Document ID: EPA-HQ-OAR-2014-0828-0001
Agency: epa
Document Type: Proposed Rule
Title: Greenhouse Gas Determinations: Emissions from Aircraft Cause or Contribute to Air Pollution that May Reasonably Be Anticipated to Endanger Public Health and Welfare
Posted Date: 2015-07-01T04:00Z

[Federal Register Volume 80, Number 126 (Wednesday, July 1, 2015)]
[Proposed Rules]
[Pages 37757-37806]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-15192]

[[Page 37757]]

Vol. 80

Wednesday,

No. 126

July 1, 2015

Part II

Environmental Protection Agency

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40 CFR Parts 87 and 1068

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

  Federal Register / Vol. 80 , No. 126 / Wednesday, July 1, 2015 / 
Proposed Rules  

[[Page 37758]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 87 and 1068

[EPA-HQ-OAR-2014-0828; FRL 9924-06-OAR]
RIN 2060-AS31

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

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule and advance notice of proposed rulemaking.

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SUMMARY: In this action, the Administrator is proposing to determine 
that greenhouse gas concentrations in the atmosphere endanger the 
public health and welfare of current and future generations within the 
meaning of section 231(a) of the Clean Air Act. She proposes to make 
this finding specifically with respect to the same six well-mixed 
greenhouse gases (GHGs)--carbon dioxide, 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 Clean Air Act and that together 
constitute the primary cause of the climate change problem. The 
Administrator is also proposing to find that greenhouse gas emissions 
from certain classes of engines used in aircraft are contributing to 
air pollution--the mix of greenhouse gases in the atmosphere--that 
endangers public health and welfare under section 231(a) of the Clean 
Air Act. Concurrent with these proposed findings, the EPA is issuing an 
Advance Notice of Proposed Rulemaking to provide an overview of and 
seek input on a variety of issues related to setting an international 
CO2 standard for aircraft at the International Civil 
Aviation Organization (ICAO), ICAO's progress in establishing global 
aircraft standards that achieve meaningful reductions in CO2 
emissions, and (provided the EPA promulgates final endangerment and 
cause and contribute findings for aircraft engine GHG emissions) the 
potential use of section 231 of the Clean Air Act to adopt and 
implement corresponding aircraft engine GHG emission standards 
domestically, ensuring transparency and the opportunity for public 
comment.

DATES: Comments. Comments must be received on or before August 31, 
2015.
    Public Hearing. The EPA will hold a public hearing on August 11, 
2015 in Washington, DC, at the William Jefferson Clinton East Building, 
Room 1153, 101 Constitution Avenue NW., Washington, DC 20004. If no one 
contacts the EPA requesting to speak at the hearing for this proposal 
by July 13, 2015 the public hearing will not take place and will be 
cancelled with no further notice. Speakers should contact Ms. JoNell 
Iffland (see FOR FURTHER INFORMATION CONTACT) to request to speak at 
the hearing. The last day to pre-register in advance to speak at the 
hearing will be August 6, 2015. The hearing will start at 10:00 a.m. 
local time and continue until everyone has had a chance to speak. 
Requests to speak will be taken the day of the hearing at the hearing 
registration desk, although preferences on speaking times may not be 
able to be fulfilled. If you require the service of a translator or 
special accommodations such as audio description, please let us know at 
the time of registration. For further information on the public hearing 
or to register to speak at the hearing, please see section I.B below or 
go to http://www.epa.gov/otaq/aviation.htm.

ADDRESSES: Comments. Submit your comments, identified by Docket ID No. 
EPA-HQ-OAR-2014-0828, by one of the following methods:
     Online: www.regulations.gov Follow the on-line 
instructions for submitting comments.
     Email: A-and-R-Docket@epamail.epa.gov Attention Docket ID 
No. EPA-HQ-OAR-2014-0828.
     Fax: (202) 566-9744, Attention Docket ID No. EPA-HQ-OAR-
2014-0828.
     Mail: U.S. Postal Service, send comments to Air and 
Radiation Docket and Information Center, Environmental Protection 
Agency, Mail Code: 28221T, 1200 Pennsylvania Ave. NW., Washington, DC 
20460. Attention Docket ID No. EPA-HQ-OAR-2014-0828.
     Hand Delivery: U.S. Environmental Protection Agency, EPA 
West, EPA Docket Center, EPA West Building, Room 3334, 1301 
Constitution Ave. NW., Washington, DC 20004. Attention Docket ID No. 
EPA-HQ-OAR-2014-0828. Such deliveries are only accepted during the 
Docket's normal hours of operation, and special arrangements should be 
made for deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2014-0828. See section I.B on ``Public Participation'' for more 
information about submitting written comments. The EPA's policy is that 
all comments received will be included in the public docket without 
change and may be made available online at http://www.regulations.gov, 
including any personal information provided, unless the comment 
includes information claimed to be confidential business information 
(CBI) or other information whose disclosure is restricted by statute. 
Do not submit information that you consider to be CBI or otherwise 
protected through http://www.regulations.gov or email. The http://www.regulations.gov Web site is an ``anonymous access'' system, which 
means the EPA will not know your identity or contact information unless 
you provide it in the body of your comment. If you send an email 
comment directly to the EPA without going through http://www.regulations.gov, your email address will be automatically captured 
and included as part of the comment that is placed in the public docket 
and made available on the Internet. If you submit an electronic 
comment, the EPA recommends that you include your name and other 
contact information in the body of your comment and with any disk or 
CD-ROM you submit. If the EPA cannot read your comment due to technical 
difficulties and cannot contact you for clarification, the EPA may not 
be able to consider your comment. Electronic files should avoid the use 
of special characters, or any form of encryption, and be free of any 
defects or viruses. For additional information about the EPA's public 
docket visit the EPA Docket Center homepage at: http://www.epa.gov/dockets. For additional instructions on submitting comments, go to 
section I.B of this document.
    Docket. 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 index. Although listed in the index, 
some information is not publicly available, e.g., 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

[[Page 37759]]

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: JoNell Iffland, Office of 
Transportation and Air Quality, Assessment and Standards Division 
(ASD), Environmental Protection Agency, 2000 Traverwood Drive, Ann 
Arbor, MI 48105; Telephone number: (734) 214-4454; Fax number: (734) 
214-4816; Email address: iffland.jonell@epa.gov. Please use this 
contact information for general questions about this rulemaking, to 
request a hearing, to determine if a hearing will be held, and to 
register to speak at the hearing, if one is held.

SUPPLEMENTARY INFORMATION: 

Table of Contents

I. General Information
    A. Does this action apply to me?
    B. Public Participation
    1. What should I consider as I prepare my comments for the EPA?
    2. Public Hearing
    C. Did the EPA conduct a peer review before issuing this notice?
    D. Children's Environmental Health
    E. Environmental Justice
II. Introduction: Overview and Context for This Proposal
    A. Summary
    B. Background Information Helpful to Understanding This Proposal
    1. Greenhouse Gases and Their Effects
    2. Statutory Basis for This Proposal
    C. The EPA's Responsibilities Under the Clean Air Act
    1. The EPA's Regulation of Greenhouse Gases
    2. Background on the Aircraft Petition, 2008 ANPR, and D.C. 
District Court Decision
    D. U.S. Aircraft Regulations and the International Community
    1. International Regulations and U.S. Obligations
    2. The International Community's Reasons for Addressing Aircraft 
GHG Emissions
    3. Relationship of the EPA's Proposed Endangerment and Cause or 
Contribute Findings to International Aircraft Standards
    E. The EPA's Regulation of Aircraft Emissions
III. Legal Framework for This Action
    A. Section 231(a)(2)(A)--Endangerment and Cause or Contribute
    1. The Statutory Language
    2. How the Origin of the Current Statutory Language Informs the 
EPA's Interpretation of Section 231(a)(2)(A)
    3. Additional Considerations for the Cause or Contribute 
Analysis
    B. Air Pollutant, Public Health and Welfare
IV. The Proposed Endangerment Finding Under CAA Section 231
    A. Scientific Basis of the 2009 Endangerment Finding Under CAA 
section 202(a)(1)
    1. The Definition of Air Pollution in the 2009 Endangerment 
Finding
    2. Public Health Impacts Detailed in the 2009 Endangerment 
Finding
    3. Public Welfare Impacts Detailed in the 2009 Endangerment 
Finding
    4. The Science Upon Which the Agency Relied
    B. Recent Science Further Supports the Administrator's Judgment 
That the Six Well-Mixed Greenhouse Gases Endanger Public Health and 
Welfare
    1. More Recent Evidence That Elevated Atmospheric Concentrations 
of the Six Greenhouse Gases Are the Root Cause of Observed Climate 
Change
    2. More Recent Evidence that Greenhouse Gases Endanger Public 
Health
    3. More Recent Evidence that Greenhouse Gases Endanger Public 
Welfare
    4. Consideration of Other Climate Forcers
    C. Summary of the Administrator's Proposed Endangerment Finding 
Under CAA Section 231
V. The Proposed Cause or Contribute Finding for Greenhouse Gases 
Under CAA Section 231
    A. The Air Pollutant
    1. Proposed Definition of Air Pollutant
    2. How the Definition of Air Pollutant in the Endangerment 
Determination Affects Section 231 Standards
    B. Proposed Cause or Contribute Finding
    1. The Administrator's Approach in Making This Proposed Finding
    2. Overview of Greenhouse Gas Emissions
    3. Proposed Contribution Finding for the Single Air Pollutant 
Comprised of the of Six Well-Mixed Greenhouse Gases
    4. Additional Considerations
VI. Advance Notice of Proposed Rulemaking: Discussion of Ongoing 
International Proceedings To Develop Aircraft CO2 
Emissions Standard and Request for Comment
    A. Purpose of the International Standard
    B. Applicability of the International CO2 Emissions 
Standard
    C. CAEP Discussion on In-Production Aircraft Applicability
    1. Applicability to In-Production Aircraft and Date of 
Implementation
    2. Reporting Requirement for New In-Production Aircraft
    D. Metric System, Applicability, and Certification Requirement
    1. CO2 Metric System
    2. Applicability
    3. Certification requirement
    4. Regulating the Entire Aircraft Instead of the Engine
    E. Stringency Options
    F. Costs, Technology Responses for Stringency Options, and Cost-
Effectiveness Analysis
    1. Non-Recurring Costs (Engineering Development Costs)
    2. Technology Responses
    3. Cost Effectiveness Analysis
    G. Request for Comment on the EPA's Domestic Implementation of 
International CO2 Standards
VII. 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
    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. Determination Under Section 307(d)
VIII. Statutory Provisions and Legal Authority

I. General Information

A. Does this action apply to me?

    These proposed findings, if finalized, would trigger new duties 
that would apply to the EPA, but would not themselves apply new 
requirements to other entities outside the federal government. 
Specifically, if the EPA issues final findings that greenhouse gas 
emissions from certain classes of engines--those used in certain 
aircraft--cause or contribute to air pollution which endangers public 
health or welfare, then the EPA would have a duty under section 231 of 
the Clean Air Act to promulgate aircraft engine emission standards 
applicable to emissions of that air pollutant from those classes of 
engines. Only those standards would apply to and have an effect on 
other entities outside the federal government. Entities potentially 
interested in this proposed action are those that manufacture and sell 
aircraft engines and aircraft in the United States. Categories that may 
be regulated in a future regulatory action include:

[[Page 37760]]

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                                                                                Examples of potentially affected
                Category                    NAICS \a\ Code      SIC \b\ Code                entities
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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 
proposed action. This table lists the types of entities that the EPA is 
now aware could potentially have an interest in this proposed action. 
If the EPA issues final affirmative findings under section 231(a) 
regarding greenhouse gases, the EPA would then be required to undertake 
a separate notice and comment rulemaking to issue emission standards 
applicable to greenhouse gas emissions from the classes of aircraft 
engines that the EPA finds cause or contribute in such a finding, and 
the FAA would be required to Prescribe regulations to insure compliance 
with these emissions standards pursuant to section 232 of the Clean Air 
Act. 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 
proposed action, consult the person listed in the preceding FOR FURTHER 
INFORMATION CONTACT section.

B. Public Participation

    The EPA requests comment on all aspects of the proposed aircraft 
endangerment and cause or contribute findings and the Advance Notice of 
Proposed Rulemaking (ANPR). This section describes how you can 
participate in this process.
    If you submitted comments on the issues raised by this proposal in 
dockets for other, earlier Agency efforts (e.g., the 2009 Endangerment 
and Cause or Contribute Findings for Greenhouse Gases Under Section 202 
of the Clean Air Act or the Advance Notice of Proposed Rulemaking on 
Regulating Greenhouse Gases under the Clean Air Act), you must still 
submit your comments to the docket for this action (EPA-HQ-OAR-2014-
0828) by the deadline if you want them to be considered.
1. What should I consider as I prepare my comments for the EPA?
    We are opening a formal comment period by publishing this document. 
We will accept comments during the period indicated in the DATES 
section. If you have an interest in the proposed aircraft endangerment 
and cause or contribute findings and/or the ANPR described in this 
document, we encourage you to comment on any aspect of this rulemaking.
Tips for Preparing Your Comments
    When submitting comments, remember to:
     Identify the rulemaking by docket number and other 
identifying information (subject heading, Federal Register date and 
page number).
     Follow directions--The agency may ask you to respond to 
specific questions or organize comments by referencing a Code of 
Federal Regulations (CFR) part or section number.
     Explain why you agree or disagree, suggest alternatives, 
and substitute language for your requested changes.
     Describe any assumptions and provide any technical 
information and/or data that you used.
     If you estimate potential costs or burdens, explain how 
you arrived at your estimate in sufficient detail to allow for it to be 
reproduced.
     Provide specific examples to illustrate your concerns, and 
suggest alternatives.
     Explain your views as clearly as possible, avoiding the 
use of profanity or personal threats.
     Make sure to submit your comments by the comment period 
deadline identified.
    Do not submit information to the EPA containing CBI through http://www.regulations.gov or email. Clearly mark the part or all of the 
information that you claim to be CBI. For CBI information on a disk or 
CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM 
as CBI and then identify electronically within the disk or CD-ROM the 
specific information that is claimed as CBI. In addition to one 
complete version of the comment that includes information claimed as 
CBI, you must submit a copy of the comment that does not contain the 
information claimed as CBI for inclusion in the public docket. 
Information so marked will not be disclosed except in accordance with 
procedures set forth in 40 CFR part 2.
2. Public Hearing
    If a hearing is held, it will provide interested parties the 
opportunity to present data, views or arguments concerning the proposed 
action. The EPA will make every effort to accommodate all speakers who 
arrive and register. Because this hearing, if held, will be at a U.S. 
government facility, individuals planning to attend the hearing should 
be prepared to show valid picture identification to the security staff 
in order to gain access to the meeting room. Please note that the REAL 
ID Act, passed by Congress in 2005, established new requirements for 
entering federal facilities. These requirements took effect July 21, 
2014. If your driver's license is issued by Alaska, American Samoa, 
Arizona, Kentucky, Louisiana, Maine, Massachusetts, Minnesota, Montana, 
New York, Oklahoma, or the state of Washington, you must present an 
additional form of identification to enter the federal buildings where 
the public hearings will be held. Acceptable alternative forms of 
identification include: Federal employee badges, passports, enhanced 
driver's licenses and military identification cards. In addition, you 
will need to obtain a property pass for any personal belongings you 
bring with you. Upon leaving the building, you will be required to 
return this property pass to the security desk. No large signs will be 
allowed in the building, cameras may only be used outside of the 
building and demonstrations will not be allowed on federal property for 
security reasons. The EPA may ask clarifying questions during the oral 
presentations but will not respond to the presentations at that time. 
Written statements and supporting information submitted during the 
comment period will be considered with the same weight as oral comments 
and supporting information presented at the public hearings.
    Speakers should contact Ms. JoNell Iffland (see FOR FURTHER 
INFORMATION CONTACT) if they will need specific equipment, or if there 
are other special needs related to providing comments at the hearing. 
Oral testimony will be limited to no more than 10 minutes for each 
commenter, although we may need to adjust the time for each speaker if 
there is a large turnout. The EPA requests that commenters provide the 
EPA with three copies of their oral testimony in hard copy form the day 
of the hearing or an electronic copy in advance of the hearing date. 
Verbatim transcripts of the hearings and written

[[Page 37761]]

statements will be included in the docket for the rulemaking. The EPA 
will make every effort to follow the schedule as closely as possible on 
the day of the hearing; however, please plan for the hearing to run 
either ahead of schedule or behind schedule.
    Information regarding the hearing (including information as to 
whether or not one will be held) will be available at http://www.epa.gov/otaq/aviation.htm. Again, if we do not receive a request to 
speak at the August 11, 2015 public hearing by July 13, 2015 the 
hearing will be cancelled.

C. Did the EPA conduct a peer review before issuing this notice?

    As outlined in section IV.A of this action, the EPA's approach to 
providing the technical and scientific information to inform the 
Administrator's judgment regarding the question of whether greenhouse 
gases endanger public health and welfare was to rely primarily upon the 
recent, major assessments by the U.S. Global Change Research Program 
(USGCRP), the Intergovernmental Panel on Climate Change (IPCC), and the 
National Research Council (NRC) of the National Academies. 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, and has determined that these assessments have been 
adequately peer reviewed in a manner commensurate with the EPA's Peer 
Review Policy \1\ and the guidelines in Office of Management and 
Budget's (OMB) Final Information Quality Bulletin for Peer Review 
(``OMB Bulletin'') for highly influential scientific assessments. 
According to guidelines in the EPA's Peer Review Handbook, if the 
Agency has determined that information has already been subject to 
adequate peer review, then it is not necessary to have further peer 
review of that information.\2\
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    \1\ U.S. EPA, 2006: EPA Peer Review Policy. Available at http://www.epa.gov/peerreview/ (Last accessed May 12, 2015).
    \2\ U.S. EPA, 2012: EPA Peer Review Handbook, Third Edition. 
Available at http://www.epa.gov/peerreview/pdfs/peer_review_handbook_2012.pdf (Last accessed May 12, 2015).
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    The EPA also cites data from its annual Inventory of U.S. 
Greenhouse Gas Emissions and Sinks report,\3\ which the Agency has 
determined to have been adequately reviewed in accordance with the OMB 
Bulletin and the EPA's Peer Review Handbook. For the presentation of 
emissions inventory information to support the cause or contribute 
finding, the EPA disaggregated the existing data in one area of the GHG 
Inventory (for the General Aviation Jet Fuel Category) and had the 
disaggregation methodology and results 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 action 
(EPA-HQ-OAR-2014-0828).
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    \3\ U.S. EPA, 2015: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2013, 564 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport, (Last 
accessed May 12, 2015).
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D. Children's Environmental Health

    As described in detail in section IV of this preamble, the 
scientific evidence and conclusions in the USGCRP, IPCC, and the NRC 
assessment reports cited in the 2009 Endangerment Finding \4\ indicate 
that children are uniquely vulnerable to climate change related health 
effects given behavioral, developmental, and physiological factors. The 
new assessment literature published since 2009 strengthens these 
conclusions by providing more detailed findings regarding children's 
vulnerabilities and projected impacts they may experience.
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    \4\ 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) (``2009 
Endangerment Finding''); 74 FR 18886 (April 24, 2009) (``Proposed 
2009 Endangerment Finding'').
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    These assessments describe that children will be disproportionately 
impacted by climate change given the unique physiological and 
developmental factors that occur during this lifestage. Impacts to 
children are expected from heat waves, air pollution, infectious and 
waterborne illnesses, and mental health effects resulting from extreme 
weather events. In addition, the assessments find that climate change 
will influence production of pollen that affects asthma and other 
allergic respiratory diseases, to which children are among those 
especially susceptible.

E. Environmental Justice

    As described in detail in section IV below, the scientific evidence 
and conclusions in the USGCRP, IPCC, and the NRC assessment reports 
cited in the 2009 Endangerment Finding indicate that certain 
populations are most vulnerable to the health and welfare effects of 
climate change, including the elderly, the poor, and indigenous peoples 
in the United States, particularly Alaska Natives. The more recent 
assessment reports strengthen these conclusions by providing more 
detail regarding these populations' vulnerabilities and projected 
impacts they may experience.
    In addition, the most recent assessment reports provide new 
analysis about how low-income populations and some populations defined 
jointly by ethnic/racial characteristics and geographic location are 
vulnerable to certain climate change health impacts, raising 
environmental justice concerns. Factors that contribute to increased 
vulnerability to the health effects of climate change include limited 
resources to adapt to and recover from climate impacts, as well as 
existing health disparities (e.g., higher prevalence of chronic health 
conditions such as diabetes).

II. Introduction: Overview and Context for This Proposal

A. Summary

    Pursuant to section 231(a)(2)(A) of the Clean Air Act (CAA or Act), 
the Administrator proposes to find that greenhouse gas (GHG) emissions 
from aircraft engines used in certain types of aircraft (referred to as 
``covered aircraft'' throughout this notice) contribute to air 
pollution that endangers public health and welfare. Covered aircraft 
would be those aircraft to which ICAO has agreed the international 
CO2 standard would apply: \5\ 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 would include smaller jet 
aircraft such as the Cessna Citation CJ2+ 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 would include larger 
turboprop aircraft, such as the ATR 72 and the Bombardier Q400.
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    \5\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for the 
Aeroplane CO2 Emissions Standards, Circular (Cir) 337, AN/192, 
Available at: http://www.icao.int/publications/catalogue/cat_2015_en.pdf. The ICAO Circular 337 is found on page 85 of the 
catalog and is copyright protected; Order No. CIR337 (last accessed 
May 12, 2015.
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    In this proposed action, the EPA relies primarily on the extensive 
scientific and technical evidence in the record supporting the 
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) (collectively

[[Page 37762]]

referred to as the 2009 Endangerment Finding in this action). This 
includes the major, peer-reviewed scientific assessments that were 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. 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). Furthermore, this 
proposed finding under section 231 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 public health and welfare. No information or analyses 
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). However, as explained below, in proposing this finding for 
purposes of section 231, we are not reopening or revising our prior 
findings under CAA section 202.
    The Administrator is proposing to define the ``air pollution'' 
referred to in section 231(a)(2)(A) of the CAA to be the mix of six 
well-mixed GHGs: CO2, methane, nitrous oxide, 
hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. 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 the 
public welfare of current and future generations within the meaning of 
section 231(a) of the Clean Air Act.
    Under section 231 of the CAA, 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 proposing to use 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)--that is, the aggregate group of the same six well-mixed GHGs. 
Based on the data summarized in section V, the Administrator is 
proposing to find that GHG emissions from aircraft engines used in 
covered aircraft, contribute to the air pollution that endangers public 
health and welfare under section 231(a).
    The Administrator's proposed 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 section 
231(a)(2)(A) of the Act for the GHG emissions from aircraft. The EPA is 
not proposing or taking action under any other provision of the CAA. 
Further, the EPA anticipates that ICAO will adopt a final 
CO2 emissions standard in February 2016. This proposal, and 
any final endangerment and cause or contribute findings for aircraft 
engine GHG emissions, are also part of preparing for a possible 
subsequent domestic rulemaking process to adopt standards that are of 
at least equivalent stringency as the anticipated ICAO CO2 
standards. Once an international standard is finalized by ICAO, member 
states are then required 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.

