Vol. 80 Wednesday, 

No. 126 July 1, 2015 

Part II 

Environmental Protection Agency 

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 


tkelley on DSK3SPTVN1PROD with PROPOSALS2
37758 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Parts 87 and 1068 

[EPA–HQ–OAR–2014–0828; FRL 9924–06– 

OAR] 

RIN 2060–AS31 

Proposed Finding That Greenhouse 

Gas Emissions From Aircraft Cause or 

Contribute to Air Pollution That May 

Reasonably Be Anticipated To 

Endanger Public Health and Welfare 

and Advance Notice of Proposed 

Rulemaking 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule and advance 

notice of proposed rulemaking. 

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 preregister in advance to speak at the 

hearing will be August 6, 2015. The 

hearing will start at 10:00 a.m. local 

time and continue until everyone has 

had a chance to speak. Requests to 

speak will be taken the day of the 

hearing at the hearing registration desk, 

although preferences on speaking times 

may not be able to be fulfilled. If you 

require the service of a translator or 

special accommodations such as audio 

description, please let us know at the 

time of registration. For further 

information on the public hearing or to 

register to speak at the hearing, please 

see section I.B below or go to http://

www.epa.gov/otaq/aviation.htm. 

ADDRESSES: Comments. Submit your 

comments, identified by Docket ID No. 

EPA–HQ–OAR–2014–0828, by one of 

the following methods: 

• Online: www.regulations.gov 

Follow the on-line instructions for 

submitting comments. 

• Email: A-and-R-Docket@

epamail.epa.gov Attention Docket ID 

No. EPA–HQ–OAR–2014–0828. 

• Fax: (202) 566–9744, Attention 

Docket ID No. EPA–HQ–OAR–2014– 

0828. 

• Mail: U.S. Postal Service, send 

comments to Air and Radiation Docket 

and Information Center, Environmental 

Protection Agency, Mail Code: 28221T, 

1200 Pennsylvania Ave. NW., 

Washington, DC 20460. Attention 

Docket ID No. EPA–HQ–OAR–2014– 

0828. 

• Hand Delivery: U.S. Environmental 

Protection Agency, EPA West, EPA 

Docket Center, EPA West Building, 

Room 3334, 1301 Constitution Ave. 

NW., Washington, DC 20004. Attention 

Docket ID No. EPA–HQ–OAR–2014– 

0828. Such deliveries are only accepted 

during the Docket’s normal hours of 

operation, and special arrangements 

should be made for deliveries of boxed 

information. 

Instructions: Direct your comments to 

Docket ID No. EPA–HQ–OAR–2014– 

0828. See section I.B on ‘‘Public 

Participation’’ for more information 

about submitting written comments. 

The EPA’s policy is that all comments 

received will be included in the public 

docket without change and may be 

made available online at http://

www.regulations.gov, including any 

personal information provided, unless 

the comment includes information 

claimed to be confidential business 

information (CBI) or other information 

whose disclosure is restricted by statute. 

Do not submit information that you 

consider to be CBI or otherwise 

protected through http://

www.regulations.gov or email. The 

http://www.regulations.gov Web site is 

an ‘‘anonymous access’’ system, which 

means the EPA will not know your 

identity or contact information unless 

you provide it in the body of your 

comment. If you send an email 

comment directly to the EPA without 

going through http://

www.regulations.gov, your email 

address will be automatically captured 

and included as part of the comment 

that is placed in the public docket and 

made available on the Internet. If you 

submit an electronic comment, the EPA 

recommends that you include your 

name and other contact information in 

the body of your comment and with any 

disk or CD–ROM you submit. If the EPA 

cannot read your comment due to 

technical difficulties and cannot contact 

you for clarification, the EPA may not 

be able to consider your comment. 

Electronic files should avoid the use of 

special characters, or any form of 

encryption, and be free of any defects or 

viruses. For additional information 

about the EPA’s public docket visit the 

EPA Docket Center homepage at: http:// 

www.epa.gov/dockets. For additional 

instructions on submitting comments, 

go to section I.B of this document. 

Docket. The EPA has established a 

docket for this rulemaking under Docket 

ID No. EPA–HQ–OAR–2014–0828. All 

documents in the docket are listed in 

the www.regulations.gov index. 

Although listed in the index, some 

information is not publicly available, 

e.g., CBI or other information whose 

disclosure is restricted by statute. 

Certain other material, such as 

copyrighted material, is not placed on 

the Internet and will be publicly 

available only in hard copy in the EPA’s 

docket. Publicly available docket 

materials are available either 

electronically in www.regulations.gov or 

in hard copy at the Air and Radiation 

Docket and Information Center, EPA/

DC, EPA WJC West, Room 3334, 1301 

Constitution Ave. NW., Washington, 

DC. The Public Reading Room is open 


tkelley on DSK3SPTVN1PROD with PROPOSALS2
Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 37759 

from 8:30 a.m. to 4:30 p.m., Monday 

through Friday, excluding legal 

holidays. The telephone number for the 

Public Reading Room is (202) 566–1744, 

and the telephone number for the Air 

Docket is (202) 566–1742. 

FOR FURTHER INFORMATION CONTACT: 

JoNell Iffland, Office of Transportation 

and Air Quality, Assessment and 

Standards Division (ASD), 

Environmental Protection Agency, 2000 

Traverwood Drive, Ann Arbor, MI 

48105; Telephone number: (734) 214– 

4454; Fax number: (734) 214–4816; 

Email address: iffland.jonell@epa.gov. 

Please use this contact information for 

general questions about this rulemaking, 

to request a hearing, to determine if a 

hearing will be held, and to register to 

speak at the hearing, if one is held. 

SUPPLEMENTARY INFORMATION: 

Table of Contents 

I. General Information 

A. Does this action apply to me? 

B. Public Participation 

1. What should I consider as I prepare my 

comments for the EPA? 

2. Public Hearing 

C. Did the EPA conduct a peer review 

before issuing this notice? 

D. Children’s Environmental Health 

E. Environmental Justice 

II. Introduction: Overview and Context for 

This Proposal 

A. Summary 

B. Background Information Helpful to 

Understanding This Proposal 

1. Greenhouse Gases and Their Effects 

2. Statutory Basis for This Proposal 

C. The EPA’s Responsibilities Under the 

Clean Air Act 

1. The EPA’s Regulation of Greenhouse 

Gases 

2. Background on the Aircraft Petition, 

2008 ANPR, and D.C. District Court 

Decision 

D. U.S. Aircraft Regulations and the 

International Community 

1. International Regulations and U.S. 

Obligations 

2. The International Community’s Reasons 

for Addressing Aircraft GHG Emissions 

3. Relationship of the EPA’s Proposed 

Endangerment and Cause or Contribute 

Findings to International Aircraft 

Standards 

E. The EPA’s Regulation of Aircraft 

Emissions 

III. Legal Framework for This Action 

A. Section 231(a)(2)(A)—Endangerment 

and Cause or Contribute 

1. The Statutory Language 

2. How the Origin of the Current Statutory 

Language Informs the EPA’s 

Interpretation of Section 231(a)(2)(A) 

3. Additional Considerations for the Cause 

or Contribute Analysis 

B. Air Pollutant, Public Health and Welfare 

IV. The Proposed Endangerment Finding 

Under CAA Section 231 

A. Scientific Basis of the 2009 

Endangerment Finding Under CAA 

section 202(a)(1) 

1. The Definition of Air Pollution in the 

2009 Endangerment Finding 

2. Public Health Impacts Detailed in the 

2009 Endangerment Finding 

3. Public Welfare Impacts Detailed in the 

2009 Endangerment Finding 

4. The Science Upon Which the Agency 

Relied 

B. Recent Science Further Supports the 

Administrator’s Judgment That the Six 

Well-Mixed Greenhouse Gases Endanger 

Public Health and Welfare 

1. More Recent Evidence That Elevated 

Atmospheric Concentrations of the Six 

Greenhouse Gases Are the Root Cause of 

Observed Climate Change 

2. More Recent Evidence that Greenhouse 

Gases Endanger Public Health 

3. More Recent Evidence that Greenhouse 

Gases Endanger Public Welfare 

4. Consideration of Other Climate Forcers 

C. Summary of the Administrator’s 

Proposed Endangerment Finding Under 

CAA Section 231 

V. The Proposed Cause or Contribute Finding 

for Greenhouse Gases Under CAA 

Section 231 

A. The Air Pollutant 

1. Proposed Definition of Air Pollutant 

2. How the Definition of Air Pollutant in 

the Endangerment Determination Affects 

Section 231 Standards 

B. Proposed Cause or Contribute Finding 

1. The Administrator’s Approach in 

Making This Proposed Finding 

2. Overview of Greenhouse Gas Emissions 

3. Proposed Contribution Finding for the 

Single Air Pollutant Comprised of the of 

Six Well-Mixed Greenhouse Gases 

4. Additional Considerations 

VI. Advance Notice of Proposed Rulemaking: 

Discussion of Ongoing International 

Proceedings To Develop Aircraft CO2

Emissions Standard and Request for 

Comment 

A. Purpose of the International Standard 

B. Applicability of the International CO2

Emissions Standard 

C. CAEP Discussion on In-Production 

Aircraft Applicability 

1. Applicability to In-Production Aircraft 

and Date of Implementation 

2. Reporting Requirement for New InProduction 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 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: 


tkelley on DSK3SPTVN1PROD with PROPOSALS2
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Category NAICSa Code SIC b Code Examples of potentially affected entities 

Industry ................... 3364412 3724 Manufacturers of new aircraft engines. 

Industry ................... 336411 3721 Manufacturers of new aircraft. 

a North American Industry Classification System (NAICS). 

bStandard Industrial Classification (SIC) code. 

This table is not intended to be 

exhaustive, but rather provides a guide 

for readers regarding entities likely to be 

interested in this proposed action. This 

table lists the types of entities that the 

EPA is now aware could potentially 

have an interest in this proposed action. 

If the EPA issues final affirmative 

findings under section 231(a) regarding 

greenhouse gases, the EPA would then 

be required to undertake a separate 

notice and comment rulemaking to issue 

emission standards applicable to 

greenhouse gas emissions from the 

classes of aircraft engines that the EPA 

finds cause or contribute in such a 

finding, and the FAA would be required 

to Prescribe regulations to insure 

compliance with these emissions 

standards pursuant to section 232 of the 

Clean Air Act. Other types of entities 

not listed in the table could also be 

interested and potentially affected by 

subsequent actions at some future time. 

If you have any questions regarding the 

scope of this proposed action, consult 

the person listed in the preceding FOR

FURTHER INFORMATION CONTACT section. 

B. Public Participation 

The EPA requests comment on all 

aspects of the proposed aircraft 

endangerment and cause or contribute 

findings and the Advance Notice of 

Proposed Rulemaking (ANPR). This 

section describes how you can 

participate in this process. 

If you submitted comments on the 

issues raised by this proposal in dockets 

for other, earlier Agency efforts (e.g., the 

2009 Endangerment and Cause or 

Contribute Findings for Greenhouse 

Gases Under Section 202 of the Clean 

Air Act or the Advance Notice of 

Proposed Rulemaking on Regulating 

Greenhouse Gases under the Clean Air 

Act), you must still submit your 

comments to the docket for this action 

(EPA–HQ–OAR–2014–0828) by the 

deadline if you want them to be 

considered. 

1. What should I consider as I prepare 

my comments for the EPA? 

We are opening a formal comment 

period by publishing this document. We 

will accept comments during the period 

indicated in the DATES section. If you 

have an interest in the proposed aircraft 

endangerment and cause or contribute 

findings and/or the ANPR described in 

this document, we encourage you to 

comment on any aspect of this 

rulemaking. 

Tips for Preparing Your Comments 

When submitting comments, 

remember to: 

• Identify the rulemaking by docket 

number and other identifying 

information (subject heading, Federal 

Register date and page number). 

• Follow directions—The agency may 

ask you to respond to specific questions 

or organize comments by referencing a 

Code of Federal Regulations (CFR) part 

or section number. 

• Explain why you agree or disagree, 

suggest alternatives, and substitute 

language for your requested changes. 

• Describe any assumptions and 

provide any technical information and/ 

or data that you used. 

• If you estimate potential costs or 

burdens, explain how you arrived at 

your estimate in sufficient detail to 

allow for it to be reproduced. 

• Provide specific examples to 

illustrate your concerns, and suggest 

alternatives. 

• Explain your views as clearly as 

possible, avoiding the use of profanity 

or personal threats. 

• Make sure to submit your 

comments by the comment period 

deadline identified. 

Do not submit information to the EPA 

containing CBI through http://

www.regulations.gov or email. Clearly 

mark the part or all of the information 

that you claim to be CBI. For CBI 

information on a disk or CD–ROM that 

you mail to the EPA, mark the outside 

of the disk or CD–ROM as CBI and then 

identify electronically within the disk or 

CD–ROM the specific information that 

is claimed as CBI. In addition to one 

complete version of the comment that 

includes information claimed as CBI, 

you must submit a copy of the comment 

that does not contain the information 

claimed as CBI for inclusion in the 

public docket. Information so marked 

will not be disclosed except in 

accordance with procedures set forth in 

40 CFR part 2. 

2. Public Hearing 

If a hearing is held, it will provide 

interested parties the opportunity to 

present data, views or arguments 

concerning the proposed action. The 

EPA will make every effort to 

accommodate all speakers who arrive 

and register. Because this hearing, if 

held, will be at a U.S. government 

facility, individuals planning to attend 

the hearing should be prepared to show 

valid picture identification to the 

security staff in order to gain access to 

the meeting room. Please note that the 

REAL ID Act, passed by Congress in 

2005, established new requirements for 

entering federal facilities. These 

requirements took effect July 21, 2014. 

If your driver’s license is issued by 

Alaska, American Samoa, Arizona, 

Kentucky, Louisiana, Maine, 

Massachusetts, Minnesota, Montana, 

New York, Oklahoma, or the state of 

Washington, you must present an 

additional form of identification to enter 

the federal buildings where the public 

hearings will be held. Acceptable 

alternative forms of identification 

include: Federal employee badges, 

passports, enhanced driver’s licenses 

and military identification cards. In 

addition, you will need to obtain a 

property pass for any personal 

belongings you bring with you. Upon 

leaving the building, you will be 

required to return this property pass to 

the security desk. No large signs will be 

allowed in the building, cameras may 

only be used outside of the building and 

demonstrations will not be allowed on 

federal property for security reasons. 

The EPA may ask clarifying questions 

during the oral presentations but will 

not respond to the presentations at that 

time. Written statements and supporting 

information submitted during the 

comment period will be considered 

with the same weight as oral comments 

and supporting information presented at 

the public hearings. 

Speakers should contact Ms. JoNell 

Iffland (see FOR FURTHER INFORMATION

CONTACT) if they will need specific 

equipment, or if there are other special 

needs related to providing comments at 

the hearing. Oral testimony will be 

limited to no more than 10 minutes for 

each commenter, although we may need 

to adjust the time for each speaker if 

there is a large turnout. The EPA 

requests that commenters provide the 

EPA with three copies of their oral 

testimony in hard copy form the day of 

the hearing or an electronic copy in 

advance of the hearing date. Verbatim 

transcripts of the hearings and written 


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1U.S. EPA, 2006: EPA Peer Review Policy. 

Available at http://www.epa.gov/peerreview/ (Last 

accessed May 12, 2015). 

2U.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). 

3U.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). 

4U.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’’). 

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. 

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

The EPA also cites data from its 

annual Inventory of U.S. Greenhouse 

Gas Emissions and Sinks report,3 which 

the Agency has determined to have been 

adequately reviewed in accordance with 

the OMB Bulletin and the EPA’s Peer 

Review Handbook. For the presentation 

of emissions inventory information to 

support the cause or contribute finding, 

the EPA disaggregated the existing data 

in one area of the GHG Inventory (for 

the General Aviation Jet Fuel Category) 

and had the disaggregation methodology 

and results peer reviewed in accordance 

with the EPA’s Peer Review Handbook. 

The EPA Science Advisory Board 

reviewed this approach to the 

underlying technical and scientific 

information supporting this action, and 

concluded that the approach had 

precedent and the action will be based 

on well-reviewed information. All 

relevant peer review documentation is 

located in the docket for today’s action 

(EPA–HQ–OAR–2014–0828). 

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. 

These assessments describe that 

children will be disproportionately 

impacted by climate change given the 

unique physiological and 

developmental factors that occur during 

this lifestage. Impacts to children are 

expected from heat waves, air pollution, 

infectious and waterborne illnesses, and 

mental health effects resulting from 

extreme weather events. In addition, the 

assessments find that climate change 

will influence production of pollen that 

affects asthma and other allergic 

respiratory diseases, to which children 

are among those especially susceptible. 

