal storms, has
increased the risk of erosion, storm surge damage, and flooding for

[[Page 54457]]

coastal communities, especially along the Gulf Coast, the Atlantic
seaboard, and in Alaska.'' \189\
---------------------------------------------------------------------------

\189\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 9.
---------------------------------------------------------------------------

The IPCC AR5 found that global sea levels rose 0.19 m (7.5 inches)
from 1901 to 2010. Contributing to this rise was the warming of the
oceans and melting of land ice from glaciers and ice sheets. It is
likely that 275 gigatons per year of ice melted from land glaciers (not
including ice sheets) from 1993-2009, and that the rate of loss of ice
from the Greenland and Antarctic ice sheets increased substantially in
recent years, to 215 gigatons per year and 147 gigatons per year
respectively from 2002-2011. For context, 360 gigatons of ice melt is
sufficient to cause global sea levels to rise one millimeter.
The IPCC AR5, the USGCRP NCA3, and three of the new NRC assessments
provide estimates of projected global average sea level rise. These
estimates, while not always directly comparable as they assume
different emissions scenarios and baselines, are at least 40 percent
larger than, and in some cases more than twice as large as, the
projected rise estimated in the IPCC AR4 assessment, which was referred
to in the 2009 Endangerment Finding.\190\ The NRC Sea Level Rise
assessment projects a global average sea level rise of 0.5 to 1.4
meters by 2100. Change of this magnitude would be sufficient to lead to
a relative rise in sea level even around the northern coasts of
Washington State, where the land is still rebounding from the
disappearance of the great ice sheets.\191\ The NRC National Security
Implications assessment suggests that ``the Department of the Navy
should expect roughly 0.4 to 2 meters global average sea-level rise by
2100.'' \192\ The NRC Climate Stabilization Targets assessment states
that a global average temperature increase of 3 [deg]C will lead to a
global average sea level rise of 0.5 to 1 meter by 2100. While these
NRC and IPCC assessments continue to recognize and characterize the
uncertainty inherent in accounting for melting ice sheets in sea level
rise projections, these revised estimates are consistent with the
assessments underlying the 2009 Endangerment Finding, and support
finding endangerment under CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

\190\ The 2007 IPCC AR4 assessment cited in 2009 Endangerment
Finding estimated a projected sea level rise of between 0.18 and
0.59 meters by the end of the century, relative to 1990. It should
be noted that in 2007, the IPCC stated that including poorly
understood ice sheet processes could lead to an increase in the
projections.
\191\ Sea level does not rise uniformly due to changes in winds,
temperature patterns, land uplift or subsidence, and other factors.
Therefore, relative sea level rise along any given point on the
coast can vary from the global average.
\192\ NRC, 2011: National Security Implications of Climate
Change for U.S. Naval Forces. The National Academies Press, p. 28.
---------------------------------------------------------------------------

Regarding climate impacts on energy, infrastructure and
settlements, the 2009 Endangerment Finding cited the assessment
literature's findings that temperature increases will change heating
and cooling demand; that declining water quantity may adversely impact
the availability of cooling water and hydropower in the energy sector;
and that changes in extreme weather events will threaten energy,
transportation, water, and other key societal infrastructure,
particularly on the coast. The most recent assessments provide further
evidence in line with the science supporting the 2009 Endangerment
Finding, to support finding endangerment under CAA section
231(a)(2)(A). For example, the USGCRP NCA3 finds, ``Coastal
infrastructure, including roads, rail lines, energy infrastructure,
airports, port facilities, and military bases, are increasingly at risk
from sea level rise and damaging storm surges.'' \193\ The NRC Arctic
assessment identifies threats to human infrastructure in the Arctic
from increased flooding, erosion, and shoreline ice pile-up, or ivu,
associated with summer sea ice loss and the increasing frequency and
severity of storms.
---------------------------------------------------------------------------

\193\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 9.
---------------------------------------------------------------------------

Regarding ecosystems and wildlife, the assessment literature cited
in the 2009 Endangerment Finding discussed a number of impacts. These
include a high confidence finding that substantial changes in the
structure and functioning of terrestrial ecosystems are very likely to
occur with a global warming greater than 2 to 3 [deg]C above pre-
industrial levels, with predominantly negative consequences for
biodiversity and the provisioning of ecosystem goods and services. In
addition, climate change and ocean acidification will likely impair a
wide range of planktonic and other marine calcifiers such as corals.
The recent assessments published since 2009 provide additional support
for finding endangerment under CAA section 231(a)(2)(A). The USGCRP
NCA3 concluded that ``The oceans are currently absorbing about a
quarter of the carbon dioxide emitted to the atmosphere annually and
are becoming more acidic as a result, leading to concerns about
intensifying impacts on marine ecosystems . . . Over the last 250
years, the oceans have absorbed 560 billion tons of CO2, increasing the
acidity of surface waters by 30%. Although the average oceanic pH can
vary on interglacial timescales, the current observed rate of change is
roughly 50 times faster than known historical change.'' \194\
---------------------------------------------------------------------------

\194\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 48.
---------------------------------------------------------------------------

The NRC Arctic assessment states that major marine and terrestrial
biomes will likely shift poleward, with significant implications for
changing species composition, food web structures, and ecosystem
function. The NRC Climate Stabilization Targets assessment found that
coral bleaching events will likely increase in frequency and severity
due warming sea surface temperatures and that ocean acidification will
likely reduce coral shell and skeleton growth and increase erosion of
coral reefs. The NRC Understanding Earth's Deep Past assessment notes
four of the five major coral reef crises of the past 500 million years
were caused by GHG-induced ocean acidification and warming that
followed releases of GHGs of similar magnitude to the emissions
increases expected over the next hundred years. Similarly, the NRC
Ocean Acidification assessment finds that ``[t]he chemistry of the
ocean is changing at an unprecedented rate and magnitude due to
anthropogenic CO2 emissions; the rate of change exceeds any
known to have occurred for at least the past hundreds of thousands of
years.'' \195\ The assessment notes that the full range of consequences
is still unknown, but the risks ``threaten coral reefs, fisheries,
protected species, and other natural resources of value to society.''
\196\ The IPCC AR5 also projects biodiversity losses in marine
ecosystems, especially in the Arctic and tropics.
---------------------------------------------------------------------------

\195\ NRC, 2010: Ocean Acidification: A National Strategy to
Meet the Challenges of a Changing Ocean. The National Academies
Press, p. 5.
\196\ Ibid.
---------------------------------------------------------------------------

The IPCC AR5 found that annual mean Arctic sea ice has been
declining at 3.5 to 4.1 percent per decade, and Northern Hemisphere
snow cover extent has decreased at about 1.6 percent per decade for
March and 11.7 percent per decade for June. The USGCRP NCA3 finds that
``rising temperatures across the U.S. have reduced lake ice, sea ice,
glaciers, and seasonal snow cover over the last few decades.'' \197\
These changes

[[Page 54458]]

are projected to continue, threatening seasonal water availability and
ecosystems reliant on ice and snow cover.
---------------------------------------------------------------------------

\197\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 46.
---------------------------------------------------------------------------

a. Welfare Impacts of Climate Change on Vulnerable Populations
In general, climate change impacts related to welfare are expected
to be unevenly distributed across different regions of the United
States and are expected to have a greater impact on certain
populations, such as indigenous peoples and the poor. The USGCRP NCA3
finds climate change impacts such as the rapid pace of temperature
rise, coastal erosion and inundation related to sea level rise and
storms, ice and snow melt, and permafrost thaw are affecting indigenous
people in the United States. Particularly in Alaska, critical
infrastructure and traditional livelihoods are threatened by climate
change, and ``[i]n parts of Alaska, Louisiana, the Pacific Islands, and
other coastal locations, climate change impacts (through erosion and
inundation) are so severe that some communities are already relocating
from historical homelands to which their traditions and cultural
identities are tied.'' \198\ The IPCC AR5 notes, ``Climate-related
hazards exacerbate other stressors, often with negative outcomes for
livelihoods, especially for people living in poverty (high confidence).
Climate-related hazards affect poor people's lives directly through
impacts on livelihoods, reductions in crop yields, or destruction of
homes and indirectly through, for example, increased food prices and
food insecurity.'' \199\
---------------------------------------------------------------------------

\198\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W.
Yohe, Eds., 2014: Climate Change Impacts in the United States: The
Third National Climate Assessment. U.S. Global Change Research
Program, p. 17.
\199\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and
Vulnerability. Part A: Global and Sectoral Aspects. Contribution of
Working Group II to the Fifth Assessment Report of the
Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros,
D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee,
K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N.
Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)].
Cambridge University Press, p. 796.
---------------------------------------------------------------------------

b. Other Considerations Regarding Endangerment to Welfare
In the 2009 Endangerment Finding, the Administrator considered
impacts on the U.S. population from climate change effects occurring
outside of the United States, such as national security concerns that
may arise as a result of climate change impacts in other regions of the
world. The most recent assessments provide further evidence in line
with the science supporting the 2009 Endangerment Finding, and further
support finding endangerment under CAA section 231(a)(2)(A). The NRC
Climate and Social Stress assessment found that it would be ``prudent
for security analysts to expect climate surprises in the coming decade
. . . and for them to become progressively more serious and more
frequent thereafter.'' \200\ The NRC National Security Implications
assessment recommends preparing for increased needs for humanitarian
aid; responding to the effects of climate change in geopolitical
hotspots, including possible mass migrations; and addressing changing
security needs in the Arctic as sea ice retreats.
---------------------------------------------------------------------------

\200\ NRC, 2013: Climate and Social Stress: Implications for
Security Analysis. The National Academies Press, p. 18.
---------------------------------------------------------------------------

In addition, the NRC Abrupt Impacts report examines the potential
for tipping points, thresholds beyond which major and rapid changes
occur in the Earth's climate system, as well as in natural and human
systems that are impacted by the changing climate. The Abrupt Impacts
report did find less cause for concern than some previous assessments
regarding some abrupt events within the next century, such as
disruption of the oceanic Atlantic Meridional Overturning Circulation
(AMOC) and sudden releases of high-latitude methane from hydrates and
permafrost. But, the same report found that the potential for abrupt
changes in ecosystems, weather and climate extremes, and groundwater
supplies critical for agriculture now seem more likely, severe, and
imminent. The assessment found that some abrupt changes were already
underway (e.g., Arctic sea ice retreat and increases in extinction risk
due to the speed of climate change), and cautioned that even abrupt
changes such disruption to the AMOC that are not expected in this
century can have severe impacts if/when they happen, such as
interference with the global transport of oceanic heat, salt, and
carbon.
c. Responses to Key Comments on Endangerment to Welfare
Public comments supported the EPA's summary of the scientific
information and finding that the well-mixed GHG air pollution is
reasonably anticipated to endanger welfare under CAA section
231(a)(2)(A). Commenters cited a number of examples of climate impacts
relevant to welfare including sea level rise and coastal erosion,
species range changes and extinctions, and reduced water availability
due to changes in snowpack and timing of snow melt. Some commenters
also agreed with the EPA's summary of welfare impacts to certain
vulnerable populations and emphasized that certain populations are more
vulnerable to the welfare impacts of climate change, in particular
tribes and indigenous groups. No commenters disagreed with the EPA's
summary of the scientific information or with its conclusion on
endangerment to welfare. The EPA agrees with the commenters that this
finding of endangerment to welfare under CAA section 231(a)(2)(A) is
well supported by the scientific assessment literature; that it covers
a range of risks associated with climate change threats to food
production and agriculture, forestry, water resources, sea level rise
and coastal areas, energy, infrastructure, and settlements, and
ecosystems and wildlife; and that certain populations are more
vulnerable to climate change welfare risks and impacts.
D. Summary of the Administrator's Endangerment Finding Under CAA
Section 231
In sum, the Administrator finds, for purposes of CAA section
231(a)(2)(A), that elevated atmospheric concentrations of the six well-
mixed GHGs constitute air pollution that endangers both public health
and welfare of current and future generations. In this final action
under CAA section 231(a)(2)(A), the EPA is informed by and places
considerable weight on the extensive scientific and technical evidence
in the record supporting the 2009 Endangerment Finding under CAA
section 202(a), including the major, peer-reviewed scientific
assessments used to address the question of whether GHGs in the
atmosphere endanger public health and welfare, and on the analytical
framework and conclusions upon which the EPA relied in making that
finding. This final finding under section 231(a)(2)(A) accounts for the
EPA's careful consideration of the scientific and technical record for
the 2009 Endangerment Finding, and of the new, major scientific
assessments issued since closing the administrative record for the 2009
Endangerment Finding, and consideration of public comments. No recent
information or assessments published since late 2009 suggest that it
would be reasonable for the EPA to now reach a different or contrary
conclusion for purposes of CAA section 231(a)(2)(A) than the Agency
reached for purposes of section 202(a); instead, the new, major
scientific assessments

[[Page 54459]]

further support finding endangerment under CAA section 231(a)(2)(A). In
making this finding for purposes of section 231(a)(2)(A), we are not
reopening or revisiting the 2009 Endangerment Finding under CAA section
202(a). To the contrary, in light of the recent judicial decisions
upholding that finding, the EPA believes the 2009 Endangerment Finding
is firmly established and well settled.\201\ Moreover, there is no need
for the EPA to reopen or revisit that finding for purposes of CAA
section 202(a) in order for the Administrator to rely on its analyses
and conclusions, supported by more recent studies, in support of making
an additional endangerment finding under section 231(a)(2)(A) of the
CAA. Today's final endangerment finding, although significantly
informed by the scientific information and the EPA's prior discussion
of that information in the 2009 Endangerment Finding, is solely for
purposes of CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

\201\ CRR, 684 F.3d at 117 (D.C. Cir. 2012), reh'g en banc
denied, 2012 U.S. App. LEXIS 25997, 26313, 26315 (D.C. Cir. 2012);
see also Utility Air Reg. Group v. EPA, 134 S. Ct. at 2438 (2014).
---------------------------------------------------------------------------

V. The Administrator's Cause or Contribute Finding for Greenhouse Gases
Emitted by Certain Classes of Engines Used by Covered Aircraft Under
CAA Section 231

As noted above, the Administrator defines the air pollution for
purposes of the endangerment finding under CAA section 231(a)(2)(A) to
be the aggregate of six well-mixed GHGs in the atmosphere, and finds
that such air pollution endangers public health and welfare of current
and future generations. The second step of the two-part endangerment
test for this finding is for the Administrator to determine whether the
emission of any air pollutant from certain classes of aircraft engines
used by certain aircraft causes or contributes to this endangering air
pollution. This is referred to as the cause or contribute finding, and
is the second finding by the Administrator in this action under CAA
section 231(a)(2)(A).
Section V.A of this document describes the Administrator's
reasoning for using under CAA section 231(a)(2) the same definition and
scope of the GHG air pollutant that was used in the 2009 Endangerment
Finding under CAA section 202(a). Section V.B puts forth the
Administrator's finding that emissions of well-mixed GHGs from certain
classes of aircraft engines used in covered aircraft contribute to the
air pollution which endangers public health and welfare under CAA
section 231(a)(2)(A). The EPA's responses to some of the most
significant comments for the cause or contribute finding are provided
later in section V.C. Responses to all significant issues raised by the
comments on the cause or contribute finding are contained in the
Response to Comments document, which is organized by subject area
(found in docket EPA-HQ-OAR-2014-0828).