B. Background Information Helpful to Understanding This Proposal

1. Greenhouse Gases and Their Effects
    GHGs in the atmosphere effectively trap 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 [0.65 
to 1.06] degrees Celsius or 1.53 [1.17 to 1.91] degrees Fahrenheit.\6\ 
The 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.\7\ A detailed explanation of 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 proposed determination under CAA section 231 (EPA-HQ-OAR-02914-
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 proposed endangerment finding under CAA 
section 231.
---------------------------------------------------------------------------

    \6\ ``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.
    \7\ Ibid.
---------------------------------------------------------------------------

    The U.S. transportation sector constitutes a meaningful part of 
total U.S. and global anthropogenic GHG emissions. In 2013, aircraft 
remained the single largest GHG-emitting transportation source not yet 
subject to any GHG regulations. Aircraft clearly contribute to U.S. 
transportation emissions, accounting for 11 percent of all U.S 
transportation GHG emissions and representing more than 3 percent of 
total U.S. GHG emissions in 2013.\8\ Globally, U.S. aircraft GHG 
emissions represent 29 percent of all global aircraft 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 proposed cause or contribute finding under CAA 
section 231.
---------------------------------------------------------------------------

    \8\ U.S. EPA, 2015: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2013, 564 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport, (last 
accessed May 12, 2015).
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2. Statutory Basis for This Proposal
    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.''

[[Page 37763]]

    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 
certain classes of aircraft engines cause or contribute to this air 
pollution.\9\ If the Administrator answers both questions in the 
affirmative, she must issue 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 preamble summarizes 
the legal framework for this proposed action under CAA section 231. 
Typically, past endangerment and cause or contribute findings have been 
proposed concurrently with proposed standards under various sections of 
the CAA, including section 231. Comment has been taken on these 
proposed findings as part of the notice and comment process for the 
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 66 FR 5002 
(January 18, 2001). However, there is no requirement that the 
Administrator propose the endangerment and cause or contribute findings 
concurrently with proposed standards. See 74 FR 66502 (December 26, 
2001), (explaining that nothing in section 202(a) requires the EPA to 
propose or issue endangerment and cause or contribute findings in the 
same rulemaking, and that Congress left the EPA discretion to choose an 
approach that satisfied the requirements of section 202(a)). The same 
analysis applies to section 231(a)(2)(A), which is analogous to section 
202(a). The EPA is choosing to propose these findings at this time for 
a number of reasons, including its previous commitment to issue such 
proposed findings in response to a 2007 citizens' petition.\10\
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    \9\ 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.
    \10\ 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. 
Available at http://www.epa.gov/otaq/aviation.htm (last accessed May 
12, 2015).
---------------------------------------------------------------------------

    The Administrator is applying 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.'' \11\ 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 proposed findings will be subject to the same rulemaking 
requirements that would apply if the proposed findings were part of a 
standard-setting rulemaking.
---------------------------------------------------------------------------

    \11\ 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. Cars, trucks, construction equipment, 
airplanes, and ships, as well as a broad range of electric generation, 
industrial, commercial and other facilities, are subject to various CAA 
programs. Implementation of the Act over the past four decades has 
resulted in significant reductions in air pollution while the nation's 
economy has continued to grow.
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 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 six key well-mixed 
GHGs--CO2, methane, nitrous oxide, hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride--in the atmosphere threaten 
the public health and welfare of current and future generations.
     Cause or Contribute Finding: The Administrator found that 
the combined emissions of these well-mixed GHGs from new motor vehicles 
and new motor vehicle engines contribute to the GHG pollution which 
threatens public health and welfare.
    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).\12\ 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).\13\ On August 29, 2012, the second phase of the GHG 
emission standards for light-duty vehicles (2017-2025 model years) was 
finalized further reducing GHG emissions from light-duty vehicles.\14\ 
In 2014, the President directed the EPA and the Department of 
Transportation to set standards by March 2016 that further increase 
fuel efficiency and reduce GHG emissions from medium- and heavy-duty 
vehicles.\15\
---------------------------------------------------------------------------

    \12\ 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).
    \13\ US EPA, 2011: Greenhouse Gas Emissions Standards and Fuel 
Efficiency Standards for Medium- and Heavy-Duty Engines and 
Vehicles; Final Rule, 76 Federal Register 57106 (September 15, 
2011).
    \14\ 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).
    \15\ 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: 
http://www.whitehouse.gov/the-press-office/2014/02/18/remarks-president-fuel-efficiency-standards-medium-and-heavy-duty-vehicl 
(last accessed May 12, 2015).

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[[Page 37764]]

    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 by 6 billion metric 
tons.16 17
---------------------------------------------------------------------------

    \16\ U.S. EPA. ``EPA and NHTSA Set Standards to Reduce 
Greenhouse Gases and Improve Fuel Economy for Model Years 2017-2025 
Cars and Light Trucks.'' Office of Transportation and Air Quality 
Document No. EPA-420-F-12-051, August 2012. Available at http://www.epa.gov/otaq/climate/documents/420f12051.pdf (last accessed May 
26, 2015). See also US EPA, 2012: Regulatory Impact Analysis: Final 
Rulemaking for 2017-2025 Light-Duty Vehicle Greenhouse Gas Emissions 
Standards and Corporation Average Fuel Economy Standards, August, 
Document No. EPA-420-R-12-016, Table 7.4-2. Available at: http://www.epa.gov/oms/climate/documents/420r12016.pdf (last accessed May 
12, 2015).
    \17\ 76 FR 57106 (September 15, 2011).
---------------------------------------------------------------------------

    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.\18\ 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.\19\ In response, in January 2014, the 
EPA proposed carbon pollution standards for new electric utility 
generating units.\20\ This was followed in June 2014, by proposed 
standards to address carbon pollution from modified and reconstructed 
power plants \21\ and from existing power plants.\22\
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    \18\ Executive Office of the President, 2013: The President's 
Climate Action Plan, June 25. Available at: http://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf (last accessed May 26, 2015).
    \19\ 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 May 12, 2015).
    \20\ U.S. EPA, 2014: Standards of Performance for Greenhouse Gas 
Emissions From New Stationary Sources: Electric Utility Generating 
Units; Proposed Rule, 79 FR 1430 (January 8, 2014).
    \21\ U.S. EPA, 2014: Carbon Pollution Standards for Modified and 
Reconstructed Stationary Sources: Electric Utility Generating Units; 
Proposed Rules, 79 FR 34960 (June 18, 2014).
    \22\ U.S. EPA, 2014: Carbon Pollution Emission Guidelines for 
Existing Stationary Sources: Electric Utility Generating Units; 
Proposed Rule, 79 FR 34830 (June 18, 2014).
---------------------------------------------------------------------------

    In the Climate Action Plan, the President also indicated that the 
U.S. 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.\23\ The proposed 
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 preamble, total U.S. aircraft GHG emissions in 
2013 represented 11 percent of GHG emissions from the U.S. 
transportation sector,\24\ and in 2010, the latest year with complete 
global emissions data, U.S. aircraft GHG emissions represented 29 
percent of global aircraft GHG emissions.25 26 U.S. aircraft 
GHG emissions are projected to increase by almost 50 percent over the 
next two decades.\27\ See section V of this preamble for more 
information about the data sources that compose the aircraft GHG 
emissions inventory.
---------------------------------------------------------------------------

    \23\ Executive Office of the President, 2013: The President's 
Climate Action Plan at 21, June. Available at: http://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf (last accessed May 12, 2015).
    \24\ U.S. EPA, 2015: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2013, 564 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport (last 
accessed May 12, 2015).
    \25\ Ibid.
    \26\ 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.
    \27\ As discussed in section V.B.2.c., fuel burn growth rates 
for air carriers and general aviation aircraft operating on jet fuel 
are projected to grow by 49 percent from 2010 to 2035, and this 
provides a scaling factor for growth in GHG emissions which would 
increase at a similar rate as the fuel burn by 2030, 2035, and 2040. 
FAA, 2015: FAA Aerospace Forecast Fiscal Years 2015-2035, 134 pp. 
Available at https://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_forecasts/2015-2035/media/2015_National_Forecast_Report.pdf (last accessed May 
12, 2015).
---------------------------------------------------------------------------

2. Background on the Aircraft Petition, 2008 ANPR, and 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.\28\ 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.
---------------------------------------------------------------------------

    \28\ 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. 
Available at http://www.epa.gov/otaq/aviation.htm (last accessed May 
12, 2015).
---------------------------------------------------------------------------

    Following the Supreme Court's decision in Massachusetts v. EPA in 
2007, the EPA issued an 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, 44468-44473 (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.
    In response to the ANPR, the EPA received comments from a wide 
range of aviation sector stakeholders including industry trade groups, 
individual manufacturers, states and local governments, and 
nongovernmental organizations (NGOs). Industry groups and individual 
manufacturers stressed that fuel costs (and market forces) created an 
economic incentive to reduce fuel consumption and thus GHG emissions. 
One industry association indicated its commitment to achieve an 
additional 30 percent fuel efficiency improvement by 2025. Another 
commenter identified engine technologies that were improving fuel 
efficiency by more than 15 percent in the next generation of aircraft. 
With regard to CO2 engine emissions standards, these 
commenters felt that

[[Page 37765]]

international CO2 standards for aircraft engines were not 
necessary and that, if pursued, such standards would burden the 
industry and necessitate the development of new test procedures if 
CO2 emissions standards were based on aircraft cruise 
conditions instead of landing and takeoff operations (LTO). Industry 
commenters also argued that other potential approaches to reducing 
aircraft related emissions, such as averaging of GHGs among existing 
aircraft fleets and cap-and-trade schemes as existed in the European 
Union, were beyond the scope of the EPA's authority under section 231 
of the CAA. Finally, industry commenters noted that any program 
developed by the EPA should incentivize market forces and provide for 
flexibility.
    State/local governments and NGO commenters felt strongly that the 
EPA had clear authority to find endangerment under section 231 and that 
there were multiple options to reduce aircraft emissions, so that the 
Agency must set a GHG emissions standard for aircraft engines as states 
were preempted from doing so under CAA section 233. These commenters 
also argued that GHG standards for aircraft engines could provide 
aircraft manufacturers the incentive to renew or redesign aircraft and 
to adopt advanced engines brought to market. In addition these 
commenters suggested that an engine GHG standard could be set as a 
function of thrust similar to ICAO's standard for oxides of nitrogen 
(NOX) \29\ and should also include provisions for an 
averaging, banking, and trading (ABT) program.\30\ Some commenters also 
stated their support for fleet-wide (in-use fleet) emission reductions 
through a cap-and-trade system. Finally, these stakeholders stated 
that, absent the EPA rulemaking, quick international actions were 
unlikely and that the EPA should engage internationally to push for 
action on reducing CO2 emissions from aircraft.
---------------------------------------------------------------------------

    \29\ Sections II.D.1 and II.E provide an overview of the history 
ICAO's regulation of aircraft engine NOX emissions from 
1981 through 2012 and the EPA's adoption of equivalent aircraft 
engine NOX standards under the CAA.
    \30\ ABT programs have been utilized in a number of Clean Air 
Act programs to provide greater flexibilities that lower overall 
costs by allowing a manufacturer to comply with performance 
standards through averaging emissions among the vehicles it 
manufactures. Companies that achieve extra pollution reductions can 
bank these as `credits'' and then `trade or sell' emission credits 
to other companies, typically those that face higher costs to 
control pollution. Well-designed ABT programs can sometimes achieve 
greater emissions reductions at less cost and provide incentives for 
technology innovation.
---------------------------------------------------------------------------

    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 or not 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 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 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 D.C. 
Circuit.
    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.
---------------------------------------------------------------------------

    \31\ U.S. EPA, 2012: Memorandum in Response to Petition 
Regarding Greenhouse Gas Emissions from Aircraft, June 14. Available 
at http://www.epa.gov/otaq/aviation.htm (last accessed May 12, 2015) 
and Docket EPA-HQ-OAR-2014-0828.
---------------------------------------------------------------------------

    Meanwhile, the Court upheld 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 this proposed findings 
regarding aircraft engine GHG emissions as a further step toward 
responding to the Petition for Rulemaking.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

D. U.S. Aircraft Regulations and the International Community

    The EPA and the Federal Aviation Administration (FAA) traditionally 
work within the standard-setting process of ICAO's Committee on 
Aviation Environmental Protection (CAEP) to establish international 
emission standards and related requirements. 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 equivalent to ICAO's 
standards where appropriate. This approach has been affirmed as 
reasonable by the U.S. Court of Appeals for the D.C. Circuit. 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 subsequent regulations to ensure compliance with these 
standards when issuing certificates under its United States Code Title 
49 authority. In exercising the EPA's standard-setting and FAA's 
enforcement authorities, we expect to proceed using a similar approach 
for the future CAA section 231 aircraft engine

[[Page 37766]]

GHG standard (which may take the form of a CO2 standard), 
provided the EPA issues final positive endangerment and cause or 
contribute findings under CAA section 231. This approach is contingent 
on ICAO's adoption of an international aircraft CO2 standard 
that is consistent with CAA section 231 and is appropriate for domestic 
needs in the United States.
1. International Regulations and U.S. Obligations
    As noted above, we have 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 
Convention on International Civil Aviation (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 standards and regulations 
necessary 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 U.S. 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. Available at: http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed May 12, 2015).
    The ICAO Document 7300 is found on page 1 of the ICAO Products & 
Services 2015 catalog and is copyright protected; Order No. 7300.
    \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 May 12, 2015).
---------------------------------------------------------------------------

    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 which 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\
---------------------------------------------------------------------------

    \36\ ICAO, 2006: Doc 7300-Convention on International Civil 
Aviation, Ninth edition, Document 7300/9. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Document 7300 is found on page 1 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. 7300.
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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. Standards and 
Recommended Practices (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 greenhouse gas emissions on 
the global climate.
    The 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, member States 
are required to recognize the airworthiness certificates of any State 
whose standards are at least as stringent as ICAO's standards, thereby 
assuring that aircraft of any member State will be permitted to operate 
in any other member State.\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. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
    \38\ ICAO, 2006: Convention on International Civil Aviation, 
Article 33, Ninth Edition, Document 7300/9. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
    \39\ ICAO, 2006: Convention on International Civil Aviation, 
Article 38, Ninth Edition, Document 7300/9. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Document 7300 is found on page 1 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. 7300.
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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\ CAEP is composed of various task groups, work 
groups, and other committees whose contributing members include 
atmospheric, economic, aviation, environmental, and other professionals 
interested in and knowledgeable about aviation and environmental 
protection. 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.
---------------------------------------------------------------------------

    \40\ CAEP's terms of reference are available at http://www.icao.int/environmental-protection/Pages/Caep.aspx#ToR (last 
accessed May 12, 2015).
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    At CAEP meetings, the U.S. is represented by the FAA and plays an 
active role.\41\ 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 
policy matters. In turn, the FAA assists and advises the EPA on

[[Page 37767]]

aviation technology and certification matters. 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). 42 43
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    \41\ 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.
    \42\ ICAO, 2008: Aircraft Engine Emissions, International 
Standards and Recommended Practices, Environmental Protection, Annex 
16, Volume II, Third Edition, July. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
    \43\ CAEP develops new emission standards based on an assessment 
of the technical feasibility, cost, and environmental benefit of 
potential requirements.
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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 adopted by ICAO in 
1981.\44\ These standards limited aircraft engine emissions of 
hydrocarbons, carbon monoxide, and 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). ICAO approved these 
recommendations in 2011, then equivalent standards (to CAEP/6 and CAEP/
8 standards) were promulgated domestically in 2012 by the EPA in 
consultation with FAA.\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. Available at 
http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last 
accessed May 12, 2015). The ICAO Annex 16 Volume II is found on page 
19 of the ICAO Products & Services 2015 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. 
Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed May 12, 2015). The ICAO Annex 16 
Volume II is found on page 19 of the ICAO Products & Services 2015 
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, 2011: Aircraft Engine Emissions, Annex 16, Volume II, 
Third Edition, July 2008, Amendment 7 effective on July 18, 2011. 
Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed May 12, 2015). The ICAO Annex 16 
Volume II is found on page 19 of the ICAO Products & Services 2015 
catalog and is copyright protected; Order No. AN16-2/E/10 (last 
accessed February 5, 2015). 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).
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2. The International Community'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\ Also, Resolution A37-19 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 and stabilizing CO2 emissions at 
2020 levels.\52\ The Resolution included the following statements 
regarding ICAO policies and practices related to climate change.
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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.
    \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, Aspirational Goals and 
Implementation Options, HLM-ENV/09-WP/5, High-Level Meeting on 
International Aviation and Climate Change, Presented by the 
Secretariat, Montreal, October 7 to 9, 2009. Available at http://www.icao.int/Meetings/AMC/MA/High%20Level%202009/hlmenv_wp005_en.pdf 
(last accessed May 12, 2015).

--. . . ICAO and its member States recognize the importance of 
providing continuous leadership to international civil aviation in 
limiting or reducing its emissions that contribute to global climate 
change;
--Reemphasizing the vital role which international aviation plays in 
global economic and social development and the need to ensure that 
international aviation continues to develop in a sustainable manner;
--. . . the ultimate objective of the United Nations Framework 
Convention on Climate Change (UNFCCC) is to achieve stabilization of 
greenhouse gas (GHG) concentrations in the atmosphere at a level 
that would prevent dangerous anthropogenic interference with the 
climate system; and
--Acknowledging that international aviation emissions, currently 
accounting for less than 2 per cent of total global CO2 
emissions, are projected to grow as a result of the continued 
development of the sector.

    As the above statements indicate, 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 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.
3. Relationship of the EPA's Proposed Endangerment and Cause or 
Contribute Findings to International Aircraft Standards
    As described earlier, the EPA and the FAA work within the ICAO/CAEP 
standard setting process to establish international emission standards 
and related requirements. Under this approach international emission 
standards have first been adopted by

[[Page 37768]]

ICAO (with U.S. participation and agreement), and subsequently the EPA 
has initiated rulemakings under CAA section 231 to establish domestic 
aircraft engine emission standards that are of at least equivalent 
stringency as ICAO's standards. This approach has been affirmed as 
reasonable by the U.S. Court of Appeals for the D.C. Circuit. NACAA v. 
EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007). In exercising the EPA's 
standard-setting authority, provided the EPA makes positive 
endangerment and cause or contribute findings under CAA section 231 and 
ICAO adopts an international aircraft CO2 standard that is 
consistent with CAA section 231 and is appropriate for domestic needs 
in the United States, the EPA expects to proceed along a similar 
approach for the future CAA section 231 aircraft GHG standard (or 
aircraft CO2 standard).
    We anticipate that ICAO/CAEP will adopt a final aircraft 
CO2 emissions standard in February 2016. This proposal, and 
any final endangerment and cause or contribute finding for aircraft GHG 
emissions, are part of preparing for the possible subsequent domestic 
rulemaking process to adopt standards that are of at least equivalent 
stringency as the anticipated ICAO CO2 standards. These 
findings, which are factual and science-based, encompass a 
determination of whether GHG emissions from aircraft cause or 
contribute to air pollution which may reasonably be anticipated to 
endanger public health or welfare. If positive findings are made, the 
EPA will be obligated under section 231 of the CAA to set emission 
standards applicable to GHG emissions from the classes of aircraft 
engines for which the EPA makes the cause or contribute finding. If 
positive findings are not made, the EPA will not have triggered its 
obligation to set GHG emission standards under CAA section 231.
    The EPA has worked diligently over the past four years within the 
ICAO/CAEP process on a range of technical issues regarding aircraft 
CO2 emission standards. The ANPR that accompanies this 
proposal, in Section VI, discusses the issues arising in the ongoing 
international proceedings and U.S. input to CAEP regarding the 
international CO2 standard to help ensure transparency about 
this process. In addition, in the ANPR the EPA requests public comments 
on a variety of issues to assist the Agency in developing its position 
with regard to these issues and the aircraft engine GHG emission 
standards that it may potentially adopt under the CAA.