E. Environmental Justice 

As described in detail in section IV 

below, the scientific evidence and 

conclusions in the USGCRP, IPCC, and 

the NRC assessment reports cited in the 

2009 Endangerment Finding indicate 

that certain populations are most 

vulnerable to the health and welfare 

effects of climate change, including the 

elderly, the poor, and indigenous 

peoples in the United States, 

particularly Alaska Natives. The more 

recent assessment reports strengthen 

these conclusions by providing more 

detail regarding these populations’ 

vulnerabilities and projected impacts 

they may experience. 

In addition, the most recent 

assessment reports provide new analysis 

about how low-income populations and 

some populations defined jointly by 

ethnic/racial characteristics and 

geographic location are vulnerable to 

certain climate change health impacts, 

raising environmental justice concerns. 

Factors that contribute to increased 

vulnerability to the health effects of 

climate change include limited 

resources to adapt to and recover from 

climate impacts, as well as existing 

health disparities (e.g., higher 

prevalence of chronic health conditions 

such as diabetes). 

II. Introduction: Overview and Context 

for This Proposal 

A. Summary 

Pursuant to section 231(a)(2)(A) of the 

Clean Air Act (CAA or Act), the 

Administrator proposes to find that 

greenhouse gas (GHG) emissions from 

aircraft engines used in certain types of 

aircraft (referred to as ‘‘covered aircraft’’ 

throughout this notice) contribute to air 

pollution that endangers public health 

and welfare. Covered aircraft would be 

those aircraft to which ICAO has agreed 

the international CO2 standard would 

apply: 5 subsonic jet aircraft with a 

maximum takeoff mass (MTOM) greater 

than 5,700 kilograms, and subsonic 

propeller-driven (e.g., turboprop) 

aircraft with a MTOM greater than 8,618 

kilograms. Examples of covered aircraft 

would include smaller jet aircraft such 

as the Cessna Citation CJ2+ and the 

Embraer E170, up to and including the 

largest commercial jet aircraft—the 

Airbus A380 and the Boeing 747. Other 

examples of covered aircraft would 

include larger turboprop aircraft, such 

as the ATR 72 and the Bombardier 

Q400. 

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 


tkelley on DSK3SPTVN1PROD with PROPOSALS2
37762 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

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. 

8U.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). 

referred to as the 2009 Endangerment 

Finding in this action). This includes 

the major, peer-reviewed scientific 

assessments that were used to address 

the question of whether GHGs in the 

atmosphere endanger public health and 

welfare, and on the analytical 

framework and conclusions upon which 

the EPA relied in making that finding. 

The Administrator’s view is that the 

body of scientific evidence amassed in 

the record for the 2009 Endangerment 

Finding also compellingly supports an 

endangerment finding under CAA 

section 231(a). Furthermore, this 

proposed finding under section 231 

reflects the EPA’s careful consideration 

not only of the scientific and technical 

record for the 2009 Endangerment 

Finding, but also of science assessments 

released since 2009, which, as 

illustrated below, strengthen and further 

support the judgment that GHGs in the 

atmosphere may reasonably be 

anticipated to endanger public health 

and welfare. No information or analyses 

published since late 2009 suggest that it 

would be reasonable for the EPA to now 

reach a different or contrary conclusion 

for purposes of CAA section 

231(a)(2)(A) than the Agency reached 

for purposes of section 202(a). However, 

as explained below, in proposing this 

finding for purposes of section 231, we 

are not reopening or revising our prior 

findings under CAA section 202. 

The Administrator is proposing to 

define the ‘‘air pollution’’ referred to in 

section 231(a)(2)(A) of the CAA to be the 

mix of six well-mixed GHGs: CO2, 

methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride. This is the 

same definition that was used for the 

finding for purposes of section 202(a). It 

is the Administrator’s judgment that the 

total body of scientific evidence 

compellingly supports a positive 

endangerment finding that elevated 

concentrations of the six well-mixed 

GHGs constitute air pollution that 

endangers both the public health and 

the public welfare of current and future 

generations within the meaning of 

section 231(a) of the Clean Air Act. 

Under section 231 of the CAA, the 

Administrator must also determine 

whether emissions of any air pollutant 

from a class or classes of aircraft engines 

cause or contribute to the air pollution 

that may reasonably be anticipated to 

endanger public health or welfare. 

Following the rationale outlined in the 

2009 Endangerment Finding, the 

Administrator in this action is 

proposing to use the same definition of 

the air pollutant as was used for 

purposes of section 202(a) for purposes 

of making the cause or contribute 

determination under section 231(a)— 

that is, the aggregate group of the same 

six well-mixed GHGs. Based on the data 

summarized in section V, the 

Administrator is proposing to find that 

GHG emissions from aircraft engines 

used in covered aircraft, contribute to 

the air pollution that endangers public 

health and welfare under section 231(a). 

The Administrator’s proposed 

findings come in response to a citizen 

petition submitted by Friends of the 

Earth, Oceana, the Center for Biological 

Diversity, and Earthjustice (Petitioners) 

requesting that the EPA issue an 

endangerment finding and standards 

under section 231(a)(2)(A) of the Act for 

the GHG emissions from aircraft. The 

EPA is not proposing or taking action 

under any other provision of the CAA. 

Further, the EPA anticipates that ICAO 

will adopt a final CO2 emissions 

standard in February 2016. This 

proposal, and any final endangerment 

and cause or contribute findings for 

aircraft engine GHG emissions, are also 

part of preparing for a possible 

subsequent domestic rulemaking 

process to adopt standards that are of at 

least equivalent stringency as the 

anticipated ICAO CO2 standards. Once 

an international standard is finalized by 

ICAO, member states are then required 

to adopt standards that are of at least 

equivalent stringency to those set by 

ICAO. Section II. D provides additional 

discussion of the international aircraft 

standard-setting process. 

B. Background Information Helpful to 

Understanding This Proposal 

1. Greenhouse Gases and Their Effects 

GHGs in the atmosphere effectively 

trap some of the Earth’s heat that would 

otherwise escape to space. GHGs are 

both naturally occurring and 

anthropogenic. The primary GHGs 

directly emitted by human activities 

include CO2, methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride. Of these six 

gases, two (CO2 and nitrous oxide) are 

emitted by aircraft engines. 

These six gases, once emitted, remain 

in the atmosphere for decades to 

centuries. Thus, they become well 

mixed globally in the atmosphere and 

their concentrations accumulate when 

emissions exceed the rate at which 

natural processes remove them from the 

atmosphere. Observations of the Earth’s 

globally averaged combined land and 

ocean surface temperature over the 

period 1880 to 2012 show a warming of 

0.85 [0.65 to 1.06] degrees Celsius or 

1.53 [1.17 to 1.91] degrees Fahrenheit.6

The heating effect caused by the humaninduced buildup of these and other 

GHGs in the atmosphere, plus other 

human activities (e.g., land use change 

and aerosol emissions), is extremely 

likely (>95 percent likelihood) to be the 

cause of most of the observed global 

warming since the mid-20th century.7 A 

detailed explanation of climate change 

and its impact on health, society, and 

the environment is included in the 

record for the 2009 Endangerment 

Finding. The relevant scientific 

information from that record has also 

been included in the docket for this 

proposed determination under CAA 

section 231 (EPA–HQ–OAR–02914– 

0828). Section IV of this preamble 

discusses this information, as well as 

information from the most recent 

scientific assessments, in the context of 

the Administrator’s proposed 

endangerment finding under CAA 

section 231. 

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. 

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.’’ 


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9To 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. 

10Center 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). 

11As 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). 

12U.S. EPA, 2010: Light-Duty Vehicle Greenhouse 

Gas Emission Standards and Corporate Average 

Fuel Economy Standards; Final Rule, 75 FR 25324 

(May 7, 2010). 

13US 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). 

14U.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). 

15Executive 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/

Continued 

Before the Administrator may issue 

standards addressing emissions of GHGs 

under section 231, the Administrator 

must satisfy a two-step test. First, the 

Administrator must decide whether, in 

her judgment, the air pollution under 

consideration may reasonably be 

anticipated to endanger public health or 

welfare. Second, the Administrator must 

decide whether, in her judgment, 

emissions of an air pollutant from 

certain classes of aircraft engines cause 

or contribute to this air pollution.9 If the 

Administrator answers both questions 

in the affirmative, she must issue 

standards under section 231. See 

Massachusetts v. EPA, 549 U.S. 497,533 

(2007) (interpreting analogous provision 

in CAA section 202). Section III of this 

preamble summarizes the legal 

framework for this proposed action 

under CAA section 231. Typically, past 

endangerment and cause or contribute 

findings have been proposed 

concurrently with proposed standards 

under various sections of the CAA, 

including section 231. Comment has 

been taken on these proposed findings 

as part of the notice and comment 

process for the emission standards. See, 

e.g., Rulemaking for non-road 

compression-ignition engines under 

section 213(a)(4) of the CAA, Proposed 

Rule at 58 FR 28809, 28813–14 (May 17, 

1993), Final Rule at 59 FR 31306, 31318 

(June 17, 1994); Rulemaking for 

highway heavy-duty diesel engines and 

diesel sulfur fuel under sections 202(a) 

and 211(c) of the CAA, Proposed Rule 

at 65 FR 35430 (June 2, 2000), and Final 

Rule 66 FR 5002 (January 18, 2001). 

However, there is no requirement that 

the Administrator propose the 

endangerment and cause or contribute 

findings concurrently with proposed 

standards. See 74 FR 66502 (December 

26, 2001), (explaining that nothing in 

section 202(a) requires the EPA to 

propose or issue endangerment and 

cause or contribute findings in the same 

rulemaking, and that Congress left the 

EPA discretion to choose an approach 

that satisfied the requirements of section 

202(a)). The same analysis applies to 

section 231(a)(2)(A), which is analogous 

to section 202(a). The EPA is choosing 

to propose these findings at this time for 

a number of reasons, including its 

previous commitment to issue such 

proposed findings in response to a 2007 

citizens’ petition.10

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. 

C. The EPA’s Responsibilities Under the 

Clean Air Act 

The CAA provides broad authority to 

combat air pollution to protect public 

health and welfare. Cars, trucks, 

construction equipment, airplanes, and 

ships, as well as a broad range of 

electric generation, industrial, 

commercial and other facilities, are 

subject to various CAA programs. 

Implementation of the Act over the past 

four decades has resulted in significant 

reductions in air pollution while the 

nation’s economy has continued to 

grow. 

1. The EPA’s Regulation of Greenhouse 

Gases 

In Massachusetts v. EPA, 549 U.S. 497 

(2007), the Supreme Court found that 

GHGs are air pollutants that can be 

regulated under the CAA. The Court 

held that the Administrator must 

determine whether emissions of GHGs 

from new motor vehicles cause or 

contribute to air pollution which may 

reasonably be anticipated to endanger 

public health and/or welfare, or whether 

the science is too uncertain to make a 

reasoned decision. In making these 

decisions, the Administrator was bound 

by the provisions of section 202(a) of the 

CAA. The Supreme Court decision 

resulted from a petition for rulemaking 

under section 202(a) filed by more than 

a dozen environmental, renewable 

energy, and other organizations. 

Following the Supreme Court 

decision, the EPA proposed (74 FR 

18886, April 24, 2009) and then 

finalized (74 FR 66496, December 15, 

2009) the 2009 Endangerment Finding, 

which can be summarized as follows: 

• Endangerment Finding: The 

Administrator found that the thencurrent and projected concentrations of 

the six key well-mixed GHGs—CO2, 

methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride—in the 

atmosphere threaten the public health 

and welfare of current and future 

generations. 

• Cause or Contribute Finding: The 

Administrator found that the combined 

emissions of these well-mixed GHGs 

from new motor vehicles and new motor 

vehicle engines contribute to the GHG 

pollution which threatens public health 

and welfare. 

The findings did not themselves 

impose any requirements on industry or 

other entities. However, these findings 

compelled the EPA to promulgate GHG 

emission standards for new motor 

vehicles under section 202(a). 

Subsequently, in May 2010 the EPA, in 

collaboration with the National 

Highway Traffic Safety Administration 

(NHTSA), finalized Phase 1 GHG 

emission standards for light-duty 

vehicles (2012–2016 model years).12

This was followed in August 2011 by 

adoption of the first-ever GHG emission 

standards for heavy-duty engines and 

vehicles (2014–2018 model years).13 On 

August 29, 2012, the second phase of 

the GHG emission standards for lightduty 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 heavyduty vehicles.15


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2014/02/18/remarks-president-fuel-efficiencystandards-medium-and-heavy-duty-vehicl (last 

accessed May 12, 2015). 

16U.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). 

18Executive Office of the President, 2013: The 

President’s Climate Action Plan, June 25. Available 

at: http://www.whitehouse.gov/sites/default/files/

image/president27sclimateactionplan.pdf (last 

accessed May 26, 2015). 

19Executive 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/presidentialmemorandum-power-sector-carbon-pollutionstandards (last accessed May 12, 2015). 

20U.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). 

21U.S. EPA, 2014: Carbon Pollution Standards for 

Modified and Reconstructed Stationary Sources: 

Electric Utility Generating Units; Proposed Rules, 

79 FR 34960 (June 18, 2014). 

22U.S. EPA, 2014: Carbon Pollution Emission 

Guidelines for Existing Stationary Sources: Electric 

Utility Generating Units; Proposed Rule, 79 FR 

34830 (June 18, 2014). 

23Executive Office of the President, 2013: The 

President’s Climate Action Plan at 21, June. 

Available at: http://www.whitehouse.gov/sites/

default/files/image/

president27sclimateactionplan.pdf (last accessed 

May 12, 2015). 

24U.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. Schlo ̈mer, C. von Stechow, T. 

Zwickel and J.C. Minx (eds.)]. Cambridge University 

Press, pp. 599–670. 

27As discussed in section V.B.2.c., fuel burn 

growth rates for air carriers and general aviation 

aircraft operating on jet fuel are projected to grow 

by 49 percent from 2010 to 2035, and this provides 

a scaling factor for growth in GHG emissions which 

would increase at a similar rate as the fuel burn by 

2030, 2035, and 2040. FAA, 2015: FAA Aerospace 

Forecast Fiscal Years 2015–2035, 134 pp. Available 

at https://www.faa.gov/about/office_org/

headquarters_offices/apl/aviation_forecasts/

aerospace_forecasts/2015–2035/media/2015_

National_Forecast_Report.pdf (last accessed May 

12, 2015). 

28Center for Biological Diversity, Center for Food 

Safety, Friends of the Earth, International Center for 

Technology Assessment, and Oceana, 2007: Petition 

for Rulemaking Under the Clean air Act to Reduce 

the Emissions of Air Pollutants from Aircraft the 

Contribute to Global Climate Change, December 5. 

Available at http://www.epa.gov/otaq/aviation.htm 

(last accessed May 12, 2015). 

The 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

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

In the Climate Action Plan, the 

President also indicated that the U.S. 

was working internationally to make 

progress in a variety of areas and 

specifically noted the progress being 

made by ICAO to develop global CO2

emission standards for aircraft.23 The 

proposed endangerment and cause or 

contribute findings for aircraft GHG 

emissions under section 231(a)(2)(A) of 

the CAA are a preliminary but necessary 

first step to begin to address GHG 

emissions from the aviation sector, the 

highest-emitting category of 

transportation sources that the EPA has 

not yet addressed. As presented in more 

detail in Section V of this preamble, 

total U.S. aircraft GHG emissions in 

2013 represented 11 percent of GHG 

emissions from the U.S. transportation 

sector,24 and in 2010, the latest year 

with complete global emissions data, 

U.S. aircraft GHG emissions represented 

29 percent of global aircraft GHG 

emissions.25 26 U.S. aircraft GHG 

emissions are projected to increase by 

almost 50 percent over the next two 

decades.27 See section V of this 

preamble for more information about 

the data sources that compose the 

aircraft GHG emissions inventory. 

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. 

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 


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29Sections 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. 

30ABT 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. 

31U.S. EPA, 2012: Memorandum in Response to 

Petition Regarding Greenhouse Gas Emissions from 

Aircraft, June 14. Available at http://www.epa.gov/ 

otaq/aviation.htm (last accessed May 12, 2015) and 

Docket EPA–HQ–OAR–2014–0828. 

32Petitions 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. 

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. 

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 thenpending 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. 

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. 