A. The Air Pollutant

1. Definition of Air Pollutant
Under section 231(a)(2)(A), the Administrator is to determine
whether emissions of any air pollutant from any class or classes of
aircraft engines cause or contribute to air pollution which may
reasonably be anticipated to endanger public health or welfare. As with
the 2009 Endangerment Finding that the EPA conducted for purposes of
CAA section 202(a), when making a cause or contribute finding under
section 231(a)(2), the Administrator must first define the air
pollutant being evaluated. The Administrator has considered the logical
relationship between the GHG air pollution and air pollutant: While the
air pollution is the concentration (e.g., stock) of the well-mixed GHGs
in the atmosphere, the air pollutant is the same combined grouping of
the well-mixed GHGs, the emissions of which are analyzed for
contribution (e.g., the flow into the stock). See 74 FR at 66536
(similar discussion with respect to the finding for CAA section
202(a)). For purposes of section 231(a)(2)(A), the Administrator is
defining the air pollutant as the same combined grouping of the six
well-mixed GHGs that comprises the air pollution. Accordingly, the
Administrator is using the same definition of the air pollutant that
was used in the 2009 Endangerment Finding for purposes of CAA section
202(a), namely, the aggregate group of the same six well-mixed GHGs:
CO2, methane, nitrous oxide, hydrofluorocarbons,
perfluorocarbons, and sulfur hexafluoride. See 74 FR at 66536-37
(discussing the definition of the GHG air pollutant with respect to the
finding for CAA section 202(a)). That is, as was done for the 2009
Endangerment Finding, the Administrator is defining a single air
pollutant made up of these six GHGs in this action under CAA section
231(a)(2)(A).
To reiterate what the Agency has previously stated on this subject,
this collective approach for the contribution test is consistent with
the treatment of GHGs by those studying climate change science and
policy, where it is common practice to evaluate GHGs on a collective,
CO2-equivalent basis.\202\ This collective approach to
defining the air pollutant is not unique; grouping of many substances
with common attributes as a single pollutant is common practice under
the CAA, for example with particulate matter and volatile organic
compounds (VOC). As noted in section IV.B, these six substances share
common attributes that support their grouping to define the air
pollution for purposes of the endangerment finding. These same common
attributes also support the Administrator grouping these six well-mixed
GHGs for purposes of defining the air pollutant for this cause or
contribute finding under CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

\202\ As detailed in the 2009 Endangerment Finding proposal (74
FR at 18904) and continuing today, the UNFCCC, the U.S. and other
Parties report their annual emissions of the six GHGs in
CO2-equivalent units. This facilitates comparisons of the
multiple GHGs from different sources and from different countries,
and provides a measure of the collective warming potential of
multiple GHGs. Emissions of different GHGs are compared using GWPs,
which as described in section IV.B of this document are measures of
the warming impact of a pulse of emissions of a given substance over
100 years relative to the same mass of CO2. Therefore,
GWP-weighted emissions are measured in teragrams of CO2
equivalent (Tg CO2eq). One teragram (Tg) = 1 million
metric tons = 1 megatonne (Mt). 1 metric ton = 1,000 kilograms =
1.102 short tons = 2,205 lbs. The EPA's Greenhouse Gas Reporting
Program (http://www.epa.gov/ghgreporting/index.html (last accessed
April 8, 2016)) also reports GHG emissions on a CO2-
equivalent basis, recognizing the common and collective treatment of
these six well-mixed GHGs.
---------------------------------------------------------------------------

The Administrator recognizes that in this case, the aircraft
engines covered by this document emit two of the six gases, but not the
other four gases. Nonetheless, it is entirely appropriate, and in
keeping with the 2009 Endangerment Finding and past EPA practice, for
the Administrator to define the air pollutant under CAA section
231(a)(2)(A) in a manner that recognizes the shared relevant properties
of all these six gases, even though they are not all emitted from the
classes of sources before her.\203\ For example, a source may emit only
20 of the possible 200-plus chemicals that meet the definition of VOC
in the EPA's regulations, but that source is evaluated based on its
emissions of VOC and not on its emissions of the 20 chemicals by name.
The fact that these six substances within the definition of GHGs share
common, relevant attributes is true regardless of the type of sources
being evaluated for

[[Page 54460]]

contribution. Moreover, the reasonableness of grouping these chemicals
as a single air pollutant does not turn on the particular source
category. By using the definition of the air pollutant as comprised of
the six GHGs with common attributes, the Administrator is taking
account of these shared attributes and how they are relevant to the air
pollution that endangers public health and welfare.
---------------------------------------------------------------------------

\203\ In the 2009 Endangerment Finding, the Administrator found
that four of the six gases that were included in the definition of
the air pollutant were emitted by section 202 sources. 74 FR at
66537.
---------------------------------------------------------------------------

In fact, as explained in the 2009 Endangerment Finding, Congress
has given the EPA broad discretion to determine that appropriate
combinations of compounds should be treated as a single air pollutant.
74 FR at 66537. Section 302(g) of the CAA defines ``air pollutant'' as
``any air pollutant agent or combination of such agents. . . .'' Thus,
it is clear that the term ``air pollutant'' is not limited to
individual chemical compounds. Moreover, in determining that GHGs are
within the scope of this definition, the Supreme Court described
section 302(g) as a ``sweeping'' and ``capacious'' definition that
unambiguously included GHGs, which are ``unquestionably `agents' of air
pollution.'' Massachusetts v. EPA, 549 U.S. at 528, 532, 529 n. 26.
Although the Court did not interpret the term ``combination of'' air
pollution agents, there is no reason to interpret this phrase more
narrowly in this context. Congress used the term ``any'' and did not
qualify the kind of combinations that EPA could define as a single air
pollutant.
2. The Definition of Air Pollutant May Include Substances Not Emitted
by CAA Section 231(a)(2) Sources.
Similar to the discussion in section IV.B.6 for the definition of
``air pollution'' for purposes of the endangerment finding under CAA
section 231(a)(2)(A), many commenters highlighted the fact that
aircraft engines emit only two of the six well-mixed GHGs that together
are defined as the ``air pollutant'' for purposes of the cause or
contribute finding under section 231(a)(2)(A) of the CAA. Commenters
point out that the majority of emissions are CO2, while
nitrous oxide emissions are described as ``nominal (<1%)'' or
``trace.'' Some commenters ultimately concluded that the EPA's approach
to defining the air pollutant as an aggregate group of six gases is
acceptable, but that the scope of future regulations should be limited
to CO2. One commenter agreed with the Agency's evaluation of
the six GHGs based on their common attributes, but questioned the EPA's
decision to aggregate the six gases rather than considering them
individually for purposes of making the findings. Other commenters
disagreed with the EPA and requested limiting the definition of air
pollutant in this action to CO2 or to CO2 and
nitrous oxide.
The EPA disagrees with comments regarding changing the definition
of the air pollutant to limit it to only those GHGs that are emitted
from aircraft or to CO2 only. The EPA has explained both in
the 2009 Endangerment Finding under CAA section 202(a) and in the
proposed findings under CAA section 231(a)(2)(A) that it is reasonable
and appropriate for the EPA to consider the logical relationship
between the GHG air pollution and air pollutant when defining the air
pollutant. The purpose of this cause or contribute inquiry is to
determine whether emissions of an air pollutant from certain aircraft
engines cause or contribute to the endangering GHG air pollution. As
described in section IV.B of this document, the endangering GHG air
pollution under consideration is defined as the aggregate group of the
six well-mixed GHGs based on shared characteristics and common
attributes relevant to climate change science and policy'' \204\--a
rationale that does not take into consideration emission source(s).
Similarly, the definition of the air pollutant in this cause or
contribute inquiry establishes well-mixed GHGs as a single air
pollutant comprised of six substances with common attributes. The
Administrator is giving effect to the shared attributes of the six
well-mixed GHGs and how they are relevant to the air pollution to which
they contribute. Thus, it is also reasonable for the EPA to evaluate
contribution for those gases in the aggregate, rather than
individually, to ensure a like-to-like comparison of aggregate
emissions contributing to an aggregate stock (atmospheric
concentration) of endangering GHG air pollution.
---------------------------------------------------------------------------

\204\ 74 FR at 66517-19; 80 FR at 37774-85.
---------------------------------------------------------------------------

The EPA recognized in the proposed findings that aircraft emit two
of the six well-mixed GHGs, but stated that nonetheless it is entirely
reasonable and appropriate, and in keeping with the 2009 Endangerment
Finding under CAA section 202(a) and other past EPA practice, for the
Administrator to group into a single class those substances that
possess shared relevant properties, even though they are not all
emitted from the classes of sources before her.\205\ The fact that
these six substances share these common, relevant attributes is true
regardless of the source category being evaluated for contribution.
After considering all the comments, this continues to be the EPA's
view. Moreover, this approach to defining an air pollutant as a
grouping of many substances is not unique to GHGs, but rather is common
practice under the CAA. For example, the EPA has heavy-duty truck
standards applicable to VOCs and PM, but it is highly unlikely that
heavy-duty trucks emit every substance that is included in the group
defined as VOC or PM. See 40 CFR 51.100(s) (defining volatile organic
compound (VOC) as ``any compound of carbon, excluding carbon monoxide,
carbon dioxide, carbonic acid, metallic carbides or carbonates, and
ammonium carbonate, which participates in atmospheric photochemical
reactions''; a list of exemptions are also included in the definition);
40 CFR 51.100(oo) (defining particulate matter (PM) as ``any airborne
finely divided solid or liquid material with an aerodynamic diameter
smaller than 100 micrometers'').
---------------------------------------------------------------------------

\205\ 80 FR at 37774-85, and 37787.
---------------------------------------------------------------------------

Grouping these six substances as one air pollutant is just as
reasonable for the contribution analysis undertaken for CAA section
231(a)(2) sources that emit one subset of the six substances as it was
for the category of sources that emits another subset under CAA section
202(a). In other words, it is not necessarily the source category,
motor vehicles or aircraft engines, being evaluated for contribution
that determines the reasonableness of defining a group air pollutant
based on the shared attributes of the group's constituent substances.
Even if the EPA defined the air pollutant as the group of two compounds
emitted by CAA section 231(a)(2) sources, it would not change the
result. The Administrator would make the same contribution finding (as
described later in section V.B.), as it would have no material effect
on the emissions comparisons discussed in section V.B.
The question of limits to the scope of future regulations is
outside of the scope of this action because the EPA has neither
proposed nor is finalizing in this action any such regulatory
standards. This final action does not itself impose any requirements on
source categories under CAA section 231. Thus, the EPA anticipates that
this question could be raised and considered, as needed, in the
standard-setting phase of the regulatory process, and invites potential
commenters to submit their views on this issue in response to EPA's
anticipated future notice of proposed rulemaking on standards.
Another commenter expressed concern about the EPA's proposed
contribution finding because it does not differentiate between
CO2 emissions that result from combustion of fossil

[[Page 54461]]

fuels and those that result from ``combustion of biomass or biofuels
derived from herbaceous crops or crop residues, as well as biogenic
CO2 emissions associated with the production, gathering and
processing of crops or crop residues used in bio-based products
including fuels.'' \206\ The commenter argues that such crop-related
biogenic CO2 emissions should be excluded from the
contribution finding because the CO2 released back to the
atmosphere when emitted from crop-derived biogenic sources contains the
same carbon that was previously removed or sequestered from
CO2 in the atmosphere, and thus does not contribute to
elevated atmospheric concentrations of the six well-mixed GHGs.
---------------------------------------------------------------------------

\206\ Biogenic CO2 Coalition, 2015: Comments on EPA's
Proposed Finding That Greenhouse Gas Emissions From Aircraft Cause
or Contribute to Air Pollution That May Reasonably Be Anticipated To
Endanger Public Health and Welfare, 80 FR 37757 (July 1, 2015).
Docket ID number EPA-HQ-OAR-2014-0828-0916. Available at
www.regulations.gov (last accessed April 11, 2016).
---------------------------------------------------------------------------

Consistent with the previously discussed response to the commenter
in the discussion of the definition of air pollution being used under
CAA section 231(a)(2)(A), the EPA reiterates that the Administrator
defines the relevant air pollutant considered in the contribution
finding as the aggregate group of the six well-mixed GHGs based on
shared physical characteristics and common attributes relevant to
climate change science and policy, and does not include consideration
of the source of the air pollutant. In the record for the 2009
Endangerment Finding under CAA section 202(a), the Agency stated that
``all CO2 emissions, regardless of source, influence
radiative forcing equally once it reaches the atmosphere and therefore
there is no distinction between biogenic and non-biogenic
CO2 regarding the CO2 and the other well-mixed
GHGs within the definition of air pollution that is reasonably
anticipated to endanger public health and welfare.'' \207\ The EPA
continues to hold that position in these findings under CAA section
231(a)(2)(A), which is supported by the evidence before it. First, the
fact that these CO2 emissions originate from combustion of
carbon-based fuels created through different processes is not relevant
to defining the air pollutant that contributes to the endangering air
pollution. The origin and constitution of a fuel prior to its
combustion and subsequent emission into the atmosphere has no bearing
on the fact that CO2 and the other well-mixed GHGs are all
sufficiently long lived to become well mixed in the atmosphere,
directly emitted, of well-known radiative forcing, and generally
grouped and considered together in climate change scientific and policy
forums as the primary driver of climate change. A molecule of biogenic
CO2 has the same radiative forcing effect as a molecule of
fossil-fuel derived CO2. In other words, no matter the
original source of the CO2, the behavior of the
CO2 molecules in the atmosphere in terms of radiative
forcing, chemical reactivity, and atmospheric lifetime is effectively
the same. Any differential treatment of biogenic CO2 in the
context of the contribution finding under CAA section 231(a)(2)(A)
would be inconsistent with the primary scientific basis for the
grouping of the six well-mixed GHGs as a single class for purposes of
identifying the air pollutant (and air pollution, as explained in
section IV.B.1). A more detailed response to the issues raised in this
comment can be found in the Response to Comments document in the
docket.
---------------------------------------------------------------------------

\207\ EPA, 2009. Response to Comments document, Volume 9: The
Endangerment Finding, EPA-HQ-OAR-2009-0171-11676. Available at
www.regulations.gov (last accessed April 11, 2016).
---------------------------------------------------------------------------

B. The Administrator's Finding Under CAA Section 231(a)(2)(A) That
Greenhouse Gas Emissions From Certain Classes of Aircraft Engines Used
in Certain Aircraft Cause or Contribute to Air Pollution That May Be
Reasonably Anticipated To Endanger Public Health and Welfare

Under CAA section 231(a)(2)(A), the Administrator finds that
emissions of the six well-mixed GHGs from classes of engines used in
U.S. covered aircraft, which are subsonic jet aircraft with a maximum
takeoff mass (MTOM) greater than 5,700 kilograms and subsonic propeller
driven (e.g., turboprop) aircraft with a MTOM greater than 8,618
kilograms, contribute to the air pollution that endangers public health
and welfare. The Administrator is not at this time making a
contribution finding regarding GHG emissions from engines not used in
covered aircraft (i.e., those used in smaller turboprops, smaller jet
aircraft, piston-engine aircraft, helicopters and military aircraft),
or regarding the emission of other substances emitted by aircraft
engines. A detailed discussion of covered aircraft and their GHG
emissions data is provided below in section V.B.4.
The Administrator reached her decision after reviewing emissions
data on the contribution of covered aircraft under CAA section 231(a)
relative to both U.S. GHG and global GHG emissions inventories. It is
the Administrator's judgment that the collective GHG emissions from the
classes of engines used in U.S. covered aircraft clearly contribute to
endangering GHG pollution, whether the comparison is--as described
later in Tables V.1 and V.3 of sections V.B.4.a and V.B.4.b
respectively--to domestic GHG inventories (10 percent of all U.S.
transportation GHG emissions, representing 2.8 percent of total U.S.
emissions), to global GHG inventories (26 percent of total global
aircraft GHG emissions representing 2.7 percent of total global
transportation emissions and 0.4 percent of all global GHG emissions),
or if using a combination of domestic and global inventory comparisons.
Both domestic and global comparisons, independently and jointly,
support the contribution finding under CAA section
231(a)(2)(A).^{208 209 210} Making this cause or contribute
finding for engines used in U.S. covered aircraft results in the vast
majority (89 percent) of total U.S. aircraft GHG emissions being
included in this determination (as described later in Table V.1 of
section V.B.4.a.). Covered U.S. aircraft GHG emissions are from
aircraft that operate in and from the U.S. and thus contribute to
emissions in the U.S. This includes emissions from U.S. domestic
flights, and emissions from U.S. international bunker flights
(emissions from the combustion of fuel used by aircraft departing the
U.S., regardless of whether they are a U.S. flagged carrier--also
described as emissions from combustion of U.S. international bunker
fuels \211\). In addition, the Administrator based her decision on all
the information in the record for this finding, including the public
comments received on the proposed finding.
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\208\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\209\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, 1435 pp.
\210\ The domestic inventory comparisons are for the year 2014,
and global inventory comparisons are for the year 2010. The
rationale for the different years is discussed later in section
V.B.4.
\211\ For example, a flight departing Los Angeles and arriving
in Tokyo, regardless of whether it is a U.S. flagged carrier, is
considered a U.S. international bunker flight. A flight from London
to Hong Kong is not.