E. The EPA's Regulation of Aircraft Emissions

    As required by the CAA, the EPA has been engaged in reducing 
harmful air pollution from aircraft engines for over 40 years. In 1973, 
the EPA began to regulate gaseous exhaust emissions, smoke, and fuel 
venting from aircraft engines.\53\ We have occasionally 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. These ICAO requirements are generally 
referred to as CAEP/2 standards.\54\ That action 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) \55\ 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).\56\ It also included a carbon monoxide emission standard for 
in-production commercial turbofan engines.\57\ In 2005, we promulgated 
more stringent NOX emission standards for newly-certified 
commercial turbofan engines.\58\ 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.59 60
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    \53\ U.S. EPA, 1973: Emission Standards and Test Procedures for 
Aircraft; Final Rule, 38 FR 19088 (July 17, 1973).
    \54\ 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.
    \55\ This does not mean that in 1997 we promulgated requirements 
for the re-certification or retrofit of existing in-use engines.
    \56\ 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.
    \57\ 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).
    \58\ U.S. EPA, 2005: Control of Air Pollution from Aircraft and 
Aircraft Engines; Emission Standards and Test Procedures; Final 
Rule, 70 FR 2521 (November 17, 2005).
    \59\ 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).
    \60\ 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 Section 231(a)(2)(A) of the Clean Air Act 
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.
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    The EPA's actions to regulate certain pollutants emitted from 
aircraft engines come directly from its authority in section 231 of the 
CAA, and we have aligned the U.S. emissions requirements with those 
promulgated by ICAO. In addressing CO2 emissions, however, 
ICAO has moved to regulating a whole aircraft. This ICAO extension 
beyond pollutant emissions from engines to the whole aircraft was 
described in a 2013 ICAO circular.\61\ Several factors are considered 
when addressing whole-aircraft CO2 emissions, as the 
CO2 emissions are influenced by aerodynamics, weight, and 
engine-specific fuel consumption. Since each of these factors may 
affect aircraft engine fuel consumption, they ultimately affect 
CO2 emissions. Rather than viewing CO2 as a 
measurable emission from engines, therefore, ICAO now addresses 
CO2 emissions as a characteristic applicable to the entirety 
of the aircraft based on fuel consumption. In this proposed action, we 
are giving advance notice that the EPA may propose to adopt domestic 
GHG emission standards (which may take the form of CO2 
standards) for aircraft engines used in covered aircraft as an 
outgrowth of the international negotiations that commenced in 2010 
under the auspices ICAO/CAEP. Such standards could then discharge the 
EPA's duties under CAA sections 231(a)(2)(A) and 231(a)(3), if 
triggered by final positive endangerment and cause or contribute 
findings, to ``issue proposed emission standards applicable to the 
emission of'' GHG

[[Page 37769]]

from aircraft engines and to issue final ``regulations with such 
modifications as [she] deems appropriate.''
---------------------------------------------------------------------------

    \61\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for the 
Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192. 
Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed May 12, 2015). The ICAO Circular 337 
is found on page 85 of the ICAO Products & Services 2015 catalog and 
is copyright protected; Order No. CIR337.
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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 proposes 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 proposed section 231 finding.
    Two provisions of the CAA govern this proposal. 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, 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.\62\
---------------------------------------------------------------------------

    \62\ 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, December 15, 2009.) 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.\63\
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    \63\ 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 D.C. 
Circuit, and as that court 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).
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    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.\64\ The Administrator is thus to consider both 
current and future risks.
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    \64\ See id. at 121-122.
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    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.\65\ 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)).
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    \65\ 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)).
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    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 welfare may involve the frontiers of 
scientific or medical knowledge.\66\ At the same time, the 
Administrator must exercise reasoned decision making, and avoid 
speculative inquiries.
---------------------------------------------------------------------------

    \66\ 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

[[Page 37770]]

considering only those impacts that can be traced to the amount of air 
pollution directly attributable to the GHGs emitted by 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 66542, December 15, 2009 (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.\67\ 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.
---------------------------------------------------------------------------

    \67\ 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 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 proposed section 231 finding, 
vulnerable subpopulations face serious health 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.'' See 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.' '' See 
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 66506, December 
15, 2009. 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 proposed 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 Sec.  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 
greenhouse gases would effectively prevent EPA from doing the job that 
Congress gave it in Sec.  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. Finally, 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 18891, (April 24, 2009); see also 74 
FR 66506, (December 15, 2009). Section 231 was one of those other CAA 
provisions included in the 1977 amendments; therefore, 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. 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 (which is the same as its interpretation of the parallel 
language in section 202(a) as explained in the 2009 Endangerment 
Finding), is fully consistent with Congress' intention in crafting 
these provisions. See H.R. Rep. 95-294 (1977),

[[Page 37771]]

as reprinted in 4 A Legislative History of the Clean Air Act Amendments 
of 1977 (1978) at 2465 (hereinafter LH).\68\
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    \68\ The committee explained that its action addressed not only 
section 211(c)(1)(A) but rather the entire proposal, and would thus 
apply its interpretation 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.
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    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.\69\ 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 \70\; (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.\71\
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    \69\ 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.
    \70\ 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'').
    \71\ 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.
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    In revising the statutory language, Congress relied heavily on the 
en banc decision in Ethyl Corp. v. EPA, which reversed a 3-judge panel 
opinion regarding an EPA rule restricting the content of lead in leaded 
gasoline.\72\ 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.
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    \72\ 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 211(c)(1)(A) (1970).
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    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 held, regulatory 
action would not only precede, but prevent, a perceived threat. Id.
    The court also rejected petitioner's 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'' \73\ 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.
---------------------------------------------------------------------------

    \73\ Throughout this Notice 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 difficulties inherent in information on public 
health and welfare. H.R. Rep. 95-294 at 51, 4 LH at 2518.\74\
---------------------------------------------------------------------------

    \74\ 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

[[Page 37772]]

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.'' 
Unlike other CAA provisions, it does not require ``significant'' 
contribution. Compare, e.g., CAA sections 111(b); 213(a)(2), (4). 
Congress made it clear that the Administrator is to exercise her 
judgment in determining contribution, and 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 need 
not be significant. 74 FR 66542, December 15, 2009. In Catawba County 
v. EPA, 571 F.3d 20 (D.C. Cir. 2009), the court upheld EPA's PM[2.5] 
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'' not attaining 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 before the EPA can regulate, 
while the EPA's view was that the CAA requires a finding only of 
contribution. Id. at 13. Section 213(a)(3), like section 231(a)(2)(A), 
is triggered by a finding that certain sources ``cause, or contribute 
to,'' air pollution, while an adjacent provision, section 213(a)(2), is 
triggered by a finding of a ``significant'' contribution. The court 
looked at the ``ordinary meaning of `contribute' '' when upholding the 
EPA's reading. 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.\75\ The court found that 
the bare ``contribute'' language 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.\76\
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    \75\ 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.
    \76\ 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 threshold to be met; a truly trivial or 
de minimis ``contribution'' might not count as such. 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.\77\ 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 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) requires some level of contribution that, 
while exceeding de minimis or trivial thresholds, does not need to rise 
to a pre-determined numerical level of significance.
---------------------------------------------------------------------------

    \77\ Section V discusses the evidence in this case that supports 
the proposed 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 
(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

[[Page 37773]]

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 
Sec.  107(d) and finding it reasonable for the agency to adopt a 
totality of the circumstances approach); see also 74 FR at 66542, 
(December 15, 2009). Further discussion of this issue can be found in 
sections IV and V of this preamble.

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, 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). Greenhouse gases 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 ``air pollutant'' for purposes of this 
section 231 proposed contribution finding, which uses the same 
definition of air pollutant as 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, 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 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 are no definitions of ``public health'' or ``public welfare'' 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 National Ambient Air Quality Standards. 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 Proposed Endangerment Finding Under CAA Section 231

    This section describes the Administrator's proposed endangerment 
finding under CAA section 231(a)(2) and its basis. Beginning with the 
air pollution under consideration, the Administrator is proposing to 
use the same definition of the ``air pollution'' under CAA section 
231(a)(2) as that used under CAA section 202(a)(1), namely the mix of 
six well-mixed GHGs mentioned above: CO2, methane, nitrous 
oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. 
As described in section IV.A below, it is the Administrator's view that 
the reasons detailed in the 2009 Endangerment Finding 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. Information from the 
new scientific assessments described in section IV.B below provides 
further support that the six well-mixed GHGs are the primary cause and 
driver of climate change. The Administrator considered other climate-
forcing agents both in the 2009 Endangerment Finding and in this 
action; however, these substances are not included in the air pollution 
definition proposed in this action for the reasons discussed below in 
section IV.B.4.
    The Administrator is proposing to find, for purposes of CAA section 
231(a)(2)(A), that elevated concentrations of the six well-mixed GHGs 
constitute air pollution that endangers both the public health and the 
public welfare of current and future generations. 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 under CAA section 231(a). Information from the new scientific 
assessments described in section IV.B below provides further support 
and justification for this proposed finding.
    Section IV.A below summarizes the 2009 Endangerment Finding under 
CAA section 202, explains the approach EPA took in compiling an 
extensive record to inform the Administrator's judgment on that 
finding, and describes the recent judicial affirmation of the 2009 
Endangerment Finding. Section IV.B provides a summary of new scientific 
assessments that strengthen or provide further scientific evidence, in 
addition to that which the Administrator relied upon in making her 
prior judgment, for a finding that GHGs endanger public health and 
welfare.\78\ Finally, section IV.C summarizes the Administrator's 
conclusion for purposes of section 231, in light of the evidence, 
analysis, and conclusions that led to the 2009 Endangerment Finding as 
well as more recent evidence, that emissions of the six well-mixed GHGs 
in the atmosphere endanger public health and welfare.
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    \78\ 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 this proposed finding for purposes of CAA 
section 231. See sections III of the 2009 Proposed Endangerment 
Finding and sections III and IV of the 2009 Endangerment Finding.
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A. Scientific Basis of the 2009 Endangerment Finding Under CAA Section 
202(a)(1)

    In the 2009 Endangerment Finding, the Administrator found that 
elevated concentrations of the well-mixed GHGs in the atmosphere may 
reasonably be

[[Page 37774]]

anticipated to endanger public health and welfare of current and future 
generations. See, e.g., 74 FR 66516, December 15, 2009. The 
Administrator reached this judgment by carefully considering a 
significant body of scientific evidence and public comments submitted 
to the Agency. The sections below summarize the scope and nature of the 
relevant air pollution for the 2009 Endangerment Finding, as well as 
the public health and welfare considerations within the finding.
1. The Definition of Air Pollution in the 2009 Endangerment Finding
    The Administrator defined the scope and nature of the relevant air 
pollution as the aggregate group of six key, well-mixed GHGs: 
CO2, methane, nitrous oxide, hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride.\79\ The Administrator 
considered five primary reasons for focusing on this aggregate group as 
the air pollution in the 2009 Endangerment Finding: (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 primary cause of human-induced climate change, are 
the best-understood driver of climate change, and are expected to 
remain the key 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).\80\
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    \79\ 74 FR 66516, December 15, 2009.
    \80\ 74 FR 66517 to 66519, December 15, 2009.
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    The common physical properties these six GHGs share that are 
relevant to the climate change problem include the following: All are 
long-lived in the atmosphere; \81\ all become globally well mixed in 
the atmosphere, resulting in similar GHG concentrations around the 
globe regardless of geographic location of emissions; all trap outgoing 
heat that would otherwise escape to space; and all are directly emitted 
as GHGs rather than becoming a GHG in the atmosphere after emission of 
a precursor gas. The Administrator acknowledged that other 
anthropogenic climate forcers also play a role in climate change but 
for various scientific and policy reasons, these substances were not 
included in the air pollution definition.\82\
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    \81\ We use ``long-lived'' here to 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. IPCC also refers to these 
six greenhouse gases as long-lived. According to the most recent 
IPCC Fifth Assessment Report (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. 
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.
    \82\ 74 FR 66519 to 66521, December 15, 2009.
---------------------------------------------------------------------------

    As explained in more detail in the 2009 Endangerment Finding, the 
EPA 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.\83\ 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).
---------------------------------------------------------------------------

    \83\ 74 FR 66518, December 15, 2009.
---------------------------------------------------------------------------

2. Public Health Impacts Detailed in the 2009 Endangerment Finding
    Climate change resulting from anthropogenic GHG emissions threatens 
multiple aspects of public health.\84\ In determining that the well-
mixed GHG air pollution is reasonably anticipated to endanger public 
health for current and future generations, the Administrator noted her 
view that climate change can increase the risk of morbidity and 
mortality.\85\ In making that public health finding, 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 was unlikely to be compensated for by decreases in cold-related 
mortality (74 FR 66525, December 15, 2009). 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 increase in the spread 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 effects.
---------------------------------------------------------------------------

    \84\ 74 FR 66524 to 66530, December 15, 2009.
    \85\ 74 FR 66524, December 15, 2009.
---------------------------------------------------------------------------

3. Public Welfare Impacts Detailed in the 2009 Endangerment Finding
    Climate change resulting from anthropogenic GHG emissions also 
threatens multiple aspects of public welfare.\86\ In determining that 
the well-

[[Page 37775]]

mixed GHG air pollution is reasonably anticipated to endanger public 
welfare for current and future generations, the Administrator 
considered the multiple pathways by which GHG air pollution and 
resultant climate change affect public welfare by evaluating the 
numerous and far-ranging risks to food production and agriculture; 
forestry; water resources; sea level rise and coastal areas; energy, 
infrastructure, and settlements; and ecosystems and wildlife. The 
Administrator also considered 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. Climate change is expected to place 
large areas of the country at serious risk of reduced water supplies, 
increased water pollution, and increased occurrence of extreme events 
such as floods and droughts. 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 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, 
particularly in Alaskan indigenous communities. 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 public 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.
---------------------------------------------------------------------------

    \86\ 74 FR 66530 to 66536, December 15, 2009.
---------------------------------------------------------------------------

4. The Science Upon Which the Agency Relied
    As outlined in section III.A of the 2009 Endangerment Finding,\87\ 
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 rely 
primarily upon the recent, major assessments by the USGCRP, the IPCC, 
and the NRC. 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. Primary reliance on the 
major scientific assessments provided assurance that the Administrator 
was basing her judgment on the best available, well-vetted science that 
reflected the consensus of the climate science research community. The 
major findings of the USGCRP, IPCC, and NRC assessments supported 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. Relevant sections of documents from the 2009 
Endangerment Finding record have been placed in the docket for this 
proposed finding under CAA section 231.
---------------------------------------------------------------------------

    \87\ 74 FR 66510 to 66512, December 15, 2009.
---------------------------------------------------------------------------

    The EPA then reviewed ten administrative petitions for 
reconsideration of the Endangerment Finding in 2010.\88\ 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 Endangerment Finding and 
their objections' lack of ``central relevance'' to the Finding. 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.\89\
---------------------------------------------------------------------------

    \88\ Administrative petitions are available from http://www.epa.gov/climatechange/endangerment/petitions.html (last accessed 
May 12, 2015), and in the docket for the 2009 Endangerment Finding: 
EPA-HQ-OAR-2009-017.
    \89\ 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.
---------------------------------------------------------------------------

    The 2009 Endangerment Finding and the 2010 Reconsideration Denial 
were challenged in a lawsuit before the U.S. Court of Appeals for the 
D.C. Circuit.\90\ On June 26, 2012, the Court 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 greenhouse 
gases) \91\ and the text and structure of the CAA, and was adequately 
supported by the administrative record.\92\ The Court also agreed with 
the EPA that the Petitioners had ``not provided substantial support for 
their argument that the Endangerment Finding should be revised.'' \93\ 
The Court 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.\94\ 
The court further noted that the EPA's reliance on assessments was 
consistent with the methods decision-makers often use to make a 
science-based judgment.\95\ Moreover, the Court supported the EPA's 
reliance on the major scientific assessment reports conducted by 
USGCRP, IPCC, and NRC and found:
---------------------------------------------------------------------------

    \90\ 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).
    \91\ 549 U.S. 497 (2007).
    \92\ CRR, 684 F.3d at 117-27.
    \93\ Id. at 125
    \94\ Id. at 120-121.
    \95\ 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

[[Page 37776]]

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.\96\
---------------------------------------------------------------------------

    \96\ Id. at 120.

    In addition, the EPA's reliance on 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.'' \97\ The D.C. Circuit subsequently noted 
that ``the existence of some uncertainty does not, without more, 
warrant invalidation of an endangerment finding.'' \98\
---------------------------------------------------------------------------

    \97\ 74 FR at 66524, December 15, 2009.
    \98\ 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.'' \99\ Thus, the Supreme 
Court did not disturb the D.C. Circuit's holding that affirmed the 2009 
Endangerment Finding.
---------------------------------------------------------------------------

    \99\ 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.).
---------------------------------------------------------------------------

B. Recent Science Further Supports the Administrator's Judgment That 
the Six Well-Mixed Greenhouse Gases Endanger Public Health and Welfare

    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 propose 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. 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, detailed in the 2009 Endangerment 
Finding. Therefore, the new scientific assessments do not provide any 
reasonable basis on which to propose under CAA section 231(a)(2)(A) a 
different conclusion than the one the EPA reached in 2009 under CAA 
section 202(a). Rather, they provide further support for this proposed 
finding under section 231. In particular, the new assessments discussed 
in this preamble provide additional detail regarding public health 
impacts, particularly on groups and people at certain lifestages 
especially vulnerable to climate change including children, the 
elderly, low-income communities and individuals, indigenous groups, and 
communities of color.
    The subsections below present brief summaries of the relevant key 
findings from the new major peer-reviewed scientific assessments, which 
include the following:
     IPCC's 2013-2014 Fifth Assessment Report (AR5) \100\
---------------------------------------------------------------------------

    \100\ 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) \101\
---------------------------------------------------------------------------

    \101\ 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) \102\
---------------------------------------------------------------------------

    \102\ 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) \103\
---------------------------------------------------------------------------

    \103\ 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) \104\
---------------------------------------------------------------------------

    \104\ 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) \105\
---------------------------------------------------------------------------

    \105\ 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) \106\
---------------------------------------------------------------------------

    \106\ 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) \107\
---------------------------------------------------------------------------

    \107\ 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) 
\108\
---------------------------------------------------------------------------

    \108\ 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) \109\
---------------------------------------------------------------------------

    \109\ NRC, 2013: Climate and Social Stress: Implications for 
Security Analysis. The National Academies Press, 280 pp.

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

[[Page 37777]]

     NRC's 2013 ``Abrupt Impacts of Climate Change'' (Abrupt 
Impacts) \110\
---------------------------------------------------------------------------

    \110\ 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) \111\.
---------------------------------------------------------------------------

    \111\ NRC, 2014: The Arctic in the Anthropocene: Emerging 
Research Questions. The National Academies Press, 220 pp.
---------------------------------------------------------------------------

1. More Recent Evidence That Elevated Atmospheric Concentrations of the 
Six Greenhouse Gases Are the Root Cause of Observed Climate Change
    The EPA has carefully reviewed the recent assessments regarding 
elevated concentrations of the six well-mixed GHGs in the atmosphere. 
The EPA finds that the new assessments of the IPCC, USGCRP, and NRC 
support and strengthen the science underlying the 2009 Endangerment 
Finding that the six well-mixed GHGs are the root cause of recently 
observed climate change. Key findings are described briefly here.
    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.\112\ The IPCC AR5 concludes 
that the global average net effect of the increase in atmospheric GHG 
concentrations, plus other human activities (e.g., land use change and 
aerosol emissions), on the global energy balance since 1750 has been 
one of warming. This total net heating effect, referred to as 
``forcing,'' is estimated to be 2.3 Watts per square meter (W/m2), 
which has increased from the previous 2007 IPCC Fourth Assessment 
Report (AR4) total net estimate of 1.6 Watts per square meter (W/m2) 
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 aerosols. The IPCC AR5 rates the level of confidence \113\ in 
their radiative forcing estimates as ``high'' for methane and ``very 
high'' for CO2 and nitrous oxide.
---------------------------------------------------------------------------

    \112\ ``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.
    \113\ 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 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 
a 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 increase in 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 \114\ 
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 gases, 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.'' \115\
---------------------------------------------------------------------------

    \114\ 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.
    \115\ 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 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, such that 
trends based on short records are very sensitive to the beginning and 
end dates and do not in general reflect long-term climate trends. As an 
example, the IPCC AR5 notes that the rate of warming over the 15 year 
period from 1998-2012 was less than that over the period 1951-2012. 
This short term variability does not alter 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.'' 116 117
---------------------------------------------------------------------------

    \116\ 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.
    \117\ Furthermore, we would note that according to both NOAA and 
NASA, 2014 was the warmest year in the modern instrumental record 
for globally averaged surface temperature, and that the ten warmest 
years, with the exception of 1998, have now occurred since 2000. 
Available at http://www.giss.nasa.gov/research/news/20150116/ (last 
accessed May 12, 2015).
---------------------------------------------------------------------------

    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.'' 
\118\ This assessment finds that if no emissions reductions are made 
CO2 concentrations by the end of the century are projected 
to increase to levels that Earth has not experienced for more than 30 
million years.
---------------------------------------------------------------------------

    \118\ NRC, 2011: Understanding Earth's Deep Past: Lessons for 
Our Climate Future. The National Academies Press, p. 138.
---------------------------------------------------------------------------

2. More Recent Evidence That Greenhouse Gases Endanger Public Health
    The EPA has carefully reviewed the key conclusions in the recent 
assessments regarding human-induced climate change risks and impacts on 
public health. 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. These key findings are described briefly 
here.