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 


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33 ICAO, 2006: Convention on International Civil 

Aviation, Ninth Edition, Document 7300/9. 

Available at: http://www.icao.int/publications/

catalogue/cat_2015_en.pdf (last accessed May 12, 

2015). 

The ICAO Document 7300 is found on page 1 of 

the ICAO Products & Services 2015 catalog and is 

copyright protected; Order No. 7300. 

34Members of ICAO’s Assembly are generally 

termed member States or contracting States. These 

terms are used interchangeably throughout this 

preamble. 

35There are currently 191 Contracting States 

according to ICAO’s Web site: www.icao.int (last 

accessed May 12, 2015). 

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. 

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. 

40CAEP’s terms of reference are available at 

http://www.icao.int/environmental-protection/

Pages/Caep.aspx#ToR (last accessed May 12, 2015). 

41Pursuant 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. 

GHG standard (which may take the form 

of a CO2 standard), provided the EPA 

issues final positive endangerment and 

cause or contribute findings under CAA 

section 231. This approach is contingent 

on ICAO’s adoption of an international 

aircraft CO2 standard that is consistent 

with CAA section 231 and is 

appropriate for domestic needs in the 

United States. 

1. International Regulations and U.S. 

Obligations 

As noted above, we have worked with 

the FAA since 1973, and later with 

ICAO, to develop domestic and 

international standards and other 

recommended practices pertaining to 

aircraft engine emissions. ICAO is a 

United Nations (UN) specialized agency, 

established in 1944 by the Convention 

on International Civil Aviation (Chicago 

Convention), ‘‘in order that 

international civil aviation may be 

developed in a safe and orderly manner 

and that international air transport 

services may be established on the basis 

of equality of opportunity and operated 

soundly and economically.’’ 33 ICAO 

sets standards and regulations necessary 

for aviation safety, security, efficiency, 

capacity and environmental protection, 

and serves as the forum for cooperation 

in all fields of international civil 

aviation. ICAO works with the Chicago 

Convention’s member States and global 

aviation organizations to develop 

international Standards and 

Recommended Practices (SARPs), 

which member States reference when 

developing their legally-enforceable 

national civil aviation regulations. The 

U.S. is currently one of 191 

participating ICAO member States.34 35

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

ICAO’s work on the environment 

focuses primarily on those problems 

that benefit most from a common and 

coordinated approach on a worldwide 

basis, namely aircraft noise and engine 

emissions. Standards and 

Recommended Practices (SARPs) for the 

certification of aircraft noise and aircraft 

engine emissions are covered by Annex 

16 of the Chicago Convention. To 

continue to address aviation 

environmental issues, in 2004, ICAO 

established three environmental goals: 

(1) Limit or reduce the number of 

people affected by significant aircraft 

noise; (2) limit or reduce the impact of 

aviation emissions on local air quality; 

and (3) limit or reduce the impact of 

aviation greenhouse gas emissions on 

the global climate. 

The Convention has a number of other 

features that govern international 

commerce. First, member States that 

wish to use aircraft in international 

transportation must adopt emissions 

standards and other recommended 

practices that are at least as stringent as 

ICAO’s standards. Member States may 

ban the use of any aircraft within their 

airspace that does not meet ICAO 

standards.37 Second, member States are 

required to recognize the airworthiness 

certificates of any State whose standards 

are at least as stringent as ICAO’s 

standards, thereby assuring that aircraft 

of any member State will be permitted 

to operate in any other member State.38

Third, to ensure that international 

commerce is not unreasonably 

constrained, a member State which 

elects to adopt more stringent domestic 

emission standards is obligated to notify 

ICAO of the differences between its 

standards and ICAO standards.39

ICAO’s CAEP, which consists of 

Members and Observers from States, 

intergovernmental and nongovernmental 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. 

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 


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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. 

43CAEP develops new emission standards based 

on an assessment of the technical feasibility, cost, 

and environmental benefit of potential 

requirements. 

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. 

45CAEP 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. 

46CAEP/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. 48CAEP/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). 

51A 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. 

52The global aspirational goal for international 

aviation of improving annual fuel efficiency by 2 

percent is for the annual international civil aviation 

in-service fleet. Fuel efficiency is measured on the 

basis of the volume of fuel used per revenue tonne 

kilometer performed. (ICAO, CAEP, Aspirational 

Goals and Implementation Options, HLM–ENV/09– 

WP/5, High-Level Meeting on International 

Aviation and Climate Change, Presented by the 

Secretariat, Montreal, October 7 to 9, 2009. 

Available at http://www.icao.int/Meetings/AMC/

MA/High%20Level%202009/hlmenv_wp005_en.pdf 

(last accessed May 12, 2015). 

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

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 newlycertified turbofan engines, which are 

those engine models that received their 

initial type certificate after the effective 

date of the regulations—also referred to 

as newly-certified engines or new 

engine designs—and to in-production 

engines, but with different effective 

dates for newly-certified engines and inproduction 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 inproduction 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

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. 

—. . . 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 


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53U.S. EPA, 1973: Emission Standards and Test 

Procedures for Aircraft; Final Rule, 38 FR 19088 

(July 17, 1973). 

54The 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. 

55This does not mean that in 1997 we 

promulgated requirements for the re-certification or 

retrofit of existing in-use engines. 

56 In the existing EPA regulations, 40 CFR part 87, 

newly-certified aircraft engines are described as 

engines of a type or model of which the date of 

manufacture of the first individual production 

model was after the implementation date. Newly 

manufactured aircraft engines are characterized as 

engines of a type or model for which the date of 

manufacturer of the individual engine was after the 

implementation date. 

57U.S. EPA, 1997: Control of Air Pollution from 

Aircraft and Aircraft Engines; Emission Standards 

and Test Procedures; Final Rule, 62 FR 25355 (May 

8, 1997). 

58U.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). 

59U.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). 

60While 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 noncommercial 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. 

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. 

ICAO (with U.S. participation and 

agreement), and subsequently the EPA 

has initiated rulemakings under CAA 

section 231 to establish domestic 

aircraft engine emission standards that 

are of at least equivalent stringency as 

ICAO’s standards. This approach has 

been affirmed as reasonable by the U.S. 

Court of Appeals for the D.C. Circuit. 

NACAA v. EPA, 489 F.3d 1221, 1230– 

32 (D.C. Cir. 2007). In exercising the 

EPA’s standard-setting authority, 

provided the EPA makes positive 

endangerment and cause or contribute 

findings under CAA section 231 and 

ICAO adopts an international aircraft 

CO2 standard that is consistent with 

CAA section 231 and is appropriate for 

domestic needs in the United States, the 

EPA expects to proceed along a similar 

approach for the future CAA section 231 

aircraft GHG standard (or aircraft CO2

standard). 

We anticipate that ICAO/CAEP will 

adopt a final aircraft CO2 emissions 

standard in February 2016. This 

proposal, and any final endangerment 

and cause or contribute finding for 

aircraft GHG emissions, are part of 

preparing for the possible subsequent 

domestic rulemaking process to adopt 

standards that are of at least equivalent 

stringency as the anticipated ICAO CO2

standards. These findings, which are 

factual and science-based, encompass a 

determination of whether GHG 

emissions from aircraft cause or 

contribute to air pollution which may 

reasonably be anticipated to endanger 

public health or welfare. If positive 

findings are made, the EPA will be 

obligated under section 231 of the CAA 

to set emission standards applicable to 

GHG emissions from the classes of 

aircraft engines for which the EPA 

makes the cause or contribute finding. If 

positive findings are not made, the EPA 

will not have triggered its obligation to 

set GHG emission standards under CAA 

section 231. 

The EPA has worked diligently over 

the past four years within the ICAO/

CAEP process on a range of technical 

issues regarding aircraft CO2 emission 

standards. The ANPR that accompanies 

this proposal, in Section VI, discusses 

the issues arising in the ongoing 

international proceedings and U.S. 

input to CAEP regarding the 

international CO2 standard to help 

ensure transparency about this process. 

In addition, in the ANPR the EPA 

requests public comments on a variety 

of issues to assist the Agency in 

developing its position with regard to 

these issues and the aircraft engine GHG 

emission standards that it may 

potentially adopt under the CAA. 

E. The EPA’s Regulation of Aircraft 

Emissions 

As required by the CAA, the EPA has 

been engaged in reducing harmful air 

pollution from aircraft engines for over 

40 years. In 1973, the EPA began to 

regulate gaseous exhaust emissions, 

smoke, and fuel venting from aircraft 

engines.53 We have occasionally revised 

these regulations. In a 1997 rulemaking, 

for example, we made our emission 

standards and test procedures more 

consistent with those of ICAO’s CAEP 

for turbofan engines used in commercial 

aviation with rated thrusts greater than 

26.7 kilonewtons. These ICAO 

requirements are generally referred to as 

CAEP/2 standards.54 That action 

included new NOX emission standards 

for newly manufactured commercial 

turbofan engines (as described earlier, 

those engines built after the effective 

date of the regulations that were already 

certified to pre-existing standards—also 

referred to as in-production engines) 55

and for newly-certified commercial 

turbofan engines (as described earlier, 

those engine models that received their 

initial type certificate after the effective 

date of the regulations—also referred to 

as new engine designs).56 It also 

included a carbon monoxide emission 

standard for in-production commercial 

turbofan engines.57 In 2005, we 

promulgated more stringent NOX

emission standards for newly-certified 

commercial turbofan engines.58 That 

final rule brought the U.S. standards 

closer to alignment with ICAO CAEP/4 

requirements that became effective in 

2004. In 2012, we issued more stringent 

two-tiered NOX emission standards for 

newly-certified and in-production 

commercial and non-commercial 

turbofan aircraft engines, and these NOX

standards align with ICAO’s CAEP/6 

and CAEP/8 requirements that became 

effective in 2013 and 2014, 

respectively.59 60

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 wholeaircraft CO2 emissions, as the CO2

emissions are influenced by 

aerodynamics, weight, and enginespecific 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 


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

analysis under section 202(a)). 

63When 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). 

64See id. at 121–122. 

65See id. at 122–123 (noting that the § 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)). 

66See id. at 121–122. 

from aircraft engines and to issue final 

‘‘regulations with such modifications as 

[she] deems appropriate.’’ 

III. Legal Framework for This Action 

The EPA has previously made an 

endangerment finding for GHGs under 

Title II of the CAA, in the 2009 

Endangerment Finding for section 

202(a) source categories. In the 2009 

Endangerment Finding, the EPA 

explained its legal framework for 

making an endangerment finding under 

section 202(a) of the CAA (74 FR 18886, 

18890–94 (April 24, 2009), and 74 FR 

66496, 66505–10 (December 15, 2009)). 

The text in section 202(a) that was the 

basis for the 2009 Endangerment 

Finding addresses ‘‘the emission of any 

air pollutant from any class or classes of 

new motor vehicles or new motor 

vehicle engines, which in [the 

Administrator’s] judgment cause, or 

contribute to, air pollution which may 

reasonably be anticipated to endanger 

public health or welfare.’’ Similarly, 

section 231(a)(2)(A) concerns ‘‘the 

emission of any air pollutant from any 

class or classes of aircraft engines which 

in [the Administrator’s] judgment 

causes, or contributes to, air pollution 

which may reasonably be anticipated to 

endanger public health or welfare.’’ 

Thus, the text of the CAA section 

concerning aircraft emissions in section 

231(a)(2)(A) mirrors the text of CAA 

section 202(a) that was the basis for the 

2009 Endangerment Finding. 

The EPA’s approach in the 2009 

Endangerment Finding (described below 

in Sections III.A and III.B) was affirmed 

by the U.S. Court of Appeals for the D.C. 

Circuit in Coalition for Responsible 

Regulation, Inc. v. EPA, 684 F.3d 102 

(D.C. Cir. 2012), reh’g denied 2012 U.S. 

App. LEXIS 26313, 26315, 25997 (D.C. 

Cir 2012) (CRR). In particular, the D.C. 

Circuit ruled that the 2009 

Endangerment Finding (including the 

agency’s denial of petitions for 

reconsideration of that Finding) was not 

arbitrary or capricious, was consistent 

with the U.S. Supreme Court’s decision 

in Massachusetts v. EPA and the text 

and structure of the CAA, and was 

adequately supported by the 

administrative record. CRR, 684 F.3d at 

116–128. The D.C. Circuit found that the 

EPA had based its decision on 

‘‘substantial scientific evidence’’ and 

noted that the EPA’s reliance on major 

scientific assessments was consistent 

with the methods that decision-makers 

often use to make a science-based 

judgment. Id. at 120–121. Petitions for 

certiorari were filed in the Supreme 

Court, and the Supreme Court granted 

six of those petitions but ‘‘agreed to 

decide only one question: ‘Whether EPA 

permissibly determined that its 

regulation of greenhouse gas emissions 

from new motor vehicles triggered 

permitting requirements under the 

Clean Air Act for stationary sources that 

emit greenhouse gases.’ ’’ Utility Air Reg. 

Group v. EPA, 134 S. Ct. 2427, 2438 

(2014); see also Virginia v. EPA, 134 S. 

Ct. 418 (2013), Pac. Legal Found. v. 

EPA, 134 S. Ct. 418 (2013), and CRR, 

134 S. Ct. 468 (2013) (all denying cert.). 

Thus, the Supreme Court did not 

disturb the D.C. Circuit’s holding that 

affirmed the 2009 Endangerment 

Finding. Accordingly, the Agency 

proposes that it is reasonable to use that 

same approach under section 

231(a)(2)(A)’s similar endangerment 

text, and as explained in the following 

discussion, is acting consistently with 

that judicially sanctioned framework for 

purposes of this proposed section 231 

finding. 

Two provisions of the CAA govern 

this proposal. Section 231(a)(2)(A) sets 

forth a two-part predicate for regulatory 

action under that provision: 

Endangerment and cause or contribute. 

Section 302 of the Act contains 

definitions of the terms ‘‘air pollutant’’ 

and ‘‘welfare’’ used in section 

231(a)(2)(A). These statutory provisions 

are discussed below. 

A. Section 231(a)(2)(A)—Endangerment 

and Cause or Contribute 

As noted above, section 231(a)(2)(A) 

of the CAA (like section 202(a)) calls for 

the Administrator to exercise her 

judgment and make two separate 

determinations: First, whether the 

relevant kind of air pollution—here, 

GHGs—may reasonably be anticipated 

to endanger public health or welfare, 

and second, whether emissions of any 

air pollutant from classes of the sources 

in question (aircraft engines under 

section 231 and new motor vehicles or 

engines under section 202) cause or 

contribute to this air pollution.62

The Administrator interprets the twopart 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

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. 

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)). 

Third, because scientific knowledge is 

constantly evolving, the Administrator 

may be called upon to make decisions 

while recognizing the uncertainties and 

limitations of the data or information 

available, as risks to public health or 

welfare may involve the frontiers of 

scientific or medical knowledge.66 At 

the same time, the Administrator must 

exercise reasoned decision making, and 

avoid speculative inquiries. 

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 


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67As the D.C. Circuit explained in reviewing the 

2009 Endangerment Finding under analogous 

language in section 202(a): ‘‘At bottom, § 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. 

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. 

Fifth, the Administrator is to consider 

the risks to all parts of our population, 

including those who are at greater risk 

for reasons such as increased 

susceptibility to adverse health effects. 

If vulnerable subpopulations are 

especially at risk, the Administrator is 

entitled to take that point into account 

in deciding the question of 

endangerment. Here too, both likelihood 

and severity of adverse effects are 

relevant. As explained previously in the 

2009 Endangerment Finding and as 

reiterated below for this proposed 

section 231 finding, vulnerable 

subpopulations face serious health risks 

as a result of climate change. 

As the Supreme Court recognized in 

Massachusetts v. EPA, 549 U.S. at 534, 

the EPA may make an endangerment 

finding despite the existence of ‘‘some 

residual uncertainty’’ in the scientific 

record. See also CRR, 684 F.2d at 122. 

Thus, this framework recognizes that 

regulatory agencies such as the EPA 

must be able to deal with the reality that 

‘‘[m]an’s ability to alter his environment 

has developed far more rapidly than his 

ability to foresee with certainty the 

effects of his alterations.’’ See Ethyl 

Corp v. EPA, 541 F.2d 1, 6 (D.C. Cir.), 

cert. denied 426 U.S. 941 (1976). Both 

‘‘the Clean Air Act ‘and common sense 

* * * demand regulatory action to 

prevent harm, even if the regulator is 

less than certain that harm is otherwise 

inevitable.’ ’’ See Massachusetts v. EPA, 

549 U.S. at 506, n.7 (citing Ethyl Corp.); 

see also CRR, 684 F.3d at 121–122. 