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[[Page 54462]]

1. The Administrator's Approach in Making This Finding
As it did for the 2009 Endangerment Finding under CAA section
202(a), and consistent with prior practice and current science, under
this CAA section 231(a)(2)(A) contribution finding the EPA uses annual
emissions as a reasonable proxy for contributions to the endangering
air pollution, i.e., the elevated atmospheric concentrations of the six
well-mixed GHGs. Cumulative anthropogenic emissions are primarily
responsible for the observed change in GHG concentrations in the
atmosphere (i.e., the fraction of a country's or an economic sector's
cumulative emissions compared to global GHG emissions over a long time
period will be roughly equal to the fraction of the change in
concentrations attributable to that country or economic sector);
likewise, annual GHG emissions are a reasonable proxy for annual
incremental changes in atmospheric GHG concentrations.
There are a number of possible ways of assessing whether a source's
emissions of air pollutants cause or contribute to the endangering air
pollution, and no single approach is required or has been used
exclusively in previous determinations under the CAA. Because under
this CAA section 231(a)(2)(A) action the air pollution against which
the contribution of air pollutant emissions is being evaluated is the
six well-mixed GHGs, one reasonable starting point for a contribution
analysis is a comparison of the emissions of the air pollutant from the
aircraft under consideration to the total U.S. and total global
emissions of these six GHGs. The Administrator recognizes that there
are other valid comparisons that can be considered in evaluating
whether emissions of the air pollutant cause or contribute to the
combined concentration of these six GHGs. To inform the Administrator's
assessment, section V.B.4 presents the following types of simple and
straightforward comparisons of covered U.S. aircraft GHG emissions:
As a share of current total U.S. GHG emissions;
As a share of current U.S. transportation GHG emissions;
As a share of current total global GHG emissions; and
As a share of the current global transportation GHG
emissions.
All annual GHG emissions data are reported on a CO2-
equivalent (CO2eq) basis, which as described above is a
commonly used metric to convert GHG emissions into standard units so
they can be compared. This approach is consistent with how the EPA
determined contribution for GHGs under section 202(a) of the CAA in
2009.
2. Details of the Administrator's Approach in Making This Cause or
Contribute Finding
The Administrator believes that consideration of the global context
is important for the cause or contribute finding under CAA section
231(a)(2)(A), but that the analysis should not solely consider the
global context. GHG emissions from engines used in U.S. covered
aircraft will become globally well-mixed in the atmosphere, and thus
will have an effect not only on the U.S. regional climate but also on
the global climate as a whole, for many decades to come. It is the
Administrator's view that it is reasonable for the cause or contribute
analysis conducted under CAA section 231(a)(2)(A) for GHGs emitted by
covered U.S. aircraft engines to be consistent with the reasoning
supporting the 2009 GHG cause or contribute finding under CAA section
202, as the relevant statutory provisions are parallel and as the
pollutant is the same. Accordingly, the Administrator finds a positive
cause or contribute finding for GHG emissions from engines used in U.S.
covered aircraft is justified whether only the domestic context is
considered, only the global context is considered, or both the domestic
and global GHG emissions comparisons are viewed in combination. Both
domestic and global comparisons, independently and jointly, are equally
important for the finding.
In the 2009 CAA section 202(a) cause or contribute finding, the
Administrator considered the totality of the circumstances in order to
best understand the role played by CAA section 202(a) source categories
in emitting air pollutants that contribute to endangering GHG air
pollution, consistent with Congress' intention for EPA to consider the
cumulative impact of all emissions from sources to the endangering air
pollution. In that context, the global nature of the air pollution
problem and the breadth of countries and sources emitting GHGs meant
that no single country or source category dominated contribution to the
endangering air pollution on the global scale.\212\ As was the case in
2009, it is still true that no single country or GHG source category
dominates contribution to the collective stock of endangering GHG air
pollution on the global scale, and contributions from individual GHG
source categories may appear small in comparison to the total stock,
when, in fact, they are very important contributors in terms of both
absolute emissions or in comparison to GHG emissions from other source
categories, globally or within the United States. That is, because
climate change is a global problem that results from global GHG
emissions, it is more the result of numerous and varied sources each
emitting what may seem to be smaller percentages of GHG pollutants
compared to the total stock of GHG pollution, than typically might be
encountered when tackling solely regional or local environmental issues
for different kinds of pollutants that may have more of a direct impact
on receptors located in the relative vicinity of the polluting sources
(such as emissions of lead, for example, or sulfur dioxide without
consideration of its role as possible precursor to particulate matter).
It is reasonable for the Administrator to take these circumstances into
account in making a contribution determination regarding emissions from
sources of GHGs, as the impacts from GHGs are not spatially or
temporally limited.\213\ Therefore, in order to address the risks
associated with global climate change, it is less likely that a single
``majority'' contributing source category could be identified and
controlled such that the risks could be eliminated, without the need to
consider contributions to the endangering stock of air pollution from
``minority'' source categories that may present smaller percentages of
contribution than may sometimes be encountered when tackling regional
or local environmental threats presented by a single or limited set of
dominant sources. Thus, in addressing GHG risks, it will be, as the
Supreme Court suggested in Massachusetts v. EPA, necessary for agencies
to take an incremental approach to resolving the larger GHG
endangerment issue, as ``[a]gencies, like legislatures, do not
generally resolve massive problems in one fell regulatory swoop. . . .
They instead whittle away at them over time, refining their preferred
approach as circumstances change and as they develop a more nuanced
understanding of how best to proceed.'' 549 U.S. 497, 524 (2007)
(citations omitted). The Administrator continues to believe that the
unique, global aspects of the climate change problem--including that
from a percentage perspective there are no dominating sources or
countries for GHG emissions contributing to the endangering GHG air
pollution and that the global problem is due more to the GHG emissions
contributed from

[[Page 54463]]

numerous and varied sources--justify consideration of contribution to
the endangering air pollution at lower percentage levels than the EPA
typically might encounter when analyzing contribution towards a more
localized air pollution problem. This is not to suggest, however, that
all or even most local or regional air pollution problems are due to a
single or small set of sources. For example, regional haze and ambient
concentrations of concern for ozone, carbon monoxide, and particulate
matter are commonly the result of a variety and great number of
contributing sources, and the EPA has frequently approached such
problems by incrementally regulating a set of sources that, in
isolation, is not contributing the dominant share of air pollutants to
the stock of air pollution, but is contributing a meaningful share.
This approach has been affirmed by reviewing courts as reasonable and
lawful under the CAA. See, e.g., Bluewater Network v. EPA, 370 F.3d 1
(D.C. Cir. 2004). Thus, the Administrator, similar to the approach
taken in the 2009 GHG cause or contribute finding under CAA section
202(a), is under CAA section 231(a)(2)(A) placing weight on the fact
that engines used in U.S. covered aircraft, as discussed in detail in
sections V.B.4.a of this document, contribute the single largest share
of GHG emissions from transportation sources in the United States that
have not yet been regulated for GHG emissions, and that such GHG
emissions from U.S. covered aircraft are a meaningful contribution to
total U.S. and total global GHG emissions inventories.
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\212\ 74 FR at 66538.
\213\ 74 FR at 66543.
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3. Additional Considerations
The Administrator also considered information that showed that
reasonable estimates of GHG emissions from engines used in U.S. covered
aircraft are projected to grow over the next 20 to 30 years, in making
her contribution finding under CAA section 231(a)(2)(A). Given the
projected growth in aircraft emissions compared to other sectors, it is
reasonable for the Administrator to consider future emissions
projections as further supporting her assessment of historical annual
emissions (recent emissions from the current fleet) and informing her
contribution determination. As described with further detail later in
section V.B.4.c, recent FAA projections reveal that by 2036 GHG
emissions from all aircraft and from U.S. covered aircraft are likely
to increase by 43 percent (from 191 Tg CO2eq to 272 Tg
CO2eq for the years 2010 to 2036).\214\ By contrast, it is
estimated that by 2036 the light-duty vehicle sector is projected to
see a 25 percent reduction in GHG emissions (1,133 Tg CO2eq
to 844 Tg CO2eq) from the 2010 baseline, while the freight
trucks sector is projected to experience a 23 percent increase in GHG
emissions (390 Tg CO2eq to 478 Tg CO2eq) from the
2010 baseline (this projected increase does not reflect the impact of
GHG reductions on the freight trucks sector anticipated from the Phase
2 heavy-duty GHG standards that have not yet been promulgated). In
addition, by 2036 the rail sector is projected to experience a 3
percent reduction in GHG emissions (44 Tg CO2eq to 43 Tg
CO2eq) from the 2010 baseline.\215\ Because the projected
growth in aircraft engine GHG emissions from U.S. covered aircraft
through 2036 is more than 80 Tg CO2eq,\216\ this
consideration of projected future emissions adds further support to the
Administrator's finding under CAA section 231(a)(2)(A) that emissions
of the six well-mixed greenhouse gases from classes of engines used in
U.S. covered aircraft contribute to the GHG air pollution that
endangers public health and welfare.\217\
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\214\ As discussed in section V.B.4.c, fuel burn growth rates
for air carriers and general aviation aircraft operating on jet fuel
are projected to grow by 43 percent from 2010 to 2036 and this
provides a scaling factor for growth in projected GHG emissions,
which are projected to increase at a similar rate as the fuel burn
by 2030, 2036, and 2040.
FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp.
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last
accessed March 29, 2016).
\215\ U.S. Energy Information Administration (EIA), 2015: Annual
Energy Outlook (AEO) 2015 with projections to 2040, DOE/EIA-0383,
154 pp. For the years 2010 to 2014, the baseline emissions for each
sector are from the 2016 Inventory of U.S. Greenhouse Gas Emissions
and Sinks Report, and after 2014 we utilize projections from the
2015 EIA AEO report. Available at http://www.eia.gov/forecasts/aeo/
(last accessed May 12, 2015).
\216\ In addition, we expect aircraft engine GHG emissions from
U.S. covered aircraft to continue contributing to the endangering
pollution in the future and to be a bigger percentage of
transportation emissions, since these emission are projected to
increase at a faster rate than other transportation sources.
\217\ In 2010, U.S covered aircraft were responsible for 10
percent of U.S. transportation sector GHG emissions, and in 2036,
U.S. covered aircraft are projected to be the source of 15 percent
of U.S. transportation GHG emissions. In 2010, light-duty vehicles
were responsible for 58 percent of U.S. transportation GHG
emissions, and in 2036 they are projected to be the source of 46
percent of such emissions. In 2010, heavy-duty vehicles emitted 20
percent of U.S. transportation GHG emissions, and in 2036, they are
projected to emit 26 percent (this projection does not reflect the
impact from the Phase 2 heavy-duty GHG standards that have not yet
been promulgated). In 2010, the rail sector contributed 2 percent of
U.S. transportation GHG emissions, and in 2036, they are projected
to contribute the same percentage.
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4. Overview of Greenhouse Gas Emissions
Atmospheric concentrations of CO2 and other GHGs are now
at essentially unprecedented levels compared to the distant and recent
past.\218\ This is the unambiguous result of human-activity emissions
of these gases. See section IV.B.2 for more information on elevated
atmospheric GHG concentrations and anthropogenic drivers of climate
change. Global emissions of well-mixed GHGs have been increasing, and
are projected to continue increasing for the foreseeable future.
According to the IPCC AR5, total global (when using inventories from
all anthropogenic emitting sources including forestry and other land
use) emissions of GHGs in 2010 were 49,000 Tg CO2eq.\219\
This represents an increase in global GHG emissions of 29 percent since
1990 and of 23 percent since 2000. In 2010, total U.S. GHG emissions
were responsible for 13 percent of global GHG emissions (when comparing
inventories from all anthropogenic emitting sources including forestry
and other land use).\220\
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\218\ IPCC, 2013: Summary for Policymakers. In: Climate Change
2013: The Physical Science Basis. Contribution of Working Group I to
the Fifth Assessment Report of the Intergovernmental Panel on
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor,
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley
(eds.)]. Cambridge University Press, p. 11.
\219\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, 1435 pp.
\220\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, 351-411 pp.
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We are also providing 2012 estimates from other widely used and
recognized global datasets, the World Resources Institute's (WRI)
Climate Analysis Indicators Tool (CAIT) and the International Energy
Agency (IEA).\221\ We are providing these data for several reasons;
first, there is value in looking at multiple data sources to see if
estimates are generally in line with one another. Second, there are
more recent