[[Page 37778]]

    Regarding temperature effects, the conclusions of the assessment 
literature cited in the 2009 Endangerment Finding were uncertain with 
respect to the exact balance of how heat- versus cold-related mortality 
will change in the future, but 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 will 
be larger than the decreases in cold-related mortality. The USGCRP NCA3 
concludes that, ``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.'' \119\ 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),'' 
\120\ but that, ``[o]verall, we conclude that the increase in heat-
related mortality by mid-century will outweigh gains due to fewer cold 
periods.'' \121\
---------------------------------------------------------------------------

    \119\ 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. 224.
    \120\ 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.
    \121\ 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. The USGCRP NCA3 similarly concludes that, ``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.'' \122\ 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 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 like ozone 
via 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.
---------------------------------------------------------------------------

    \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. 222.
---------------------------------------------------------------------------

    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. Similarly, the USGCRP NCA3 discusses elevated waterborne 
disease outbreaks and the potential for mold contamination and degraded 
indoor air quality following heavy precipitation. Other impacts include 
mortality associated with flooding and impacts on mental health, such 
as anxiety and post-traumatic stress disorder. The IPCC AR5 also 
discusses 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 and health risks associated 
with drought conditions, which includes impacts from wildfires, dust 
storms, extreme heat events, flash flooding, degraded water quality, 
reduced water quantity, and water-related diseases. The IPCC SREX 
assessment projects further increases in some extreme weather and 
climate events during this century, and specifically notes that changes 
in extreme weather events have implications for disaster risk in the 
health sector.
    The effects of climate change on climate-sensitive diseases were 
also cited in the 2009 Endangerment Finding, including a likely 
increase in the spread of several food and water-borne pathogens among 
susceptible populations, and 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'' \123\ 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.'' \124\
---------------------------------------------------------------------------

    \123\ 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.
    \124\ 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 that definitive 
data or conclusions were lacking on how climate change might impact 
aeroallergens in the United States. The most recent assessments now 
express greater confidence that climate change will influence 
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, ``warming will 
lead

[[Page 37779]]

to further changes in the seasonal timing of pollen release (high 
confidence).'' \125\
---------------------------------------------------------------------------

    \125\ 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. 1465-1466.
---------------------------------------------------------------------------

    The assessment literature cited in the 2009 Endangerment Finding 
concluded that certain populations, including children, the elderly, 
and the poor, are most vulnerable to climate-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 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 that, ``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.'' \126\ 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.
---------------------------------------------------------------------------

    \126\ 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.'' \127\ In addition, increasing temperatures and loss 
of Arctic sea ice increases the risk of drowning for those engaged in 
traditional hunting and fishing.
---------------------------------------------------------------------------

    \127\ 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 will suffer 
disproportionately from climate change given the unique physiological 
and developmental factors that occur during this lifestage. Impacts on 
children are expected from heat waves, air pollution, infectious and 
waterborne illnesses, and mental health effects resulting from extreme 
weather events. The IPCC AR5 indicates that children are among those 
especially susceptible to most allergic diseases, as well as health 
effects associated with heat waves, storms, and floods.
    Both the USGCRP and IPCC conclude that climate change will increase 
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.
3. More Recent Evidence That Greenhouse Gases Endanger Public Welfare
    The EPA has carefully reviewed the recent scientific conclusions in 
the assessments regarding human-induced climate change impacts on 
public welfare.\128\ The EPA finds that they are largely consistent 
with or strengthen the underlying science supporting the 2009 
Endangerment Finding regarding public welfare effects on food 
production and agriculture; forestry; water resources; sea level rise 
and coastal areas; energy, infrastructure, and settlements; 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.
    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. 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.'' \129\ The IPCC AR5 concludes, ``Overall 
yields of major crops in North America are projected to decline

[[Page 37780]]

modestly by mid-century and more steeply by 2100 among studies that do 
not consider adaptation (very high confidence).'' \130\ 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.
---------------------------------------------------------------------------

    \128\ 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.
    \129\ 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.
    \130\ 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 this conclusion. 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 
will impact water quality and 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. 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.'' \131\ 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.'' \132\ The IPCC AR5 also projects that climate 
change will degrade surface water quality, including the Great Lakes, 
and will negatively affect drinking water treatment/distribution and 
sewage collection systems.
---------------------------------------------------------------------------

    \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. 70.
    \132\ 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. 1456-1457.
---------------------------------------------------------------------------

    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 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. The USGCRP NCA3 finds that, 
``Sea level rise, combined with coastal storms, has increased the risk 
of erosion, storm surge damage, and flooding for coastal communities, 
especially along the Gulf Coast, the Atlantic seaboard, and in 
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. 9.
---------------------------------------------------------------------------

    The IPCC AR5, the USGCRP NCA3, and three of the new NRC assessments 
provide estimates of projected global 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.\134\ The NRC Sea Level Rise assessment projects a global sea 
level rise of 0.5 to 1.4 meters by 2100, which is 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. 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.'' \135\ The NRC Climate Stabilization Targets assessment states 
that an increase of 3[deg]C will lead to a 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 
ice sheet processes, these revised estimates are consistent with the 
assessments underlying the 2009 Endangerment Finding.
---------------------------------------------------------------------------

    \134\ 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.
    \135\ 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. For example, the USGCRP NCA3 finds that, ``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.'' \136\ The NRC Arctic 
assessment identifies threats to human infrastructure in the Arctic 
from increased flooding, erosion, and shoreline ice pile-up, or ivu, 
associated

[[Page 37781]]

with summer sea ice loss and the increasing frequency and severity of 
storms.
---------------------------------------------------------------------------

    \136\ 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 found that climate change will 
predominantly adversely impact both terrestrial and marine biodiversity 
and the ability of these ecosystems to provide goods and services. The 
NRC Arctic assessment states that major marine and terrestrial biomes 
will likely shift pole ward, with significant implications for changing 
species composition, food web structures, and ecosystem function. The 
NRC Climate Stabilization Targets assessment found that coral bleaching 
will increase due both to warming and ocean acidification. 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 
acidification and warming that followed GHG increases 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.'' \137\ 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.'' \138\ The IPCC AR5 also projects biodiversity 
losses in marine ecosystems, especially in the Arctic and tropics.
---------------------------------------------------------------------------

    \137\ NRC, 2010: Ocean Acidification: A National Strategy to 
Meet the Challenges of a Changing Ocean. The National Academies 
Press, p. 5.
    \138\ Ibid.
---------------------------------------------------------------------------

    In general, climate change impacts related to public welfare are 
expected to be unevenly distributed across different regions of the 
United States and 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.'' \139\ 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.'' \140\
---------------------------------------------------------------------------

    \139\ 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.
    \140\ 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.
---------------------------------------------------------------------------

    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. 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.'' \141\ 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.
---------------------------------------------------------------------------

    \141\ 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 as the AMOC disruption that are not expected in this century can 
have severe impacts if/when they happen.
4. Consideration of Other Climate Forcers
    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 
affect Earth's climate (referred to as climate forcers). These can be 
grouped into two categories: (1) other substances with similar physical 
properties to the six well-mixed GHGs--these include the ozone-
depleting substances of chlorofluorocarbons, hydrochlorofluorocarbons, 
and halons, as well as nitrogen trifluoride and similar recently 
identified substances; and (2) short-lived substances--tropospheric 
ozone and its precursor gases, water vapor, and aerosol particles and 
precursors. For some short-lived substances--namely, water vapor; 
NOX; and aerosol particles including black carbon--their 
physical properties result in these substances having different, and 
often larger, climate effects when emitted at high altitudes. 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, long-lived GHGs--lead to more uncertainty in the 
scientific understanding of these short-lived substances' total effect 
on Earth's climate. More detail is provided below.
    As described in section III.B of the 2009 Endangerment Finding and 
in section IV.A.1 of this preamble, the primary reasons for defining 
the air pollution as the aggregate group of the six well-mixed GHGs 
include their common physical properties relevant to climate change 
(i.e., long-lived, well-mixed, directly emitted), the fact that these 
gases are considered the primary drivers of climate change, and the 
fact that these gases remain the best

[[Page 37782]]

understood drivers of anthropogenic climate change. The common physical 
properties of the six well-mixed GHGs not only support grouping them 
together as a class, but also contribute to their higher degree of 
scientific understanding related to climate change, relative to short-
lived substances that are not well-mixed, or substances that are formed 
indirectly rather than being directly emitted. After considering 
additional information in the new assessments regarding the climate-
relevant substances outside the basket of the six well-mixed GHGs, it 
is the Administrator's view that the reasons originally stated for not 
including these substances in the scope of the GHG air pollution still 
apply at this time. For example, nitrogen triflouride and some other 
recently discovered substances are not as well studied or understood as 
the six well-mixed GHGs. Similarly, for tropospheric ozone--a short-
lived gas in the atmosphere that is not directly emitted (it forms from 
emissions of various precursor gases)--the understanding and 
quantification of the link between precursor emissions and climate 
change is not as strong as for the six well-mixed GHGs.
    Regarding the short-lived substances with different climate effects 
when emitted at high altitudes, the Aircraft Petition (see section II 
of this preamble) mentions the effects of water vapor and 
NOX on clouds and atmospheric chemistry. The major peer-
reviewed scientific assessments of the IPCC and NRC provide the current 
state of scientific understanding of these effects; the USGCRP 
assessments have not dealt specifically with emissions at high 
altitude. The EPA 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),\142\ the IPCC 
Special Report: Aviation and the Global Atmosphere (IPCC 1999),\143\ 
the NRC's Advancing the Science of Climate Change (NRC 2010),\144\ and 
the NRC's Atmospheric Effects of Aviation: A Review of NASA's Subsonic 
Assessment Project (NRC 1999).\145\ In addition to high altitude water 
vapor and NOX, the 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.
---------------------------------------------------------------------------

    \142\ 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.
    \143\ 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.
    \144\ NRC, 2010: Advancing the Science of Climate Change. The 
National Academies Press, 528 pp.
    \145\ NRC, 1999: Atmospheric Effects of Aviation: A Review of 
NASA's Subsonic Assessment Project. The National Academies Press, 54 
pp.
---------------------------------------------------------------------------

    The state of the science as represented in the assessment 
literature highlights significant scientific uncertainties regarding 
the total net forcing effect of water vapor, NOX, and 
aerosol particles when emitted at high altitudes. Given these 
uncertainties, the Agency is not including them in the proposed 
definition of air pollution for purposes of the endangerment finding 
under section 231 of the CAA. The short-lived nature of these 
substances means that, unlike the long-lived GHGs, 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). 
As the climatic effects of these substances when emitted at high 
altitudes were not addressed at length in the 2009 Endangerment 
Finding, the following subsections briefly summarize the findings of 
the major scientific assessments regarding these substances' climatic 
effects at altitude and the various sources of uncertainty surrounding 
these estimates.
a. Changes in Clouds From High Altitude Emissions of Water Vapor and 
Particles
    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 the six long-lived, well-mixed 
GHGs, the warming effects associated with changes in cloud cover are 
more regional and temporal in nature. The three key components of 
aviation-induced cloudiness are 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. The NRC estimates that 
persistent contrails increased cloudiness above the United States by 
two percent between 1950 and 1988, with similar results reported over 
Europe.\146\ 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\).\147\ To put this number 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

[[Page 37783]]

range of .013 to 0.21 W/m\2\).\148\ 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).
---------------------------------------------------------------------------

    \146\ NRC, 1999: Atmospheric Effects of Aviation: A Review of 
NASA's Subsonic Assessment Project. The National Academies Press, 54 
pp.
    \147\ 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.
    \148\ 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 climate 
forcing effect, 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\).\149\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    Particles emitted or formed in the atmosphere as a result of 
aircraft emissions may also act as ice nuclei and modify naturally 
forming cirrus clouds, an effect referred to as ``induced cirrus.'' The 
two primary aviation-induced particles are sulfates and black carbon, 
and their effects on cirrus cloud modification is an area of active 
research. There are significant challenges in estimating the climatic 
impacts of induced cirrus; for example, 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.\150\ Neither IPCC AR4 nor AR5 provided 
global or regional estimates related to this forcing.
---------------------------------------------------------------------------

    \150\ 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 
components of aviation-induced cloudiness, the more recent assessments 
have not provided estimates of the net climate forcing effect of 
changes in clouds from high altitude emissions of water vapor and 
particles. Going back to the 1999 IPCC assessment, the science is 
characterized as ``very uncertain'' with a range for the best estimate 
between 0 to 0.040 W/m\2\.\151\
---------------------------------------------------------------------------

    \151\ 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.
---------------------------------------------------------------------------

b. Direct Radiative Forcing Effects of High Altitude Particle Emissions
    The 2009 Endangerment Finding noted that much of the uncertainty 
range surrounding the estimate of total net forcing due to all human 
activities was due to uncertainties about the cooling and warming 
effects of aerosols \152\ (though from all sources, not just aircraft). 
The Finding noted that the magnitude of aerosol effects can vary 
immensely with location and season of emissions, and also discussed 
black carbon as a specific type of aerosol particle, noting that 
estimates of its total climate forcing effect have a large uncertainty 
range.\153\ Here, we discuss the direct radiative forcing effects of 
high altitude emissions of the two primary aviation-induced particles, 
sulfates and black carbon.
---------------------------------------------------------------------------

    \152\ 74 FR at 66517, December 15, 2009.
    \153\ 74 FR at 66520, December 15, 2009.
---------------------------------------------------------------------------

    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 results in 
cooling. The more recent assessments have not quantified this effect 
from aviation. Going back to the 1999 IPCC assessment, the direct 
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\.\154\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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. The more 
recent assessments have not quantified this effect from aviation. The 
1999 IPCC assessment estimates the global mean radiative forcing of 
black carbon emissions to be 0.003 W/m\2\ with uncertainty spanning 
0.001 to 0.009 W/m\2\.\155\ The IPCC 1999 assessment suggests that 
because the contribution of black carbon in the stratosphere (which 
actually contribute to cooling of the surface rather than warming) was 
not included in its calculations, its estimates of radiative forcing 
were likely to be too high.
---------------------------------------------------------------------------

    \155\ Ibid.
---------------------------------------------------------------------------

c. Changes in Atmospheric Chemistry From High Altitude Nitrogen Oxides 
Emissions
    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. Quantifying these impacts is an area of active 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 aviation NOX emissions on ozone and methane 
concentrations, the location of aircraft emissions would be an 
important additional factor. In addition, NOX has different 
residence times in the atmosphere depending on the altitude at which it 
is emitted. The residence time of NOX in the upper 
troposphere, or roughly the cruise altitude for jet aircraft, is on the 
order of several days. Going back to the IPCC 1999 assessment, the 
globally averaged radiative forcing estimates for aircraft emissions of 
NOX in 1992 were 0.023 W/m\2\ for O3-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\).\156\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    The IPCC AR5 presents the impact of aviation NOX 
emissions using a different metric, global warming potential (GWP), 
which is a measure of the warming impact of a pulse of

[[Page 37784]]

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.\157\ The uncertainty in sign indicates 
uncertainty 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.
---------------------------------------------------------------------------

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

    The Administrator notes that NOX emissions are already 
regulated under the EPA's rules implementing CAA section 231, at 40 CFR 
part 87. 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 NOX emissions as a 
precursor to ozone formation in areas that did not meet the National 
Ambient Air Quality Standard (NAAQS) for ozone.\158\ The continuing 
significant uncertainties regarding NOX as a climate forcer 
do not undermine the Agency's prior conclusion under CAA section 231 
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.
---------------------------------------------------------------------------

    \158\ 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.
---------------------------------------------------------------------------

d. Summary
    Overall, the state of the science as represented in the assessment 
literature highlights 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 long-lived, well-mixed GHGs. Given the aforementioned 
scientific uncertainties at present, the Agency is not including these 
constituents in the proposed definition of air pollution for purposes 
of the endangerment finding under section 231 of the CAA.

C. Summary of the Administrator's Proposed Endangerment Finding Under 
CAA Section 231

    In sum, the Administrator proposes to find, 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 the 
public health and the public welfare of current and future generations. 
In this proposed action under CAA section 231(a)(2)(A), the EPA relies 
primarily 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 proposed finding under section 231 
accounts for the EPA's careful consideration not only of the scientific 
and technical record for the 2009 Endangerment Finding, but also of 
new, major scientific assessments issued since closing the 
administrative record for the 2009 Endangerment Finding. No recent 
information or analyses 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). In proposing this finding for 
purposes of section 231, we are not reopening or revisiting our 2009 
Endangerment Finding. To the contrary, in light of the recent judicial 
decisions upholding those findings, the EPA believes the 2009 
Endangerment Finding is firmly established and well settled.\159\ 
Moreover, there is no need for the EPA to reopen or revisit that 
finding for purposes of making an additional finding under section 231 
of the CAA. Therefore, public comments addressing this finding for 
purposes of section 231(a)(2)(A) should be limited to the section 231 
context; the EPA will not consider or respond to comments on this 
proposal that seek a reevaluation of our 2009 Endangerment Finding for 
purposes of section 202(a).
---------------------------------------------------------------------------

    \159\ 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 Proposed Cause or Contribute Finding for Greenhouse Gases Under 
CAA Section 231

    As noted above, the Administrator has proposed to define the air 
pollution for purposes of the endangerment finding under CAA section 
231 to be the aggregate of six well-mixed GHGs in the atmosphere. The 
second step of the two-part endangerment test for this proposed finding 
is for the Administrator to determine whether the emission of any air 
pollutant from certain classes of aircraft engines causes or 
contributes to this air pollution. This is referred to as the cause or 
contribute finding, and is the second proposed finding by the 
Administrator in this action.
    Section V.A of this proposal describes the Administrator's 
reasoning for using the same definition and scope of the GHG air 
pollutant that was used in the 2009 Endangerment Finding. Section V.0 
puts forth the Administrator's proposed finding that emissions of well-
mixed GHGs from classes of aircraft engines used in covered aircraft 
contribute to the air pollution which endangers public health and 
welfare.

A. The Air Pollutant

1. Proposed Definition of Air Pollutant
    Under section 231, 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 reasonably and logically considered 
the 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 66537, 
(December 15, 2009), (similar discussion with respect to the finding 
for section 202). Thus, for purposes of section 231, the Administrator 
is proposing to use the same definition of the air pollutant that was 
used in the 2009 Endangerment Finding, namely, the aggregate group of 
the same six GHGs: CO2, methane, nitrous oxide, 
hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. See 74 
Federal Register at 66536-66537, (December 15, 2009), (discussing the 
definition of the GHG air pollutant with respect to the finding for 
section 202). That is, as for the 2009 Endangerment Finding, the 
Administrator is proposing to define a

[[Page 37785]]

single air pollutant made up of these six GHGs.
    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.\160\ 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, these substances share common 
attributes that support their grouping as the air pollution for 
purposes of the endangerment finding. These same common attributes also 
support the Administrator grouping the six GHGs for purposes of 
defining the air pollutant for the proposed cause or contribute finding 
under CAA section 231.
---------------------------------------------------------------------------

    \160\ As detailed in the 2009 Endangerment Finding proposal (74 
FR 18904 (April 24, 2009) 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 preamble 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). The EPA's Greenhouse Gas Reporting 
Program (http://www.epa.gov/ghgreporting/index.html, (last accessed 
May 12, 2015)) also reports GHG emissions on a CO2-
equivalent basis, recognizing the common and collective treatment of 
the six GHGs.
---------------------------------------------------------------------------

    The Administrator recognizes that in this case, the aircraft 
engines covered by this notice 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 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.\161\ 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 contribution. By proposing to use 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.
---------------------------------------------------------------------------

    \161\ 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 66496, 
66537 (December 15, 2009).
---------------------------------------------------------------------------

2. How the Definition of Air Pollutant in the Endangerment 
Determination Affects Section 231 Standards
    Under section 231(a), the Administrator is required to set 
``emission standards applicable to the emission of any air pollutant'' 
from classes of aircraft engines that the Administrator determines 
causes or contributes to air pollution that endangers public health or 
welfare. If the Administrator makes a final determination under section 
231 that the emissions of the GHG air pollutant from certain classes of 
aircraft engines contribute to the air pollution that may reasonably be 
anticipated to endanger public health and welfare, then she is called 
on to set standards applicable to the emissions of this air pollutant. 
The term ``standards applicable to the emissions of any air pollutant'' 
is not defined, and the Administrator has the discretion to interpret 
it in a reasonable manner to effectuate the purposes of section 231 to 
set standards that either control the emissions of the group of six 
well-mixed gases as a whole and/or control emissions of individual 
gases, as constituents of the class. For example, it might be 
appropriate to set a standard that measures and controls the aggregate 
emissions of the group of GHGs, weighted by CO2 equivalent. 
Depending on the circumstances, however, it may be appropriate to set 
standards for certain individual gases, or some combination of group 
and individual standards. These and other similar approaches could 
appropriately be considered in setting a standard or standards 
applicable to the emissions of the group of GHGs that are defined as 
the air pollutant. The Administrator would consider a variety of 
factors in determining what approach to take in setting the standard or 
standards; for example, she would consider the characteristics of the 
aircraft emissions, such as rate and variability, the kind and 
availability of control technology, and other matters relevant to 
setting standards under section 231.\162\
---------------------------------------------------------------------------

    \162\ In setting GHG emissions standards for model years 2012-
2016 light-duty vehicles, the EPA set fleet-wide average 
CO2 equivalent standards for cars and trucks based on a 
technology assessment analysis which indicated that there was a wide 
range of technologies available for manufacturers to use when 
upgrading vehicles to reduce CO2 emissions and improve 
fuel economy. The final standards were based on CO2 
emissions-footprint curves, where each vehicle has a different 
CO2 emissions compliance target depending on its 
footprint value (related to the size of the vehicle). The EPA also 
set standards to cap tailpipe nitrous oxide, methane emissions, and 
provided compliance credits to manufacturers who improved air 
conditioning systems, such as through reduced refrigerant leakage 
(hydrofluorocarbons) and indirect CO2 emissions related 
to the increased load on the engine. 75 FR 25324 (May 7, 2010).
---------------------------------------------------------------------------

B. Proposed Cause or Contribute Finding

1. The Administrator's Approach in Making This Proposed Finding
    As it did for the 2009 Endangerment Finding, and consistent with 
prior practice and current science, the EPA uses annual emissions as a 
reasonable proxy for contributions to the air pollution, i.e., elevated 
atmospheric concentrations of GHGs. Cumulative anthropogenic emissions 
are primarily responsible for the observed change in concentrations in 
the atmosphere (i.e., the fraction of a country's or an economic 
sector's cumulative emissions compared to the world's 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 emissions are a reasonable proxy for annual 
incremental changes in atmospheric concentrations.
    There are a number of possible ways of assessing whether air 
pollutants cause or contribute to the air pollution which may 
reasonably be anticipated to endanger public health and welfare, and no 
single approach is required or has been used exclusively in previous 
determinations under the CAA. Because the air pollution against which 
the contribution is being evaluated is the six well-mixed GHGs, the 
logical starting point for any contribution analysis is a comparison of 
the emissions of the air pollutant from the section 231 category to the 
total U.S. and total global emissions of the 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 the six GHGs. To 
inform the Administrator's assessment, section V.B.2 presents the 
following types of simple and straightforward comparisons of 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;

[[Page 37786]]

     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 accepted metric for comparing different GHGs. This approach is 
consistent with how EPA determined contribution for GHGs under section 
202 of the CAA in 2009.
2. 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.\163\ This is the unambiguous result of human emissions of these 
gases. Global emissions of well-mixed GHGs have been increasing, and 
are projected to continue increasing for the foreseeable future. 
According to IPCC AR5, total global (from all major emitting sources 
including forestry and other land use) emissions of GHGs in 2010 were 
about 49,000 teragrams \164\ of CO2 equivalent (Tg 
CO2eq).\165\ This represents an increase in global GHG 
emissions of about 29 percent since 1990 and 23 percent since 2000. In 
2010, total U.S. GHG emissions were responsible for about 14 percent of 
global GHG emissions (and about 12 percent when factoring in the effect 
of carbon sinks from U.S. land use and forestry).
---------------------------------------------------------------------------

    \163\ 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.
    \164\ One teragram (Tg) = 1 million metric tons = 1 megatonne 
(Mt). 1 metric ton = 1,000 kg = 1.102 short tons = 2,205 lbs.
    \165\ 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.
---------------------------------------------------------------------------

    Because 2010 is the most recent year for which IPCC emissions data 
are available, we provide 2011 estimates from another widely used and 
recognized global dataset, the World Resources Institute's (WRI) 
Climate Analysis Indicators Tool (CAIT),\166\ for comparison. According 
to WRI/CAIT, the total global GHG emissions in 2011 were 43,816 Tg of 
CO2eq, representing an increase in global GHG emissions of 
about 42 percent since 1990 and 30 percent since 2000 (excluding land 
use, land use change and forestry). These estimates are generally 
consistent with those of IPCC. In 2011, WRI/CAIT data indicate that 
total U.S. GHG emissions were responsible for about 16 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, which was 
responsible for 24 percent of total global GHG emissions.
---------------------------------------------------------------------------

    \166\ World Resources Institute (WRI) Climate Analysis 
Indicators Tool (CAIT) Data Explorer (Version 2.0). Available at 
http://cait.wri.org (last accessed May 12, 2015).
---------------------------------------------------------------------------