In the 2009 Endangerment Finding, 

the Administrator recognized that the 

scientific context for an action 

addressing climate change was unique 

at that time because there was a very 

large and comprehensive base of 

scientific information that had been 

developed over many years through a 

global consensus process involving 

numerous scientists from many 

countries and representing many 

disciplines. 74 FR 66506, December 15, 

2009. That informational base has since 

grown. The Administrator also 

previously recognized that there are 

varying degrees of uncertainty across 

many of these scientific issues, which 

remains true. It is in this context that 

she is exercising her judgment and 

applying the statutory framework in this 

proposed section 231 finding. Further 

discussion of the language in section 

231(a)(2)(A), and parallel language in 

202(a), is provided below to explain 

more fully the basis for this 

interpretation, which the D.C. Circuit 

upheld in the 202(a) context. 

1. The Statutory Language 

The interpretation described above 

flows from the statutory language itself. 

The phrase ‘‘may reasonably be 

anticipated’’ and the term ‘‘endanger’’ in 

section 231(a)(2)(A) (as in section 

202(a)) authorize, if not require, the 

Administrator to act to prevent harm 

and to act in conditions of uncertainty. 

They do not limit her to merely reacting 

to harm or to acting only when certainty 

has been achieved; indeed, the 

references to anticipation and to 

endangerment imply that to fail to look 

to the future or to less than certain risks 

would be to abjure the Administrator’s 

statutory responsibilities. As the D.C. 

Circuit explained, the language ‘‘may 

reasonably be anticipated to endanger 

public health or welfare’’ in CAA 

§ 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 § 202(a)—utilizing 

emission standards to prevent 

reasonably anticipated endangerment 

from maturing into concrete harm.’’ Id. 

The same language appears in section 

231(a)(2)(A), and the same 

interpretation applies in that context. 

Moreover, by instructing the 

Administrator to consider whether 

emissions of an air pollutant cause or 

contribute to air pollution in the second 

part of the two-part test, the Act makes 

clear that she need not find that 

emissions from any one sector or class 

of sources are the sole or even the major 

part of an air pollution problem. The 

use of the term ‘‘contribute’’ clearly 

indicates that such emissions need not 

be the sole or major cause of the 

pollution. Finally, the phrase ‘‘in [her] 

judgment’’ authorizes the Administrator 

to weigh risks and to consider 

projections of future possibilities, while 

also recognizing uncertainties and 

extrapolating from existing data. 

Finally, when exercising her 

judgment in making both the 

endangerment and cause-or-contribute 

findings, the Administrator balances the 

likelihood and severity of effects. 

Notably, the phrase ‘‘in [her] judgment’’ 

modifies both ‘‘may reasonably be 

anticipated’’ and ‘‘cause or contribute.’’ 

2. How the Origin of the Current 

Statutory Language Informs the EPA’s 

Interpretation of Section 231(a)(2)(A) 

In the proposed and final 2009 

Endangerment Finding, the EPA 

explained that when Congress revised 

the section 202(a) language that 

governed that finding, along with other 

provisions, as part of the 1977 

amendments to the CAA, it was 

responding to decisions issued by the 

D.C. Circuit in Ethyl Corp. v. EPA 

regarding the pre-1977 version of 

section 211(c) of the Act. 74 FR 18891, 

(April 24, 2009); see also 74 FR 66506, 

(December 15, 2009). Section 231 was 

one of those other CAA provisions 

included in the 1977 amendments; 

therefore, the Agency’s discussion for 

the 2009 Endangerment Finding 

regarding the history of section 202 and 

how it supports the EPA’s approach is 

also relevant for section 231. The 

legislative history of those amendments, 

particularly the report by the House 

Committee on Interstate and Foreign 

Commerce, demonstrates that the EPA’s 

interpretation of the section 231(a)(2)(A) 

language as set forth here in support of 

the Agency’s section 231 finding (which 

is the same as its interpretation of the 

parallel language in section 202(a) as 

explained in the 2009 Endangerment 

Finding), is fully consistent with 

Congress’ intention in crafting these 

provisions. See H.R. Rep. 95–294 (1977), 


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68The 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. 

69The 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. 

70See 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’’). 

71Congress 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. 

72At 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). 

73Throughout 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. 

74Thus, 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. 

as reprinted in 4 A Legislative History 

of the Clean Air Act Amendments of 

1977 (1978) at 2465 (hereinafter LH).68

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

In revising the statutory language, 

Congress relied heavily on the en banc 

decision in Ethyl Corp. v. EPA, which 

reversed a 3-judge panel opinion 

regarding an EPA rule restricting the 

content of lead in leaded gasoline.72

After reviewing the relevant facts and 

law, the full court evaluated the 

statutory language at issue to see what 

level of ‘‘certainty [was] required by the 

Clean Air Act before EPA may act.’’ 541 

F.2d at 7. 

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. 

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

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 


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75Specifically, 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. 

76The 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. 

77Section 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. 

contribute clearly indicates a lower 

threshold than the sole or major cause. 

Moreover, like the section 202(a) 

language that governed the 2009 

Endangerment Finding, the statutory 

language in section 231(a)(2)(A) does 

not contain a modifier on its use of the 

term ‘‘contribute.’’ Unlike other CAA 

provisions, it does not require 

‘‘significant’’ contribution. Compare, 

e.g., CAA sections 111(b); 213(a)(2), (4). 

Congress made it clear that the 

Administrator is to exercise her 

judgment in determining contribution, 

and authorized regulatory controls to 

address air pollution even if the air 

pollution problem results from a wide 

variety of sources. While the 

endangerment test looks at the entire air 

pollution problem and the risks it poses, 

the cause or contribute test is designed 

to authorize the EPA to identify and 

then address what may well be many 

different sectors, classes, or groups of 

sources that are each part of the 

problem. 

As explained for the 2009 

Endangerment Finding, the D.C. Circuit 

has discussed the concept of 

contribution in the CAA, and its case 

law supports the EPA’s interpretation 

that the level of contribution need not 

be significant. 74 FR 66542, December 

15, 2009. In Catawba County v. EPA, 

571 F.3d 20 (D.C. Cir. 2009), the court 

upheld EPA’s PM[2.5] attainment and 

nonattainment designation decisions, 

analyzing CAA section 107(d), which 

requires EPA to designate an area as 

nonattainment if it ‘‘contributes to 

ambient air quality in a nearby area’’ not 

attaining the national ambient air 

quality standards. Id. at 35. The court 

noted that it had previously held that 

the term ‘‘contributes’’ is ambiguous in 

the context of CAA language. See EDF 

v. EPA, 82 F.3d 451, 459 (D.C. Cir. 

1996). ‘‘[A]mbiguities in statutes within 

an agency’s jurisdiction to administer 

are delegations of authority to the 

agency to fill the statutory gap in 

reasonable fashion.’’ 571 F.3d at 35 

(citing Nat’l Cable & Telecomms. Ass’c 

v. Brand X Internet Servs, 545 U.S. 967, 

980 (2005)). The court then proceeded 

to consider and reject petitioners’ 

argument that the verb ‘‘contributes’’ in 

CAA section 107(d) necessarily 

connotes a significant causal 

relationship. Specifically, the D.C. 

Circuit again noted that the term is 

ambiguous, leaving it to EPA to 

interpret in a reasonable manner. In the 

context of this discussion, the court 

noted that ‘‘a contribution may simply 

exacerbate a problem rather than cause 

it * * *.’’ 571 F.3d at 39. 

This is consistent with the D.C. 

Circuit’s discussion of the concept of 

contribution in the context of CAA 

section 213 and rules for nonroad 

vehicles in Bluewater Network v. EPA, 

370 F.3d 1 (D.C. Cir. 2004). In that case, 

industry argued that section 213(a)(3) 

requires a finding of a significant 

contribution before the EPA can 

regulate, while the EPA’s view was that 

the CAA requires a finding only of 

contribution. Id. at 13. Section 213(a)(3), 

like section 231(a)(2)(A), is triggered by 

a finding that certain sources ‘‘cause, or 

contribute to,’’ air pollution, while an 

adjacent provision, section 213(a)(2), is 

triggered by a finding of a ‘‘significant’’ 

contribution. The court looked at the 

‘‘ordinary meaning of ‘contribute’ ’’ 

when upholding the EPA’s reading. 

After referencing dictionary definitions 

of ‘‘contribute,’’ the court also noted 

that ‘‘[s]tanding alone, the term has no 

inherent connotation as to the 

magnitude or importance of the relevant 

‘share’ in the effect; certainly it does not 

incorporate any ‘significance’ 

requirement.’’ 370 F.3d at 13.75 The 

court found that the bare ‘‘contribute’’ 

language invests the Administrator with 

discretion to exercise judgment 

regarding what constitutes a sufficient 

contribution for the purpose of making 

a cause or contribute finding. Id. at 14.76

Like the statutory language 

considered in Catawba County and 

Bluewater Network, as well as the 

section 202(a) language that governed 

the Agency’s previous findings for 

GHGs emitted by other types of mobile 

sources, section 231(a)(2)(A) refers to 

contribution and does not specify that 

the contribution must be significant 

before an affirmative finding can be 

made. To be sure, any finding of a 

‘‘contribution’’ requires some threshold 

to be met; a truly trivial or de minimis 

‘‘contribution’’ might not count as such. 

The Administrator therefore has ample 

discretion in exercising her reasonable 

judgment and determining whether, 

under the circumstances presented, the 

cause or contribute criterion has been 

met.77 As noted above, in addressing 

provisions in section 202(a), the D.C. 

Circuit has explained that the Act at the 

endangerment finding step did not 

require the EPA to identify a precise 

numerical value or ‘‘a minimum 

threshold of risk or harm before 

determining whether an air pollutant 

endangers.’’ CRR, 684 F.3d at 122–123. 

Accordingly, EPA ‘‘may base an 

endangerment finding on ‘a lesser risk 

of greater harm . . . or a greater risk of 

lesser harm’ or any combination in 

between.’’ Id. (quoting Ethyl Corp., 541 

F.2d at 18). Recognizing the substantial 

record of empirical data and scientific 

evidence that the EPA relied upon in 

the 2009 Endangerment Finding, the 

court determined that its ‘‘failure to 

distill this ocean of evidence into a 

specific number at which greenhouse 

gases cause ‘dangerous’ climate change 

is a function of the precautionary thrust 

of the CAA and the multivariate and 

sometimes uncertain nature of climate 

science, not a sign of arbitrary or 

capricious decision-making.’’ Id. at 123. 

As the language in section 231(a)(2)(A) 

is analogous to that in section 202(a), it 

is clearly reasonable to apply this 

interpretation to the endangerment 

determination under section 

231(a)(2)(A). Moreover, the logic 

underlying this interpretation supports 

the general principle that under CAA 

section 231 the EPA is not required to 

identify a specific minimum threshold 

of contribution from potentially subject 

source categories in determining 

whether their emissions ‘‘cause or 

contribute’’ to the endangering air 

pollution. The reasonableness of this 

principle is further supported by the 

fact that section 231 does not impose on 

the EPA a requirement to find that such 

contribution is ‘‘significant,’’ let alone 

the sole or major cause of the 

endangering air pollution. This context 

further supports the EPA’s 

interpretation that section 231(a)(2)(A) 

requires some level of contribution that, 

while exceeding de minimis or trivial 

thresholds, does not need to rise to a 

pre-determined numerical level of 

significance. 

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 


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78While 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. 

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 

§ 107(d) and finding it reasonable for the 

agency to adopt a totality of the 

circumstances approach); see also 74 FR 

at 66542, (December 15, 2009). Further 

discussion of this issue can be found in 

sections IV and V of this preamble. 

B. Air Pollutant, Public Health and 

Welfare 

The CAA defines both ‘‘air pollutant’’ 

and ‘‘welfare.’’ Air pollutant is defined 

as: ‘‘Any air pollution agent or 

combination of such agents, including 

any physical, chemical, biological, 

radioactive (including source material, 

special nuclear material, and byproduct 

material) substance or matter which is 

emitted into or otherwise enters the 

ambient air. Such term includes any 

precursors to the formation of any air 

pollutant, to the extent the 

Administrator has identified such 

precursor or precursors for the 

particular purpose for which the term 

‘air pollutant’ is used.’’ CAA section 

302(g). Greenhouse gases fit well within 

this capacious definition. See 

Massachusetts v. EPA, 549 U.S. at 532. 

They are ‘‘without a doubt’’ physical 

chemical substances emitted into the 

ambient air. Id. at 529. Section V below 

contains further discussion of the ‘‘air 

pollutant’’ for purposes of this section 

231 proposed contribution finding, 

which uses the same definition of air 

pollutant as the EPA adopted for 

purposes of the 2009 Endangerment 

Finding. 

Regarding ‘‘welfare,’’ the CAA states 

that ‘‘[a]ll language referring to effects 

on welfare includes, but is not limited 

to, effects on soils, water, crops, 

vegetation, man-made materials, 

animals, wildlife, weather, visibility, 

and climate, damage to and 

deterioration of property, and hazards to 

transportation, as well as effects on 

economic values and on personal 

comfort and well-being, whether caused 

by transformation, conversion, or 

combination with other air pollutants.’’ 

CAA section 302(h). This definition is 

quite broad. Importantly, it is not an 

exclusive list due to the use of the term 

‘‘includes, but is not limited to, * * *.’’ 

Effects other than those listed here may 

also be considered effects on welfare. 

Moreover, the terms contained within 

the definition are themselves expansive. 

For example, deterioration to property 

could include damage caused by 

extreme weather events. Effects on 

vegetation could include impacts from 

changes in temperature and 

precipitation as well as from the 

spreading of invasive species or insects. 

Prior welfare effects evaluated by the 

EPA in other contexts include impacts 

on vegetation, as well as reduced 

visibility, changes in nutrient balance 

and acidity of the environment, soiling 

of buildings and statues, and erosion of 

building materials. See, e.g., Final 

Secondary National Ambient Air 

Quality Standards for Oxides of 

Nitrogen and Sulfur, 77 FR 20218, April 

3, 2012; Control of Emissions from 

Nonroad Large Spark Ignition Engines 

and Recreational Engines (Marine and 

Land-Based), 67 FR 68242, November 8, 

2002; Final Heavy-Duty Engine and 

Vehicle Standards and Highway Diesel 

Sulfur Control Requirements, 66 FR 

5002, January 18, 2001. 

Although the CAA defines ‘‘effects on 

welfare’’ as discussed above, there are 

no definitions of ‘‘public health’’ or 

‘‘public welfare’’ in the Clean Air Act. 

The Supreme Court has discussed the 

concept of ‘‘public health’’ in the 

context of whether costs can be 

considered when setting National 

Ambient Air Quality Standards. 

Whitman v. American Trucking Ass’n, 

531 U.S. 457 (2001). In Whitman, the 

Court imbued the term with its most 

natural meaning: ‘‘The health of the 

public.’’ Id. at 466. When considering 

public health, the EPA has looked at 

morbidity, such as impairment of lung 

function, aggravation of respiratory and 

cardiovascular disease, and other acute 

and chronic health effects, as well as 

mortality. See, e.g., Final National 

Ambient Air Quality Standard for 

Ozone, 73 FR 16436, March 27, 2008. 

IV. The Proposed Endangerment 

Finding Under CAA Section 231 

This section describes the 

Administrator’s proposed endangerment 

finding under CAA section 231(a)(2) 

and its basis. Beginning with the air 

pollution under consideration, the 

Administrator is proposing to use the 

same definition of the ‘‘air pollution’’ 

under CAA section 231(a)(2) as that 

used under CAA section 202(a)(1), 

namely the mix of six well-mixed GHGs 

mentioned above: CO2, methane, nitrous 

oxide, hydrofluorocarbons, 

perfluorocarbons, and sulfur 

hexafluoride. As described in section 

IV.A below, it is the Administrator’s 

view that the reasons detailed in the 

2009 Endangerment Finding for 

defining the scope and nature of the air 

pollution to be these six well-mixed 

GHGs remain valid and well-supported 

by the current science and are therefore 

reasonable bases for adopting the same 

definition of ‘‘air pollution’’ in this 

section 231(a)(2)(A) finding. Information 

from the new scientific assessments 

described in section IV.B below 

provides further support that the six 

well-mixed GHGs are the primary cause 

and driver of climate change. The 

Administrator considered other 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. 

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 


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79 74 FR 66516, December 15, 2009. 

80 74 FR 66517 to 66519, December 15, 2009. 

81We 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. 