[[Page 54464]]

data available in the WRI/CAIT and IEA datasets (2010 IPCC data vs.
2012 WRI/CAIT and IEA data). Third and finally, these other datasets
provide additional utility for examining different disaggregations of
the data (by country, sector, and with or without forestry and other
land use emissions). Unless otherwise noted, we are presenting data
points from these other datasets without including data regarding
forestry and other land use inventories to enable straightforward
comparisons of gross emission estimates from transportation sources
specifically. The total global GHG emissions in 2012 from WRI/CAIT were
44,816 Tg of CO2eq, representing an increase in global GHG
emissions of 47 percent since 1990 and 32 percent since 2000. In
comparison, WRI/CAIT's estimate of total global GHG emissions in 2012
when including forestry and other land use inventories were 47,599 Tg
of CO2eq (representing an increase in global GHG emissions
of 40 percent since 1990 and 30 percent since 2000). In past years,
WRI/CAIT estimates have generally been consistent with those of IPCC.
In 2012, WRI/CAIT data indicate that total U.S. GHG emissions were
responsible for 15 percent of global emissions, which is also generally
in line with the percentages using IPCC's 2010 estimate described
above. According to WRI/CAIT, current U.S. GHG emissions rank only
behind China's, and China was responsible for 24 percent of total
global GHG emissions.
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\221\ World Resources Institute (WRI) Climate Analysis
Indicators Tool (CAIT) Data Explorer (Version 2.0). Available at
http://cait.wri.org (last accessed January 19, 2016). International
Energy Agency, Data Services. Available at http://data.iea.org (last
accessed January 21, 2016).
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As described earlier in section IV.A, in the proposed finding and
this final finding, the Administrator considers the recent, major
scientific assessments of the IPCC, USGCRP, and the NRC as the primary
scientific and technical basis informing her judgment. Thus, the
Administrator is informed by and places considerable weight upon the
IPCC's data on global GHG emissions. She also considers but places less
emphasis on the WRI/CAIT and IEA emissions data, which in comparison
have a different aggregation of underlying data but are available for
more recent years (2010 IPCC data vs. 2012 WRI/CAIT and IEA data).
The approach of considering the major scientific assessments,
including IPCC's assessment, provides assurance that the
Administrator's judgment is informed by the best available, well-vetted
science that reflects the consensus of the climate science research
community. The major findings of the assessments, including IPCC's
assessment, support the Administrator's findings in this action. While
the EPA uses the IPCC data as the primary data source for informing
this contribution finding, it has reasonably used additional data
sources from widely used and recognized global datasets to provide
context and information from more recent years. These additional data
supplement and confirm the IPCC data, as they are generally in line
with IPCC. Comparing their 2010 total global GHG emissions, IPCC data
are 49,000 Tg CO2eq, and WRI/CAIT data indicates 42,968 Tg
CO2eq (a 12 percent difference).\222\ Also, comparing their
2010 global aircraft GHG emissions estimates, IPCC data are 743 Tg
CO2eq, and IEA data indicate 749 Tg CO2eq (a 1
percent difference).\223\ Ultimately, whether the Agency utilizes the
IPCC data alone or the WRI/CAIT dataset (and IEA data) alone, or both
datasets together, it would have no material effect on the emissions
comparisons discussed in section V.B and the Administrator would make
the same contribution finding.
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\222\ Comparing their 2010 total global GHG emissions, IPCC data
are 49,000 Tg CO2eq, and WRI/CAIT data, including
forestry and land use inventories, indicates 45,748 Tg
CO2eq (a 7 percent difference).
\223\ Comparing 2012 WRI/CAIT to 2010 IPCC data, WRI/CAIT data
for total global GHG emissions indicates 44,816 Tg CO2eq
for 2012 (a 9 percent difference), and including forestry and land
use inventories WRI/CAIT data indicates 47,599 Tg CO2eq
for 2012 (a 3 percent difference). Comparing 2012 IEA data to 2010
IPCC data, IEA data for global aircraft GHG emissions indicates 775
Tg CO2eq for 2012 (a 4 percent difference).
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The Inventory of U.S. Greenhouse Gas Emissions and Sinks Report
\224\ (hereinafter ``U.S. Inventory''), in which 2014 is the most
recent year for which data are available, indicates that total U.S. GHG
emissions increased by 7.3 percent from 1990 to 2014 (or by 7.8 percent
when using inventories that include forestry and other land use), and
emissions increased from 2013 to 2014 by 1.1 percent.\225\ This 2013 to
2014 increase was attributable to multiple factors including an
increase in vehicle miles traveled and vehicle fuel use, a colder
winter resulting in an increased demand for heating fuel, and an
increase in industrial production across multiple sectors. The U.S.
Inventory also shows that while overall U.S. GHG emissions grew between
1990 and 2014, transportation GHG emissions grew at a significantly
higher rate, 16 percent, more rapidly than any other U.S. sector.
Within the transportation sector, aircraft remain the single largest
source of GHG emissions not yet subject to any GHG regulations (U.S.
covered aircraft GHG emissions grew by 15 percent between 1990 and
2014, and total U.S. aircraft GHG emissions decreased by 3 percent over
this same time period).\226\
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\224\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016). The EPA has determined that the U.S. Inventory has
been adequately reviewed in accordance with the EPA's Peer Review
Handbook. For the presentation of emissions inventory information in
this contribution finding, the EPA disaggregated the existing data
in one area of the U.S. Inventory (for the General Aviation Jet Fuel
Category) and had the disaggregation methodology peer reviewed in
accordance with the EPA's Peer Review Handbook. The EPA Science
Advisory Board reviewed this approach to the underlying technical
and scientific information supporting this action, and concluded
that the approach had precedent and the action will be based on
well-reviewed information. All relevant peer review documentation is
located in the docket for today's final action (EPA-HQ-OAR-2014-
0828).
\225\ As described later in detail, total U.S. GHG emissions,
include emissions from combustion of U.S. international bunker
fuels, which are fuels used for transport activities from aviation
(both commercial and military) and marine sources.
\226\ As described later in detail, total U.S. GHG emissions,
U.S. transportation GHG emissions, total U.S. aircraft GHG
emissions, and U.S. covered aircraft GHG emissions include emissions
from combustion of U.S. international bunker fuels. More
specifically, total U.S. aircraft GHG emissions include
international bunker fuel emissions from both commercial and
military aviation. U.S. covered aircraft GHG emissions include
international bunker fuel emissions from only commercial aviation.
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Section V.B.4.a which follows describes U.S. aircraft GHG emissions
within the domestic context, while section V.B.4.b describes these same
GHG emissions in the global context. Section V.B.4.c addresses future
projections of aircraft GHG emissions.
a. U.S. Aircraft GHG Emissions Relative to U.S. GHG Transportation and
Total U.S. GHG Inventory
Relying on data from the U.S. Inventory, we compare total U.S.
aircraft GHG emission and U.S. covered aircraft GHG emissions to the
transportation sector and to total U.S. GHG emissions as an indication
of the role this source plays in the total domestic portion of the air
pollution that is endangering by causing climate change. We are
providing information about total U.S. aircraft GHG emissions for
purposes of giving context for the discussion of GHG emissions from
U.S. covered aircraft, which are included in this contribution finding
under CAA section 231(a)(2)(A). As explained in more detail below, the
contribution finding under CAA section 231(a)(2)(A) in this action does
not include GHG emissions from all aircraft that operate in and from
the U.S. and thus emit GHGs in the U.S.
In 2014, total U.S. GHG emissions from all sources were 6,975 Tg
CO2eq. As stated above, total U.S. GHG emissions have
increased by 7.3 percent

[[Page 54465]]

between 1990 and 2014, while U.S. transportation GHG emissions from all
categories have grown 16 percent since 1990. The U.S. transportation
sector was the second largest GHG-emitting sector (behind electricity
generation), contributing 1,919 Tg CO2eq or 28 percent of
total U.S. GHG emissions in 2014. This sectoral total and the total
U.S. GHG emissions include emissions from combustion of U.S.
international bunker fuels, which are fuels used for transport
activities from aviation (both commercial and military) and marine
sources. Following the IPCC guidelines for common and consistent
accounting and reporting of GHGs, the UNFCCC requires countries to
report both total national GHG emissions and international bunker fuel
emissions (aviation and marine international bunker fuel emissions),
and though these emissions are reported separately, both are assigned
to the reporting country. In meeting the UNFCCC reporting requirements,
the U.S. Inventory calculates international bunker fuel GHG emissions
in a consistent manner with domestic GHG emissions. In this final
contribution finding, the EPA maintains its approach used in the
proposed findings to include aviation international bunker fuel
emissions attributable to the United States with the national emissions
number from the U.S. Inventory as reported to the UNFCCC. It is the
EPA's view that it is reasonable and appropriate for the analysis in
the contribution finding to reflect the full contribution of U.S.
emissions from certain classes of aircraft engines, including those
from domestic flights of U.S. aircraft and those associated with
international aviation bunker fuel emissions. Consistent with IPCC
guidelines for common and consistent accounting and reporting of GHGs
under the UNFCCC, the ``U.S. international aviation bunker fuels''
category includes emissions from combustion of fuel used by aircraft
departing from the United States, regardless of whether they are a U.S.
flagged carrier. Total U.S. aircraft GHG emissions (which include
emissions from international commercial and military aviation bunker
fuels) clearly are included in the U.S. transportation sector's GHG
emissions, accounting for 222 Tg CO2eq or 12 percent of such
emissions (see Table V.1). In 2014, total U.S. aircraft GHG emissions
(222 Tg CO2eq) were the third largest transportation source
of GHGs within the United States, behind GHG emissions from light-duty
vehicles and medium- and heavy-duty trucks (totaling 1,508 Tg
CO2eq).
For purposes of making this cause or contribute finding, the EPA
includes a set of aircraft engine classes used in types of aircraft as
described below, which corresponds to the scope of the international
CO2 emissions standard agreed to by ICAO. These emissions
are from what we have previously described as ``covered aircraft''
(which include emissions from international commercial aviation bunker
fuels).
As mentioned earlier in section II.D, traditionally the U.S.
government (EPA and FAA) participates at ICAO in the development of
international standards, and then where appropriate, the EPA
establishes domestic aircraft engine emission standards under CAA
section 231 of at least equivalent stringency to ICAO's standards. An
international CO2 emissions standard was agreed to in
February 2016, and we expect to proceed with proposing emissions
standards of at least equivalent stringency domestically as soon as is
practicable. The thresholds of applicability for the international
CO2 emissions standard are based on weight as follows: For
subsonic jet aircraft, a maximum takeoff mass (MTOM) greater than 5,700
kilograms; and for subsonic propeller driven (e.g., turboprop)
aircraft, a MTOM greater than 8,618 kilograms.\227\ Applying these
weight thresholds, our contribution finding applies to GHG emissions
from classes of engines used in covered aircraft that meet these MTOM
criteria. For purposes of the contribution finding, examples of covered
aircraft include smaller jet aircraft such as the Cessna Citation CJ3+
and the Embraer E170, up to the largest commercial jet aircraft--the
Airbus A380 and the Boeing 747. Other examples of covered aircraft
include larger turboprop aircraft, such as the ATR 72 and the
Bombardier Q400. The scope of the contribution finding corresponds to
the aircraft engine GHG emissions that are from aircraft that match the
applicability thresholds for the international aircraft CO2
standard. We have also identified aircraft that are not covered
aircraft for purposes of this contribution finding. That includes
aircraft that fall below the international applicability thresholds:
Smaller turboprop aircraft, such as the Beechcraft King Air 350i, and
smaller jet aircraft, such as the Cessna Citation M2. In addition, ICAO
(with U.S. participation) has agreed to exclude ``piston-engine
aircraft,'' ``helicopters,'' and ``military aircraft'' \228\ from the
types of aircraft that will be subject to the ICAO standards.\229\ As
these aircraft will not be subject to the ICAO standards, in this
contribution finding we are also not including GHG emissions from
classes of engines used in these types of aircraft. We stress that our
exclusion of these aircraft does not reflect a final scientific or
technical determination regarding their GHG emissions. Rather,
consistent with how the endangerment finding does not include various
other climate forcers within the scope of the ``air pollution'' defined
in this final action, we are not prepared to make final decisions
regarding the GHG emissions from these excluded aircraft.
---------------------------------------------------------------------------

\227\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for
the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, 40 pp.,
AN/192, Available at http://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Circular 337
is found on page 87 of the ICAO Products & Services 2016 catalog and
is copyright protected; Order No. CIR337.
\228\ ICAO regulations only apply to civil aviation (aircraft
and aircraft engines); consequently, ICAO regulations do not apply
to military aircraft.
\229\ The applicability of the international CO2
standard is limited to subsonic aircraft, and does not extend to
supersonic aircraft.
---------------------------------------------------------------------------

The majority of the GHG emissions from all classes of aircraft
engines are within the scope of this contribution finding, which
corresponds to that agreed to by ICAO. Below we describe the
contribution of these U.S. covered aircraft GHG emissions to U.S. GHG
emissions, and later in section V.B.4.b we discuss the contribution of
these U.S. covered aircraft emissions to global GHG emissions, in
support of our conclusion that GHG emissions from engines used by U.S.
covered aircraft contribute to endangering GHG air pollution.
In 2014, GHG emissions from U.S. covered aircraft (197 Tg
CO2eq), which includes non-military GHG emissions from
combustion of U.S. international aviation bunker fuels,\230\ comprised
89 percent of total U.S. aircraft GHG emissions \231\ (222 Tg
CO2eq) and 10 percent of total U.S. transportation sector
GHG emissions (1,919 Tg CO2eq) (See Table V.1). Overall,
U.S. covered aircraft comprised the third largest source of GHG
emissions in the U.S. transportation sector behind only the light-duty
vehicle and medium- and heavy-duty truck sectors (totaling 1,508 Tg
CO2eq),\232\ which is the same ranking

[[Page 54466]]

as total U.S. aircraft.\233\ The U.S. covered aircraft also represent
2.8 percent of total U.S. GHG emissions (6,975 Tg CO2eq),
which is approximately equal to the contribution from total U.S.
aircraft of 3.2 percent (Table V.1).\234\ Also, in Table V.2 for
background information and context, we provide similar information, but
excluding GHG emissions from aviation combustion of U.S. international
bunker fuels.\235\
---------------------------------------------------------------------------

\230\ U.S. covered aircraft does not include military aircraft
that use U.S. international bunker fuels.
\231\ Eastern Research Group, Incorporated (ERG), 2015: U.S. Jet
Fuel Use and CO2 Emissions Inventory for Aircraft Below ICAO CO2
Standard Thresholds, Final Report, EPA Contract Number EP-D-11-006,
38 pp.
\232\ In 2014, the U.S. light-duty vehicle (passenger cars and
light-duty trucks) GHG emissions were 1,101 Tg CO2eq and
the medium- and heavy-duty truck GHG emissions were 407 Tg
CO2eq.
\233\ Compared independently, total U.S. aircraft GHG emissions
and U.S. covered aircraft GHG emissions are both ranked the third
largest source in the U.S. transportation sector, behind only light-
duty vehicle and medium- and heavy-duty truck sectors.
\234\ Total U.S. aircraft GHG emissions and U.S. covered
aircraft GHG emissions were from 12 to 31 percent greater in 2000
and 2005 than in 1990. These increases in aircraft GHG emissions are
primarily because aircraft operations (or number of flights) grew by
similar amounts during this time period. Also, total U.S. aircraft
GHG emissions and U.S. covered aircraft GHG emissions were from 10
to 15 percent greater in 2000 and 2005 than in 2014. These decreases
in aircraft GHG emissions are partly because aircraft operations
decreased by similar amounts during this time period. In addition,
the decreases in aircraft emissions are due in part to improved
operational efficiency that results in more direct flight routing,
improvements in aircraft and engine technologies to reduce fuel burn
and emissions, and the accelerated retirement of older, less fuel
efficient aircraft. Also, the U.S. transportation GHG emissions were
changing at similar rates as total U.S. aircraft GHG emissions and
U.S. covered aircraft GHG emissions for these same time periods, and
thus, the aircraft GHG emissions share of U.S. Transportation
remains approximately constant (over these time periods). (U.S. EPA,
2016: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-
2014, 558 pp. Available at http://www3.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2016-Main-Text.pdf (last
accessed April 22, 2016)).
\235\ For Table V.2, total U.S. aircraft GHG emissions and U.S.
covered aircraft GHG emissions exclude emissions from aviation
combustion of U.S. international bunker fuels. The U.S.
transportation sector GHG emissions and total U.S. GHG emissions (in
Table V.2) exclude emissions from both aviation and marine
combustion of U.S. international bunker fuels.
---------------------------------------------------------------------------