    The Inventory of U.S. Greenhouse Gas Emissions and Sinks Report 
\167\ (hereinafter ``U.S. Inventory''), in which 2013 is the most 
recent year for which data are available, indicates that total U.S. GHG 
emissions increased by 5.7 percent from 1990 to 2013 (or by about 4.7 
percent when including the effects of carbon sinks), and emissions 
increased from 2012 to 2013 by 1.8 percent. This 2012 to 2013 increase 
was attributable to multiple factors including an increase in carbon 
intensity of fuels consumed for electricity generation, a small 
increase in vehicle miles traveled and vehicle fuel use, and a colder 
winter leading to an increase in heating requirements. The U.S. 
Inventory also shows that while overall U.S. GHG emissions grew between 
1990 and 2013, transportation GHG emissions grew at a significantly 
higher rate, 15 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.
---------------------------------------------------------------------------

    \167\ U.S. EPA, 2015: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2013, 564 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport, (last 
accessed May 12, 2015).
---------------------------------------------------------------------------

    Section V.B.2.a which follows describes U.S. aircraft GHG emissions 
within the domestic context, while section V.B.2.b describes these same 
GHG emissions in the global context. Section V.B.2.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 U.S. 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 contribution to the air pollution that is causing climate 
change. In 2013, total U.S. GHG emissions from all sources were 6,774 
Tg CO2eq. As stated above, total U.S. GHG emissions have 
increased by almost 6 percent between 1990 and 2013, while U.S. 
transportation GHG emissions from all categories have grown 15 percent 
since 1990. The U.S. transportation sector was the second largest GHG 
emitting sector (behind electricity generation), contributing 1,911 Tg 
CO2eq or about 30 percent of total U.S. GHG emissions in 
2013. 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.\168\ 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 purchased in and used by 
aircraft departing from the United States, regardless of whether they 
are a U.S. flagged carrier. Total U.S. aircraft emissions clearly 
contribute to the U.S. transportation sector's emissions, accounting 
for 216 Tg CO2eq or 11 percent of such emissions (see Table 
V.1.). In 2013, emissions from aircraft (216 Tg CO2eq) were 
the third largest transportation source of GHGs within the United 
States, behind light-duty vehicles and medium- and heavy-duty trucks 
(totaling 1,494 Tg CO2eq).
---------------------------------------------------------------------------

    \168\ According to IPCC guidelines for common and consistent 
accounting and reporting of GHGs under the UNFCCC, the total U.S. 
GHG emissions from the U.S. Inventory that is reported to the UNFCCC 
excludes international bunker fuel emissions (aviation and marine 
international bunker fuel emissions) from the reported total 
national GHG emissions. However, the total U.S. GHG emissions in 
this proposed cause or contribute finding section of this action do 
include international bunker fuel emissions because we want to 
capture the full contribution of U.S. emissions, including those 
from U.S. aircraft.
---------------------------------------------------------------------------

    For purposes of making this cause or contribute finding, the EPA is 
focused on, and proposes to include, 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 
contemplated by ICAO.
    As mentioned earlier in section II.D, traditionally the 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 is anticipated in February 2016, and 
provided that the EPA makes a positive endangerment finding and ICAO 
adopts an

[[Page 37787]]

international CO2 emissions standard that is both consistent 
with CAA section 231 and appropriate for domestic needs, we would 
expect to proceed with promulgating a CO2 emissions standard 
(or GHG standard) of at least equivalent stringency domestically. As 
described later in section VI.D, the thresholds of applicability for 
the international CO2 emissions standard are based on gross 
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.\169\ 
Applying these gross weight thresholds, our proposed cause or 
contribute finding applies to GHG emissions from classes of engines 
used in covered aircraft. Examples of covered aircraft would include 
smaller jet aircraft such as the Cessna Citation CJ2+ and the Embraer 
E170, up to the largest commercial jet aircraft--the Airbus A380 and 
the Boeing 747. Other examples of covered aircraft would include larger 
turboprop aircraft, such as the ATR 72 and the Bombardier Q400. Our 
intention is for the scope of the contribution finding to correspond to 
the aircraft engine GHG emissions that are from aircraft that match the 
applicability thresholds for the international aircraft CO2 standard. 
As such we have also identified aircraft that are not covered aircraft 
for purposes of our proposed 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'' \170\ from the 
types of aircraft that would be covered by the anticipated ICAO 
standards.\171\ These aircraft would not be covered aircraft and 
consequently, we are also not including GHG emissions from classes of 
engines used in these types of aircraft in our proposed cause or 
contribute finding.
---------------------------------------------------------------------------

    \169\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192, 
Available at http://www.icao.int/publications/ICAOProducts&Services2015catalogue/cat_2015en.pdf (last accessed May 
12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
    \170\ ICAO regulations only apply to civil aviation (aircraft 
and aircraft engines), and consequently, ICAO regulations do not 
apply to military aircraft.
    \171\ The applicability of the anticipated international 
CO2 standard would be limited to subsonic aircraft, and 
would not extend to supersonic aircraft. Since space vehicles (or 
spacecraft) will be operated at supersonic speeds, space vehicles 
would not be covered by the anticipated international CO2 
standard.
---------------------------------------------------------------------------

    Thus, for the purposes of the cause or contribute finding, the EPA 
proposes to include GHG emissions from aircraft engines used in covered 
aircraft in the scope of this proposed cause or contribute finding. 
This is an equivalent scope of applicability as that contemplated by 
ICAO. The majority of the GHG emissions from all classes of aircraft 
engines would be covered by this scope of applicability. Below we 
describe the contribution of these U.S. covered aircraft GHG emissions 
to U.S. GHG emissions, and later in section V.B.2.b we discuss the 
contribution of these U.S. covered aircraft emissions to global GHG 
emissions.
    In 2013, GHG emissions from U.S. covered aircraft (which includes 
U.S. international aviation bunker fuels in certain cases) comprised 90 
percent (195 Tg CO2eq) of total U.S. aircraft GHG emissions 
\172\ and 10 percent of total U.S. transportation sector GHG emissions 
(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, which is the same ranking as total U.S. aircraft.\173\ The 
U.S. covered aircraft also represent 3 percent of total U.S. GHG 
emissions, which is approximately equal to the contribution from total 
U.S. aircraft of 3.2 percent (Table V.1).\174\
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    \172\ Eastern Research Group, Incorporated (ERG), 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, May 7, 
2015.
    \173\ 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. transportations sector, behind only 
light-duty vehicle and medium- and heavy-duty truck sectors.
    \174\ Total U.S. aircraft GHG emissions and U.S. covered 
aircraft GHG emissions were from 12 to 32 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 17 percent greater in 2000 and 2005 than in 2013. 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, 2015: Inventory of U.S. Greenhouse Gas Emissions and 
Sinks: 1990-2013, 564 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport, Last 
accessed May 12, 2015; U.S. FAA. 2015, APO Terminal Area Forecast 
Summary Report--Forecast Issued January 2015, http://aspm.faa.gov/apowtaf/.).
---------------------------------------------------------------------------

    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.\175\ CO2 represents 
99 percent of all GHGs from both total aircraft (214 Tg 
CO2eq) and U.S. covered aircraft (193 Tg CO2eq), 
and nitrous oxide represents about one percent from total aircraft (2 
Tg CO2eq) and covered aircraft (1.8 Tg CO2eq). 
Modern aircraft do not emit methane,\176\ and hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride are not products of aircraft 
engine combustion.
---------------------------------------------------------------------------

    \175\ U.S. EPA, 2015: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2013, 564 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport, (last 
accessed May 12, 2015).
    \176\ 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 http://www.epa.gov/otaq/regs/nonroad/aviation/420r09901.pdf (last accessed May 12, 2015)). 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).

[[Page 37788]]

                     Table V.1--Comparisons of U.S. Aircraft GHG Emissions to Total U.S. Transportation and Total U.S. GHG Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                   1990         2000         2005         2010         2011         2012         2013
--------------------------------------------------------------------------------------------------------------------------------------------------------
Total U.S. Aircraft GHG emissions (Tg CO2eq).................          228          262          254          216          215          212          216
Share of U.S. Transportation.................................          14%          13%          12%          11%          11%          11%          11%
Share of total U.S. Inventory................................         3.6%         3.6%         3.4%         3.1%         3.1%         3.2%         3.2%
U.S. Covered Aircraft GHG emissions (Tg CO2eq)...............          169          223          217          190          193          190          195
Share of U.S. aircraft GHG emissions.........................          74%          85%          85%          88%          90%          90%          90%
Share of U.S. Transportation.................................          10%          11%          10%         9.7%          10%         9.9%          10%
Share of total U.S. Inventory................................         2.6%           3%         2.9%         2.7%         2.8%         2.9%         2.9%
Transportation Sector emissions (Tg CO2eq)...................        1,659        2,044        2,137        1,966        1,932        1,907        1,911
Share of total U.S. Inventory................................          26%          28%          29%          28%          28%          29%          28%
    Total U.S. GHG emissions.................................        6,406        7,315        7,464        7,017        6,889        6,652        6,744
--------------------------------------------------------------------------------------------------------------------------------------------------------

b. U.S. Aircraft GHG Emissions Relative to Global Aircraft GHG 
Inventory and the Total Global GHG Inventory
    For background information and context, we first provide 
information on the contribution 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 that would be 
covered by the anticipated 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 
contribution to the air pollution that is causing climate change. As in 
the preceding section, we present comparisons from both total U.S. 
aircraft and U.S. covered aircraft.
    According to IPCC AR5, global aircraft GHG emissions in 2010 were 
11 percent of global transport GHG emissions and 2 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 would be covered by 
the anticipated ICAO CO2 standard (``ICAO covered 
aircraft'').\177\ When compared to global data from IPCC AR5, worldwide 
GHG emissions from ICAO covered aircraft represented about 93 percent 
(688 Tg CO2eq) of global aircraft GHG emissions,\178\ 10 
percent of global transport GHG emissions, and 1.5 percent of total 
global GHG emissions in 2010.
---------------------------------------------------------------------------

    \177\ ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation 
and Climate Change, 224 pp. Available at http://cfapp.icao.int/Environmental-Report-2013/ (last accessed May 12, 2015).
    \178\ 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 about 29 percent of 
global aircraft GHG emissions, about 3.1 percent of global transport 
GHG emissions, and about 0.5 percent of total global GHG emissions in 
2010 (see Table V.2). For U.S. covered aircraft in 2010 GHG emissions 
represented about 26 percent of global aircraft GHG emissions, 2.7 
percent of global transport GHG emissions, and 0.5 percent of total 
global GHG emissions (see Table V.2). Because 2010 is the most recent 
year for which IPCC emissions data are available, we also made 
comparisons using 2011 estimates from WRI/CAIT and the International 
Energy Agency (IEA) \179\ and found that they yield very similar 
results.\180\
---------------------------------------------------------------------------

    \179\ International Energy Agency, Data Services. Available at 
http://data.iea.org (last accessed May 12, 2015).
    \180\ Data from WRI/CAIT and IEA show that, in 2011, total U.S. 
aircraft emissions represented about 28 percent of global aircraft 
GHG emissions, about 3.7 percent of global transport GHG emissions, 
and about 0.5 percent of total global GHG emissions. U.S. covered 
aircraft represented about 25 percent of global aircraft GHG 
emissions, 3.3 percent of global transport GHG emissions, and 0.5 
percent of total global GHG emissions in 2011.

     Table V.2--Comparisons of U.S. Aircraft GHG Emissions to Total Global Greenhouse Gas Emissions in 2010
----------------------------------------------------------------------------------------------------------------
                                                                          Total U.S.  U.S. Covered     Global
                                                              2010 (Tg     Aircraft     Aircraft      Aircraft
                                                              CO2 eq)     Share (%)     Share (%)     Share (%)
----------------------------------------------------------------------------------------------------------------
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           0.5           2
----------------------------------------------------------------------------------------------------------------

    For additional background information and context, we used 2011 
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 
2011 ranked 9th overall, behind only China, United States, India, 
Russian Federation, Japan, Brazil, Germany, and Indonesia, and ahead of 
about 175 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 7 times higher than aircraft GHG emissions from China, which 
globally is the second ranked country for aircraft GHG emissions, and 
about 5 times higher than aircraft GHG emissions from all of Asia. U.S. 
covered aircraft GHG emissions are about 6 times more than aircraft GHG 
emissions from China, and about 4 times more than aircraft GHG 
emissions from all of Asia. If U.S.

[[Page 37789]]

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 and about 150 
other countries in the world.
c. Aircraft GHG Emissions Are Projected To Increase in the Future
    While overall GHG emissions from U.S. covered aircraft increased by 
about 13 percent from 1990 to 2010, the portion attributable to U.S. 
international aviation bunker fuels \181\ increased by about 90 
percent.\182\ During this same time period, global aircraft GHG 
emissions grew by about 40 percent, and the portion attributable to 
global international aviation bunker fuels increased by 80 
percent.183 184 Notwithstanding the substantial growth in 
GHG emissions from U.S. international aviation bunker fuels, U.S. 
covered aircraft emissions have not increased as much as global 
aircraft emissions 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.185 186 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.\187\ 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.\188\
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    \181\ The U.S. international aviation bunker fuels category 
includes emissions from combustion of fuel purchased in and 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 169 to 190 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 169 to 192 Tg CO2eq (about 14 percent), and 
GHG emissions from the portion attributable to U.S. international 
aviation bunker fuels grew from 30 to 62 Tg CO2eq (about 110 
percent).
    \182\ U.S. EPA, 2015: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2013, 564 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport, (last 
accessed May 12, 2015).
    \183\ 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.
    \184\ According to IEA, from 1990 to 2011, global aircraft GHG 
emissions grew by about 50 percent, and global international 
aviation bunker fuels increased by 80 percent. International Energy 
Agency Data Services, Available at http://data.iea.org (last 
accessed May 12, 2015, 2015).
    \185\ FAA, 2014: FAA Aerospace Forecast Fiscal Years 2014-2034, 
129 pp. Available at https://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_forecasts/2014-2034/media/2014_FAA_Aerospace_Forecast.pdf (last accessed May 
12, 2015).
    \186\ These shocks include the September 11 terror attacks, 
significant increases in fuel prices, debt restructuring in Europe 
and U.S., and a global recession.
    \187\ According to the FAA Aerospace Forecast 2014-2034, in 2013 
U.S. air carriers were profitable for the fourth consecutive year.
    \188\ 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, 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).\189\ The FAA 
projects that the fuel consumption from U.S. air carriers and general 
aviation aircraft operating on jet fuel will grow by 49 percent from 
2010 to 2035, corresponding to an average annual increase rate in fuel 
consumption of 1.6 percent.\190\ 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 proposed 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 would increase at a similar 
rate as the fuel burn by 2030, 2035, and 2040.
---------------------------------------------------------------------------

    \189\ ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation 
and Climate Change, 224 pp. Available at http://cfapp.icao.int/Environmental-Report-2013/ (last accessed May 12, 2015).
    \190\ FAA, 2015: FAA Aerospace Forecast Fiscal Years 2015-2035, 
134 pp. Available at https://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_forecasts/2015-2035/media/2015_National_Forecast_Report.pdf (last accessed May 
12, 2015).
---------------------------------------------------------------------------

3. Proposed Contribution Finding for the Single Air Pollutant Comprised 
of the of Six Well-Mixed Greenhouse Gases
    Taking into consideration the data summarized in section V.B.2 
above, the Administrator proposes to find that GHG emissions 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 proposing a contribution finding for 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). We solicit comment on the scope of the proposed 
contribution finding, whether a broader contribution finding (e.g., 
including all engines used in aircraft certified by the FAA) would be 
appropriate, and the extent to which EPA has discretion to establish 
standards pursuant to a contribution finding that do not impose 
requirements on every engine or class of engines within the scope of 
that finding.
    It is the Administrator's judgment that the collective GHG 
emissions from the classes of engines used in U.S. covered aircraft 
clearly contribute, whether the comparison is domestic (10 percent of 
all U.S. transportation GHG emissions, representing 3 percent of total 
U.S. emissions) or global (26 percent of total global aircraft GHG 
emissions representing 3 percent of total global transportation 
emissions and 0.5 percent of all global GHG emissions). The proposed 
scope of GHG emissions from engines used in U.S. covered aircraft under 
this cause or contribute finding would result in the vast majority (90 
percent) of U.S. aircraft GHG emissions being included in this 
determination. The Administrator believes that consideration of the 
global context is important for the cause or contribute test, 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 years and indeed many decades to come. It is the 
Administrator's view that the cause or contribute test used here

[[Page 37790]]

under CAA section 231 can follow the same reasoning that was used in 
the 2009 GHG cause or contribute finding under CAA section 202; that 
is, the Administrator believes 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.
    As was the case in 2009, no single GHG source category dominates on 
the global scale, and many (if not all) individual GHG source 
categories could appear small in comparison to the total, when, in 
fact, they could be very important contributors in terms of both 
absolute emissions or in comparison to other source categories, 
globally or within the United States. If the United States and the rest 
of the world are to combat the risks associated with global climate 
change, contributors must do their part even if their contributions to 
the global problem, measured in terms of percentage, are smaller than 
typically encountered when tackling solely regional or local 
environmental issues.'' \191\ Moreover, as the Supreme Court explained 
in Massachusetts v. EPA, agencies commonly take an incremental approach 
to resolving large issues, stating that, ``[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 these unique, global aspects of the climate change 
problem--including that from a percentage perspective there are no 
dominating sources emitting GHGs and few sources that would even be 
considered to be close to dominating--tend to support consideration of 
contribution to the air pollution at lower percentage levels than EPA 
typically encounters when analyzing contribution towards a more 
localized air pollution problem. Thus, the Administrator, similar to 
the approach taken in the 2009 GHG cause or contribute finding under 
CAA section 202, is placing weight on the fact that engines \192\ used 
in U.S. covered aircraft contribute 3 percent of total U.S. GHG 
emissions for the proposed contribution finding and comprise the single 
largest transportation source in the United States that has not yet 
been regulated for GHG emissions.
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    \191\ 74 FR 66543 (December 15, 2009).
    \192\ For a standard promulgated under CAA section 231 to be 
``applicable to'' emissions of air pollutants from aircraft engines, 
it could take many forms, and include multiple elements in addition 
to numeric permissible engine exhaust rate. For example, under CAA 
section 231, EPA's rules have long-standing regulations addressing 
fuel venting, as well as test procedures. See 40 CFR part 87, 
subparts B, G and H. Given both the absence of a statutory directive 
on what form a CAA section 231 standard must take (in contrast to, 
for example, CAA section 129(a)(4), which requires numerical 
emissions limitations for emissions of certain pollutants from solid 
waste incinerators), and the U.S. Court of Appeals for the DC 
Circuit's 2007 NACAA v. EPA ruling that section 231 confers an 
unusually broad degree of discretion in establishing aircraft engine 
emission standards, it should be possible to reconcile an ICAO 
``aircraft standard'' that effectively limits aircraft engine GHG 
emissions with a CAA section 231 aircraft engine emission standard 
that achieves the same result, even if the GHG standards take a 
different form than the traditional thrust-based NOx aircraft engine 
emission standards recently issued by ICAO and the EPA. See 40 CFR 
part 87, subpart C.
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4. Additional Considerations
    The Administrator is also concerned 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. Given the projected growth in 
aircraft emissions compared to other sectors, it is reasonable for the 
Administrator to consider future emissions projections as adding weight 
to her primary reliance on annual emissions. Recent projections reveal 
that by 2035 GHG emissions from all aircraft and U.S. covered aircraft 
engines are likely to increase by almost 50 percent.\193\ By contrast, 
it is estimated that by 2035 the light duty vehicle sector will see a 
30 percent reduction in GHG emissions from the 2010 baseline, while the 
heavy duty vehicle sector will experience a 33 percent increase in GHG 
emissions from the 2010 baseline (this projected increase does not 
reflect the impact of GHG reductions anticipated from the Phase 2 heavy 
duty GHG standards that have not yet been promulgated). In addition, by 
2035 the rail sector is projected to experience a 6 percent reduction 
in GHG emissions from 2010 baseline.\194\ Because the projected growth 
in aircraft engine GHG emissions from U.S. covered aircraft appears to 
be greater in percentage terms than other transportation sources, this 
future consideration adds weight to the Administrator's proposed 
positive contribution finding.
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    \193\ As discussed in Section V.B.2.c fuel burn growth rates for 
air carriers and general aviation aircraft operating on jet fuel are 
projected to grow by 49 percent from 2010 to 2035 and this provides 
a scaling factor for growth in GHG emissions which would increase at 
a similar rate as the fuel burn by 2030, 2035, and 2040.
    \194\ U.S. Energy Information Administration (EIA), 2015: Annual 
Energy Outlook (AEO) 2015 with projections to 2040, DOE/EIA-0383, 
154 pp. EIA's reference case (used as the baseline in this 
comparison) assumes fuel economy levels for light duty vehicles 
required to meet federal light duty GHG standards for years 2012-
2025, and for heavy duty trucks GHG standards for years 2014-2018, 
plus improvements in vehicles and engines for all subsectors due to 
availability of fuel-saving technologies and fuel price effects. EIA 
counts biofuels as zero tailpipe GHG emissions. Because the 
comparison in this section focuses on tailpipe emissions, we include 
them here, at volumes as forecast in the AEO 2015 reference case. 
Available at http://www.eia.gov/forecasts/aeo/ (last accessed May 
12, 2015).
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VI. Advance Notice of Proposed Rulemaking: Discussion of Ongoing 
International Proceedings To Develop Aircraft CO2 Emissions 
Standard and Request for Comment

    For more than four years, the EPA and FAA have been engaged with 
the ICAO's Committee on Aviation Environmental Protection (ICAO/CAEP) 
to establish an international CO2 emissions standard which 
the EPA could then consider proposing for adoption under its section 
231 authority of the CAA. This section of this document serves as an 
ANPR to discuss the key issues of the ongoing international proceedings 
prior to February 2016, when ICAO/CAEP is expected to finalize an 
international aircraft CO2 standard. An ANPR is intended to 
solicit comments and/or information from the public prior to an agency 
determining whether to propose a rulemaking. As such, an ANPR does not 
propose or impose any regulatory requirements. The EPA may choose to 
develop an ANPR for actions (such as the promulgation of standards 
pursuant to CAA section 231 to implement an international aircraft 
CO2 standard domestically) which are still in the early 
stages of development and for which public input may be particularly 
helpful. This also helps ensure transparency, while assisting the EPA 
in obtaining input from a wide range of stakeholders as we continue 
work within CAEP to establish an international CO2 aircraft 
standard. The EPA is seeking comments from all interested parties, 
including small businesses, on a variety of issues related to setting 
an international CO2 standard for aircraft, including 
whether such standards should apply to in-production aircraft instead 
of new aircraft types only, the appropriate effective dates for the 
potential international CO2 standard, as well as the 
appropriate stringency levels.
    CAEP met an important milestone at its 9th meeting (CAEP/9) in 2013 
in reaching an agreement on the