83 74 FR 66518, December 15, 2009. 

84 74 FR 66524 to 66530, December 15, 2009. 

85 74 FR 66524, December 15, 2009. 

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

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, wellmixed GHGs: CO2, methane, nitrous 

oxide, hydrofluorocarbons, 

perfluorocarbons, and sulfur 

hexafluoride.79 The Administrator 

considered five primary reasons for 

focusing on this aggregate group as the 

air pollution in the 2009 Endangerment 

Finding: (1) They share common 

physical properties that influence their 

climate effects; (2) on the basis of these 

common physical properties, they have 

been determined to be the primary 

cause of human-induced climate 

change, are the best-understood driver 

of climate change, and are expected to 

remain the key driver of future climate 

change; (3) they are the common focus 

of climate change science research and 

policy analyses and discussions; (4) 

using the combined mix of these gases 

as the definition (versus an individual 

gas-by-gas approach) is consistent with 

the science, because risks and impacts 

associated with GHG-induced climate 

change are not assessed on an 

individual gas-by-gas basis; and (5) 

using the combined mix of these gases 

is consistent with past EPA practice, 

where separate substances from 

different sources, but with common 

properties, may be treated as a class 

(e.g., oxides of nitrogen, particulate 

matter, volatile organic compounds).80

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

As explained in more detail in the 

2009 Endangerment Finding, the EPA 

made the judgment that the scientific 

evidence is compelling that elevated 

concentrations of heat-trapping GHGs 

are the root cause of recently observed 

climate change and that the scientific 

record showed that most of the observed 

increase in global average temperatures 

since the mid-20th century is very likely 

due to the observed increase in 

anthropogenic GHG concentrations. The 

attribution of observed climate change 

to anthropogenic activities was based on 

multiple lines of evidence.83 The first 

line of evidence arises from our basic 

physical understanding of the effects of 

changing concentrations of GHGs, 

natural factors, and other human 

impacts on the climate system. The 

second line of evidence arises from 

indirect, historical estimates of past 

climate changes that suggest that the 

changes in global surface temperature 

over the last several decades are 

unusual. The third line of evidence 

arises from the use of computer-based 

climate models to simulate the likely 

patterns of response of the climate 

system to different forcing mechanisms 

(both natural and anthropogenic). 

2. Public Health Impacts Detailed in the 

2009 Endangerment Finding 

Climate change resulting from 

anthropogenic GHG emissions threatens 

multiple aspects of public health.84 In 

determining that the well-mixed GHG 

air pollution is reasonably anticipated to 

endanger public health for current and 

future generations, the Administrator 

noted her view that climate change can 

increase the risk of morbidity and 

mortality.85 In making that public health 

finding, the Administrator considered 

direct temperature effects, air quality 

effects, the potential for changes in 

vector-borne diseases, and the potential 

for changes in the severity and 

frequency of extreme weather events. In 

addition, the Administrator considered 

whether and how susceptible 

populations may be particularly at risk. 

As explained in more detail in the 2009 

Endangerment Finding, with respect to 

direct temperature effects, by raising 

average temperatures, climate change 

increases the likelihood of heat waves, 

which are associated with increased 

deaths and illnesses. Climate change is 

also expected to lead to reductions in 

cold-related mortality. The 2009 

Endangerment Finding, while noting 

uncertainty about how heat and cold 

related mortality would change in the 

future, also pointed to a USGCRP 

assessment report discussion that 

increases in heat-related mortality due 

to global warming in the United States 

was unlikely to be compensated for by 

decreases in cold-related mortality (74 

FR 66525, December 15, 2009). With 

regard to air quality effects, climate 

change is expected to increase ozone 

pollution over broad areas of the 

country, including large metropolitan 

population centers, and thereby increase 

the risks of respiratory infection, 

aggravation of asthma, and premature 

death. Other public health threats stem 

from the potential for increased deaths, 

injuries, infectious and waterborne 

diseases, stress-related disorders, and 

other adverse effects associated with 

increased hurricane intensity and 

increased frequency of intense storms 

and heavy precipitation associated with 

climate change. In addition, climate 

change is expected to be associated with 

an increase in the spread of food-, 

water-, and vector-borne diseases in 

susceptible populations. Climate change 

also has the potential to change 

aeroallergen production (for example, 

through lengthening the growing season 

for allergen-producing plants), and 

subsequent human exposures could 

increase allergenic illnesses. Children, 

the elderly, and the poor are among the 

most vulnerable to climate-related 

health effects. 

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 wellVerDate Sep<11>2014 19:14 Jun 30, 2015 Jkt 235001 PO 00000 Frm 00018 Fmt 4701 Sfmt 4702 E:\FR\FM\01JYP2.SGM 01JYP2

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87 74 FR 66510 to 66512, December 15, 2009. 88Administrative 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. 89U.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. 

90Coalition for Responsible Regulation, Inc. v. 

Environmental Protection Agency, 684 F.3d 102 

(D.C. Cir. 2012),), reh’g en banc denied, 2012 U.S. 

App. LEXIS 25997, 26313, 26315 (D.C. Cir. 2012) 

(CRR). 

91 549 U.S. 497 (2007). 

92CRR, 684 F.3d at 117–27. 

93 Id. at 125 

94 Id. at 120–121. 

95 Id. at 121 

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. 

4. The Science Upon Which the Agency 

Relied 

As outlined in section III.A of the 

2009 Endangerment Finding,87 the 

EPA’s approach to providing the 

technical and scientific information to 

inform the Administrator’s judgment 

regarding the question of whether GHGs 

endanger public health and welfare was 

to rely primarily upon the recent, major 

assessments by the USGCRP, the IPCC, 

and the NRC. These assessments 

addressed the scientific issues that the 

EPA was required to examine, were 

comprehensive in their coverage of the 

GHG and climate change issues, and 

underwent rigorous and exacting peer 

review by the expert community, as 

well as rigorous levels of U.S. 

government review, in which the EPA 

took part. Primary reliance on the major 

scientific assessments provided 

assurance that the Administrator was 

basing her judgment on the best 

available, well-vetted science that 

reflected the consensus of the climate 

science research community. The major 

findings of the USGCRP, IPCC, and NRC 

assessments supported the 

Administrator’s determination that 

elevated concentrations of GHGs in the 

atmosphere may reasonably be 

anticipated to endanger the public 

health and welfare of current and future 

generations. The EPA presented this 

scientific support at length in the 

comprehensive record for the 2009 

Endangerment Finding. Relevant 

sections of documents from the 2009 

Endangerment Finding record have been 

placed in the docket for this proposed 

finding under CAA section 231. 

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

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 decisionmakers often use to make a sciencebased judgment.95 Moreover, the Court 

supported the EPA’s reliance on the 

major scientific assessment reports 

conducted by USGCRP, IPCC, and NRC 

and found: 

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 


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96 Id. at 120. 

97 74 FR at 66524, December 15, 2009. 

98CRR, 684 F.3d at 121. 

99Utility 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.). 

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. Schlo ̈mer, C. von Stechow, T. 

Zwickel and J.C. Minx (eds.)]. Cambridge University 

Press, 1435 pp. 

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. 

102Melillo, 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. 

103NRC, 2010: Ocean Acidification: A National 

Strategy to Meet the Challenges of a Changing 

Ocean. The National Academies Press, 188 pp. 

104NRC Institute of Medicine, 2011: Climate 

Change, the Indoor Environment, and Health. 

Washington, DC: The National Academies Press, 

272 pp. 

105NRC 2011: Climate Stabilization Targets: 

Emissions, Concentrations, and Impacts over 

Decades to Millennia. The National Academies 

Press, 298 pp. 

106NRC, 2011: National Security Implications of 

Climate Change for U.S. Naval Forces. The National 

Academies Press, 226 pp. 

107NRC, 2011: Understanding Earth’s Deep Past: 

Lessons for Our Climate Future. The National 

Academies Press, 212 pp. 

108NRC, 2012: Sea-Level Rise for the Coasts of 

California, Oregon, and Washington: Past, Present, 

and Future. The National Academies Press, 201 pp. 

109NRC, 2013: Climate and Social Stress: 

Implications for Security Analysis. The National 

Academies Press, 280 pp. 

represented. Based on these evaluations, the 

EPA determined the assessments represented 

the best source material to use in deciding 

whether GHG emissions may be reasonably 

anticipated to endanger public health or 

welfare. . . . It makes no difference that 

much of the scientific evidence in large part 

consisted of ‘‘syntheses’’ of individual 

studies and research. Even individual studies 

and research papers often synthesize past 

work in an area and then build upon it. This 

is how science works. The EPA is not 

required to re-prove the existence of the atom 

every time it approaches a scientific 

question.96

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

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. 

B. Recent Science Further Supports the 

Administrator’s Judgment That the Six 

Well-Mixed Greenhouse Gases Endanger 

Public Health and Welfare 

Since the closure of the 

administrative record concerning the 

2009 Endangerment Finding (including 

the denial of petitions for 

reconsideration), a number of new 

major, peer-reviewed scientific 

assessments have been released. The 

EPA carefully reviewed the updated 

scientific conclusions in these 

assessments, largely to evaluate whether 

they would lead the EPA in this CAA 

section 231(a)(2)(A) finding to propose a 

different interpretation of, or place more 

or less weight on, the major findings 

reflected in the previous assessment 

reports that underpinned the 

Administrator’s judgment that the six 

well-mixed GHGs endanger public 

health and welfare. From its review, the 

EPA finds that these new assessments 

are largely consistent with, and in many 

cases strengthen and add to, the already 

compelling and comprehensive 

scientific evidence detailing the role of 

the six well-mixed GHGs in driving 

climate change, detailed in the 2009 

Endangerment Finding. Therefore, the 

new scientific assessments do not 

provide any reasonable basis on which 

to propose under CAA section 

231(a)(2)(A) a different conclusion than 

the one the EPA reached in 2009 under 

CAA section 202(a). Rather, they 

provide further support for this 

proposed finding under section 231. In 

particular, the new assessments 

discussed in this preamble provide 

additional detail regarding public health 

impacts, particularly on groups and 

people at certain lifestages especially 

vulnerable to climate change including 

children, the elderly, low-income 

communities and individuals, 

indigenous groups, and communities of 

color. 

The subsections below present brief 

summaries of the relevant key findings 

from the new major peer-reviewed 

scientific assessments, which include 

the following: 

• IPCC’s 2013–2014 Fifth Assessment 

Report (AR5) 100

• IPCC’s 2012 ‘‘Special Report on 

Managing the Risks of Extreme Events 

and Disasters to Advance Climate 

Change Adaptation’’ (SREX) 101

• USGCRP’s 2014 ‘‘Climate Change 

Impacts in the United States: the Third 

National Climate Assessment’’ 

(NCA3) 102

• NRC’s 2010 ‘‘Ocean Acidification: 

A National Strategy to Meet the 

Challenges of a Changing Ocean’’ 

(Ocean Acidification) 103

• NRC’s 2011 ‘‘Climate Change, the 

Indoor Environment, and Health’’ 

(Indoor Environment) 104

• NRC’s 2011 ‘‘Report on Climate 

Stabilization Targets: Emissions, 

Concentrations, and Impacts over 

Decades to Millennia’’ (Climate 

Stabilization Targets) 105

• NRC’s 2011 ‘‘National Security 

Implications for U.S. Naval Forces’’ 

(National Security Implications) 106

• NRC’s 2011 ‘‘Understanding Earth’s 

Deep Past: Lessons for Our Climate 

Future’’ (Understanding Earth’s Deep 

Past) 107

• NRC’s 2012 ‘‘Sea Level Rise for the 

Coasts of California, Oregon, and 

Washington: Past, Present, and Future’’ 

(Sea Level Rise) 108

• NRC’s 2013 ‘‘Climate and Social 

Stress: Implications for Security 

Analysis’’ (Climate and Social Stress) 109


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110NRC, 2013: Abrupt Impacts of Climate 

Change: Anticipating Surprises. The National 

Academies Press, 250 pp. 

111NRC, 2014: The Arctic in the Anthropocene: 

Emerging Research Questions. The National 

Academies Press, 220 pp. 

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. 

113The 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. 

114The NCA expresses levels of confidence using 

four qualifiers: low, medium, high, and very high. 

These levels are based on the strength and 

consistency of the observed evidence; the skill, 

range, and consistency of model projections; and 

insights from peer-reviewed sources. 

115Melillo, 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 

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. 

117Furthermore, 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). 

118NRC, 2011: Understanding Earth’s Deep Past: 

Lessons for Our Climate Future. The National 

Academies Press, p. 138. 

• NRC’s 2013 ‘‘Abrupt Impacts of 

Climate Change’’ (Abrupt Impacts) 110

• NRC’s 2014 ‘‘The Arctic in the 

Anthropocene: Emerging Research 

Questions’’ (Arctic) 111. 

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. 

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

These recent and strong conclusions 

attributing recent observed global 

warming to human influence have been 

made despite what some have termed a 

warming slowdown or ‘‘hiatus’’ over the 

past 15 years or so. The IPCC AR5 notes 

that global mean surface temperature 

exhibits substantial natural decadal and 

interannual variability, such that trends 

based on short records are very sensitive 

to the beginning and end dates and do 

not in general reflect long-term climate 

trends. As an example, the IPCC AR5 

notes that the rate of warming over the 

15 year period from 1998–2012 was less 

than that over the period 1951–2012. 

This short term variability does not alter 

the long-term climate trend that the 

IPCC AR5 finds after its review of 

independently verified observational 

records: ‘‘Each of the past three decades 

has been successively warmer at the 

Earth’s surface than all the previous 

decades in the instrumental record, and 

the first decade of the 21st century has 

been the warmest.’’ 116 117

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. 

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 climatesensitive diseases and aeroallergens. 

These key findings are described briefly 

here. 


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119Melillo, 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. 

122Melillo, 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. 

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. 

124Melillo, 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 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 heatrelated deaths.’’ 119 The IPCC AR5 also 

notes a potential benefit of climate 

change could include ‘‘modest 

reductions in cold-related mortality and 

morbidity in some areas due to fewer 

cold extremes (low confidence),’’ 120 but 

that, ‘‘[o]verall, we conclude that the 

increase in heat-related mortality by 

mid-century will outweigh gains due to 

fewer cold periods.’’ 121

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 climatechange 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 changerelated 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. 

Regarding extreme weather events 

(e.g., storms, heavy precipitation, and, 

in some regions of the United States, 

floods and droughts), the conclusions of 

the assessment literature cited in the 

2009 Endangerment Finding found 

potential for increased deaths, injuries, 

infectious and waterborne diseases, and 

stress-related disorders. Similarly, the 

USGCRP NCA3 discusses elevated 

waterborne disease outbreaks and the 

potential for mold contamination and 

degraded indoor air quality following 

heavy precipitation. Other impacts 

include mortality associated with 

flooding and impacts on mental health, 

such as anxiety and post-traumatic 

stress disorder. The IPCC AR5 also 

discusses death and injury in coastal 

zones and regions vulnerable to inland 

flooding. The USGCRP NCA3 and the 

IPCC AR5 both find that climate change 

may increase exposure to and health 

risks associated with drought 

conditions, which includes impacts 

from wildfires, dust storms, extreme 

heat events, flash flooding, degraded 

water quality, reduced water quantity, 

and water-related diseases. The IPCC 

SREX assessment projects further 

increases in some extreme weather and 

climate events during this century, and 

specifically notes that changes in 

extreme weather events have 

implications for disaster risk in the 

health sector. 

The effects of climate change on 

climate-sensitive diseases were also 

cited in the 2009 Endangerment 

Finding, including a likely increase in 

the spread of several food and waterborne pathogens among susceptible 

populations, and the potential for range 

expansion of some zoonotic disease 

carriers such as the Lyme diseasecarrying 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 vectorhuman contact, among other 

factors.’’ 124

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 


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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. 

126Melillo, 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. 

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. 

128The 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 wellbeing, 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. 

129Melillo, 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. 

to further changes in the seasonal timing 

of pollen release (high confidence).’’ 125

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. 

According to the USGCRP NCA3 and 

IPCC AR5, some populations defined 

jointly by ethnic/racial characteristics 

and geographic location are more 

vulnerable to certain health effects of 

climate change due to factors such as 

existing health disparities (e.g., higher 

prevalence of chronic health 

conditions), increased exposure to 

health stresses, and social factors that 

affect local resilience and ability to 

recover from impacts. 

The USGCRP NCA3 also finds that 

climate change, in addition to chronic 

stresses such as extreme poverty, is 

affecting indigenous peoples’ health in 

the United States through impacts such 

as reduced access to traditional foods, 

decreased water quality, and increasing 

exposure to health and safety hazards. 