It is important to note that in regard to the six well-mixed GHGs
(CO2, methane, nitrous oxide, hydrofluorocarbons,
perfluorocarbons, and sulfur hexafluoride), only two of these gases--
CO2 and nitrous oxide--are reported as non-zero emissions
for total aircraft and covered aircraft.\236\ CO2 represents
99 percent of all GHGs from both total U.S. aircraft (220 Tg
CO2eq) and U.S. covered aircraft (195 Tg CO2eq),
and nitrous oxide represents 1 percent from total aircraft (2.1 Tg
CO2eq) and covered aircraft (1.9 Tg CO2eq).
Modern aircraft do not emit methane,\237\ and hydrofluorocarbons,
perfluorocarbons, and sulfur hexafluoride are not products of aircraft
engine combustion.
---------------------------------------------------------------------------

\236\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\237\ Emissions of methane from jet fuels are no longer
considered to be emitted (based on the latest studies) across the
time series from aircraft gas turbine engines burning jet fuel A at
higher power settings (EPA, Recommended Best Practice for
Quantifying Speciated Organic Gas Emissions from Aircraft Equipped
with Turbofan, Turbojet and Turboprop Engines, EPA-420-R-09-901, May
27, 2009 (see https://www3.epa.gov/otaq/regs/nonroad/aviation/420r09901.pdf (last accessed April 22, 2016)). Based on this data,
methane emissions factors for jet aircraft were reported as zero to
reflect the latest emissions testing data. Also, the 2006 IPCC
Guidelines indicate the following: ``Methane (CH4) may be
emitted by gas turbines during idle and by older technology engines,
but recent data suggest that little or no CH4 is emitted
by modern engines.'' (IPCC, 2006: IPCC Guidelines for National
Greenhouse Gas Inventories, The National Greenhouse Gas Inventories
Programme, The Intergovernmental Panel on Climate Change, H.S.
Eggleston, L. Buendia, K. Miwa, T. Ngara, and K. Tanabe (eds.).
Hayama, Kanagawa, Japan.) The EPA uses an emissions factor of zero
to maintain consistency with the IPCC reporting guidelines, while
continuing to stay abreast of the evolving research in this area.
For example, one recent study has indicated that modern aircraft jet
engines operating at higher power modes consume rather than emit
methane (Santoni et al., 2011: Aircraft Emissions of Methane and
Nitrous Oxide during the Alternative Aviation Fuel Experiment,
Environ. Sci. Technol., 45 pp. 7075-7082).
\238\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\239\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA
Contract Number EP-D-11-006, 38 pp.
\240\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).

Table V.1 238 239--Comparisons of U.S. Aircraft GHG Emissions to Total U.S. Transportation and Total U.S. GHG
Emissions
----------------------------------------------------------------------------------------------------------------
1990 2000 2005 2010 2012 2013 2014
----------------------------------------------------------------------------------------------------------------
Total U.S. Aircraft GHG emissions 228 262 254 216 212 216 222
(Tg CO2eq)........................
Share of U.S. Transportation... 14% 13% 12% 11% 11% 11% 12%
Share of total U.S. Inventory.. 3.5% 3.6% 3.4% 3% 3.1% 3.1% 3.2%
U.S. Covered Aircraft GHG emissions 171 223 218 191 190 195 197
(Tg CO2eq)........................
Share of U.S. aircraft GHG 75% 85% 86% 88% 90% 90% 89%
emissions.....................
Share of U.S. Transportation... 10% 11% 10% 9.8% 10% 10% 10%
Share of total U.S. Inventory.. 2.6% 3% 2.9% 2.7% 2.8% 2.8% 2.8%
U.S. Transportation GHG emissions 1,659 2,029 2,119 1,950 1,891 1,895 1,919
(Tg CO2eq)........................
Share of total U.S. Inventory.. 26% 28% 28% 28% 28% 28% 28%
Total U.S. GHG emissions (Tg CO2eq) 6,502 7,362 7,493 7,104 6,750 6,901 6,975
----------------------------------------------------------------------------------------------------------------

Table V.2 240 241--Comparisons of U.S. Aircraft GHG Emissions to Total U.S. Transportation and Total U.S. GHG
Emissions--Excluding U.S. International Bunker Fuels 242
----------------------------------------------------------------------------------------------------------------
1990 2000 2005 2010 2012 2013 2014
----------------------------------------------------------------------------------------------------------------
Total U.S. Aircraft GHG emissions 190 200 194 155 147 151 152
(Tg CO2eq)........................
Share of U.S. Transportation... 12% 10% 9.7% 8.5% 8.2% 8.4% 8.4%
Share of total U.S. Inventory.. 3% 2.8% 2.6% 2.2% 2.2% 2.2% 2.2%
U.S. Covered Aircraft GHG emissions 141 166 162 133 128 132 130
(Tg CO2eq)........................
Share of U.S. aircraft GHG 74% 83% 84% 86% 87% 88% 86%
emissions.....................
Share of U.S. Transportation... 9% 8.6% 8.1% 7.3% 7.2% 7.4% 7.2%
Share of total U.S. Inventory.. 2.2% 2.3% 2.2% 1.9% 1.9% 1.9% 1.9%
U.S. Transportation GHG emissions 1,554 1,927 2,004 1,832 1,784 1,794 1,815
(Tg CO2eq)........................
Share of total U.S. Inventory.. 24% 27% 27% 26% 27% 26% 26%
Total U.S. GHG emissions (Tg CO2eq) 6,397 7,259 7,379 6,986 6,643 6,800 6,871
----------------------------------------------------------------------------------------------------------------

[[Page 54467]]

b. U.S. Aircraft GHG Emissions Relative to Global Aircraft GHG
Inventory and the Total Global GHG Inventory
---------------------------------------------------------------------------

\241\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA
Contract Number EP-D-11-006, 38 pp.
\242\ International bunker fuels emissions are emissions
resulting from the combustion of fuels used for international
transport activities, which includes aviation and marine. U.S.
international bunker fuels includes aviation and marine bunker fuels
allocated to the U.S. The U.S. international aviation bunker fuels
category includes emissions from combustion of fuel used by aircraft
departing from the United States, regardless of whether they are a
U.S. flagged carrier. The U.S. international marine bunker fuels
category includes emissions from the combustion of fuel used by
vessels of all flags (that are engaged in international water-borne
navigation) departing from the United States.
---------------------------------------------------------------------------

For background information and context, we first provide
information on the portion of GHG emissions from global aircraft and
the global transportation sector to total global GHG emissions, and
describe how this compares to the emissions from aircraft covered by
the ICAO CO2 standard. We then compare U.S. aircraft GHG
emissions to the global aircraft sector, to the global transport
sector, and to total global GHG emissions as an indication of the role
this source plays in the total global portion of the air pollution that
is causing climate change. As in the preceding section, we present
comparisons from both total U.S. aircraft GHG emissions and U.S.
covered aircraft GHG emissions.
According to IPCC AR5, global aircraft GHG emissions in 2010 were
11 percent of global transport GHG emissions and 1.5 percent of total
global GHG emissions. Data from ICAO's 2013 Environmental Report
indicate that the vast majority of global emissions from the aircraft
sector are emitted by the types of aircraft that are covered by the
ICAO CO2 standard (``ICAO covered aircraft''), which was
agreed to in February 2016.\243\ When compared to global data from IPCC
AR5, worldwide GHG emissions from ICAO covered aircraft represented 93
percent (688 Tg CO2eq) of global aircraft GHG
emissions,\244\ 9.8 percent of global transport GHG emissions, and 1.4
percent of total global GHG emissions in 2010.
---------------------------------------------------------------------------

\243\ ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation
and Climate Change, 224 pp. Available at http://cfapp.icao.int/Environmental-Report-2013/ (last accessed April 8, 2016).
\244\ Worldwide GHG emissions from ICAO covered aircraft include
emissions from both international and domestic aircraft operations
around the world.
---------------------------------------------------------------------------

Comparing data from the U.S. Inventory to IPCC AR5, we find that
total U.S. aircraft GHG emissions represented 29 percent of global
aircraft GHG emissions, 3.1 percent of global transport GHG emissions,
and 0.5 percent of total global GHG emissions in 2010 (see Table V.3).
U.S. covered aircraft in 2010 GHG emissions represented 26 percent of
global aircraft GHG emissions, 2.7 percent of global transport GHG
emissions, and 0.4 percent of total global GHG emissions (see Table
V.3).\245\ For reasons described above in section V.B.4, we also made
comparisons using 2012 estimates from WRI/CAIT and the IEA and found
that they yield very similar results.\246\ Also, in Table V.4 for
background information and context in regard to the global GHG
inventory, we provide similar information, but excluding aviation GHG
emissions from combustion of U.S. international bunker fuels.
---------------------------------------------------------------------------

\245\ We are providing information about total U.S. aircraft GHG
emissions for purposes of giving context for the discussion of GHG
emissions from U.S. covered aircraft, which are included in this
contribution finding under CAA section 231(a)(2)(A). As explained in
more detail below, the contribution finding under CAA section
231(a)(2)(A) in this action does not include GHG emissions from all
aircraft that operate in and from the U.S and thus emit GHGs in the
U.S.
\246\ Data from WRI/CAIT (that excludes forestry and other land
use inventories) and IEA show that, in 2012, total U.S. aircraft
emissions represented 27 percent of global aircraft GHG emissions,
2.9 percent of global transport GHG emissions, and 0.5 percent of
total global GHG emissions. U.S. covered aircraft represented 25
percent of global aircraft GHG emissions, 2.6 percent of global
transport GHG emissions, and 0.4 percent of total global GHG
emissions in 2012.
\247\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, 1435 pp.
U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions and
Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and Radiation,
EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\248\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA
Contract Number EP-D-11-006, 38 pp.
\249\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, 1435 pp. U.S. EPA, 2016:
Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014,
1,052 pp., U.S. EPA Office of Air and Radiation, EPA 430-R-16-002,
April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed June 14, 2016).
\250\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA
Contract Number EP-D-11-006, 38 pp.

Table V.3 \247\--Comparisons of U.S. Aircraft GHG Emissions to Total Global Greenhouse Gas Emissions in 2010
----------------------------------------------------------------------------------------------------------------
Total U.S. U.S. covered Global
2010 (Tg CO2 aircraft share aircraft share aircraft share
eq) (%) (%) \248\ (%)
----------------------------------------------------------------------------------------------------------------
Global Aircraft GHG emissions.................. 743 29 26 ..............
Global Transport GHG emissions................. 7,000 3.1 2.7 11
Total Global GHG emissions..................... 49,000 0.5 0.4 1.5
----------------------------------------------------------------------------------------------------------------

Table V.4 \249\--Comparisons of U.S. Aircraft GHG Emissions to Total Global Greenhouse Gas Emissions in 2010--
Excluding Aviation GHG Emissions From Combustion of U.S. International Bunker Fuels From the U.S. Aircraft GHG
Emissions
----------------------------------------------------------------------------------------------------------------
Total U.S. U.S. covered Global
2010 (Tg CO2 aircraft share aircraft share aircraft share
eq) (%) (%) \250\ (%)
----------------------------------------------------------------------------------------------------------------
Global Aircraft GHG emissions.................. 743 21 18 ..............
Global Transport GHG emissions................. 7,000 2.2 1.9 11
Total Global GHG emissions..................... 49,000 0.4 0.3 1.5
----------------------------------------------------------------------------------------------------------------

[[Page 54468]]

For additional background information and context, we used 2012
WRI/CAIT and IEA data to make comparisons between the aircraft sector
and the emissions inventories of entire countries and regions. When
compared to entire countries, total global aircraft GHG emissions in
2012 ranked 8th overall, behind only China, United States, India,
Russian Federation, Japan, Brazil, and Germany, and ahead of about 177
other countries. Total U.S. aircraft GHG emissions have historically
been and continue to be by far the largest contributor to global
aircraft GHG emissions. Total U.S. aircraft GHG emissions are about 6
times higher than aircraft GHG emissions from China, which globally is
the second ranked country for aircraft GHG emissions, and about 4 times
higher than aircraft GHG emissions from all of Asia. U.S. covered
aircraft GHG emissions are about 5 times more than total aircraft GHG
emissions from China, and about 4 times more than total aircraft GHG
emissions from all of Asia. If U.S. covered aircraft emissions of GHGs
were ranked against total GHG emissions for entire countries, these
covered aircraft emissions would rank ahead of Belgium, Czech Republic,
Ireland, Sweden, Switzerland and about 150 other countries in the
world.
c. Aircraft GHG Emissions Are Projected To Increase in the Future
Global and U.S. covered aircraft GHG emissions have increased
between 1990 and 2010, and are predicted to continue to increase in
future years. While overall GHG emissions from U.S. covered aircraft
increased by 12 percent from 1990 to 2010, the portion attributable to
combustion of U.S. international aviation bunker fuels \251\ increased
by 91 percent.\252\ During this same time period, global aircraft GHG
emissions grew by 40 percent, and the portion attributable to
combustion of global international aviation bunker fuels increased by
80 percent.^{253 254} Notwithstanding the substantial growth in
GHG emissions from combustion of U.S. international aviation bunker
fuels, U.S. covered aircraft emissions have not increased as much as
global aircraft emissions from 1990 to 2010, primarily because the U.S.
aviation market was relatively mature compared to the markets in Europe
and other emergent markets, and because during this time period the
U.S. commercial air carriers suffered several major shocks that reduced
demand for air travel.\255\ In fact, U.S. covered aircraft emissions
decreased from 2000 to 2010 (13 percent), but then have increased from
2010 to 2014 (3 percent).\256\ After consolidation and restructuring in
recent years, the U.S. commercial air carriers have regained
profitability and are forecasted by the FAA to grow more over the next
20 to 30 years.\257\ With regard to global aircraft GHG emissions, the
aviation markets in Asia/Pacific, Europe (where airline deregulation
has stimulated significant new demands in this period), and the Middle
East (and other emerging markets) have been growing rapidly, and the
global market is expected to continue to grow significantly over the
next 20 to 30 years.\258\
---------------------------------------------------------------------------