[[Page 37791]]

appropriate metric to be used in assessing fuel efficiency (or 
CO2 emissions) \195\ of an engine/aircraft combination. They 
also reached agreement on a mature certification requirement \196\ to 
evaluate CO2 emissions for new aircraft types and also 
agreed on certain aspects of the scope of applicability of the 
CO2 emissions standard; however, work on applicability 
options for in-production aircraft continues.
---------------------------------------------------------------------------

    \195\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192, 
Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed May 12, 2015). The ICAO Circular 337 
is found on page 85 of the ICAO Products & Services 2015 catalog and 
is copyright protected; Order No. CIR337. Section 3.2 of this 
Circular states the following: ``An important Phase 1 milestone in 
the development of the CO2 Standard was reached on 11 
July 2012, when the CAEP Steering Group agreed unanimously on a 
CO2 metric system to measure the aeroplane fuel burn 
performance and therefore the CO2 emissions produced.''
    \196\ ICAO defines a certification requirement as a combination 
of metric, procedures, instrumentation and measurement methodology, 
and compliance requirements.
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    At the CAEP Steering Group meeting in November 2013, there was 
agreement on a set of stringency options to be used for the cost-
effectiveness analysis, and at the Steering Group meeting in September 
2014 there was a decision on the associated inputs for costs and 
technology responses to be utilized in the cost-effectiveness analysis 
of these stringency options. This analysis, and work on the 
applicability of the standard to in-production aircraft and the 
certification requirement are scheduled to be completed prior to the 
10th CAEP meeting (CAEP/10) in February 2016. As described in section 
II.A, the EPA and the FAA traditionally work within the ICAO/CAEP 
standard-setting process to establish international emission standards 
and related requirements. 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 of at least equal stringency as ICAO's standards. 
This approach has been affirmed as reasonable by the U.S. Court of 
Appeals for the DC Circuit. Provided the EPA makes a positive 
endangerment finding \197\ under CAA section 231 and ICAO adopts an 
international aircraft CO2 standard that is consistent with 
CAA section 231 and U.S. domestic needs, we would expect to proceed 
with a similar approach promulgating a CO2 emissions 
standard (or GHG standard) of at least equivalent stringency 
domestically.
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    \197\ As shorthand in this action, in many places we will use 
the term ``endangerment finding'' for both endangerment and cause or 
contribute findings.
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A. Purpose of the International Standard

    At the CAEP Steering Group meeting in 2011, the U.S provided a 
paper recommending that CAEP agree that the purpose of the 
international CO2 emissions standard be ``to achieve 
CO2 emissions reductions from the aviation sector beyond 
expected `business as usual'--i.e., a standard that achieves 
CO2 emissions reductions from the aviation sector beyond 
what would be achieved in the absence of a standard. This would be 
analyzed using ICAO criteria of technical feasibility, environmental 
benefit, cost effectiveness, and impacts of interdependencies.'' \198\ 
The Steering Group accepted the U.S. proposal for the purpose of the 
international CO2 standard, and it is expected to be 
included in the standard setting process. The metric system, stringency 
options, costs, technology responses (inputs to be utilized in the 
cost-effectiveness analysis), and applicability ultimately chosen will 
all have an effect on whether the international CO2 
emissions standard adheres to this stated purpose of the standard. The 
U.S. continues to support the adoption of an international 
CO2 emissions standard that meets this stated purpose, and 
the EPA requests comment on this continued support. The EPA requests 
comment on how to achieve the purpose of the standard.

B. Applicability of the International CO2 Emissions Standard
---------------------------------------------------------------------------

    \198\ CAEP (U.S. Working Paper), ``U.S. Position on the 
Development of ICAO'S Aircraft CO2 Standard,'' CAEP-SG/
20112-WP/25, Presented by the United States, U.S. Working Paper for 
CAEP Steering Group meeting, Beijing, China, 12 to 16 September 
2011.
---------------------------------------------------------------------------

    The EPA requests comments on the applicability approaches that CAEP 
is considering. Specifically, we request comment on whether the 
aircraft CO2 standard should apply to in-production 
aircraft, including aircraft with any engineered fuel efficiency 
improvements (e.g., different engines, redesigned wings, or engine 
performance improvement packages, etc.) or whether the aircraft 
CO2 standard should apply only to completely new aircraft 
type designs. CAEP is also considering a third, alternative approach, 
which would redefine a new aircraft type for CO2 purposes to 
include in-production aircraft that have a significant change in 
CO2 emissions. We are also requesting comment on this 
potential alternative option.
    In-production aircraft and new aircraft types are defined as 
follows:
--In-production aircraft: Those aircraft types which have already 
received a Type Certificate, and for which manufacturers either have 
existing undelivered sales orders or would be willing and able to 
accept new sales orders.199 200 201
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    \199\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015).The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
    \200\ As described earlier in section D, in existing U.S. 
aviation emissions regulations, in-production means newly-
manufactured or built after the effective date of the regulations--
and already certified to pre-existing standards (if emission 
standards were established previously).). This is similar to the 
current CAEP definition for in-production aircraft types for 
purposes of the CO2 standard.
    \201\ According to ICAO Cir 337, a Type Certificate is ``[a] 
document issued by a Contracting State to define the design of an 
aircraft type and to certify that this design meets the appropriate 
airworthiness requirements of that State''.
---------------------------------------------------------------------------

--New aircraft types: Aircraft types that have applied for a Type 
Certificate \202\ after the effective date of a standard and that have 
never been manufactured prior to the effective date of a standard.
---------------------------------------------------------------------------

    \202\ A Type Certificate is a design approval process whereby 
the FAA ensures the manufacturer's designs meet the minimum 
requirements for aircraft safety and environmental regulations. This 
is typically issued only once for each aircraft, and modified as 
needed as an aircraft is modified over the course of its production 
life. This Type Certificate (for new aircraft types) would be the 
initial or new Type Certificate for this aircraft.
---------------------------------------------------------------------------

    In addition, for context, out of production aircraft are those 
aircraft types which have already received a Type Certificate, but for 
which manufacturers either have no existing undelivered sales orders or 
would not be willing and able to accept new sales orders. These 
aircraft are aircraft types that are no longer in active 
production.\203\
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    \203\ Out of production aircraft that are still in operational 
use would become subject to the international standard only if the 
standard applied to ``in-use'' aircraft, which it will not since 
CAEP has agreed that the international aircraft CO2 
standard should not apply to out of production aircraft types. Note, 
the EPA's CAA section 231 aircraft engine standards have applied to 
in-use aircraft only in very limited situations, such as the 
prohibition against fuel venting at 40 CFR 87.11 and smoke number 
standards at 40 CFR 87.31. Note, however, that unlike the EPA's 
authority to promulgate emission standards for motor vehicles under 
CAA section 202(a) or for nonroad engines and vehicles under section 
213(a), section 231 of the CAA does not restrict the EPA's authority 
to set standards for only new aircraft.
---------------------------------------------------------------------------

    As described earlier in section II.E, CAEP's Steering Group meeting 
in 2010

[[Page 37792]]

agreed that the scope of applicability for the international aircraft 
CO2 standard will be subsonic jets with an applicability 
weight threshold of maximum takeoff mass (MTOM) greater than 5,700 kg 
(12,566 lb) and turboprop aircraft with a MTOM greater than 8,618 kg 
(19,000 lb). CAEP also agreed that the international CO2 
standard will apply to new aircraft types, but not apply to out of 
production aircraft types, and that applying the standard to in-
production aircraft types should not be ruled out.\204\
---------------------------------------------------------------------------

    \204\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
---------------------------------------------------------------------------

    It is important to further describe the difference between new 
aircraft types and in-production aircraft. There are three categories 
of aircraft under consideration when describing a CO2 
standard: New aircraft types submitted for certification (known as 
clean sheet designs), those with lesser levels of design change, such 
as a new series in an established type and model (considered to be 
significant partial redesigns), or an aircraft with incremental 
improvements.\205\ New aircraft types or new type designs are 
significant investments for manufacturers and are used for new and 
significantly different designs (also characterized as complete 
redesigns). Significant partial redesigns may be characterized as a new 
or later series of an established model that may incorporate newly 
designed wings and give purchasers more choices of engines. Incremental 
improvements are less extensive changes to an aircraft such as 
performance improvement packages that may be added to an aircraft or 
engine at some point during the production cycle.
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    \205\ New aircraft types fall under the initial or new Type 
Certificate, and significant partial redesigns and incremental 
improvements fall under an amended Type Certificate. Significant 
partial redesigns would be a new or later series of an established 
model, and incremental improvements would be a part of the same 
series as the established model.
---------------------------------------------------------------------------

    New aircraft types or new type designs are infrequent. The most 
recent new type designs introduced in service, such as the Airbus A380 
in 2007, the Boeing 787 in 2011, and the original Boeing 777 in 
1995,206 207 208 indicate that it is unlikely a new type 
design will seek certification in the next 10 to 15 years.\209\ (New 
aircraft types (and similarly for significant partial redesigns) 
typically yield large fuel burn reductions--10 percent to 20 percent 
over the prior generation they replace, and as one might expect, these 
significant fuel burn reductions do not happen frequently. Also, 
aircraft development programs are expensive. It is not unusual for new 
type designs to take 8-10 years to develop, from preliminary design to 
entry into service. 210 211) Significant partial redesigns 
do not occur often, but are slightly more frequent than new type 
designs. For example, after the current significant partial redesign 
wave \212\ has passed (which includes the Boeing 747-8, Boeing 737 Max, 
Airbus 320 Neo, and Boeing 777-X), we do not currently have knowledge 
of many additional significant partial redesigns anticipated over the 
next decade (as the previous wave of significant partial redesigns 
included the Boeing 777-200LR in 2004, 777-300ER in 2006, 737NG in 
1998, Airbus 319 in 1996, and Airbus 330-200 in 
1998).213 214 Incremental improvements will likely be 
frequent and occur in the near term. One approach CAEP is considering 
would be to limit the applicability of any international CO2 
standard to only new type designs (or new aircraft types). Under this 
approach the international CO2 standard would not apply to 
significant partial redesigned aircraft and incremental improvements. 
Under another approach CAEP is considering, CAEP would also apply the 
international CO2 standard to in-production aircraft (in 
addition to new aircraft types). Significant partial redesigned 
aircraft and incremental improvements would be characterized as changes 
made to in-production aircraft; thus, these categories of aircraft (or 
these changes) would need to meet the international CO2 
standard under this approach (or they would need to meet the standard 
if it also applied to in-production aircraft).\215\
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    \206\ Boeing, 2011: Boeing Unveils First 787 to Enter Service 
for Japan Airlines, December 14. Available at http://boeing.mediaroom.com/2011-12-14-Boeing-Unveils-First-787-to-Enter-Service-for-Japan-Airlines (last accessed May 12, 2015).
    \207\ The Independent, 2012: BA reveals Airbus A380 superjumbo 
flight plans, by Peter Woodman, December 11. Available at http://www.independent.co.uk/travel/news-and-advice/ba-reveals-airbus-a380-superjumbo-flight-plans-8405961.html (last accessed May 12, 2015).
    \208\ ICF International, CO2 Analysis of 
CO2-Reducing Technologies for Aircraft, Final Report, EPA 
Contract Number EP-C-12-011, March 17, 2015.
    \209\ Ibid.
    \210\ Ibid.
    \211\ Analysts estimate a new single aisle would have cost $10-
12 billion to develop. The A380 and 787 are estimated to each have 
cost around $20 billion to develop; the A350 is estimated to have 
cost $15 billion, excluding engine development. Due to the large 
development cost of a totally new aircraft design, manufacturers are 
opting to re-wing or just re-engine their aircraft (significant 
partial redesigns). Boeing is said to have budgeted $5 billion for 
the re-wing of the 777 and Airbus and Boeing have budgeted $1-2 
billion each for the re-engine of the A320 and the 737, respectively 
(excluding engine development costs). Embraer has publically stated 
they will need to spend $1-2 billion to re-wing the EMB-175 and 
variants. (ICF International, CO2 Analysis of 
CO2-Reducing Technologies for Aircraft, Final Report, EPA 
Contract Number EP-C-12-011, March 17, 2015.)
    \212\ In general, design waves are prompted by the combination 
of market demand for new aircraft performance needs (e.g., more 
seats for longer range) and the age of existing aircraft, and design 
waves are typically enabled by advances in propulsion technology.
    \213\ ICF International, CO2 Analysis of 
CO2-Reducing Technologies for Aircraft, Final Report, EPA 
Contract Number EP-C-12-011, March 17, 2015.
    \214\ Insofar as we are going through a wave of major redesign 
and service entry now, prospects for further step-function 
improvements will be low in the coming 10-15 years. (ICF 
International, CO2 Analysis of CO2-Reducing 
Technologies for Aircraft, Final Report, EPA Contract Number EP-C-
12-011, March 17, 2015.)
    \215\ As described earlier, CAEP has not ruled out applying the 
international CO2 standard to in-production aircraft 
types, which are aircraft types that have already received a Type 
Certificate and are produced after the effective date of the 
standard. In-production aircraft types would include significant 
partial redesigned aircraft and incremental improvements. CAEP is 
currently considering and analyzing in-production applicability.
---------------------------------------------------------------------------

    Another approach for applicability of the international 
CO2 standard that CAEP could adopt (or CAEP is considering) 
would be an approach based on criteria addressing significant changes 
to aircraft designs, which could be considered an applicability 
requirement different than that for new aircraft types only and in-
production aircraft. This alternative approach could redefine a new 
aircraft type for CO2 purposes to include in-production 
aircraft that have a significant change in CO2 emissions, 
thus including in-production aircraft in the applicability of the 
CO2 standard. The alternative approach could even cover 
significant partial redesigned aircraft, depending upon the definition. 
CAEP's current mature certification requirement for the international 
CO2 standard \216\ provides further detail on technology 
changes to aircraft that would affect the aircraft's CO2 
metric value. A changed version of an aircraft could be defined as 
follows: An aircraft which incorporates changes in type design that may 
adversely affect \217\ its CO2 emissions. This possible 
definition could also note the

[[Page 37793]]

following: (1) Where the proposed change in design, configuration, 
power or mass is so extensive that a substantially new investigation of 
compliance with the applicable airworthiness regulations is required, 
the aircraft should be considered to be a new type design rather than a 
changed version, and (2) ``adversely'' refers to an increase in 
CO2 emissions of more than an amount (or percentage) that 
has yet to be determined (this amount or criterion is still being 
considered by CAEP). The EPA requests comment on this change-based 
criteria approach, including how to identify those changes that would 
result in treating in-production aircraft as new types subject to the 
standard.
---------------------------------------------------------------------------

    \216\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337. See Chapter 1.
    \217\ Due to substantial market forces to alleviate any adverse 
effects on aircraft fuel burn or CO2 emissions, adverse 
changes are rare.
---------------------------------------------------------------------------

    If CAEP were to limit the scope of applicability to new aircraft 
types only (and without the significant change criteria approach 
described above), the international CO2 standard would not 
apply to later series aircraft with redesigned wings, aircraft that are 
available with different engines, or aircraft that undergo incremental 
improvements. Following are several examples that illustrate this 
situation. The re-engined Boeing 737 Max is an example of a significant 
partial redesigned aircraft that is expected to enter into service in 
2017.\218\ This aircraft would fall under the original Boeing 737 Type 
Certificate that was issued in 1967 (and entered into service in 
1968)--or more specifically it would fall under an amended Type 
Certificate, and it would not be considered a new aircraft type as 
defined by CAEP. The current in-production 737s (Next Generation 737s 
or commonly abbreviated as 737 NGs) feature newer engines, have 
redesigned wings, and entered service in 1998 under the original 737 
Type Certificate that was issued in 1967, and these also were not 
considered a new type aircraft when they were introduced in 1998.\219\ 
Another example of an aircraft that does not qualify as a new type is 
the Boeing 747-8 aircraft, that entered into service in 2011, and which 
included a new wing, new engines, and a lengthened fuselage but fell 
under an amended Type Certificate for the original Boeing 747 that was 
certified in 1969 (and entered into service in 1969). An example of 
incremental improvements to in-production aircraft, is the Boeing Next 
Generation 737 performance improvement package which was implemented 
between 2011 and 2013 and the Boeing 767-300 winglets that entered into 
service in 2008, both of which improve aircraft fuel efficiency. There 
are many other examples that exist for different manufacturers and 
aircraft around the world as well, but for conciseness, we are limiting 
our discussion to these above examples. These examples illustrate the 
typical certification for significant partial redesigns and incremental 
improvements by various aircraft certificating or certifying 
authorities (or national airworthiness authorities) around the world.
---------------------------------------------------------------------------

    \218\ Boeing, 737 Max Program ``LEAPS'' into Engine Testing, 
Article by Eric Olson, July 11, 2014. Available at http://www.boeing.com/boeing/Features/2014/07/bca_737max_leap_07_11_14.page, (last accessed May 12, 2015).
    \219\ The original 737 entered service in 1968. The 737 Classic 
entered service in 1984, and it had new high bypass engines, an 
updated wing, and other aerodynamic improvements. The 737 NGs 
entered service in 1998, and they featured a new wing and updated 
engines. Several mid-life upgrades were produced for the 737 NGs, 
offering improved range, payload, and efficiency. (ICF 
International, CO2 Analysis of CO2-Reducing Technologies for 
Aircraft, Final Report, EPA Contract Number EP-C-12-011, March 17, 
2015.)
---------------------------------------------------------------------------

    Using CAEP's current definition of new aircraft types (clean sheet 
designs, which are completely new aircraft) we cannot today identify 
the first aircraft to which the new standard would apply. As the 
examples above illustrate, new aircraft types are infrequent,\220\ and 
there are no currently announced new type designs that are expected to 
be introduced after the implementation dates being analyzed by CAEP--
2020 and 2023. Furthermore, based on provisions to which CAEP has 
already agreed,\221\ new aircraft types subject to the CO2 
standard would be aircraft that submit an application for a Type 
Certificate after the implementation dates of 2020 and 2023 (dates for 
the stringency analysis) which would likely result in entry into 
service dates of about 2025 or 2028.\222\ If the international 
CO2 standard is applied only to new aircraft types, then 
CO2 emissions would not be expected to begin to deviate from 
business-as-usual (in comparison to CO2 emissions reductions 
that would be achieved in the absence of a standard) before 2025. 
Therefore, an international standard developed for only new aircraft 
types may not actually apply to any new aircraft for at least a decade. 
Even if a few new type aircraft are introduced in this timeframe, it 
will take even longer for these aircraft to comprise any significant 
portion of the fleet. Therefore, applying an international standard 
which applies only to new aircraft types will likely result in no 
additional CO2 reductions beyond what would have occurred 
absent a CO2 standard, either for the near- and mid-term, 
about 5 to 10 years from 2016, or even in the longer-term of 20 years 
plus.223 224
---------------------------------------------------------------------------

    \220\ ICF International, CO2 Analysis of CO2-Reducing 
Technologies for Aircraft, Final Report, EPA Contract Number EP-C-
12-011, March 17, 2015.
    \221\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May.12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337. Section 1.5 states that that the date to be used in 
determining the applicability of the CO2 standard is the 
date the application for a Type Certificate was submitted to the 
certificating authority having jurisdiction over the manufacturer 
responsible for the aircraft design. Section 1.6 specifies that an 
application shall be effective for the period specified in the 
designation of the airworthiness regulations appropriate to the 
aircraft type. An application for a Type Certificate is valid for 5 
years.
    \222\ These dates assume 5 years from application for the 
aircraft Type Certificate to entry into service, which is how long 
an application is valid for a Type Certificate.
    \223\ Approximate time-scales are considered to be 5 years for 
near-term, 10 years for mid-term, and 20 years or more for long-
term.
    \224\ ICF International, CO2 Analysis of CO2-Reducing 
Technologies for Aircraft, Final Report, EPA Contract Number EP-C-
12-011, March 17, 2015.
---------------------------------------------------------------------------

    The EPA requests comments on the timeframes described above for 
introducing new aircraft types and their subsequent penetration into 
the fleet. Are there any aircraft manufacturer announcements that we 
missed in regard to new aircraft types that will be introduced or apply 
for a Type Certificate after 2020 and 2023 (or new aircraft types that 
will be introduced or apply for a Type Certificate five years after 
these dates)? \225\ If so, what are these new aircraft types? How many 
new types are projected to enter the fleet in this timeframe and what 
portion of the fleet will they represent?
---------------------------------------------------------------------------

    \225\ In November 2014, Boeing indicated that it would replace 
the 737 with a new aircraft type in 2030. Earlier this decade, 
Boeing was assessing an all new clean sheet 737 replacement, but 
eventually they decided to re-engine the 737 (the 737 Max) instead. 
(Flight Club, Paul Thompson, Here's The Skinny On What's Next For 
Boeing, November 16, 2014. Available at http://flightclub.jalopnik.com/heres-the-skinny-on-whats-next-for-boeing-1656206527 (last accessed May 12, 2015), Also, Wichita Business 
Journal, Daniel McCoy, Boeing planning 737 MAX replacement by 2030--
What it could mean for Spirit AeroSystems, November 5, 2014. 
Available at http://www.bizjournals.com/wichita/blog/2014/11/boeing-planning-737-max-replacement-by-2030-what.html) (last accessed May 
12, 2015). We would consider this as a Boeing projection or 
sketching out of plans for a new aircraft type, but it is not a 
commitment from Boeing.
---------------------------------------------------------------------------

    The alternative approach being considered by CAEP and described 
earlier (addressing changes in design of in-production aircraft) may 
offer an opportunity to cover more aircraft in an earlier timeframe 
(including significant partial redesigns), but it is unclear what 
effect this approach would have on

[[Page 37794]]

additional CO2 emissions reductions compared to a standard 
for only new aircraft types. The EPA requests comments on the timeframe 
for CO2 emissions reductions and the likely share of annual 
aircraft production (or share of in-production aircraft built annually) 
that would be affected under this alternative approach.
    If ICAO applies the aircraft CO2 emission standard to 
in-production aircraft, and subsequently (provided the EPA makes a 
positive endangerment finding under CAA section 231(a)) the EPA 
establishes domestic aircraft engine standards that are equivalent to 
the ICAO international aircraft CO2 standard, this means 
that all aircraft built (in-production) after the effective date would 
need to certify and comply with the standard to remain in production. 
This includes (as described earlier) in-production aircraft with 
incremental improvements (though we reiterate this would not include 
in-use aircraft). As an example of in-production aircraft, the 
Gulfstream G650, which is currently in production and expected to 
remain so after 2020, would need to certify and comply with the new 
CO2 standard. In the next section we discuss in more detail 
how applicability to in-production aircraft could work.