The IPCC AR5 finds that climate 

change-induced warming in the Arctic 

and resultant changes in environment 

(e.g., permafrost thaw, effects on 

traditional food sources) have 

significant observed and projected 

impacts on the health and well-being of 

Arctic residents, especially indigenous 

peoples. Small, remote, predominantlyindigenous 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. 

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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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. 

131Melillo, 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. 

133Melillo, 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. 

134The 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. 

135NRC, 2011: National Security Implications of 

Climate Change for U.S. Naval Forces. The National 

Academies Press, p. 28. 

136Melillo, 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. 

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. 

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°C 

above pre-industrial levels, the area 

burnt by wildfires in western North 

America will likely more than double. 

Regarding water resources, the 

assessment literature cited in the 2009 

Endangerment Finding concluded that 

increasing temperatures and increased 

variability in precipitation associated 

with climate change will impact water 

quality and quantity through changes in 

snowpack, increased risk of floods, 

drought, and other concerns such as 

water pollution. Similarly, the new 

assessments further support projections 

of water resource impacts associated 

with increased floods and short-term 

drought in most U.S. regions. The 

USGCRP NCA3 also finds that, 

‘‘[c]limate change is expected to affect 

water demand, groundwater 

withdrawals, and aquifer recharge, 

reducing groundwater availability in 

some areas.’’ 131 The IPCC AR5 finds 

that in part of the western United States, 

‘‘water supplies are projected to be 

further stressed by climate change, 

resulting in less water availability and 

increased drought conditions.’’ 132 The 

IPCC AR5 also projects that climate 

change will degrade surface water 

quality, including the Great Lakes, and 

will negatively affect drinking water 

treatment/distribution and sewage 

collection systems. 

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

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°C 

will lead to a sea level rise of 0.5 to 1 

meter by 2100. While these NRC and 

IPCC assessments continue to recognize 

and characterize the uncertainty 

inherent in accounting for ice sheet 

processes, these revised estimates are 

consistent with the assessments 

underlying the 2009 Endangerment 

Finding. 

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 


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137NRC, 2010: Ocean Acidification: A National 

Strategy to Meet the Challenges of a Changing 

Ocean. The National Academies Press, p. 5. 

138 Ibid. 

139Melillo, 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. 

141NRC, 2013: Climate and Social Stress: 

Implications for Security Analysis. The National 

Academies Press, p. 18. 

with summer sea ice loss and the 

increasing frequency and severity of 

storms. 

Regarding ecosystems and wildlife, 

the assessment literature cited in the 

2009 Endangerment Finding found that 

climate change will predominantly 

adversely impact both terrestrial and 

marine biodiversity and the ability of 

these ecosystems to provide goods and 

services. The NRC Arctic assessment 

states that major marine and terrestrial 

biomes will likely shift pole ward, with 

significant implications for changing 

species composition, food web 

structures, and ecosystem function. The 

NRC Climate Stabilization Targets 

assessment found that coral bleaching 

will increase due both to warming and 

ocean acidification. The NRC 

Understanding Earth’s Deep Past 

assessment notes four of the five major 

coral reef crises of the past 500 million 

years were caused by acidification and 

warming that followed GHG increases of 

similar magnitude to the emissions 

increases expected over the next 

hundred years. Similarly, the NRC 

Ocean Acidification assessment finds 

that ‘‘[t]he chemistry of the ocean is 

changing at an unprecedented rate and 

magnitude due to anthropogenic CO2

emissions; the rate of change exceeds 

any known to have occurred for at least 

the past hundreds of thousands of 

years.’’ 137 The assessment notes that the 

full range of consequences is still 

unknown, but the risks ‘‘threaten coral 

reefs, fisheries, protected species, and 

other natural resources of value to 

society.’’ 138 The IPCC AR5 also projects 

biodiversity losses in marine 

ecosystems, especially in the Arctic and 

tropics. 

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, ‘‘Climaterelated 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

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. 

In addition, the NRC Abrupt Impacts 

report examines the potential for tipping 

points, thresholds beyond which major 

and rapid changes occur in the Earth’s 

climate system, as well as in natural and 

human systems that are impacted by the 

changing climate. The Abrupt Impacts 

report did find less cause for concern 

than some previous assessments 

regarding some abrupt events within the 

next century such as disruption of the 

oceanic Atlantic Meridional 

Overturning Circulation (AMOC) and 

sudden releases of high-latitude 

methane from hydrates and permafrost. 

But, the same report found that the 

potential for abrupt changes in 

ecosystems, weather and climate 

extremes, and groundwater supplies 

critical for agriculture now seem more 

likely, severe, and imminent. The 

assessment found that some abrupt 

changes were already underway (e.g., 

Arctic sea ice retreat and increases in 

extinction risk due to the speed of 

climate change), and cautioned that 

even abrupt changes such as the AMOC 

disruption that are not expected in this 

century can have severe impacts if/

when they happen. 

4. Consideration of Other Climate 

Forcers 

Both in the 2009 Endangerment 

Finding and in this action, the 

Administrator recognizes that there are 

other substances in addition to the six 

well-mixed GHGs that are emitted from 

human activities and affect Earth’s 

climate (referred to as climate forcers). 

These can be grouped into two 

categories: (1) other substances with 

similar physical properties to the six 

well-mixed GHGs—these include the 

ozone-depleting substances of 

chlorofluorocarbons, 

hydrochlorofluorocarbons, and halons, 

as well as nitrogen trifluoride and 

similar recently identified substances; 

and (2) short-lived substances— 

tropospheric ozone and its precursor 

gases, water vapor, and aerosol particles 

and precursors. For some short-lived 

substances—namely, water vapor; NOX; 

and aerosol particles including black 

carbon—their physical properties result 

in these substances having different, 

and often larger, climate effects when 

emitted at high altitudes. However, the 

very properties that lead to differential 

climate effects depending on the 

altitude of emission—properties that are 

different from those of the six wellmixed, 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, wellmixed, directly emitted), the fact that 

these gases are considered the primary 

drivers of climate change, and the fact 

that these gases remain the best 


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37782 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

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. 

144NRC, 2010: Advancing the Science of Climate 

Change. The National Academies Press, 528 pp. 

145NRC, 1999: Atmospheric Effects of Aviation: A 

Review of NASA’s Subsonic Assessment Project. 

The National Academies Press, 54 pp. 

146NRC, 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. 

understood drivers of anthropogenic 

climate change. The common physical 

properties of the six well-mixed GHGs 

not only support grouping them together 

as a class, but also contribute to their 

higher degree of scientific 

understanding related to climate 

change, relative to short-lived 

substances that are not well-mixed, or 

substances that are formed indirectly 

rather than being directly emitted. After 

considering additional information in 

the new assessments regarding the 

climate-relevant substances outside the 

basket of the six well-mixed GHGs, it is 

the Administrator’s view that the 

reasons originally stated for not 

including these substances in the scope 

of the GHG air pollution still apply at 

this time. For example, nitrogen 

triflouride and some other recently 

discovered substances are not as well 

studied or understood as the six wellmixed GHGs. Similarly, for tropospheric 

ozone—a short-lived gas in the 

atmosphere that is not directly emitted 

(it forms from emissions of various 

precursor gases)—the understanding 

and quantification of the link between 

precursor emissions and climate change 

is not as strong as for the six well-mixed 

GHGs. 

Regarding the short-lived substances 

with different climate effects when 

emitted at high altitudes, the Aircraft 

Petition (see section II of this preamble) 

mentions the effects of water vapor and 

NOX on clouds and atmospheric 

chemistry. The major peer-reviewed 

scientific assessments of the IPCC and 

NRC provide the current state of 

scientific understanding of these effects; 

the USGCRP assessments have not dealt 

specifically with emissions at high 

altitude. The EPA considered the 

following assessment reports to obtain 

the best estimates of these substances’ 

net impact on the climate system, which 

is generally discussed in terms of 

radiative forcing: the IPCC AR5, the 

IPCC 2007 Fourth Assessment Report 

(AR4),142 the IPCC Special Report: 

Aviation and the Global Atmosphere 

(IPCC 1999),143 the NRC’s Advancing 

the Science of Climate Change (NRC 

2010),144 and the NRC’s Atmospheric 

Effects of Aviation: A Review of NASA’s 

Subsonic Assessment Project (NRC 

1999).145 In addition to high altitude 

water vapor and NOX, the literature 

indicates that aerosol particles, 

including black carbon, emitted at high 

altitudes have more interactions with 

clouds and therefore have different 

effects on the global energy balance than 

do particles emitted at the surface. 

The state of the science as represented 

in the assessment literature highlights 

significant scientific uncertainties 

regarding the total net forcing effect of 

water vapor, NOX, and aerosol particles 

when emitted at high altitudes. Given 

these uncertainties, the Agency is not 

including them in the proposed 

definition of air pollution for purposes 

of the endangerment finding under 

section 231 of the CAA. The short-lived 

nature of these substances means that, 

unlike the long-lived GHGs, the climatic 

impact of the substance is dependent on 

a number of factors such as the location 

and time of its emission. The 

magnitude, and often the direction 

(positive/warming or negative/cooling), 

of the globally averaged climate impact 

will differ depending on the location of 

the emission due to the local 

atmospheric conditions (e.g., due to 

differing concentrations of other 

compounds with which the emissions 

can react, background humidity levels, 

or the presence or absence of clouds). In 

addition, for emissions at any given 

location, the spatial and temporal 

pattern of the climate forcing will be 

heterogeneous, again often differing in 

direction (for example, in the case of 

NOX emissions, the near term effect in 

the hemisphere in which the emissions 

occur is usually warming due to 

increased ozone concentrations, but the 

longer term effects, and effects in the 

other hemisphere, are often cooling due 

to increased destruction of methane). As 

the climatic effects of these substances 

when emitted at high altitudes were not 

addressed at length in the 2009 

Endangerment Finding, the following 

subsections briefly summarize the 

findings of the major scientific 

assessments regarding these substances’ 

climatic effects at altitude and the 

various sources of uncertainty 

surrounding these estimates. 

a. Changes in Clouds From High 

Altitude Emissions of Water Vapor and 

Particles 

Aviation-induced cloudiness 

(sometimes called AIC) refers to all 

changes in cloudiness associated with 

aviation operations, which are primarily 

due to the effects of high altitude 

emissions of water vapor and particles 

(primarily sulfates and black carbon). 

Changes in cloudiness affect the climate 

by both reflecting solar radiation 

(cooling) and trapping outgoing 

longwave radiation (warming). Unlike 

the warming effects associated with the 

six long-lived, well-mixed GHGs, the 

warming effects associated with changes 

in cloud cover are more regional and 

temporal in nature. The three key 

components of aviation-induced 

cloudiness are persistent contrails, 

contrail-induced cirrus, and induced 

cirrus. 

Aircraft engine emissions of water 

vapor at high altitudes during flight can 

lead to the formation of condensation 

trails, or contrails, under certain 

conditions such as ice-supersaturated 

air masses with specific humidity levels 

and temperature. The NRC estimates 

that persistent contrails increased 

cloudiness above the United States by 

two percent between 1950 and 1988, 

with similar results reported over 

Europe.146 As stated above, clouds can 

have both warming and cooling effects, 

and persistent contrails were once 

considered to have significant net 

warming effects. However, more recent 

estimates suggest a smaller overall 

climate forcing effect of persistent 

contrails. The IPCC AR5 best estimate 

for the global mean radiative forcing 

from contrails is 0.01 W/m2 (medium 

confidence and with an uncertainty 

range of 0.005 to 0.03 W/m2).147 To put 

this number into context, some 

examples of other IPCC AR5 best 

estimates for global mean radiative 

forcing include: 1.68 W/m2 for CO2

(very high confidence and with an 

uncertainty range of 1.33 to 2.03 W/m2), 

0.97 W/m2 for methane (high 

confidence and with an uncertainty 

range of 0.74 to 1.20 W/m2), and 0.17 

W/m2 for nitrous oxide (very high 

confidence and with an uncertainty 


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148 IPCC, 2013: Summary for Policymakers. In: 

Climate Change 2013: The Physical Science Basis. 

Contribution of Working Group I to the Fifth 

Assessment Report of the Intergovernmental Panel 

on Climate Change [Stocker, T.F., D. Qin, G.-K. 

Plattner, M. Tignor, S.K. Allen, J. Boschung, A. 

Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. 

Cambridge University Press, 29 pp. 

149 IPCC, 2013: Climate Change 2013: The 

Physical Science Basis. Contribution of Working 

Group I to the Fifth Assessment Report of the 

Intergovernmental Panel on Climate Change 

[Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, 

S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex 

and P.M. Midgley (eds.)].Cambridge University 

Press, 1535 pp. 

150 IPCC, 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. 

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. 

152 74 FR at 66517, December 15, 2009. 

153 74 FR at 66520, December 15, 2009. 

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. 

155 Ibid. 

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. 

range of .013 to 0.21 W/m2).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). 

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/m2 (low confidence and with an 

uncertainty range of 0.02 and 0.15 W/

m2).149

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. 

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/m2.151

b. Direct Radiative Forcing Effects of 

High Altitude Particle Emissions 

The 2009 Endangerment Finding 

noted that much of the uncertainty 

range surrounding the estimate of total 

net forcing due to all human activities 

was due to uncertainties about the 

cooling and warming effects of 

aerosols 152 (though from all sources, not 

just aircraft). The Finding noted that the 

magnitude of aerosol effects can vary 

immensely with location and season of 

emissions, and also discussed black 

carbon as a specific type of aerosol 

particle, noting that estimates of its total 

climate forcing effect have a large 

uncertainty range.153 Here, we discuss 

the direct radiative forcing effects of 

high altitude emissions of the two 

primary aviation-induced particles, 

sulfates and black carbon. 

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/m2 with an uncertainty range 

between ¥0.001 and ¥0.009 W/m2.154

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/m2 with 

uncertainty spanning 0.001 to 0.009 W/ 

m2.155 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. 

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 longterm net warming effect. Thus, the net 

radiative impact of NOX emissions 

depends on the balance between the 

reductions in methane versus the 

production of ozone, which in turn 

depends on the time scale under 

consideration. Quantifying these 

impacts is an area of active study with 

large uncertainties. The quantification 

of the net global effect of NOX is 

difficult because the atmospheric 

chemistry effects are heavily dependent 

on highly localized atmospheric 

properties and mixing ratios. Because 

the background atmospheric 

concentration of NOX is important for 

quantifying the impact of aviation NOX

emissions on ozone and methane 

concentrations, the location of aircraft 

emissions would be an important 

additional factor. In addition, NOX has 

different residence times in the 

atmosphere depending on the altitude at 

which it is emitted. The residence time 

of NOX in the upper troposphere, or 

roughly the cruise altitude for jet 

aircraft, is on the order of several days. 

Going back to the IPCC 1999 

assessment, the globally averaged 

radiative forcing estimates for aircraft 

emissions of NOX in 1992 were 0.023 

W/m2 for O3-induced changes 

(uncertainty range of 0.011 to 0.046 W/ 

m2), and ¥0.014 W/m2 for methaneinduced changes (uncertainty range of 

¥0.005 to ¥0.042 W/m2).156

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 


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37784 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

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. 

158U.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. 

159CRR, 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). 

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. 

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. 

d. Summary 

Overall, the state of the science as 

represented in the assessment literature 

highlights significant scientific 

uncertainties regarding the total net 

forcing effect of water vapor, NOX, and 

aerosol particles, when emitted at high 

altitudes. The dependence of the effects 

on where the substance is emitted, and 

the complex temporal and spatial 

patterns that result, mean that the 

current level of understanding regarding 

these short-lived substances is much 

lower than for the six long-lived, wellmixed 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). 

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 twopart endangerment test for this proposed 

finding is for the Administrator to 

determine whether the emission of any 

air pollutant from certain classes of 

aircraft engines causes or contributes to 

this air pollution. This is referred to as 

the cause or contribute finding, and is 

the second proposed finding by the 

Administrator in this action. 