\251\ The U.S. international aviation bunker fuels category
includes emissions from combustion of fuel used by aircraft
departing from the United States, regardless of whether they are a
U.S. flagged carrier. GHG emissions from U.S. international aviation
bunker fuels are a subset of GHG emissions from U.S. covered
aircraft. From 1990 to 2010, GHG emissions from U.S. covered
aircraft increased from 171 to 191 Tg CO2eq, and GHG
emissions from the portion attributable to U.S. international
aviation bunker fuels grew from 30 to 58 Tg CO2eq during
this same time period. From 1990 to 2011, GHG emissions from U.S.
covered aircraft increased from 171 to 193 Tg CO2eq (13
percent), and GHG emissions from the portion attributable to U.S.
international aviation bunker fuels grew from 30 to 62 Tg
CO2eq (110 percent). From 1990 to 2012, GHG emissions
from U.S. covered aircraft increased from 171 to 190 Tg
CO2eq (11 percent), and GHG emissions from the portion
attributable to U.S. international aviation bunker fuels grew from
30 to 62 Tg CO2eq (110 percent).
\252\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\253\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, pp. 599-670.
\254\ According to IEA, from 1990 to 2012, global aircraft GHG
emissions grew by 53 percent, and global international aviation
bunker fuels increased by 86 percent. International Energy Agency
Data Services, Available at http://data.iea.org (last accessed
January 21, 2016).
\255\ According to the FAA Aerospace Forecast 2014-2034, these
shocks include the September 11, 2001, terror attacks, significant
increases in fuel prices, debt restructuring in Europe and U.S., and
a global recession. FAA, 2014: FAA Aerospace Forecast Fiscal Years
2014-2034, 129 pp. Available at http://www.faa.gov/data_research/aviation/aerospace_forecasts/media/2014_faa_aerospace_forecast.pdf
(last accessed April 8, 2016).
\256\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\257\ According to the FAA Aerospace Forecast 2016-2036, in 2015
U.S. air carriers were profitable for the sixth consecutive year.
FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp.
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last
accessed March 29, 2016).
\258\ According to the FAA Aerospace Forecast 2014-2034, the
International Air Transport Association (IATA) reports that world
air carriers (including U.S. airlines) are expected to register an
operating profit for 2013. Based on financial data compiled by ICAO
and IATA, between 2004 and 2013 world airlines produced cumulative
operating profits (with nine years out of ten posting gains) and net
profits (with six years out of ten posting gains).
---------------------------------------------------------------------------

Recent studies estimate that both ICAO covered aircraft and U.S.
covered aircraft will experience substantial growth over the next 20 to
30 years in their absolute fuel burn,\259\ and that this will translate
into increased GHG emissions. ICAO estimates that the global fuel burn
from ICAO covered aircraft will increase by about 120 percent from 2010
to 2030 and by about 210 percent from 2010 to 2040 (for a scenario with
moderate technology and operational improvements).\260\ The FAA
projects that the fuel consumption from U.S. air carriers and general
aviation aircraft operating on jet fuel will grow by 43 percent from
2010 to 2036, corresponding to an average annual increase rate in fuel
consumption of 1.4 percent.\261\ These aircraft groups (U.S. air
carriers and general aviation aircraft operating on jet fuel) are of
similar scope to the U.S. covered aircraft whose engine GHG emissions
are the subject of this contribution finding. Using fuel burn growth
rates provided above as a scaling factor for growth in GHG emissions
(globally and nationally), it is estimated that GHG emissions from ICAO
covered aircraft and U.S. covered aircraft will increase at a similar
rate as the fuel burn by 2030, 2036, and 2040.
---------------------------------------------------------------------------

\259\ FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036,
94 pp. Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last
accessed March 29, 2016).
ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation and
Climate Change, 224 pp. Available at http://cfapp.icao.int/Environmental-Report-2013/ (last accessed April 8, 2016).
\260\ ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation
and Climate Change, 224 pp. Available at http://cfapp.icao.int/Environmental-Report-2013/ (last accessed April 8, 2016).
\261\ FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036,
94 pp. Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last
accessed March 29, 2016).
---------------------------------------------------------------------------

C. Response to Key Comments on the Administrator's Cause or Contribute
Finding

EPA received numerous comments regarding the Administrator's
proposed cause or contribute finding. Below is a brief discussion of
some of the key comments. Responses to comments on

[[Page 54469]]

this topic (and further details for the key comments) are also
contained in the Response to Comments document.
1. The Administrator Reasonably Defined the Scope of the Cause or
Contribute Finding
a. Applicability Weight Thresholds Match Those of International
CO2 Standard
Several commenters stated that the EPA should undertake another
cause or contribute finding for a broader range of aircraft not covered
in our proposed finding, including smaller turboprop aircraft (such as
the Beechcraft King Air 350i), smaller jet aircraft (such as the Cessna
Citation M2), piston-engine aircraft, and helicopters. These commenters
stated, however, that this comment did not affect the validity of the
conclusions in the proposed finding. Numerous commenters stated their
support for our proposed finding's scope matching the applicability
(weight or MTOM) thresholds of the international CO2
standard.
As described earlier, at this time and for the purposes of this
cause or contribute finding under CAA section 231(a)(2)(A), the EPA is
including emissions of the six well-mixed greenhouse gases from classes
of engines used in U.S. covered aircraft which are subsonic jet
aircraft with a maximum takeoff mass (MTOM) greater than 5,700
kilograms and subsonic propeller driven (e.g., turboprop) aircraft with
a MTOM greater than 8,618 kilograms. We are not at this time taking
final action with respect to the GHG emissions from aircraft other than
those included in the scope of this finding.\262\ The cause or
contribute finding is a prerequisite under CAA section 231 for EPA to
adopt standards that are of at least equivalent stringency to those set
by ICAO. Accordingly, in this finding, the EPA is focusing on matching
the scope of our contribution finding to the applicability thresholds
of the international standard. The covered aircraft match the
applicability (or MTOM) thresholds of the international aircraft
CO2 standard. This is a reasonable approach for this first
finding regarding the contribution of aircraft GHG emissions to the
endangering air pollution, as the vast majority of U.S. emissions from
all classes of aircraft engines (89 percent of U.S. aircraft GHG
emissions) will be covered by this scope of applicability, which
corresponds to 26 percent of global aircraft GHG emissions. This
approach is also consistent with our past practice in promulgating
aircraft engine NOX standards. In ruling on a petition for
judicial review of the 2005 rule for further stringency of aircraft
engine NOX standards,\263\ the D.C. Circuit held that the
EPA's approach in that action of tracking the applicability criteria of
the ICAO standards was reasonable and permissible under the CAA. NACAA
v. EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007). (The Court also held
that section 231 of the CAA confers a broad degree of discretion on the
EPA to adopt aircraft emission standards that the Agency determines are
reasonable. Id.) Also, by using the phrase ``any class or classes of
aircraft engines which in [her] judgment causes, or contributes to,''
the endangering air pollution, section 231(a)(2)(A) gives the EPA
discretion to determine which class or classes of aircraft engines to
evaluate in making a cause or contribute finding, and whether to focus
on a single class or multiple classes of aircraft engines in satisfying
the requirements of section 231(a)(2)(A).
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\262\ Consequently, this final action does not restrict the
EPA's future discretion to address GHG emissions from aircraft that
are not included in the scope of this finding, or prejudge how the
Agency would respond to a petition to address those GHG emissions
should one be submitted in the future.
\263\ U.S. EPA, 2005: Control of Air Pollution from Aircraft and
Aircraft Engines; Emission Standards and Test Procedures; Final
Rule, 70 FR 69664 (November 17, 2005).
In 2005, we promulgated more stringent NOX emission
standards for newly certified commercial turbofan engines. That
final rule brought the U.S. standards closer to alignment with ICAO
CAEP/4 requirements that became effective in 2004.
---------------------------------------------------------------------------

In response to the commenters who asked the EPA to undertake an
additional cause and contribute finding regarding GHG emissions from
non-covered U.S. aircraft, the Agency will take that request under
advisement and consideration among its other duties and priorities, but
is not prepared at this time to either reject or grant that request. At
this point, given the nearly complete process for ICAO's adoption of an
international standard, which will under the Chicago Convention trigger
the duties of the U.S. and other member states to adopt domestically
standards that are of at least equal stringency, it is most important
for the EPA to prepare for having to meet that nearly certain duty by
expeditious completion of the pre-requisite endangerment and cause or
contribute findings, without possibly delaying final action to consider
the possibility of proposing a broader cause or contribute finding
before taking final action.
b. The Administrator Reasonably Defined U.S. Covered Aircraft
A commenter stated that they understand that the scope of the
finding corresponds to the aircraft engine GHG emissions that are from
aircraft that match the applicability thresholds (or MTOM thresholds)
for the international aircraft CO2 standard; however, they
requested clarification on the difference between ``U.S. covered
aircraft'' and non-U.S. covered aircraft. This commenter requested
clarification on whether U.S. covered aircraft means aircraft made in
the U.S., registered in the U.S., operated by an entity holding an air
carrier certificate issued by the U.S., operated by an air carrier in
the National Air Space, or operated by anyone in the U.S. (National)
Air Space. The commenter expressed that the EPA must explain the basis
for its definition, and its claimed authority to regulate U.S. covered
aircraft.
As described earlier in section V.B.4, U.S. covered aircraft for
this cause or contribute finding refers to aircraft that are a subset
of all aircraft that meet the applicability thresholds of the
international aircraft CO2 standard, namely those that fly
domestically with starting and ending points within the U.S. and those
that depart the U.S. for international destinations. U.S. covered
aircraft include aircraft that operate in the U.S., and thus contribute
to GHG emissions in the U.S. This includes emissions from U.S. domestic
flights of these aircraft. In addition, the scope of this finding
reaches GHG emissions from non-military aircraft combusting U.S.
international bunker fuels departing the U.S., regardless of whether
they are a U.S. flagged carrier--also described as emissions from
combustion of U.S. international bunker fuels.\264\ Similar to
statements earlier in section V.B.4, in defining U.S. covered aircraft
for this specific contribution finding, in advance of needing to meet
the expected duties imposed by the ICAO standards, the EPA is focused
on the GHG emissions that the atmosphere receives as a result of
aviation activities occurring inside the U.S. and originating from the
U.S., in order to capture the full contribution of covered aircraft to
U.S. GHG emissions, consistent with the scope of the ICAO international
standard. It is important for the EPA's finding to reach the subset of
aircraft that meet the definition of U.S. covered aircraft, and that
subset

[[Page 54470]]

will not necessarily be covered by any other member state with
responsibilities to meet the ICAO standard under the Chicago
Convention. For U.S. covered aircraft, the EPA has chosen to combine
GHG emissions from all flights both domestic and those reflected in
international bunker fuel inventories to determine the contribution of
U.S. covered aircraft GHG emissions to the endangering air pollution.
We additionally note that the IPCC and UNFCCC guidance states that for
an international bunker flight the entire flight's emissions are
calculated and reported (for the country from where the flight
departed), and the GHG emission calculation methodologies are the same
for both domestic and international aviation bunker fuel flights. We
have followed this guidance in our calculation methodologies for this
contribution finding.\265\ Ultimately, GHG emissions inventories from
U.S. covered aircraft with or without GHG emissions from combustion of
U.S. international aviation bunker fuels are sufficient to support the
Administrator's cause or contribute finding in this action, whether we
consider the inventories both together, or just the inventory from
domestic flights of U.S. covered aircraft.
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\264\ For example, a flight departing Los Angeles and arriving
in Tokyo--regardless of whether it is a U.S. flagged carrier--is
considered a U.S. international bunker flight. A flight from London
to Hong Kong is not.
\265\ As described earlier, following the IPCC guidelines for
common and consistent accounting and reporting of GHGs, the UNFCCC
requires countries to report both total national GHG emissions and
international bunker fuel emissions (aviation and marine
international bunker fuel emissions), and though these emissions are
reported separately, both are assigned to the reporting country. In
meeting the UNFCCC reporting requirements, the U.S. Inventory
calculates international bunker fuel GHG emissions in a consistent
manner with domestic GHG emissions. In this final contribution
finding, the EPA maintains its approach used in the proposed
findings to include aviation international bunker fuel emissions
attributable to the United States with the national emissions number
from the U.S. Inventory as reported to the UNFCCC. It is the EPA's
view that it is reasonable and appropriate for the analysis in the
contribution finding to reflect the full contribution of U.S.
emissions from certain classes of aircraft engines, including those
from domestic flights of U.S. aircraft and those associated with
international aviation bunker fuel emissions. Consistent with IPCC
guidelines for common and consistent accounting and reporting of
GHGs under the UNFCCC, the ``U.S. international aviation bunker
fuels'' category includes emissions from combustion of fuel used by
aircraft departing from the United States, regardless of whether
they are a U.S. flagged carrier.
---------------------------------------------------------------------------

In response to the comment that EPA must explain its claimed
authority to regulate U.S. covered aircraft, as described earlier, the
endangerment and cause or contribute findings are a prerequisite under
CAA section 231(a)(2)(A) for EPA to adopt standards (that are of at
least equivalent stringency to those set by ICAO). If the Administrator
makes these findings in the affirmative, she must issue standards under
section 231(a)(2)(A).
c. It Is Reasonable for the Administrator To Limit the Contribution
Finding to U.S. Covered Aircraft
Some commenters stated that the EPA should issue a broader
contribution finding and wait until the standard setting phase to
exercise discretion as to what classes of aircraft engines should be
covered by standards. These commenters stated that the EPA has
authority to set aircraft engine GHG emission standards, following a
cause or contribute finding, that do not impose requirements on every
engine or class of aircraft engine within the scope of that finding.
They also argued that in this instance there does not seem to be a
sufficiently reasoned basis for EPA to exclude the non-covered aircraft
for purposes of making the cause or contribute finding.
As described earlier in section III, the endangerment and
contribution findings for aircraft GHG emissions under section
231(a)(2)(A) of the CAA are a necessary first step to begin to address
GHG emissions from the aviation sector, the highest-emitting category
of transportation GHG sources that the EPA has not yet addressed. As
presented in more detail in section V.B.4 of this preamble, covered
U.S. aircraft GHG emissions in 2014 represented 10 percent of GHG
emissions from the U.S. transportation sector,\266\ and in 2010, the
latest year with complete global emissions data, U.S. covered aircraft
GHG emissions represented 26 percent of global aircraft GHG
emissions.^{267 268} U.S. covered aircraft GHG emissions are
projected to increase by 43 percent over the next two decades.\269\
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\266\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed
June 14, 2016).
\267\ Ibid.
\268\ IPCC, 2014: Climate Change 2014: Mitigation of Climate
Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer,
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth,
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J.
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, 599-670 pp.
\269\ As discussed in section V.B.4.c, fuel burn growth rates
for air carriers and general aviation aircraft operating on jet fuel
are projected to grow by 43 percent from 2010 to 2036, and this
provides a scaling factor for growth in GHG emissions which would
increase at a similar rate as the fuel burn by 2030, 2036, and 2040.
FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp.
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last
accessed March 29, 2016).
---------------------------------------------------------------------------