C. CAEP Discussion on In-Production Aircraft Applicability

    At the request of the CAEP Steering Group meeting in November 2013, 
CAEP began work on defining potential options to implement 
applicability requirements for in-production aircraft. Subsequently, 
based on the options provided to the 2014 Steering Group meeting, CAEP 
decided that it should continue to investigate potential in-production 
aircraft applicability options, and that these should be presented at 
the July 2015 Steering Group meeting, so that a decision can be taken 
at the 10th meeting of CAEP (CAEP/10) in February 2016 regarding 
whether the international CO2 standard will apply to in-
production aircraft. There are a wide range of options under 
consideration, including both mandatory and voluntary options for 
reporting and certification processes for in-production aircraft 
applicability, but the 2014 Steering Group meeting requested that CAEP 
focus on defining the mandatory options (in contrast to options such as 
voluntary reporting and certification).
1. Applicability to In-Production Aircraft and Date of Implementation
    At the 2014 Steering Group meeting, CAEP also agreed that 2023 
represented the earliest possible date for an in-production aircraft 
standard to allow time to promulgate domestic regulations and process 
manufacturer certification applications. CAEP did not rule out later 
dates though and could consider implementation dates for an in-
production aircraft CO2 standard later than 2023 (CAEP could 
consider applicability dates for in-production aircraft that are five 
years following the new aircraft type applicability date, i.e. dates 
ranging from 2023 to 2028).
    The EPA seeks comments on both a 2023 implementation date and on 
possible later implementation dates for an in-production domestic 
CO2 (or GHG) aircraft engine emissions standard that would 
be adopted under CAA section 231,\226\ the impact the date of 
implementation might have on per-aircraft GHG or CO2 
emissions rates \227\ and the ability of a domestic GHG or 
CO2 standard to achieve aircraft emission reductions beyond 
what would occur in the absence of such a standard.
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    \226\ Traditionally, international emission standards have first 
been adopted by ICAO, and subsequently the EPA had initiated 
rulemakings under CAA section 231 to establish domestic standards 
equivalent to ICAO's standards where appropriate. Provided ICAO 
adopts an international aircraft CO2 standard that is 
consistent with CAA section 231 and it is appropriate for domestic 
needs in the United States, we expect to proceed along a similar 
approach for the future CAA section 231 aircraft engine 
CO2 standard (or aircraft engine GHG standard), provided 
the EPA issues final positive endangerment and cause or contribute 
findings under CAA section 231.
    \227\ For a standard promulgated under CAA section 231 to be 
``applicable to'' emissions of air pollutants from aircraft engines, 
it could take many forms, and include multiple elements in addition 
to numeric permissible engine exhaust rate. For example, under CAA 
section 231, EPA's rules have long-standing regulations addressing 
fuel venting, as well as test procedures. See 40 CFR part 87, 
subparts B, G and H. Given both the absence of a statutory directive 
on what form a CAA section 231 standard must take (in contrast to, 
for example, CAA section 129(a)(4), which requires numerical 
emissions limitations for emissions of certain pollutants from solid 
waste incinerators), and the U.S. Court of Appeals for the D.C. 
Circuit's 2007 NACAA v. EPA ruling that section 231 confers an 
unusually broad degree of discretion in establishing aircraft engine 
emission standards, it should be possible to reconcile an ICAO 
``aircraft standard'' that effectively limits aircraft engine GHG 
emissions with a CAA section 231 aircraft engine emission standard 
that achieves the same result, even if the GHG standards take a 
different form than the traditional thrust-based NOX 
aircraft engine emission standards recently issued by ICAO and the 
EPA. See 40 CFR part 87, subpart C.
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    As described in section VI.F.2, the technologies considered for the 
CAEP analyses are those technologies that will be widely used on in-
production aircraft by 2016 or shortly thereafter.\228\ The EPA 
requests comments regarding whether applying an international 
CO2 standard to in-production aircraft is consistent with 
the purpose of the standard as accepted by the CAEP Steering Group 
meeting in 2011: ``to achieve CO2 emission reductions from 
the aviation sector beyond expected `business as usual' . . . analyzed 
using ICAO criteria of technical feasibility, environmental benefit, 
cost effectiveness, and impacts of interdependencies.'' \229\ The 
International Coalition for Sustainable Aviation (ICSA),\230\ which is 
a CAEP Observer organization, submitted papers to CAEP that analyzed 
this issue. Also, a member of ICSA \231\ has developed similar analyses 
which indicate that applying the international standard only to new 
aircraft types would likely result in no additional CO2 
reductions beyond what would have occurred absent a CO2 
standard, either for the near- and mid-term, about 5 to 10 years from 
2016, or even in the longer-term of 20 years plus. This occurs, the 
ICCT states, because the development cycles for new aircraft are very 
lengthy and it is not unusual for new aircraft to take 8 to 10 years to 
develop from preliminary design to entry into service and once in 
service it takes significant time for new aircraft types to penetrate 
the fleet.232 233

[[Page 37795]]

Another study funded by the EPA corroborates this analysis.\234\ The 
EPA requests comments on whether applying the international 
CO2 aircraft standard only to new aircraft types would be 
consistent with the accepted purpose of the international standard (the 
purpose of the standard that has been accepted by the CAEP Steering 
Group). Lastly, the EPA requests comment on the appropriateness of a 
possible EPA regulation following either of these approaches 
(applicability to only new aircraft types or applicability to both new 
types and in-production aircraft) which are under consideration at 
CAEP.
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    \228\ CAEP determined in 2012 that all technology responses 
would have to be based on technology that would be in common use by 
the time the standard was to be decided upon in 2016 or shortly 
thereafter. This generation of technology was defined within CAEP as 
a Technology Readiness Level (TRL) 8--an actual system completed and 
``flight qualified'' through test and demonstration--by 2016 or 
shortly thereafter.
    \229\ CAEP (U.S. Working Paper), ``U.S. Position on the 
Development of ICAO'S Aircraft CO2 Standard,'' CAEP-SG/
20112-WP/25, Presented by the United States, U.S. Working Paper for 
CAEP Steering Group meeting, Beijing, China, 12 to 16 September 
2011. Available at http://www.epa.gov/otaq/aviation.htm. (last 
accessed May 12, 2015).
     International Coalition for Sustainable Aviation (ICSA), 
``ICAO'S CO2 Standard as Part of a Basket of Measures to 
Meet Emission Reduction Goals'', ICAO Assembly--38th Session, 
Executive Committee, Agenda Item 17--Environmental Protection, A38-
WP/297, EX/99, September 19, 2013.
    \230\ The International Coalition for Sustainable Aviation 
(ICSA) is a structured network of environmental non-governmental 
organizations (NGOs) who share a common concern with civil 
aviation's contribution to air quality issues, climate change and 
noise, and who are committed to developing and providing technical 
expertise, common policy positions and strategies with a view to 
reducing emissions and noise from aviation. See http://www.icsa-aviation.org/ (last accessed May 12, 2015).
    \231\ The International Council on Clean Transportation (ICCT) 
is a member of ICSA, and ICCT is an independent nonprofit 
organization founded to provide research and technical and 
scientific analysis to environmental regulators. See http://www.theicct.org/ (last accessed May 12, 2015).
    \232\ ICCT, Efficiency Trends for New Commercial Jet Aircraft 
1960 to 2008, November 2009. Available at http://www.theicct.org/sites/default/files/publications/ICCT_Aircraft_Efficiency_final.pdf 
(last accessed May 12, 2015).
    \233\ ICCT, ``Could ICAO's CO2 Standard Not Actually 
Cover Any Aircraft? Yes, If Nobody's Watching''. Blog, December 9, 
2014. Available at http://www.theicct.org/blogs/staff/could-icaos-co2-standard-not-cover-any-aircraft (last accessed May 12, 2015).
    \234\ ICF International, CO2 Analysis of CO2-Reducing 
Technologies for Aircraft, Final Report, EPA Contract Number EP-C-
12-011, March 17, 2015.
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    Also, there have been concerns raised in CAEP about applying the 
international CO2 standard to in-production aircraft. These 
concerns include (a) the added resource burden on certificating 
authorities \235\ to process manufacturers' certification applications, 
which will be more numerous compared to new aircraft types; and (b) the 
potential added costs to manufacturers to certify in-production 
aircraft. The EPA requests comment on these two concerns, including 
providing supporting documentation on the extent of these concerns and 
any other issues the commenters may identify with applying the 
international CO2 standard to in-production aircraft.
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    \235\ Pursuant to CAA section 232, the FAA, after consultation 
with the EPA, shall prescribe regulations to insure compliance with 
all standards prescribed by the EPA under CAA section 231. Section 
232 then directs the FAA to include provisions making the EPA's 
standards applicable in the issuance, amendment, modification, 
suspension, or revocation of any certificate authorized by the FAA 
under part A of subtitle VII of Title 49. Under this unique 
statutory structure, the EPA promulgates the substantive emission 
standards, and the FAA enforces the EPA's standards and insures all 
necessary inspections are accomplished.
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2. Reporting Requirement for New In-Production Aircraft
    CAEP is working to define mandatory in-production aircraft options, 
and one possible option is a reporting requirement 
236 237 238  for in-production aircraft CO2 
emissions rates (measured according to the aircraft test procedure that 
was agreed upon at CAEP/9) as an alternative to establishing an 
aircraft CO2 standard for in-production aircraft. Although a 
reporting requirement provides policy relevant information, it does not 
necessarily translate into specific emissions reductions. The EPA 
recognizes that only a mandatory standard for in-production aircraft 
would ensure that the aircraft CO2 standard reduces per-
aircraft CO2 emissions rates. However, a reporting 
requirement could be an important component of an in-production 
aircraft CO2 standard, especially if it is implemented 
shortly after an in-production aircraft standard is adopted. It would 
ensure that CO2 emissions rates data are gathered quickly 
prior to an effective date for the final standard (tracking 
CO2 emissions rates is beneficial for the reasons discussed 
later in this section and for potentially assisting with the assessment 
of a future CO2 standard). The EPA requests comment on an 
aircraft manufacturer reporting requirement that is implemented soon 
after the adoption of an in-production international aircraft 
CO2 standard, as a component of the in-production aircraft 
CO2 standard.
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    \236\ Currently, CAEP is developing a publicly available 
database for aircraft CO2 emissions (CAEP is now 
considering format, parameters, etc. for the database), but 
submissions to this database by aircraft manufacturers would be 
voluntary. There will not be a CAEP mandatory reporting requirement 
associated with this potential CO2 database. In addition, 
if the international aircraft CO2 standard applies to 
only new aircraft types, it could be many years before any data 
exists in this database.
    \237\ For many years, ICAO has maintained an Aircraft Engine 
Emissions Databank for landing and takeoff certificated emissions 
values of NOX, hydrocarbon, carbon monoxide, and smoke 
number (ICAO and the EPA also have aircraft engine emission 
standards for these pollutants). It contains certified emissions 
data voluntarily reported from each aircraft engine manufacturer. 
This databank is available at https://easa.europa.eu/document-library/icao-aircraft-engine-emissions-databank (last accessed May 
12, 2015).
    \238\ In 2012, the EPA promulgated annual reporting requirements 
for aircraft engine emissions of NOX, hydrocarbon, carbon 
monoxide, and smoke number and related parameters. One of the 
reasons that the EPA issued these reporting requirements was due to 
the varying amount of voluntary data reported by aircraft engine 
manufacturers. (U.S. EPA, ``Control of Air Pollution from Aircraft 
and Aircraft Engines; Emission Standards and Test Procedures.'' 
Final Rule, 77 FR 36342 (June 18, 2012)).
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    In 2009 the EPA promulgated a final GHG reporting rule that applies 
to many sectors in the United States, including manufacturers of heavy-
duty and offroad vehicles and engines, and manufacturers of aircraft 
engines.239 240 The EPA's experience with reporting programs 
indicates that the EPA and the public would be able to track 
CO2 emissions rates trends (i.e., trends of aircraft cruise 
fuel burn rates) from aircraft over time. Requiring the reporting of 
aircraft CO2 emissions rates trends from aircraft over time 
is appropriate and feasible. Requiring aircraft manufacturers to report 
aircraft CO2 emissions rates shortly after an in-production 
international aircraft standard is adopted would enable and expedite 
the tracking and understanding of these emission trends. In addition, 
reporting programs typically raise awareness of emissions and can 
improve the understanding of the factors that influence emission rates 
as well as the actions that can be taken to reduce emissions. When 
similar methods for monitoring, measurement, and reporting are applied 
across an industry, it can lead to more consistent, accurate, and 
timely data to inform decision-making for individual manufacturers and 
the EPA (including a comparison of the CO2 emissions rates 
from aircraft of various manufacturers). Thus, a reporting requirement 
could potentially contribute to efforts to identify and implement 
future aircraft CO2 emission reduction opportunities.
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    \239\ EPA's 2009 rule on Mandatory Reporting of Greenhouse Gases 
included engine manufacturers for the following mobile source 
sectors: Highway heavy-duty (engine and vehicle), non-road, 
aircraft, locomotive, marine, snowmobiles, and motorcycles. 
Manufacturers of aircraft jet engines of rated output (or thrust) 
greater than 26.7 kilonewtons are required under this program to 
report annually to the EPA CO2 and NOX 
emissions from aircraft engines during the landing and takeoff 
cycle. Manufacturers of these engines were already measuring and 
recording CO2 emissions as part of existing criteria air 
pollutant emission requirements for the landing and takeoff cycle, 
but prior to this 2009 rule, these data were not reported to the 
EPA. Manufacturers voluntarily reported the data to ICAO, but there 
was no assurance that the EPA would receive this information, and 
thus, the 2009 rule required reporting of the aircraft engine 
CO2 and NOX emissions during the landing and 
takeoff cycle to the EPA.
    \240\ An aircraft manufacturer reporting requirement for in-
production aircraft CO2 emission rates would require the 
reporting of aircraft CO2 emissions during the cruise 
phase of operation to the EPA. The majority of aircraft 
CO2 emissions occurs in the cruise phase of operation, 
and thus, reporting CO2 emission rates from this phase 
will improve our ability to track full-flight aircraft 
CO2 emission rates over time (in addition to reporting 
the aircraft engine CO2 emissions during the landing and 
takeoff cycle). Also, the aircraft test procedure that was agreed 
upon at CAEP/9 now enables us to measure aircraft CO2 
emissions during cruise.
---------------------------------------------------------------------------

    Independent of action that CAEP may or may not take in February 
2016, the EPA could under its CAA section 114(a) authority pursue a 
reporting requirement for aircraft cruise GHG or CO2 
emissions rates--to ensure we have GHG or CO2 emissions 
rates data on all in-production aircraft (and any new aircraft types 
that enter service).241 The EPA could use the same metric 
agreed to at CAEP/9 (and in ICAO circular 337). This will be described 
in detail in

[[Page 37796]]

VI.D.1 below. In general, the EPA asks for comment on a mandatory 
reporting requirement for in-production aircraft GHG or CO2 
emissions rates--either as part of the CAEP international standard or 
as an independent domestic requirement to be adopted by the EPA. If the 
EPA were to pursue this requirement independently from CAEP, what lead 
time would be appropriate for manufacturers to report the GHG or 
CO2 emissions rates from all of their in-production aircraft 
242 (after we promulgate such a requirement)? Additionally, 
if we were to pursue such an independent reporting requirement, should 
we require the annual reporting of the GHG or CO2 emissions 
rates from in-production aircraft (and any new type aircraft) 
243 to enable us to track any updates? We are not at this 
time proposing to promulgate such a requirement in advance of ICAO's 
decision. Due to the possibility of ICAO's adoption of a reporting 
requirement, we believe it is reasonable to await the outcome of that 
decision in order to determine whether to strictly follow ICAO's 
possible reporting requirement or make changes to it in the form of an 
additional U.S. domestic requirement, as appropriate.
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    \241\ This GHG or CO2 emissions rate data will help 
to track trends, raise awareness, better understand the technology 
in the fleet, etc.
    \242\ In this case, manufacturers would need to report the GHG 
or CO2 emission rates for in-production aircraft 
(aircraft types which have already received a Type Certificate, and 
for which manufacturers either have existing undelivered sales order 
or would be willing and able to accept new sales orders) that are 
built after a certain date, which has yet to be determined but would 
likely be a date that occurs shortly after we promulgate the 
requirement.
    \243\ By applying a reporting requirement to in-production 
aircraft after a certain implementation date, this reporting 
requirement also includes new aircraft types that are produced after 
this implementation date.
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D. Metric System, Applicability, and Certification Requirement

    The CO2 metric system and mature certification procedure 
were agreed upon by CAEP in 2013.244 This section describes 
the metric system that was developed, the scope of aircraft to be 
covered by the international CO2 standard, the certification 
test procedures that would be used to demonstrate compliance with the 
international CO2 standard, and CAEP's decision to focus on 
the entire aircraft for the international CO2 standard.
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    \244\ As described earlier, the certification requirement is the 
combination of metric, procedures, instrumentation and measurement 
methodology, and compliance requirements. We are using the terms 
metric system and certification test procedures to describe these 
elements of the certification requirement.
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1. CO2 Metric System
    The metric system was developed to cover a wide range of aircraft 
types, designs, technology, and uses. To do this, the metric system was 
designed to differentiate between generations of aircraft and to 
equitably capture improvements in aerospace technology (structural, 
propulsion, and aerodynamic) that contribute to a reduction in the 
airplane CO2 emissions. In addition, the metric system 
accommodates a wide range of technologies and designs which 
manufacturers may choose to implement to reduce CO2 
emissions from their aircraft.
    The metric system agreed to at CAEP uses multiple Specific Air 
Range (SAR) test points to represent cruise fuel burn. SAR is a 
traditional measure of aircraft cruise performance which measures the 
distance an aircraft can travel for a unit of fuel. This is similar to 
the instantaneous ``miles per gallon'' readings in many cars today. 
However, here the inverse of SAR is used (1/SAR); therefore a lower 
metric value represents a better fuel efficiency. The SAR data are 
gathered at three gross weight points. The three equally weighted 
points are used to represent a range of day to day aircraft 
operations.\245\ The functional form of the metric system is provided 
below.
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    \245\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
[GRAPHIC] [TIFF OMITTED] TP01JY15.000

(1/SAR)avg is calculated at 3 gross weight fractions of 
Maximum Takeoff Mass (MTOM):
High gross mass: 92% MTOM
Mid gross mass: Average of high gross mass and low gross mass
Low gross mass: (0.45 * MTOM) + (0.63 * (MTOM-0.924))

    The Reference Geometric Factor (RGF) is a measure of the fuselage 
size on a given aircraft. In analyzing various metric system options it 
was found that in some instances, namely stretch aircraft, changes in 
aircraft size, and thus capability, were not reflected in changes to 
the aircraft's gross weight (MTOM). To account for these occurrences, 
and the variety of methods that manufacturers may use to make such a 
change, an adjustment factor was added (the RGF with a 0.24 exponent 
used in the metric system).
2. Applicability
    CAEP has decided the scope of applicability for a future 
international CO2 standard should be subsonic jet and 
propeller-driven aircraft meeting the following criteria:
    All subsonic jet aircraft over 12,566 lbs (5,700 kg) MTOM.
    All subsonic propeller driven (e.g., turboprop) aircraft over 
19,000 lbs (8618 kg) MTOM, except amphibious airplanes and those 
designed and used for fire-fighting operations.
    No military aircraft will be subject to this international 
standard.
3. Certification Requirement
    CAEP has developed a mature certification requirement \246\ that 
would allow for the determination of an aircraft CO2 metric 
value for any aircraft meeting the applicability criteria set forth 
above. This certification requirement incudes the metric system and 
test procedure. The test procedure was based upon industry's current 
best practices for establishing the cruise performance of their 
aircraft, and input from certification authorities. These procedures 
include specifications for aircraft conformity, weighing, fuel 
specifications, test condition stability criteria, required confidence 
intervals, measurement instrumentation required, and corrections to 
reference conditions.
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    \246\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR337.
---------------------------------------------------------------------------

    These CO2 test procedures are based upon manufacturer's 
existing practices when certifying new aircraft. This means that there 
is a very heavy reliance on dedicated flight testing of the aircraft. 
This potentially poses challenges for the certification of in-
production aircraft. Manufacturers have stated that there could be 
logistical challenges associated with the certification of aircraft for 
CO2 that have previously been type certificated (e.g. 
procuring and instrumenting an aircraft for flight testing). To address 
this, the EPA is currently working within CAEP to encourage the 
development of a modified or separate equivalent certification test 
procedure that would reduce this burden on manufacturers

[[Page 37797]]

and allow for quicker/simpler certification of in-production types.
4. Regulating the Entire Aircraft Instead of the Engine
    The CO2 metric system intends to equitably reward 
improvements in aircraft technologies that reduce emissions, including 
advances in structures (aircraft weight), propulsion (engine specific 
fuel consumption), and aerodynamics. These three factors are key to the 
overall aircraft CO2 emissions. In addition, CAEP has 
indicated (and EPA agrees) that it is best to consider the aircraft as 
a whole instead of only the aircraft engine technology in addressing 
factors that influence CO2 emissions, because of the effects 
and interaction these key factors have on the aircraft CO2 
emissions from engines.\247\ The three factors--and technology 
categories that improve these factors--are described as follows: \248\
    Structures: Reducing basic aircraft weight to increase the 
commercial payload or extend range for the same amount of thrust and 
fuel burn;
    Propulsion (thermodynamic and propulsion efficiency): Advancing the 
overall specific performance of the engine, to reduce the fuel burn per 
unit of delivered thrust; and
    Aerodynamics: Advancing the aircraft aerodynamics, to reduce drag 
and its associate impacts on thrust.
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    \247\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard. Available at http://www.icao.int/publications/catalogue/cat_2015_en.pdf (last accessed 
May 12, 2015). The ICAO Circular 337 is found on page 85 of the ICAO 
Products & Services 2015 catalog and is copyright protected; Order 
No. CIR33.
    \248\ ICAO, Environmental Report 2010--Aviation and Climate 
Change, 2010, which is located at http://www.icao.int/environmental-protection/Pages/EnvReport10.aspx (last accessed May 12, 2015).
---------------------------------------------------------------------------

