8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

 Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015) 

[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

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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.

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 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-OAR2014-0828.

 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-OAR2014-0828. 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 

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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

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 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 CostEffectiveness 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 

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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 

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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 

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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 

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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 

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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 

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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 

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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).

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

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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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 compressionignition 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\

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

 \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).

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 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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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 firstever 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-efficie

ncy-standards-medium-and-heavy-duty-vehicl 

(last accessed May 12, 2015).

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[[Page 37764]]

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

 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\

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

 \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.pd

f (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-powersector-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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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.pd

f (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/aer

ospace_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, 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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.

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

 \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 

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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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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

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

 \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).

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 In the interest of global harmonization and international air 

commerce, the Chicago Convention urges its member States to collaborate 

in securing the highest practicable degree of uniformity in 

regulations, standards, procedures and organization. The Chicago 

Convention also recognizes that member States may adopt standards that 

are more stringent than those agreed upon by ICAO. Any member State 

which finds it impracticable to comply in all respects with any 

international standard or procedure, or 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\

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 \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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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.

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 \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]]

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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 inproduction 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 newlycertified 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 

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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 

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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 preexisting 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, newlycertified 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 

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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.''

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 \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 

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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\

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 \62\ See CRR, 684 F.3d at 117 (explaining two-part analysis 

under section 202(a)).

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 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 

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scientific or medical knowledge.\66\ At the same time, the 

Administrator must exercise reasoned decision making, and avoid 

speculative inquiries.

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 \66\ See id. at 121-122.

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 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 

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* * * 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 

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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\

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

 \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.

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

 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\

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

 \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.

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

 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 

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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.

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

 \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).

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

 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.

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

 \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] 

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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\

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

 \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 

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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 

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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 

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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 climateforcing 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.

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

 \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.

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

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 

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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\

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

 \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\

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

 \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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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.

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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 wellmixed 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 vectorborne 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.

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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 wellPage 39
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[[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.

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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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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 reprove 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 

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8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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 wellmixed 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\

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 \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.

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 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.

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

 \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 peerreviewed 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 

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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.

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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 

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morbidity in some areas due to fewer cold extremes (low confidence),'' 

\120\ but that, ``[o]verall, we conclude that the increase in heatrelated 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 

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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]]

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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. 

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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

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[[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 

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pollution. Similarly, the new assessments further support projections 

of water resource impacts associated with increased floods and shortterm 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 

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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 

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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.

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

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 \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 ozonedepleting 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 shortlived 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 climaterelevant 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 shortPage 56
8_Federal Register, Volume 80 Issue 126 (Wednesday, July 1, 2015).txt

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 peerreviewed 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). 

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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 

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(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 

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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 

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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 

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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.

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 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 wellmixed 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 

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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 

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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.

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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 

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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.

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 For purposes of making this cause or contribute finding, the EPA is 

focused on, and proposes to include, a set of aircraft engine classes 

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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 

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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\

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

 \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, 

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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

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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\

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 \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 

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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/aer

ospace_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).

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

 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/aer

ospace_forecasts/2015-2035/media/2015_National_Forecast_Report.pdf (last accessed 

May 

12, 2015).

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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 

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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 

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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 

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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.

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 \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 costeffectiveness 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 

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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.

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 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:

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--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

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

 \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 newlymanufactured 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''.

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--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.

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

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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 inproduction 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.

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 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, 

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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-superjumb

o-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-C12-011, March 17, 2015.)

 \215\ As described earlier, CAEP has not ruled out applying the 

international CO2 standard to in-production aircraft 

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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 inproduction 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.

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 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 

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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.

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 \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.)

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 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 

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plus.223 224

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 \220\ ICF International, CO2 Analysis of CO2-Reducing 

Technologies for Aircraft, Final Report, EPA Contract Number EP-C12-011, 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 longterm.

 \224\ ICF International, CO2 Analysis of CO2-Reducing 

Technologies for Aircraft, Final Report, EPA Contract Number EP-C12-011, 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-replacementby-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 

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(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 inproduction 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 inproduction 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 

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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 inproduction 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 

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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.

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

 \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_fin

al.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-C12-011, March 17, 2015.

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

 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.

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

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 peraircraft 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.

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

 \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 

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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)).

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

 In 2009 the EPA promulgated a final GHG reporting rule that applies 

to many sectors in the United States, including manufacturers of heavyduty 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.

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

 \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 inproduction 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 

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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.

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

 \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.

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

 \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.

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

 \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 

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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.

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

 \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 inproduction 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.

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

 \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).

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

 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-bywire).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).

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

 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).

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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 

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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.

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

 \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 inproduction 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 nonmanufacturer provided estimates of the performance of various aircraft. 

In contrast, CAEP is using manufacturer-provided estimates of the 

aircraft metric value performance.

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

 \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

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[[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 inproduction 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 inproduction 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.

[[Page 37801]]

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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 CostEffectiveness 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 

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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\

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

 \258\ ICF International, CO2 Analysis of CO2-Reducing 

Technologies for Aircraft, Final Report, EPA Contract Number EP-C12-011, 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.

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

 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 

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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\

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

 \260\ ICF International, CO2 Analysis of CO2-Reducing 

Technologies for Aircraft, Final Report, EPA Contract Number EP-C12-011, March 17, 2015.

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

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.

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

 \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-C12-011, see page 40, March 17, 2015.

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

3. Cost Effectiveness Analysis

 CAEP is currently conducting the cost effectiveness analysis for 

new-type and in-production aircraft. With rare exceptions CAEP has 

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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 inproduction 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\

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

 \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 

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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.

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

 \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

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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 

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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, lowincome, 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, lowincome, 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).

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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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