Section III of this preamble summarizes the legal framework for
this action under CAA section 231. As discussed there, section
231(a)(2)(A) of the CAA states that ``The Administrator shall, from
time to time, issue proposed emission standards applicable to the
emission of any air pollutant from any class or classes of aircraft
engines which in [her] judgment causes, or contributes to, air
pollution which may reasonably be anticipated to endanger public health
or welfare.'' Before the Administrator may issue standards addressing
emissions of GHGs under section 231, the Administrator must satisfy a
two-step test. First, the Administrator must decide whether, in her
judgment, the air pollution under consideration may reasonably be
anticipated to endanger public health or welfare. Second, the
Administrator must decide whether, in her judgment, emissions of an air
pollutant from the classes of aircraft engines under consideration
cause or contribute to this air pollution.\270\ If the Administrator
answers both questions in the affirmative, she must issue standards
under section 231. While we agree that the EPA has significant
discretion in the standard-setting phase, we disagree with the comment
to the extent that it suggests the standard-setting phase is the only
appropriate place for the EPA to exercise discretion as to the scope of
covered aircraft engine classes in this first instance of findings
regarding aircraft GHG emissions. By using the phrase ``any class or
classes of aircraft engines which in [her] judgment causes, or
contributes to,'' the endangering air pollution, section 231(a)(2)(A)
gives the EPA discretion to determine which class or classes of
aircraft engines to evaluate in making a cause or contribute finding,
and whether to focus on a single class or multiple classes of aircraft
engines in satisfying the requirements of section 231(a)(2)(A). Because
the scope of the first international CO2 standard adopted by
ICAO is limited to aircraft over the specified MTOM levels, and the
U.S. will have a duty to set domestic standards in order to meet its
obligations under the Chicago Convention, it is reasonable in this case
to similarly limit the scope of and issue this first aircraft GHG
contribution

[[Page 54471]]

finding and not delay this determination in order to possibly
additionally consider and re-propose our finding to reach a broader
scope. We do not necessarily disagree with the commenters who suggested
that we could issue a broader contribution finding and then narrow the
scope of future standards at that stage, but doing so in this action
would require further analysis and development of an additional
proposed finding, which could impede expeditious final issuance of the
finding we proposed and thereby possibly impede prompt development of
domestic standards that are of at least equivalent stringency as
ICAO's. We expect to proceed with promulgating a domestic
CO2 standard (or GHG standard) of at least equivalent
stringency to the international CO2 standard as soon as it
is practicable, and to begin to take action along this expected path,
we are exercising our discretion in matching the applicability
thresholds of the international CO2 standard. The majority
of the GHG emissions from all classes of aircraft engines would be
covered by these applicability thresholds. We are not making either
positive or negative contribution findings regarding GHG emissions from
engines used in non-covered aircraft at this time, but nothing prevents
us from doing so in the future.
---------------------------------------------------------------------------

\270\ To clarify the distinction between air pollution and air
pollutant, the air pollution is the atmospheric concentrations and
can be thought of as the total, cumulative stock of GHGs in the
atmosphere. The air pollutants, on the other hand, are the emissions
of GHGs and can be thought of as the flow that changes the size of
the total stock.
---------------------------------------------------------------------------

2. The Administrator's Cause or Contribute Analysis Is Reasonable
a. It Is Reasonable To Include GHG Emissions From Combustion of
International Aviation Bunker Fuels in the U.S. Aircraft GHG Inventory
Some commenters stated that the EPA's choice of data for the cause
or contribute analysis was selective and biased. They contended that
emissions resulting from combustion of the international aviation
bunker fuels should not be part of the U.S. covered aircraft GHG
inventory or of the total U.S. aircraft GHG inventory, since the EPA's
own U.S. inventory for UNFCCC reporting purposes does not include
emissions from combustion of these fuels in the national GHG totals and
reports them separately to the UNFCCC, pursuant to UNFCCC inventory
reporting guidelines.\271\ Consequently, they asserted that the total
emissions from domestic commercial aircraft accounts for less than 2
percent (1.7%) of total U.S. aircraft GHG emissions. Because of this,
commenters believe that EPA inappropriately specified that the U.S.
covered aircraft GHG emissions represent 3 percent of the total U.S.
GHG emissions.
---------------------------------------------------------------------------

\271\ EPA GHG Emissions Inventory at A-31 (reporting and
methods) is available at: http://www.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2015-Annex-2-Emissions-Fossil-Fuel-Combustion.pdf (last accessed April 8, 2016).
---------------------------------------------------------------------------

The EPA disagrees with this comment. As stated earlier in this
section, U.S. covered aircraft GHG emissions \272\ (and total U.S.
aircraft GHG emissions) in this cause or contribute finding include
those GHG emissions resulting from combustion of international aviation
bunker fuel because we want to capture the full contribution of GHG
emissions from aircraft that are attributable to covered aircraft
activity in or originating from the U.S. In tracking aircraft GHG
emissions, the EPA is focused on the U.S.'s contributions from this
sector to the atmosphere. Accordingly, the EPA includes GHG emissions
for all aircraft departing from U.S. airports in a calendar year
(domestic and international flights) in determining total U.S. GHG
emissions and total U.S. aircraft GHG emissions. Thus, consistent with
that practice, for assessing GHG emissions from U.S. covered aircraft,
EPA has chosen to combine all flights, both those with domestic takeoff
and landing points, and those with domestic takeoff points and
international landing points. In addition, guidance from the IPCC and
UNFCCC states that for an international bunker fuel-combusting flight
the entire flight's emissions are calculated and reported, and the GHG
emission calculation methodologies are the same for both domestic and
international bunker fuel-combusting flights. The U.S. calculates and
reports emissions resulting from combustion of international bunker
fuels in accordance with this guidance. However, pursuant to UNFCCC
reporting guidelines, emissions from combustion of international bunker
fuels are reported separately from other aircraft emissions in the U.S.
Inventory, in order to meet the reporting commitments under the UNFCCC.
We follow the IPCC and UNFCC guidance in our calculation and reporting
methodologies.\273\
---------------------------------------------------------------------------

\272\ As described earlier in section V.B.4, U.S. covered
aircraft do not include military aircraft that use U.S.
international aviation bunker fuels.
\273\ As described earlier, following the IPCC guidelines for
common and consistent accounting and reporting of GHGs, the UNFCCC
requires countries to report both total national GHG emissions and
international bunker fuel emissions (aviation and marine
international bunker fuel emissions), and though these emissions are
reported separately, both are assigned to the reporting country. In
meeting the UNFCCC reporting requirements, the U.S. Inventory
calculates international bunker fuel GHG emissions in a consistent
manner with domestic GHG emissions. In this final contribution
finding, the EPA maintains its approach used in the proposed
findings to include aviation international bunker fuel emissions
attributable to the United States with the national emissions number
from the U.S. Inventory as reported to the UNFCCC. It is the EPA's
view that it is reasonable and appropriate for the analysis in the
contribution finding to reflect the full contribution of U.S.
emissions from certain classes of aircraft engines, including those
from domestic flights of U.S. aircraft and those associated with
international aviation bunker fuel emissions. Consistent with IPCC
guidelines for common and consistent accounting and reporting of
GHGs under the UNFCCC, the ``U.S. international aviation bunker
fuels'' category includes emissions from combustion of fuel used by
aircraft departing from the United States, regardless of whether
they are a U.S. flagged carrier.
---------------------------------------------------------------------------

b. The Administrator Does Not Need To Find Significant Contribution, or
Establish a Bright Line
One comment letter stated that aircraft GHG emissions are extremely
small relative to both domestic and global GHG emissions in the
aggregate, and questioned whether there is a reasoned basis for EPA to
find that GHG emissions from U.S. aircraft cause or contribute to air
pollution that endangers public health and welfare when assessed not
only relative to contributions from other sectors, but also relative to
climate impacts. For example, this commenter indicated the EPA
estimates that total U.S. aircraft GHG emissions accounted for about
0.5 percent of total global GHG emissions in 2010. Thus, the commenter
stated that the total U.S. aircraft GHG emission contributions from the
U.S. aviation sector are extremely small relative to total global GHG
emissions, or negligible as a percentage of total global GHG emissions.
The EPA disagrees with this comment and has fully explained the
reasoning for this contribution finding in section V.B. In addition,
the Administrator interprets CAA section 231(a)(2)(A) to require some
level of contribution that, while more than de minimis or trivial, does
not need to rise to the level of significance to support a contribution
finding. By its terms, section 231(a)(2)(A) does not contain a modifier
on its use of the term ``contribute,'' which contrasts with some other
provisions of the CAA, such as sections 213(a)(2) and (4), and
110(a)(2)(D)(i)(I), that expressly require a ``significant''
contribution. The Administrator's interpretation is consistent with the
interpretation of parallel language in CAA section 202(a), which was
described in the 2009 Findings,\274\ and is also supported by past
court decisions. For example, the D.C. Circuit's opinion in Catawba
County v. EPA, 571 F.3d 20 (D.C. Cir. 2009),

[[Page 54472]]

discusses the concept of contribution in the area designations context
under section 107(d)(1)(A), which, like section 231(a)(2)(A), does not
include the term ``significant'' to modify ``contribute.'' This
decision, along with others, supports the Administrator's
interpretation that CAA section 231(a)(2)(A) does not require a
significant contribution, but rather, in the absence of specific
language regarding the degree of contribution, provides the EPA
discretion such that a positive finding may be based on a determination
that the air pollutant emissions from the relevant class or classes of
aircraft engines merely ``contribute to'' the air pollution which may
reasonably be anticipated to endanger public health or welfare. In
addition, similar to the interpretation of section 202(a) described in
the 2009 Findings, the Administrator is not required under section
231(a)(2)(A) to establish a bright-line, objective test for
contribution, but is to exercise her judgment in determining
contribution.\275\ As explained above, and similar to the approach used
in the 2009 Findings, when exercising her judgment under section
231(a)(2)(A), in this context the Administrator considers both the
cumulative impact and also the totality of the circumstances. It is
reasonable for the Administrator to apply a ```totality-of-the-
circumstances test to implement a statute that confers broad
discretionary authority, even if the test lacks a definite `threshold'
or `clear line of demarcation to define an open-ended term.' '' Id. at
39 (citations omitted).
---------------------------------------------------------------------------

\274\ 74 FR at 66541-42.
\275\ 74 FR at 66542.
---------------------------------------------------------------------------

In Catawba County the D.C. Circuit upheld the EPA's
PM2.5 area designation decisions and analyzed CAA section
107(d), which requires the EPA to designate an area as nonattainment if
it ``contributes to ambient air quality in a nearby area'' not meeting
the national ambient air quality standards. Id. at 35. CAA section
107(d)(1), as mentioned above, like section 231(a)(2)(A), does not use
the term ``significant'' in establishing this duty, or set forth any
other bright-line benchmark that must be met for the EPA to find
``contribution.'' The court noted that it had previously held that the
term ``contributes'' is ambiguous in the context of CAA language. See
EDF v. EPA, 82 F.3d 451, 459 (D.C. Cir. 1996). ``[A]mbiguities in
statutes within an agency's jurisdiction to administer are delegations
of authority to the agency to fill the statutory gap in reasonable
fashion.'' 571 F.3d at 35 (citing Nat'l Cable & Telecomms. Ass'c v.
Brand X Internet Servs, 545 U.S. 967, 980 (2005)).
The D.C. Circuit then proceeded to consider and reject petitioners'
argument that the verb ``contributes'' in CAA section 107(d)
necessarily connotes a significant causal relationship. Specifically,
the court again noted that the term is ambiguous, leaving it to the EPA
to interpret in a reasonable manner. In the context of this discussion,
the court noted that ``a contribution may simply exacerbate a problem
rather than cause it . . .'' 571 F.3d at 39. This is consistent with
the D.C. Circuit's decision in Bluewater Network v. EPA, 370 F.3d 1
(D.C. Cir. 2004), in which the court, in evaluating EPA's judgment that
emissions from a specific class or category of nonroad engines
contribute to air pollution for which findings of ``significant''
contribution had already been made with respect to nonroad engines'
emissions in the aggregate, noted that the term ``contribute'' in CAA
section 213(a)(3) ``[s]tanding alone, . . . has no inherent connotation
as to the magnitude or importance of the relevant `share' in the
effect; certainly it does not incorporate any `significance'
requirement.'' 370 F.3d at 13. In that context, the court found that
the bare term ``contribute'' invests the Administrator with discretion
to exercise judgment regarding what constitutes a sufficient
contribution for the purpose of making a contribution finding. Id. at
14.
Finally, in Catawba County, the D.C. Circuit also rejected
``petitioners' argument that the EPA violated the statute by failing to
articulate a quantified amount of contribution that would trigger'' the
regulatory action. 571 F.3d at 39. Although petitioners preferred that
the EPA establish a bright-line test, the court recognized that the
statute did not require that EPA ``quantify a uniform amount of
contribution.'' Id.
Given this context, it is entirely reasonable for the Administrator
to interpret CAA section 231(a)(2)(A) to require some level of
contribution that, while more than de minimis or trivial, need not be
significant. It is also reasonable for the EPA to find contribution
without establishing a ``bright-line `objective' test of
contribution.'' 571 F.3d at 39. As in the 2009 Endangerment Finding,
when exercising her judgment under CAA section 231(a)(2)(A), the
Administrator not only considers the cumulative impact, but also looks
at the totality of the circumstances (e.g., the air pollutant, the air
pollution, the nature of the endangerment, the type of source category,
the number of sources in the source category, and the number and type
of other source categories that may emit the air pollutant) when
determining whether the emissions justify regulation under the CAA. See
id. (finding it reasonable for an agency to adopt a totality-of-the-
circumstances test under similar circumstances). In the context of GHG
emissions, which come from many different sectors no single one of
which is primarily responsible as their source, and which aggregate
together into a common pollution stock that itself impacts public
health and welfare, it is particularly reasonable to address those
emissions from contributing sectors, even if looked at individually a
sector may not be considered dominant. Therefore, in the specific
context of making a contribution finding regarding GHG emissions from
aircraft engines under CAA section 231, it is reasonable for the EPA to
interpret that provision to not require some level of contribution that
rises to a pre-determined numerical level or percentage- or mass-based
portion of the overall endangering GHG air pollution.
In addition, the EPA disagrees with the assertion that we do not
have a reasoned basis to make this contribution finding. As described
earlier in section V.B.4, the collective GHG emissions from the classes
of engines used in U.S. covered aircraft (197 Tg CO2eq) clearly
contribute to the endangering GHG air pollution, whether the comparison
is domestic (89 percent of total U.S. aircraft GHG emissions, 10
percent of all U.S. transportation GHG emissions, representing 2.8
percent of total U.S. GHG emissions), global (26 percent of total
global aircraft GHG emissions representing 2.7 percent of total global
transportation GHG emissions and 0.4 percent of all global GHG
emissions), or a combination of domestic and global. Both domestic and
global comparisons, independently and jointly, support the finding.
Moreover, these comparisons also support the finding even if GHG
emissions from combustion of U.S. international aviation bunker fuels
are excluded. Making this cause or contribute finding for engines used
in U.S. covered aircraft will result in the vast majority of total U.S.
aircraft GHG emissions being included in this determination.
Also, even if the EPA were required to determine that a
contribution met or exceeded a level of significance to make a
contribution finding, for the reasons discussed above, the EPA would
find that the contribution to the U.S. and global stocks of GHG air
pollution from GHG emissions from classes of engines