Section V.A of this proposal describes 

the Administrator’s reasoning for using 

the same definition and scope of the 

GHG air pollutant that was used in the 

2009 Endangerment Finding. Section 

V.0 puts forth the Administrator’s 

proposed finding that emissions of 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 wellmixed 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 


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160As detailed in the 2009 Endangerment Finding 

proposal (74 FR 18904 (April 24, 2009) and 

continuing today, the UNFCCC, the U.S. and other 

Parties report their annual emissions of the six 

GHGs in CO2-equivalent units. This facilitates 

comparisons of the multiple GHGs from different 

sources and from different countries, and provides 

a measure of the collective warming potential of 

multiple GHGs. Emissions of different GHGs are 

compared using GWPs, which as described in 

section IV.B of this preamble are measures of the 

warming impact of a pulse of emissions of a given 

substance over 100 years relative to the same mass 

of CO2. Therefore, GWP-weighted emissions are 

measured in teragrams of CO2 equivalent (Tg 

CO2eq). The EPA’s Greenhouse Gas Reporting 

Program (http://www.epa.gov/ghgreporting/

index.html, (last accessed May 12, 2015)) also 

reports GHG emissions on a CO2-equivalent basis, 

recognizing the common and collective treatment of 

the six GHGs. 

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). 

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). 

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. 

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. 

2. How the Definition of Air Pollutant 

in the Endangerment Determination 

Affects Section 231 Standards 

Under section 231(a), the 

Administrator is required to set 

‘‘emission standards applicable to the 

emission of any air pollutant’’ from 

classes of aircraft engines that the 

Administrator determines causes or 

contributes to air pollution that 

endangers public health or welfare. If 

the Administrator makes a final 

determination under section 231 that 

the emissions of the GHG air pollutant 

from certain classes of aircraft engines 

contribute to the air pollution that may 

reasonably be anticipated to endanger 

public health and welfare, then she is 

called on to set standards applicable to 

the emissions of this air pollutant. The 

term ‘‘standards applicable to the 

emissions of any air pollutant’’ is not 

defined, and the Administrator has the 

discretion to interpret it in a reasonable 

manner to effectuate the purposes of 

section 231 to set standards that either 

control the emissions of the group of six 

well-mixed gases as a whole and/or 

control emissions of individual gases, as 

constituents of the class. For example, it 

might be appropriate to set a standard 

that measures and controls the aggregate 

emissions of the group of GHGs, 

weighted by CO2 equivalent. Depending 

on the circumstances, however, it may 

be appropriate to set standards for 

certain individual gases, or some 

combination of group and individual 

standards. These and other similar 

approaches could appropriately be 

considered in setting a standard or 

standards applicable to the emissions of 

the group of GHGs that are defined as 

the air pollutant. The Administrator 

would consider a variety of factors in 

determining what approach to take in 

setting the standard or standards; for 

example, she would consider the 

characteristics of the aircraft emissions, 

such as rate and variability, the kind 

and availability of control technology, 

and other matters relevant to setting 

standards under section 231.162

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; 


tkelley on DSK3SPTVN1PROD with PROPOSALS2
37786 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

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. 

164One 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. Schlo ̈mer, C. von Stechow, T. 

Zwickel and J.C. Minx (eds.)]. Cambridge University 

Press, 1435 pp. 

166World Resources Institute (WRI) Climate 

Analysis Indicators Tool (CAIT) Data Explorer 

(Version 2.0). Available at http://cait.wri.org (last 

accessed May 12, 2015). 

167U.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). 

168According 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. 

• As a share of current total global 

GHG emissions; and 

• As a share of the current global 

transportation GHG emissions. 

All annual GHG emissions data are 

reported on a CO2-equivalent (CO2eq) 

basis, which as described above is a 

commonly accepted metric for 

comparing different GHGs. This 

approach is consistent with how EPA 

determined contribution for GHGs 

under section 202 of the CAA in 2009. 

2. Overview of Greenhouse Gas 

Emissions 

Atmospheric concentrations of CO2

and other GHGs are now at essentially 

unprecedented levels compared to the 

distant and recent past.163 This is the 

unambiguous result of human emissions 

of these gases. Global emissions of wellmixed 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). 

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. 

The Inventory of U.S. Greenhouse Gas 

Emissions and Sinks Report 167

(hereinafter ‘‘U.S. Inventory’’), in which 

2013 is the most recent year for which 

data are available, indicates that total 

U.S. GHG emissions increased by 5.7 

percent from 1990 to 2013 (or by about 

4.7 percent when including the effects 

of carbon sinks), and emissions 

increased from 2012 to 2013 by 1.8 

percent. This 2012 to 2013 increase was 

attributable to multiple factors 

including an increase in carbon 

intensity of fuels consumed for 

electricity generation, a small increase 

in vehicle miles traveled and vehicle 

fuel use, and a colder winter leading to 

an increase in heating requirements. 

The U.S. Inventory also shows that 

while overall U.S. GHG emissions grew 

between 1990 and 2013, transportation 

GHG emissions grew at a significantly 

higher rate, 15 percent, more rapidly 

than any other U.S. sector. Within the 

transportation sector, aircraft remain the 

single largest source of GHG emissions 

not yet subject to any GHG regulations. 

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). 

For purposes of making this cause or 

contribute finding, the EPA is focused 

on, and proposes to include, a set of 

aircraft engine classes used in types of 

aircraft as described below, which 

corresponds to the scope of the 

international CO2 emissions standard 

contemplated by ICAO. 

As mentioned earlier in section II.D, 

traditionally the EPA (and FAA) 

participates at ICAO in the development 

of international standards, and then 

where appropriate, the EPA establishes 

domestic aircraft engine emission 

standards under CAA section 231 of at 

least equivalent stringency to ICAO’s 

standards. An international CO2

emissions standard is anticipated in 

February 2016, and provided that the 

EPA makes a positive endangerment 

finding and ICAO adopts an 


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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. 

171The applicability of the anticipated 

international CO2 standard would be limited to 

subsonic aircraft, and would not extend to 

supersonic aircraft. Since space vehicles (or 

spacecraft) will be operated at supersonic speeds, 

space vehicles would not be covered by the 

anticipated international CO2 standard. 

172Eastern 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. 

173Compared 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 lightduty vehicle and medium- and heavy-duty truck 

sectors. 

174Total 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/ 

.). 

175U.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). 

176Emissions 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). 

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. 

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

It is important to note that in regard 

to the six well-mixed GHGs (CO2, 

methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride), only two of 

these gases—CO2 and nitrous oxide—are 

reported as non-zero emissions for total 

aircraft and covered aircraft.175 CO2

represents 99 percent of all GHGs from 

both total aircraft (214 Tg CO2eq) and 

U.S. covered aircraft (193 Tg CO2eq), 

and nitrous oxide represents about one 

percent from total aircraft (2 Tg CO2eq) 

and covered aircraft (1.8 Tg CO2eq). 

Modern aircraft do not emit methane,176

and hydrofluorocarbons, 

perfluorocarbons, and sulfur 

hexafluoride are not products of aircraft 

engine combustion. 


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177 ICAO CAEP, 2013: ICAO Environmental 

Report 2013, Aviation and Climate Change, 224 pp. 

Available at http://cfapp.icao.int/EnvironmentalReport-2013/ (last accessed May 12, 2015). 

178Worldwide GHG emissions from ICAO 

covered aircraft include emissions from both 

international and domestic aircraft operations 

around the world. 

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.1—COMPARISONS OF U.S. AIRCRAFT GHG EMISSIONS TO TOTAL U.S. TRANSPORTATION AND TOTAL U.S. GHG 

EMISSIONS

1990 2000 2005 2010 2011 2012 2013 

Total U.S. Aircraft GHG emissions (Tg 

CO2eq) .................................................. 228 262 254 216 215 212 216 

Share of U.S. Transportation ................... 14% 13% 12% 11% 11% 11% 11% 

Share of total U.S. Inventory ................... 3.6% 3.6% 3.4% 3.1% 3.1% 3.2% 3.2% 

U.S. Covered Aircraft GHG emissions 

(Tg CO2eq) ........................................... 169 223 217 190 193 190 195 

Share of U.S. aircraft GHG emissions .... 74% 85% 85% 88% 90% 90% 90% 

Share of U.S. Transportation ................... 10% 11% 10% 9.7% 10% 9.9% 10% 

Share of total U.S. Inventory ................... 2.6% 3% 2.9% 2.7% 2.8% 2.9% 2.9% 

Transportation Sector emissions (Tg 

CO2eq) .................................................. 1,659 2,044 2,137 1,966 1,932 1,907 1,911 

Share of total U.S. Inventory ................... 26% 28% 29% 28% 28% 29% 28% 

Total U.S. GHG emissions ............... 6,406 7,315 7,464 7,017 6,889 6,652 6,744 

b. U.S. Aircraft GHG Emissions Relative 

to Global Aircraft GHG Inventory and 

the Total Global GHG Inventory 

For background information and 

context, we first provide information on 

the contribution of GHG emissions from 

global aircraft and the global 

transportation sector to total global GHG 

emissions, and describe how this 

compares to the emissions from aircraft 

that would be covered by the 

anticipated ICAO CO2 standard. We 

then compare U.S. aircraft GHG 

emissions to the global aircraft sector, to 

the global transport sector, and to total 

global GHG emissions as an indication 

of the role this source plays in the total 

global contribution to the air pollution 

that is causing climate change. As in the 

preceding section, we present 

comparisons from both total U.S. 

aircraft and U.S. covered aircraft. 

According to IPCC AR5, global aircraft 

GHG emissions in 2010 were 11 percent 

of global transport GHG emissions and 

2 percent of total global GHG emissions. 

Data from ICAO’s 2013 Environmental 

Report indicate that the vast majority of 

global emissions from the aircraft sector 

are emitted by the types of aircraft that 

would be covered by the anticipated 

ICAO CO2 standard (‘‘ICAO covered 

aircraft’’).177 When compared to global 

data from IPCC AR5, worldwide GHG 

emissions from ICAO covered aircraft 

represented about 93 percent (688 Tg 

CO2eq) of global aircraft GHG 

emissions,178 10 percent of global 

transport GHG emissions, and 1.5 

percent of total global GHG emissions in 

2010. 

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

TABLE V.2—COMPARISONS OF U.S. AIRCRAFT GHG EMISSIONS TO TOTAL GLOBAL GREENHOUSE GAS EMISSIONS IN

2010 

2010 

(Tg CO2 eq) 

Total U.S. 

Aircraft 

Share (%) 

U.S. Covered 

Aircraft Share 

(%) 

Global Aircraft 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. 


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181The 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). 

182U.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. Schlo ̈mer, C. von Stechow, T. 

Zwickel and J.C. Minx (eds.)]. Cambridge University 

Press, pp. 599–670. 

184According 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). 

185FAA, 2014: FAA Aerospace Forecast Fiscal 

Years 2014–2034, 129 pp. Available at https://

www.faa.gov/about/office_org/headquarters_

offices/apl/aviation_forecasts/aerospace_forecasts/

2014-2034/media/2014_FAA_Aerospace_

Forecast.pdf (last accessed May 12, 2015). 

186These shocks include the September 11 terror 

attacks, significant increases in fuel prices, debt 

restructuring in Europe and U.S., and a global 

recession. 

187According to the FAA Aerospace Forecast 

2014–2034, in 2013 U.S. air carriers were profitable 

for the fourth consecutive year. 

188According 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). 

189 ICAO CAEP, 2013: ICAO Environmental 

Report 2013, Aviation and Climate Change, 224 pp. 

Available at http://cfapp.icao.int/EnvironmentalReport-2013/ (last accessed May 12, 2015). 

190FAA, 2015: FAA Aerospace Forecast Fiscal 

Years 2015–2035, 134 pp. Available at https://

www.faa.gov/about/office_org/headquarters_

offices/apl/aviation_forecasts/aerospace_forecasts/

2015-2035/media/2015_National_Forecast_

Report.pdf (last accessed May 12, 2015). 

covered aircraft emissions of GHGs were 

ranked against total GHG emissions for 

entire countries, these covered aircraft 

emissions would rank ahead of Belgium, 

Czech Republic, Ireland, Sweden and 

about 150 other countries in the world. 

c. Aircraft GHG Emissions Are Projected 

To Increase in the Future 

While overall GHG emissions from 

U.S. covered aircraft increased by about 

13 percent from 1990 to 2010, the 

portion attributable to U.S. international 

aviation bunker fuels 181 increased by 

about 90 percent.182 During this same 

time period, global aircraft GHG 

emissions grew by about 40 percent, and 

the portion attributable to global 

international aviation bunker fuels 

increased by 80 percent.183 184

Notwithstanding the substantial growth 

in GHG emissions from U.S. 

international aviation bunker fuels, U.S. 

covered aircraft emissions have not 

increased as much as global aircraft 

emissions primarily because the U.S. 

aviation market was relatively mature 

compared to the markets in Europe and 

other emergent markets, and because 

during this time period the U.S. 

commercial air carriers suffered several 

major shocks that reduced demand for 

air travel.185 186 After consolidation and 

restructuring in recent years, the U.S. 

commercial air carriers have regained 

profitability and are forecasted by the 

FAA to grow more over the next 20 to 

30 years.187 With regard to global 

aircraft GHG emissions, the aviation 

markets in Asia/Pacific, Europe (where 

airline deregulation has stimulated 

significant new demands in this period), 

and the Middle East (and other 

emerging markets) have been growing 

rapidly, and the global market is 

expected to continue to grow 

significantly over the next 20 to 30 

years.188

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. 

3. Proposed Contribution Finding for 

the Single Air Pollutant Comprised of 

the of Six Well-Mixed Greenhouse 

Gases 

Taking into consideration the data 

summarized in section V.B.2 above, the 

Administrator proposes to find that 

GHG emissions from classes of engines 

used in U.S. covered aircraft, which are 

subsonic jet aircraft with a maximum 

takeoff mass (MTOM) greater than 5,700 

kilograms and subsonic propeller driven 

(e.g., turboprop) aircraft with a MTOM 

greater than 8,618 kilograms, contribute 

to the air pollution that endangers 

public health and welfare. The 

Administrator is not at this time 

proposing a contribution finding for 

GHG emissions from engines not used 

in covered aircraft (i.e., those used in 

smaller turboprops, smaller jet aircraft, 

piston-engine aircraft, helicopters and 

military aircraft). We solicit comment 

on the scope of the proposed 

contribution finding, whether a broader 

contribution finding (e.g., including all 

engines used in aircraft certified by the 

FAA) would be appropriate, and the 

extent to which EPA has discretion to 

establish standards pursuant to a 

contribution finding that do not impose 

requirements on every engine or class of 

engines within the scope of that finding. 

It is the Administrator’s judgment that 

the collective GHG emissions from the 

classes of engines used in U.S. covered 

aircraft clearly contribute, whether the 

comparison is domestic (10 percent of 

all U.S. transportation GHG emissions, 

representing 3 percent of total U.S. 

emissions) or global (26 percent of total 

global aircraft GHG emissions 

representing 3 percent of total global 

transportation emissions and 0.5 

percent of all global GHG emissions). 

The proposed scope of GHG emissions 

from engines used in U.S. covered 

aircraft under this cause or contribute 

finding would result in the vast majority 

(90 percent) of U.S. aircraft GHG 

emissions being included in this 

determination. The Administrator 

believes that consideration of the global 

context is important for the cause or 

contribute test, but that the analysis 

should not solely consider the global 

context. GHG emissions from engines 

used in U.S. covered aircraft will 

become globally well-mixed in the 

atmosphere, and thus will have an effect 

not only on the U.S. regional climate but 

also on the global climate as a whole, for 

years and indeed many decades to 

come. It is the Administrator’s view that 

the cause or contribute test used here 


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191 74 FR 66543 (December 15, 2009). 

192For a standard promulgated under CAA 

section 231 to be ‘‘applicable to’’ emissions of air 

pollutants from aircraft engines, it could take many 

forms, and include multiple elements in addition to 

numeric permissible engine exhaust rate. For 

example, under CAA section 231, EPA’s rules have 

long-standing regulations addressing fuel venting, 

as well as test procedures. See 40 CFR part 87, 

subparts B, G and H. Given both the absence of a 

statutory directive on what form a CAA section 231 

standard must take (in contrast to, for example, 

CAA section 129(a)(4), which requires numerical 

emissions limitations for emissions of certain 

pollutants from solid waste incinerators), and the 

U.S. Court of Appeals for the DC Circuit’s 2007 

NACAA v. EPA ruling that section 231 confers an 

unusually broad degree of discretion in establishing 

aircraft engine emission standards, it should be 

possible to reconcile an ICAO ‘‘aircraft standard’’ 

that effectively limits aircraft engine GHG emissions 

with a CAA section 231 aircraft engine emission 

standard that achieves the same result, even if the 

GHG standards take a different form than the 

traditional thrust-based NOx aircraft engine 

emission standards recently issued by ICAO and the 

EPA. See 40 CFR part 87, subpart C. 

193As 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. 

194U.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). 