    Specific examples of technologies that affect these three factors 
help to further illustrate that it is best to consider the aircraft as 
a whole in addressing CO2 emissions. For structural 
improvements, aircraft manufacturers have shown significant weight 
reduction results over time due to the progressive introduction of new 
technologies such as: Advanced alloys and composite materials, improved 
and new manufacturing processes and techniques (including integration 
and global evaluation simulation), and new systems (e.g. fly-by-
wire).249 250
---------------------------------------------------------------------------

    \249\ Ibid.
    \250\ Fly-by-wire refers to a system which transmits signals 
from the cockpit to the aircraft's control surfaces electronically 
rather than mechanically. AirlineRatings.com, Available at http://www.airlineratings.com/did-you-know.php?id=18 (last accessed on May 
12, 2015, 2015).
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    For propulsion improvements, technologies include enhanced 
compressors (e.g., intercooled compressors) and reduced hub-tip ratio 
fans.\251\ As another example, manufacturers seek higher operating 
pressure ratios (OPR) to improve combustion and engine cycle 
refinements.
---------------------------------------------------------------------------

    \251\ ICF International, CO2 Analysis of 
CO2-Reducing Technologies for Aircraft, Final Report, EPA 
Contract Number EP-C-12-011, March 17, 2015.
---------------------------------------------------------------------------

    For aerodynamics, friction and lift-dependent drag are the biggest 
contributors to aerodynamic drag. Advances in aerodynamics enable 
significant lift-dependent drag reduction by maximizing effective wing 
span extension. For example, wing-tip devices can give an increase in 
the effective aerodynamic span of wings, particularly where wing 
lengths are limited by airport gate sizes. Manufacturers are also 
looking at ways of decreasing the drag caused by skin friction. An 
example of a technology to improve aircraft local skin friction is to 
utilize riblets (which are micro-grooves on the surface) to maintain 
laminar flow via Natural Laminar Flow and Hybrid Laminar Flow Control 
(HLFC) to reduce turbulent skin friction.\252\ The first production 
example of a HLFC system went into service on the new Boeing 787-9 in 
2014.
---------------------------------------------------------------------------

    \252\ ICAO, Environmental Report 2010--Aviation and Climate 
Change, 2010, which is located at http://www.icao.int/environmental-protection/Pages/EnvReport10.aspx.(last accessed May 12, 2015).
---------------------------------------------------------------------------

E. Stringency Options
    At the Steering Group meeting in November 2013, CAEP agreed to 
analyze a range of CO2 stringency options that cover the 
full range of aircraft in-production and in-development around the 
world (within the applicable weight thresholds and categories), and 
this includes the wide range of technology that is currently in the 
aircraft fleet.\253\ Generally, the stringency options that are being 
evaluated fall into three categories as follows: (1) CO2 
stringency levels that could impact \254\ 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 standard becomes effective. We are requesting comment on 
the level(s) at which the CO2 stringency options should be 
set, what factors should be considered in establishing the stringency 
of the CO2 standard, and on their potential relationship to 
any future CAA section 231 standard.
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    \253\ The ICAO standard has the following applicability weight 
thresholds: Maximum takeoff mass greater than 5,700 kilograms for 
subsonic jet aircraft and maximum takeoff mass greater than 8,618 
kilograms for turboprops.
    \254\ The aircraft shown in these charts 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.
---------------------------------------------------------------------------

    The figures below are intended to show the range of stringency 
levels under consideration at CAEP and CO2 metric value 
levels of today's in-production and in-development \255\ aircraft. The 
data shown were generated by the EPA using a commercially available 
aircraft modeling tool called PIANO.\256\ This model contains non-
manufacturer provided estimates of the performance of various aircraft. 
In contrast, CAEP is using manufacturer-provided estimates of the 
aircraft metric value performance.
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    \255\ 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.
    \256\ 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 May 12, 2015). This is a commercially available aircraft 
design and performance software suite used across the industry and 
academia.
---------------------------------------------------------------------------

    The stringency options under consideration at CAEP are functions of 
the aircraft CO2 Metric Value and have a correlating 
parameter of MTOM. They are upwards sloping and have a ``kink'' at 
60,000 kilograms MTOM. The ``kink'' was included in the stringency 
options as a technical approach to reflect the different behaviors 
observed between the larger and smaller aircraft.
    The official stringency options under consideration at CAEP have 
not been cleared for release outside of the participating members since 
deliberations on the standard are still ongoing (proceedings are 
expected to be completed at CAEP/10 in February 2016). To show the 
relative efficiency of the aircraft, Figure 1 and Figure 2 below show 
the aircraft metric values \257\ versus MTOM. In place of the official 
stringency options under consideration, lines of constant technology 
are used to notionally show how the stringency options were set across 
the fleet. These lines reflect the three ranges of options discussed 
above. Lower metric values, for a given MTOM, represent an increased 
fuel efficiency. Figure 1

[[Page 37798]]

shows the makeup of the current production fleet and the in-development 
aircraft. This is what CAEP is using as the starting point for modeling 
the effect of the CO2 standard. Figure 2 shows what the EPA 
expects the market to look like in 2023, considering the publicly 
announced plans by industry to replace existing aircraft with new 
products.
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    \257\ Metric values were generated using PIANO.
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[[Page 37799]]

[GRAPHIC] [TIFF OMITTED] TP01JY15.002

    A standard set near the upper-most line of constant technology in 
Figures 1 and 2 would affect a very modest number of aircraft, namely 
the oldest, least efficient types. Many of the aircraft that would be 
affected by such a stringency level are being produced in very limited 
numbers and may not be eligible to operate in U.S. air space (e.g., 
Russian and Ukraine aircraft).
    Aircraft around the middle two lines of constant technology in 
Figures 1 and 2 reflect the performance of many aircraft that are 
currently in production and compose much of the current operational 
fleet. The current generation of single aisle aircraft from Boeing and 
Airbus are in this middle range.
    Aircraft near the lowest line of constant technology in Figures 1 
and 2 reflect the most advanced aircraft currently for sale on the 
market. These are aircraft that have either just entered production or 
are still in-development

[[Page 37800]]

but will be in-production by the effective date of a potential in-
production the standard. The replacement single aisle aircraft and new 
twin aisle aircraft from Boeing and Airbus are modeled to be clustered 
around the lowest line.
    While Figures 1 and 2 show the ranges of stringency under 
consideration and how aircraft fall within those ranges, because of the 
scale, it is hard to see the range of technology present in the fleet. 
Therefore Figure 3 and 4 expand the view and show percent differences 
between the four constant technology lines represented in Figures 1 and 
2. This allows for a clearer view of best and worst performing 
aircraft; Figure 3 provides the perspective from the current in-
production and in-development fleet, and Figure 4 projects out to the 
2023 fleet. In addition, these figures allow one to compare the 
technology level and efficiency of aircraft with differing MTOMs.

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[[Page 37802]]

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    The EPA requests comment on a range of stringency options within 
the constant technology lines identified in Figure 1 and Figure 2, on 
their potential impact, and on their potential relationship to any 
future CAA section 231 standard.
    CAEP is considering the possibility of adopting two separate 
CO2 stringency levels, one for new type aircraft and one for 
in-production aircraft. This would allow stringencies to be set for 
both new types and in-production aircraft at a level closer to what 
could be achieved by each aircraft type. Issues surrounding the 
potential for in-production standards are discussed in section VI.C.1.

[[Page 37803]]

    There is ongoing discussion on what appropriate levels of 
stringency may be for new type and in-production aircraft. Any final 
decisions will have to wait until the full analysis has been conducted 
at CAEP. As explained in sections VI.B and VI.C.1, new types are 
infrequently developed and typically represent a step change in 
technology. It may be possible to set a level of stringency that is 
reasonable for in-production aircraft to meet, but at the same time 
provide an incentive for new type aircraft to improve. However, this is 
challenging to develop because of the significant efficiency 
improvements typically seen between in-production and new type 
aircraft. The EPA requests comment on the potential for developing a 
standard with two stringency levels at CAEP.
    The development of a new aircraft type standard must take into 
consideration the standard's potential effect on any future type 
designs. Even the most stringent option under consideration at CAEP is 
still based on technology available today. Any new type aircraft that 
may be developed and certified 10 years or more from now would be 
expected to use more advanced fuel efficient technology that is not yet 
developed or tested.
    The implications for an in-production standard are more significant 
in the near term for manufacturers. Aircraft currently in-production, 
and not meeting the level of an in-production standard, would need to 
be modified to meet the standard to remain in production; this would 
take time and resources from the manufacturers. The full implications 
of this have not yet been resolved in CAEP. However, we expect that the 
effect on aircraft CO2 emissions would be minimal for less 
stringent options. The aircraft with the highest CO2 metric 
values generally rely on older technology and were designed in the 
1980's to early 1990's. Many of these aircraft are also expected to be 
replaced with updated versions in the near future, before a 
CO2 standard would be implemented and go into effect. The 
EPA requests comment on the levels at which in-production and new type 
standards might be set and on what factors should be considered in 
establishing the stringency.

F. Costs, Technology Responses for Stringency Options, and Cost-
Effectiveness Analysis

    The EPA has been involved in CAEP's effort to analyze the 
CO2 stringency options and the potential costs and 
environmental impacts that would result from both new type only 
CO2 standards and in-production international CO2 
standards. CAEP is still determining the best way to conduct portions 
of this analysis. The inputs that have been developed by the CAEP 
include non-recurring costs data and technology responses for the 
various stringency options under consideration. This section describes 
the development of these inputs. The EPA requests comments on how the 
modeling should be conducted to differentiate in-production and new 
type scenarios.
1. Non-Recurring Costs (engineering development costs)
    CAEP developed a single cost estimate that could be used for all 
aircraft as a function of MTOM and percent metric value improvement 
required. Based on past practice, industry provided estimates for 
developing clean sheet designs and significant partial redesigns, only 
including high level information that has been made available to the 
public. This was considered to be a top down estimate because it 
included all aircraft development costs (airworthiness certification, 
noise, etc.) not just those for CO2 improvements.
    Since the initial dataset provided by industry only included major 
changes (or major improvements), the EPA saw the need to supplement 
this dataset with an estimate of CO2-only changes (or 
CO2-only improvements), which was considered to be a bottom 
up estimate. These changes would be much smaller, on the order of a few 
percent, and could be applied to in-production aircraft at a cost much 
lower than projected by industry. The EPA contracted with ICF 
International to develop an estimate of the cost to modify in 
production aircraft to comply with a CO2 standard. ICF 
International conducted a detailed literature search, conducted a 
number of interviews with industry leaders, and did its own modeling to 
estimate the cost of making modifications to in production 
aircraft.\258\ The results from this peer-reviewed study (small 
changes) were then combined with inputs from the industry and the other 
CAEP participants (large changes) to develop the CO2 
technology response and cost estimation. For the cost estimation, the 
CAEP combined the two different methodologies to develop the final cost 
surface.\259\
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    \258\ ICF International, CO2 Analysis of CO2-Reducing 
Technologies for Aircraft, Final Report, EPA Contract Number EP-C-
12-011, March 17, 2015.
    \259\ The two datasets were merged together and a single cost 
surface was then generated to calculate the cost to modify any 
aircraft based on the MTOM, and percent metric value change needed.
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    A top-down approach is being used to model large changes to 
aircraft design, such as what would be seen in significant partial 
redesigns or new types. For significant partial redesigns that result 
in new series of an established model, these types of changes may 
include: Redesigned wings, new engine options, longer fuselages, 
improved aerodynamics, or reduced weight. When making significant 
changes to an aircraft many other changes and updates get wrapped into 
the process that do not have an effect on the CO2 emissions 
of the aircraft, and significant partial redesigns may not have been 
spurred by changes to fuel efficiency (CO2 reductions). This 
confluence of changes led CAEP to agree that it was reasonable to use 
the full development cost for a new type (clean sheet) or significant 
partial redesign for major changes. Total costs for past projects were 
used to estimate non-recurring cost for the CAEP analysis. This type of 
aircraft improvement/development program has historically ranged 
approximately from 1 to 15 billion Dollars (U.S.) depending on the size 
of the aircraft and scope of the improvements desired.
    A bottom-up approach was used, by CAEP, to model smaller 
incremental metric value changes to aircraft design. The CAEP agreed 
that the above top-down approach would not be the best approach for 
minor changes or incremental improvements because the significant 
design efforts include many changes that would not be required for 
smaller CO2 reductions. The EPA used the information 
gathered by ICF International to provide input on the cost for 
individual technologies which were used to build up non-recurring costs 
for these incremental improvements (a bottom-up approach). The 
technologies available to make incremental improvements to aircraft is 
wide ranging and aircraft specific. Some examples of technologies that 
could be integrated into an aircraft for incremental improvements 
include improved fan blade design or reduction in turbine clearances in 
the engine, reducing the gap between control surfaces, carbon brake 
pads, or advanced wing tip devices. As an example, ICF International 
estimated that depending on the additive nature of specific 
technologies and the magnitude improvement required, the cost to 
incrementally improve the Boeing 767 could range from approximately 230

[[Page 37804]]

million to 1.3 billion US dollars (3.5% to 11% metric value 
improvement).\260\
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    \260\ ICF International, CO2 Analysis of CO2-Reducing 
Technologies for Aircraft, Final Report, EPA Contract Number EP-C-
12-011, March 17, 2015.
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2. Technology Responses
    When CAEP started to develop the technology responses for the 
stringency options, a determination needed to be made on what level of 
technology could be considered as a response to the standard. At the 
outset, CAEP decided the international CO2 standard would be 
a technology following standard, rather than a technology forcing one. 
This means that the international standard would reflect a level of 
emissions performance that is already achieved by some portion of 
current in-production aircraft.
    Additionally, CAEP determined in 2012 that all technology responses 
would have to be based on technology that would be in common use by the 
time the standard was to be decided upon in 2016 or shortly thereafter. 
This generation of technology was defined within CAEP as a Technology 
Readiness Level (TRL) 8 \261\--an actual system completed and qualified 
through test and demonstration--by 2016 or shortly thereafter. This 
means that the technology responses considered for the future 
international CO2 standard, going into effect in 2020 or 
2023 for new types and potentially in 2023 or later for in-production, 
are based on what will be in operation by 2016 or shortly thereafter. 
Considering the technology response assumptions agreed to at CAEP, the 
EPA requests comment on how the international CO2 standard 
should be established so that it meets the purpose of the standard--to 
achieve reductions beyond what would have been achieved in the absence 
of a standard.
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    \261\ TRL is a measure of Technology Readiness Level. CAEP has 
defined TRL8 as the ``actual system completed and `flight qualified' 
through test and demonstration.'' TRL is a scale from 1 to 9, TRL1 
is the conceptual principle, and TRL9 is the ``actual system `flight 
proven' on operational flight.'' The TRL scale was originally 
developed by NASA. ICF International, CO2 Analysis of CO2-Reducing 
Technologies for Aircraft, Final Report, EPA Contract Number EP-C-
12-011, see page 40, March 17, 2015.
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3. Cost Effectiveness Analysis
    CAEP is currently conducting the cost effectiveness analysis for 
new-type and in-production aircraft. With rare exceptions CAEP has 
historically developed new type only standards. To model cost impacts 
of a new type standard, CAEP has historically used an assumption that 
the in-production aircraft will respond to the new type standard, even 
though the standard would not apply to them and has assumed that the 
aviation sector is competitive enough that market forces will drive 
manufacturers to voluntarily upgrade their fleet to meet any new type 
aircraft standard. This scenario is modeled no differently from a 
mandatory in-production standard. The EPA requests comment on modeling 
cost and environmental impacts of new-type standards based on the 
assumed attainment of such emissions levels by in-production aircraft.
    Because CAEP has modeled all in-production aircraft as responding 
by the implementation date of the new-type standard, CAEP has by 
definition, performed an in-production analysis. More stringent options 
for new-type aircraft may be restricted due to the assumed in-
production impacts.
    CAEP has recognized that its past methods for modeling a new-type 
only standard (by assuming in-production aircraft comply) may not be 
sufficient for the CO2 standard analysis. Thus, CAEP 
developed new methods to model what cost and environmental impacts 
would result from only new types being regulated under a new-type 
emission standard. CAEP is still determining the best way to conduct an 
analysis of impacts only on new types using the agreed upon technology 
responses and cost estimates. The EPA requests comments on how to model 
cost impacts for only new types for the future international 
CO2 standard, if it were to apply only to new types. The EPA 
also requests comment on how the modeling should be conducted to 
differentiate in-production and new type scenarios.

G. Request for Comment on EPA's Domestic Implementation of 
International CO2 Standards

    As described earlier in section II.E, traditionally international 
emission standards for aircraft engines have first been adopted by 
ICAO, and subsequently the EPA has initiated rulemakings to establish 
domestic standards that are of at least equal stringency as ICAO's 
engine standards. However, the Chicago Convention,\262\ which 
established ICAO, recognizes that ICAO member states may adopt their 
own unique standards that are more stringent than ICAO standards. A 
participating member state (or nation) that adopts more stringent 
standards is obligated to notify ICAO of the differences between its 
standards and ICAO's standards.\263\
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    \262\ ICAO, 2006: Doc 7300-Convention on International Civil 
Aviation, Ninth edition, Document 7300/9. Available at: http://www.icao.int/publications/ICAOProducts&Services2015catalogue/cat_2015en.pdf (last accessed May 12, 2015). The ICAO Document 7300 
is found on page 1 of the ICAO Products & Services 2015 catalog and 
is copyright protected; Order No. 7300.
    \263\ According to the Chicago Convention, a participating 
member State that adopts regulations or practices differing in any 
particular respect from those established by an international 
standard is obligated to notify ICAO of the differences between its 
standards and ICAO's standards. However, 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.
---------------------------------------------------------------------------

    Section 231(b) of the CAA requires that any emission standards 
``take effect after such period as the Administrator finds necessary 
(after consultation with the Secretary of Transportation) to permit the 
development and application of the requisite technology, giving 
appropriate consideration to the cost of compliance during such 
period.'' 42 U.S.C. 7571(b). Section 231(a)(2)(B) provides that the 
Administrator shall consult with the Administrator of the FAA on 
standards, and ``shall not change the aircraft engine emission 
standards if such change would significantly increase noise and 
adversely affect safety.'' 42 U.S.C. 7571(a)(2)(B).
    As discussed in the 2005 rule (CAEP/4 aircraft engine 
NOX standard),\264\ the EPA needs to have a technical basis 
for expecting the standards will be achievable in a specific period of 
time. While the statutory language of section 231 is not identical to 
other provisions in title II of the CAA that direct the EPA to 
establish technology-based standards for various types of mobile 
sources, the EPA interprets its authority under section 231 to be 
similar to those provisions that grant us significant discretion to 
identify a reasonable balance of specified emissions reduction, and 
cost without adversely affecting safety or increasing noise. See, e.g., 
Husqvarna AB v. EPA, 254 F.3d 195 (D.C. Cir. 2001) (upholding the EPA's 
promulgation of technology-based standards for small non-road engines 
under section 213(a)(3) of the CAA). In this regard, we note CAEP's 
intent for the purpose of the international CO2 standard (as 
accepted by the CAEP Steering Group in 2011), which is to achieve 
aircraft CO2 emissions reductions beyond that which would

[[Page 37805]]

have occurred in the absence of a standard.
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    \264\ U.S. EPA, ``Control of Air Pollution from Aircraft and 
Aircraft Engines; Emission Standards and Test Procedures;'' Final 
Rule, 70 FR 2521, November 17, 2005.
---------------------------------------------------------------------------

    In ruling on a petition for judicial review of the 2005 rule,\265\ 
the U.S. Court of Appeals for the D.C. Circuit held that the EPA's 
approach in that action of tracking 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.
---------------------------------------------------------------------------

    \265\ Ibid.
---------------------------------------------------------------------------

    Although the EPA has traditionally established domestic standards 
that track the ICAO standards, for purposes of having a robust ANPR 
process, we ask for comment on the possibility of the EPA adopting a 
more stringent aircraft engine emissions standard than ICAO, provided 
ICAO/CAEP promulgates a standard in 2016 and the EPA makes a positive 
endangerment finding. In the same vein, the EPA requests that 
commenters consider the following factors (among others): The potential 
to reflect the CO2 emissions performance of products from 
U.S. manufacturers, competitive advantages and disadvantages for U.S. 
manufacturers, certification reciprocity with certificating authorities 
of other nations, and the EPA's role in the ongoing ICAO negotiations. 
In addition, the EPA asks for comment on what action the EPA should 
take if the ICAO/CAEP process fails to result in the adoption of an 
aircraft CO2 emissions standard.

VII. 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 proposes a finding 
that GHG emissions from aircraft cause or contribute to air pollution 
that may be reasonably anticipated to endanger public health and 
welfare along with an ANPR which provides an overview of the 
international efforts to reduce GHG emissions, progress to date in 
establishing global aircraft standards that achieve meaningful 
CO2 reductions and, if the EPA finds that aircraft GHG 
emissions do cause or contribute to endangerment, the potential use of 
CAA section 231 to implement these standards domestically ensuring 
transparency and the opportunity for public comment. Any changes made 
in response to OMB recommendations have been documented in the docket.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA. The proposed endangerment and cause or contribute findings 
under CAA section 231 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 proposed 
endangerment and cause or contribute findings under CAA section 231 do 
not in-and-of-themselves impose any new requirements but rather set 
forth the Administrator's proposed 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 proposal.

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 proposed endangerment and cause or 
contribute findings under CAA section 231 do not in-and-of-themselves 
impose any new requirements but rather set forth the Administrator's 
proposed 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. 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 
this proposed endangerment finding under CAA section 231. 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 are contained in sections IV and I.D of the preamble titled 
``Children's Environmental Health.'' 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 
proposed endangerment and cause or contribute findings under section 
231 do not in-and-of themselves impose any new requirements but rather 
set forth the Administrator's proposed 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-

[[Page 37806]]

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 this proposed 
endangerment finding under CAA section 231. This action's discussion of 
climate change impacts on public health and welfare is found in section 
IV of the preamble. Specific discussion with regard to minority, low-
income, and indigenous populations are found in sections IV and I.E of 
this preamble titled ``Environmental Justice.'' 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. 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).

VIII. 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: June 10, 2015.
Gina McCarthy,
Administrator.
[FR Doc. 2015-15192 Filed 6-30-15; 8:45 am]
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