[[Page 54473]]

used in U.S. covered aircraft is significant. As discussed in more
detail above, their GHG emissions are larger than those from the great
majority of emitting countries, they are larger than those of several
major emitting countries, and they constitute one of the largest
remaining unregulated contributing parts of the U.S. GHG emissions
inventory.
Finally, in response to the suggestion in the comments that a
positive contribution finding is not supportable unless the EPA finds
that GHG emissions from covered aircraft themselves cause climate
impacts, without consideration of the impacts caused by the larger
aggregate stock of GHG air pollution, we stress that the comment
conflates the endangerment and contribution steps of the analysis. In
making the contribution finding, the EPA need not additionally and
separately find whether the contribution alone causes endangerment.
That endangerment finding has already been made with respect to the
stock of GHG air pollution to which covered aircraft GHG emissions
contribute. The only remaining issue at the second step of the analysis
is whether the analyzed GHG source sector in fact emits GHG air
pollutants that contribute to the air pollution that has already been
found to endanger public health and welfare. The covered aircraft, as
we have shown and explained, clearly do emit GHG air pollutants that
measurably contribute to that stock.
c. The Administrator Reasonably Provided Context in Comparing Aircraft
GHG Emissions to Other Sector GHG Emissions
Some commenters asserted that the EPA did not show important
context in comparing covered aircraft GHG emissions to other mobile
source categories' GHG emissions. The EPA does not describe the very
low level of aircraft emissions in general relative to emissions from
other sources. The commenters assert that, for example, the EPA does
not point out that the growth in emissions from U.S. medium-duty and
heavy-duty trucks since 1990 is 53 percent greater than the GHG
emissions from the U.S. commercial aircraft sector today, and 18
percent higher than the total U.S. aircraft (or entire U.S. aviation
sector) GHG emissions today.
In the proposed finding and this final finding, the EPA provides
context for covered aircraft GHG emissions relative to other sectors'
GHG emissions, including other categories within the transportation
sector. As described earlier in section V.B.4, from a national
perspective, the EPA provided tables to compare total U.S. aircraft and
U.S. covered aircraft GHG emissions to U.S. transportation and total
U.S. inventory GHG emissions, over an extended timeframe (1990-2014).
We also noted that overall U.S. covered aircraft comprised the third
largest source of GHG emissions in the U.S. transportation sector
behind only the light-duty vehicle sector and medium- and heavy-duty
truck sectors. This is the same ranking as total U.S. aircraft, if U.S.
covered aircraft and total U.S. aircraft are compared to the other
transportation sectors independent of one another. Finally, we note
that the U.S. inventory also shows that while overall U.S. GHG
emissions grew between 1990 and 2014, transportation GHG emissions grew
at a notably higher rate, 16 percent, more rapidly than any other U.S.
sector. U.S. covered aircraft GHG emissions grew by 15 percent in this
time period.\276\ Within the transportation sector, aircraft remain the
single largest source of GHG emissions not yet subject to any GHG
standards.
---------------------------------------------------------------------------

\276\ Total U.S. aircraft GHG emissions decreased by 3 percent
from 1990 to 2014. U.S. non-covered aircraft GHG emissions decreased
by 56 percent in this same time period.
---------------------------------------------------------------------------

In our proposal and again in this finding in section V.B.4, the
Administrator also stated her concern that recent projections indicate
that by 2036 GHG emissions both from all aircraft and from U.S. covered
aircraft are likely to increase by 43 percent (from 191 Tg
CO2eq to 272 Tg CO2eq for the years 2010 to
2036).\277\ This was contrasted with projections of GHG emissions
changes in other transportation sectors in the same timeframe. For
example, projections estimate that by 2036 the light-duty vehicle
sector is projected to see a 25 percent reduction in GHG emissions
(from 1,133 Tg CO2eq to 844 Tg CO2eq) from the
2010 baseline, while the freight trucks sector is projected to
experience a 23 percent increase in GHG emissions (from 390 Tg
CO2eq to 478 Tg CO2eq) from the 2010 baseline.
(However, this projected increase does not reflect the impact of GHG
reductions on the freight trucks sector anticipated from the Phase 2
heavy-duty GHG standards that have not yet been promulgated.) In
addition, by 2036 the rail sector is projected to experience a 3
percent reduction in GHG emissions (44 Tg CO2eq to 43 Tg
CO2eq) from the 2010 baseline.\278\ Therefore, in the context of
projected growth it appears that U.S. covered aircraft GHG emissions
through 2036 are estimated to increase by more than 80 Tg
CO2eq.^{279 280}
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\277\ As discussed in section V.B.4.c, fuel burn growth rates
for air carriers and general aviation aircraft operating on jet fuel
are projected to grow by 43 percent from 2010 to 2036 and this
provides a scaling factor for growth in GHG emissions which would
increase at a similar rate as the fuel burn by 2030, 2036, and 2040.
FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp.
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last
accessed March 29, 2016).
\278\ U.S. Energy Information Administration (EIA), 2015: Annual
Energy Outlook (AEO) 2015 with projections to 2040, DOE/EIA-0383,
154 pp. For the years 2010 to 2014, the baseline emissions for each
sector are from the 2016 Inventory of U.S. Greenhouse Gas Emissions
and Sinks Report, and after 2014 we utilize projections from the
2015 EIA AEO report. Available at http://www.eia.gov/forecasts/aeo/
(last accessed April 8, 2016).
\279\ As described earlier in section V.B.3, in 2010, U.S.
covered aircraft were 10 percent of U.S. transportation sector GHG
emissions, and in 2036, U.S. covered aircraft are projected to be 15
percent of U.S. transportation GHG emissions. In 2010, light-duty
vehicles were 58 percent of U.S. transportation GHG emissions, and
in 2036 they are projected to be 46 percent. In 2010, heavy-duty
vehicles were 20 percent of U.S. transportation GHG emissions, and
in 2036, they are projected to be 26 percent (does not reflect the
impact from the Phase 2 heavy-duty GHG standards that have not been
promulgated). In 2010, the rail sector was 2 percent of U.S.
transportation GHG emissions, and in 2036, they are projected to be
the same percentage.
\280\ Some commenters stated that section 231(a)(2)(A) of the
CAA does not give the EPA the authority to legally base the
contribution finding on future emission projections. As described
earlier in section V.B, the EPA considered future emission
projections as information to further support our assessment of
annual actual emissions (recent emissions from the current fleet)
for the contribution finding.
---------------------------------------------------------------------------

Also, the EPA provided a global perspective by showing how total
U.S. aircraft and U.S. covered aircraft GHG emissions compare to global
aircraft, global transport, and total global GHG emissions. In
addition, the EPA shows the ranking of the total U.S. aircraft and U.S.
covered GHG emissions relative to other global transportation sectors
and entire country GHG emissions.
One commenter stated that it is inappropriate and misleading to
compare U.S. aircraft GHG emissions with those of other, individual
countries. They indicated that to fairly compare the U.S. airlines' GHG
emissions contribution, EPA should analyze, as ICAO does, contributions
from other world regions with comparable land masses and levels of
economic activity. (In terms of landmass, the U.S. ranks third
globally, behind only Russia and Canada.) The EPA disagrees with this
comment. The language of CAA section 231(a)(2)(A) is silent regarding
how the Administrator is to make her contribution analysis. While it
requires that the Administrator assess whether emissions of an air
pollutant cause or contribute to air pollution which may reasonable be
anticipated to endanger public health or

[[Page 54474]]

welfare, it does not limit how she may undertake that assessment. It
surely is reasonable that the Administrator look at how total U.S.
aircraft GHG emissions and U.S. covered aircraft GHG emissions compare
to U.S. and global GHG emissions on an absolute and relative basis,
including ranking compared to other transportation sectors and entire
country emissions. It is entirely appropriate for the Administrator to
decide that part of understanding how a U.S. source category emitting
GHGs fits into the bigger picture of global climate change is to
determine how that source category fits into the contribution from the
United States as a whole (including U.S. transportation and total U.S.
inventory GHG emissions), where the United States as a country is a
major emitter of GHGs. Knowing how total U.S. aircraft GHG emissions
and U.S. covered aircraft GHG emissions rank compared to entire country
GHG emissions is relevant to understanding what role they play in the
global problem and hence whether they ``contribute'' to the global
problem. Moreover, the Administrator is looking at these emissions
comparisons as appropriate under the applicable science, facts, and
law. Therefore, the EPA appropriately compared and provided sufficient
context for total U.S. aircraft GHG emissions and U.S. covered aircraft
GHG emissions.
d. The Administrator Reasonably Utilized Multiple Databases for Global
GHG Emissions
Some commenters stated that the mix of data from different years
utilizing emissions data from IPCC, WRI/CAIT, and IEA was confusing and
potentially misleading. The EPA acknowledges that we presented data
from a variety of sources, but the EPA does not agree that the analysis
and presentation was misleading. We note that the global analysis for
this covered aircraft contribution finding is consistent with the
analytical approach originally developed and used in the 2009
Endangerment Finding. As described earlier in section IV.A, in the
proposed finding and this final finding, the Administrator considers
the recent, major scientific assessments of the IPCC, USGCRP, and the
NRC as the primary scientific and technical basis informing her
judgment. Thus, the Administrator is informed by and places
considerable weight upon the IPCC's data on global GHG emissions. She
places less emphasis on the WRI/CAIT and IEA emissions data, which in
comparison have a different aggregation of underlying data but are
available for more recent years (in comparison to the IPCC data). As
described earlier in section V.B.4, the WRI/CAIT data are generally in
line with the IPCC data. For 2010 total global GHG emissions, IPCC data
are 49,000 Tg CO2eq, and WRI/CAIT indicates 42,968 Tg
CO2eq (a 12 percent difference).\281\ Also, for 2010 global
aircraft GHG emissions, IPCC data are 743 Tg CO2eq, and IEA
data indicate 749 Tg CO2eq (a 1 percent difference).\282\
---------------------------------------------------------------------------

\281\ Comparing their 2010 total global GHG emissions, IPCC data
are 49,000 Tg CO2eq, and WRI/CAIT data, including
forestry and land use inventories, indicates 45,748 Tg
CO2eq (a 7 percent difference).
\282\ Comparing 2012 WRI/CAIT to 2010 IPCC data, WRI/CAIT data
for total global GHG emissions indicates 44,816 Tg CO2eq
for 2012 (a 9 percent difference), and including forestry and land
use inventories WRI/CAIT data indicates 47,599 Tg CO2eq
for 2012 (a 3 percent difference). Comparing 2012 IEA data to 2010
IPCC data, IEA data for global aircraft GHG emissions indicates 775
Tg CO2eq for 2012 (a 4 percent difference).
---------------------------------------------------------------------------

The approach of considering the major scientific assessments,
including IPCC's assessment, provides assurance that the
Administrator's judgment is informed by the best available, well-vetted
science that reflects the consensus of the climate science research
community. The major findings of the assessments, including IPCC's
assessment, support the Administrator's findings in this action. While
the EPA uses the IPCC data as the primary data source for this
contribution finding, it has reasonably used additional data sources
from widely used and recognized global datasets to provide context and
information from more recent years. These additional data supplement
and confirm the IPCC data. Ultimately, whether the Agency utilizes the
IPCC data alone or the WRI/CAIT dataset (and IEA data) alone, or both
datasets together, it would have no material effect on the emissions
comparisons discussed in section V.B and the Administrator would make
the same contribution finding.

VI. Statutory Authority and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review

This action is a significant regulatory action because it raises
novel policy issues. Accordingly, it was submitted to the Office of
Management and Budget (OMB) for review. This action finalizes a finding
that GHG emissions from aircraft cause or contribute to air pollution
that may be reasonably anticipated to endanger public health and
welfare. Any changes made in response to OMB recommendations have been
documented in the docket for this action.

B. Paperwork Reduction Act (PRA)

This action does not impose an information collection burden under
the PRA. The endangerment and cause or contribute findings under CAA
section 231(a)(2)(A) do not contain any information collection
activities.

C. Regulatory Flexibility Act (RFA)

I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities. The
endangerment and cause or contribute findings under CAA section
231(a)(2)(A) do not in-and-of-themselves impose any new requirements
but rather set forth the Administrator's determination that GHG
emissions from certain classes of aircraft engines--those used in U.S.
covered aircraft--cause or contribute to air pollution that may be
reasonably anticipated to endanger public health and welfare.
Accordingly, this action affords no opportunity for the EPA to fashion
for small entities less burdensome compliance or reporting requirements
or timetables or exemptions from all or part of the findings.

D. Unfunded Mandates Reform Act (UMRA)

This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. The action imposes no enforceable duty on any state,
local or tribal governments or the private sector.

E. Executive Order 13132: Federalism

This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.

F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments

This action does not have tribal implications as specified in
Executive Order 13175. The final endangerment and cause or contribute
findings under CAA section 231(a)(2)(A) do not in-and-of-themselves
impose any new requirements but rather set forth the Administrator's
determination that GHG emissions from certain classes of aircraft
engines--those used in U.S. covered

[[Page 54475]]

aircraft--cause or contribute to air pollution that may be reasonably
anticipated to endanger public health and welfare. Thus, Executive
Order 13175 does not apply to this action.

G. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks

This action is not subject to Executive Order 13045 because it is
not economically significant as defined in Executive Order 12866. The
Administrator considered climate change risks to children as part of
the endangerment and cause or contribute findings under CAA section
231(a)(2)(A). This action's discussion of climate change impacts on
public health and welfare is found in section IV of this preamble.
Specific discussion with regard to children is contained in sections
IV.C.1.a of the preamble. A copy of all documents pertaining to the
impacts on children's health from climate change have been placed in
the public docket for this action.

H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use

This action is not a ``significant energy action'' because it is
not likely to have a significant adverse effect on the supply,
distribution or use of energy. Further, we have concluded that this
action is not likely to have any adverse energy effects because the
endangerment and cause or contribute findings under section
231(a)(2)(A) do not in-and-of themselves impose any new requirements
but rather set forth the Administrator's determination that GHG
emissions from certain classes of aircraft engines--those used in U.S.
covered aircraft--cause or contribute to air pollution that may be
reasonably anticipated to endanger public health and welfare.

I. National Technology Transfer and Advancement Act (NTTAA)

This action does not involve technical standards.

J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations

The EPA believes this action will not have potential
disproportionately high and adverse human health or environmental
effects on minority, low-income, or indigenous populations because this
action does not affect the level of protection provided to human health
or the environment. The Administrator considered climate change risks
to minority, low-income, and indigenous populations as part of these
endangerment and cause or contribute findings under CAA section
231(a)(2)(A). This action's discussion of climate change impacts on
public health and welfare is found in section IV.C of the preamble.
Specific discussion with regard to minority, low-income, and indigenous
populations are found in sections IV.C.1.a and IV.C.2.a of this
preamble. A copy of all documents pertaining to the impacts on these
communities from climate change have been placed in the public docket
for this action.

K. Congressional Review Act (CRA)

The EPA will submit a rule report to each House of the Congress and
to the Comptroller General of the United States. This action is not a
``major rule'' as defined by 5 U.S.C. 804(2).

L. Determination Under Section 307(d)

Section 307(d)(1)(V) of the CAA provides that the provisions of
section 307(d) apply to ``such other actions as the Administrator may
determine.'' Pursuant to section 307(d)(1)(V), the Administrator
determines that this action is subject to the provisions of section
307(d).

VII. Statutory Provisions and Legal Authority

Statutory authority for this action comes from 42 U.S.C. 7571, 7601
and 7607.

List of Subjects

40 CFR Part 87

Environmental protection, Air pollution control, Aircraft, Aircraft
engines.

40 CFR Part 1068

Environmental protection, Administrative practice and procedure,
Confidential business information, Imports, Motor vehicle pollution,
Penalties, Reporting and recordkeeping requirements, Warranties.

Dated: July 25, 2016.
Gina McCarthy,
Administrator.
[FR Doc. 2016-18399 Filed 8-12-16; 8:45 am]
BILLING CODE 6560-50-P