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. 

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. 

VI. Advance Notice of Proposed 

Rulemaking: Discussion of Ongoing 

International Proceedings To Develop 

Aircraft CO2 Emissions Standard and 

Request for Comment 

For more than four years, the EPA and 

FAA have been engaged with the 

ICAO’s Committee on Aviation 

Environmental Protection (ICAO/CAEP) 

to establish an international CO2

emissions standard which the EPA 

could then consider proposing for 

adoption under its section 231 authority 

of the CAA. This section of this 

document serves as an ANPR to discuss 

the key issues of the ongoing 

international proceedings prior to 

February 2016, when ICAO/CAEP is 

expected to finalize an international 

aircraft CO2 standard. An ANPR is 

intended to solicit comments and/or 

information from the public prior to an 

agency determining whether to propose 

a rulemaking. As such, an ANPR does 

not propose or impose any regulatory 

requirements. The EPA may choose to 

develop an ANPR for actions (such as 

the promulgation of standards pursuant 

to CAA section 231 to implement an 

international aircraft CO2 standard 

domestically) which are still in the early 

stages of development and for which 

public input may be particularly 

helpful. This also helps ensure 

transparency, while assisting the EPA in 

obtaining input from a wide range of 

stakeholders as we continue work 

within CAEP to establish an 

international CO2 aircraft standard. The 

EPA is seeking comments from all 

interested parties, including small 

businesses, on a variety of issues related 

to setting an international CO2 standard 

for aircraft, including whether such 

standards should apply to in-production 

aircraft instead of new aircraft types 

only, the appropriate effective dates for 

the potential international CO2

standard, as well as the appropriate 

stringency levels. 

CAEP met an important milestone at 

its 9th meeting (CAEP/9) in 2013 in 

reaching an agreement on the 


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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. 

197As shorthand in this action, in many places 

we will use the term ‘‘endangerment finding’’ for 

both endangerment and cause or contribute 

findings. 

198CAEP (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. 

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. 

200As described earlier in section D, in existing 

U.S. aviation emissions regulations, in-production 

means newly-manufactured or built after the 

effective date of the regulations—and already 

certified to pre-existing standards (if emission 

standards were established previously).). This is 

similar to the current CAEP definition for inproduction aircraft types for purposes of the CO2

standard. 

201According 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’’. 

202A 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. 

203Out 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. 

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. 

At the CAEP Steering Group meeting 

in November 2013, there was agreement 

on a set of stringency options to be used 

for the cost-effectiveness analysis, and 

at the Steering Group meeting in 

September 2014 there was a decision on 

the associated inputs for costs and 

technology responses to be utilized in 

the cost-effectiveness analysis of these 

stringency options. This analysis, and 

work on the applicability of the 

standard to in-production aircraft and 

the certification requirement are 

scheduled to be completed prior to the 

10th CAEP meeting (CAEP/10) in 

February 2016. As described in section 

II.A, the EPA and the FAA traditionally 

work within the ICAO/CAEP standardsetting process to establish international 

emission standards and related 

requirements. Under this approach, 

international emission standards have 

first been adopted by ICAO, and 

subsequently the EPA has initiated 

rulemakings under CAA section 231 to 

establish domestic standards that are of 

at least equal stringency as ICAO’s 

standards. This approach has been 

affirmed as reasonable by the U.S. Court 

of Appeals for the DC Circuit. Provided 

the EPA makes a positive endangerment 

finding 197 under CAA section 231 and 

ICAO adopts an international aircraft 

CO2 standard that is consistent with 

CAA section 231 and U.S. domestic 

needs, we would expect to proceed with 

a similar approach promulgating a CO2

emissions standard (or GHG standard) of 

at least equivalent stringency 

domestically. 

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 

The EPA requests comments on the 

applicability approaches that CAEP is 

considering. Specifically, we request 

comment on whether the aircraft CO2

standard should apply to in-production 

aircraft, including aircraft with any 

engineered fuel efficiency 

improvements (e.g., different engines, 

redesigned wings, or engine 

performance improvement packages, 

etc.) or whether the aircraft CO2

standard should apply only to 

completely new aircraft type designs. 

CAEP is also considering a third, 

alternative approach, which would 

redefine a new aircraft type for CO2

purposes to include in-production 

aircraft that have a significant change in 

CO2 emissions. We are also requesting 

comment on this potential alternative 

option. 

In-production aircraft and new 

aircraft types are defined as follows: 

—In-production aircraft: Those aircraft 

types which have already received a 

Type Certificate, and for which 

manufacturers either have existing 

undelivered sales orders or would be 

willing and able to accept new sales 

orders.199 200 201

—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. 

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

As described earlier in section II.E, 

CAEP’s Steering Group meeting in 2010 


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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. 

205New 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. 

206Boeing, 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-forJapan-Airlines (last accessed May 12, 2015). 

207The Independent, 2012: BA reveals Airbus 

A380 superjumbo flight plans, by Peter Woodman, 

December 11. Available at http://

www.independent.co.uk/travel/news-and-advice/

ba-reveals-airbus-a380-superjumbo-flight-plans8405961.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. 211Analysts 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 reengine of the A320 and the 737, respectively 

(excluding engine development costs). Embraer has 

publically stated they will need to spend $1–2 

billion to re-wing the EMB–175 and variants. (ICF 

International, CO2 Analysis of CO2-Reducing 

Technologies for Aircraft, Final Report, EPA 

Contract Number EP–C–12–011, March 17, 2015.) 

212 In general, design waves are prompted by the 

combination of market demand for new aircraft 

performance needs (e.g., more seats for longer 

range) and the age of existing aircraft, and design 

waves are typically enabled by advances in 

propulsion technology. 

213 ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, March 17, 

2015. 

214 Insofar as we are going through a wave of 

major redesign and service entry now, prospects for 

further step-function improvements will be low in 

the coming 10–15 years. (ICF International, CO2

Analysis of CO2-Reducing Technologies for Aircraft, 

Final Report, EPA Contract Number EP–C–12–011, 

March 17, 2015.) 

215As described earlier, CAEP has not ruled out 

applying the international CO2 standard to inproduction aircraft types, which are aircraft types 

that have already received a Type Certificate and 

are produced after the effective date of the standard. 

In-production aircraft types would include 

significant partial redesigned aircraft and 

incremental improvements. CAEP is currently 

considering and analyzing in-production 

applicability. 

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. 

agreed that the scope of applicability for 

the international aircraft CO2 standard 

will be subsonic jets with an 

applicability weight threshold of 

maximum takeoff mass (MTOM) greater 

than 5,700 kg (12,566 lb) and turboprop 

aircraft with a MTOM greater than 8,618 

kg (19,000 lb). CAEP also agreed that the 

international CO2 standard will apply to 

new aircraft types, but not apply to out 

of production aircraft types, and that 

applying the standard to in-production 

aircraft types should not be ruled out.204

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. 

New aircraft types or new type 

designs are infrequent. The most recent 

new type designs introduced in service, 

such as the Airbus A380 in 2007, the 

Boeing 787 in 2011, and the original 

Boeing 777 in 1995,206 207 208 indicate 

that it is unlikely a new type design will 

seek certification in the next 10 to 15 

years.209 (New aircraft types (and 

similarly for significant partial 

redesigns) typically yield large fuel burn 

reductions—10 percent to 20 percent 

over the prior generation they replace, 

and as one might expect, these 

significant fuel burn reductions do not 

happen frequently. Also, aircraft 

development programs are expensive. It 

is not unusual for new type designs to 

take 8–10 years to develop, from 

preliminary design to entry into service. 

210 211) Significant partial redesigns do 

not occur often, but are slightly more 

frequent than new type designs. For 

example, after the current significant 

partial redesign wave 212 has passed 

(which includes the Boeing 747–8, 

Boeing 737 Max, Airbus 320 Neo, and 

Boeing 777–X), we do not currently 

have knowledge of many additional 

significant partial redesigns anticipated 

over the next decade (as the previous 

wave of significant partial redesigns 

included the Boeing 777–200LR in 

2004, 777–300ER in 2006, 737NG in 

1998, Airbus 319 in 1996, and Airbus 

330–200 in 1998).213 214 Incremental 

improvements will likely be frequent 

and occur in the near term. One 

approach CAEP is considering would be 

to limit the applicability of any 

international CO2 standard to only new 

type designs (or new aircraft types). 

Under this approach the international 

CO2 standard would not apply to 

significant partial redesigned aircraft 

and incremental improvements. Under 

another approach CAEP is considering, 

CAEP would also apply the 

international CO2 standard to inproduction 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

Another approach for applicability of 

the international CO2 standard that 

CAEP could adopt (or CAEP is 

considering) would be an approach 

based on criteria addressing significant 

changes to aircraft designs, which could 

be considered an applicability 

requirement different than that for new 

aircraft types only and in-production 

aircraft. This alternative approach could 

redefine a new aircraft type for CO2

purposes to include in-production 

aircraft that have a significant change in 

CO2 emissions, thus including inproduction 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 


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218Boeing, 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). 219The 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.) 

220 ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, March 17, 

2015. 221 ICAO, 2013: CAEP/9 Agreed Certification 

Requirement for the Aeroplane CO2 Emissions 

Standard. Available at http://www.icao.int/

publications/catalogue/cat_2015_en.pdf (last 

accessed May.12, 2015). The ICAO Circular 337 is 

found on page 85 of the ICAO Products & Services 

2015 catalog and is copyright protected; Order No. 

CIR337. Section 1.5 states that that the date to be 

used in determining the applicability of the CO2

standard is the date the application for a Type 

Certificate was submitted to the certificating 

authority having jurisdiction over the manufacturer 

responsible for the aircraft design. Section 1.6 

specifies that an application shall be effective for 

the period specified in the designation of the 

airworthiness regulations appropriate to the aircraft 

type. An application for a Type Certificate is valid 

for 5 years. 

222These 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. 

223Approximate time-scales are considered to be 

5 years for near-term, 10 years for mid-term, and 20 

years or more for long-term. 

224 ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, March 17, 

2015. 

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-boeing1656206527 (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-maxreplacement-by-2030-what.html) (last accessed May 

12, 2015). We would consider this as a Boeing 

projection or sketching out of plans for a new 

aircraft type, but it is not a commitment from 

Boeing. 

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 inproduction aircraft as new types subject 

to the standard. 

If CAEP were to limit the scope of 

applicability to new aircraft types only 

(and without the significant change 

criteria approach described above), the 

international CO2 standard would not 

apply to later series aircraft with 

redesigned wings, aircraft that are 

available with different engines, or 

aircraft that undergo incremental 

improvements. Following are several 

examples that illustrate this situation. 

The re-engined Boeing 737 Max is an 

example of a significant partial 

redesigned aircraft that is expected to 

enter into service in 2017.218 This 

aircraft would fall under the original 

Boeing 737 Type Certificate that was 

issued in 1967 (and entered into service 

in 1968)—or more specifically it would 

fall under an amended Type Certificate, 

and it would not be considered a new 

aircraft type as defined by CAEP. The 

current in-production 737s (Next 

Generation 737s or commonly 

abbreviated as 737 NGs) feature newer 

engines, have redesigned wings, and 

entered service in 1998 under the 

original 737 Type Certificate that was 

issued in 1967, and these also were not 

considered a new type aircraft when 

they were introduced in 1998.219

Another example of an aircraft that does 

not qualify as a new type is the Boeing 

747–8 aircraft, that entered into service 

in 2011, and which included a new 

wing, new engines, and a lengthened 

fuselage but fell under an amended 

Type Certificate for the original Boeing 

747 that was certified in 1969 (and 

entered into service in 1969). An 

example of incremental improvements 

to in-production aircraft, is the Boeing 

Next Generation 737 performance 

improvement package which was 

implemented between 2011 and 2013 

and the Boeing 767–300 winglets that 

entered into service in 2008, both of 

which improve aircraft fuel efficiency. 

There are many other examples that 

exist for different manufacturers and 

aircraft around the world as well, but for 

conciseness, we are limiting our 

discussion to these above examples. 

These examples illustrate the typical 

certification for significant partial 

redesigns and incremental 

improvements by various aircraft 

certificating or certifying authorities (or 

national airworthiness authorities) 

around the world. 

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 midterm, about 5 to 10 years from 2016, or 

even in the longer-term of 20 years 

plus.223 224

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? 

The alternative approach being 

considered by CAEP and described 

earlier (addressing changes in design of 

in-production aircraft) may offer an 

opportunity to cover more aircraft in an 

earlier timeframe (including significant 

partial redesigns), but it is unclear what 

effect this approach would have on 


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226Traditionally, international emission 

standards have first been adopted by ICAO, and 

subsequently the EPA had initiated rulemakings 

under CAA section 231 to establish domestic 

standards equivalent to ICAO’s standards where 

appropriate. Provided ICAO adopts an international 

aircraft CO2 standard that is consistent with CAA 

section 231 and it is appropriate for domestic needs 

in the United States, we expect to proceed along a 

similar approach for the future CAA section 231 

aircraft engine CO2 standard (or aircraft engine GHG 

standard), provided the EPA issues final positive 

endangerment and cause or contribute findings 

under CAA section 231. 

227For 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. 

228CAEP 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. 229CAEP (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. 230The 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). 

231The International Council on Clean 

Transportation (ICCT) is a member of ICSA, and 

ICCT is an independent nonprofit organization 

founded to provide research and technical and 

scientific analysis to environmental regulators. See 

http://www.theicct.org/ (last accessed May 12, 

2015). 

232 ICCT, Efficiency Trends for New Commercial 

Jet Aircraft 1960 to 2008, November 2009. Available 

at http://www.theicct.org/sites/default/files/

publications/ICCT_Aircraft_Efficiency_final.pdf 

(last accessed May 12, 2015). 

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 inproduction 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 inproduction aircraft applicability 

options, and that these should be 

presented at the July 2015 Steering 

Group meeting, so that a decision can be 

taken at the 10th meeting of CAEP 

(CAEP/10) in February 2016 regarding 

whether the international CO2 standard 

will apply to in-production aircraft. 

There are a wide range of options under 

consideration, including both 

mandatory and voluntary options for 

reporting and certification processes for 

in-production aircraft applicability, but 

the 2014 Steering Group meeting 

requested that CAEP focus on defining 

the mandatory options (in contrast to 

options such as voluntary reporting and 

certification). 

1. Applicability to In-Production 

Aircraft and Date of Implementation 

At the 2014 Steering Group meeting, 

CAEP also agreed that 2023 represented 

the earliest possible date for an inproduction 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 peraircraft 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. 

As described in section VI.F.2, the 

technologies considered for the CAEP 

analyses are those technologies that will 

be widely used on in-production aircraft 

by 2016 or shortly thereafter.228 The 

EPA requests comments regarding 

whether applying an international CO2

standard to in-production aircraft is 

consistent with the purpose of the 

standard as accepted by the CAEP 

Steering Group meeting in 2011: ‘‘to 

achieve CO2 emission reductions from 

the aviation sector beyond expected 

‘business as usual’ . . . analyzed using 

ICAO criteria of technical feasibility, 

environmental benefit, cost 

effectiveness, and impacts of 

interdependencies.’’ 229 The 

International Coalition for Sustainable 

Aviation (ICSA),230 which is a CAEP 

Observer organization, submitted papers 

to CAEP that analyzed this issue. Also, 

a member of ICSA 231 has developed 

similar analyses which indicate that 

applying the international standard only 

to new aircraft types would likely result 

in no additional CO2 reductions beyond 

what would have occurred absent a CO2

standard, either for the near- and midterm, 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


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233 ICCT, ‘‘Could ICAO’s CO2 Standard Not 

Actually Cover Any Aircraft? Yes, If Nobody’s 

Watching’’. Blog, December 9, 2014. Available at 

http://www.theicct.org/blogs/staff/could-icaos-co2- 

standard-not-cover-any-aircraft (last accessed May 

12, 2015). 

234 ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, March 17, 

2015. 

235Pursuant 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. 

236Currently, 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. 

237For 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/documentlibrary/icao-aircraft-engine-emissions-databank 

(last accessed May 12, 2015). 

238 In 2012, the EPA promulgated annual 

reporting requirements for aircraft engine emissions 

of NOX, hydrocarbon, carbon monoxide, and smoke 

number and related parameters. One of the reasons 

that the EPA issued these reporting requirements 

was due to the varying amount of voluntary data 

reported by aircraft engine manufacturers. (U.S. 

EPA, ‘‘Control of Air Pollution from Aircraft and 

Aircraft Engines; Emission Standards and Test 

Procedures.’’ Final Rule, 77 FR 36342 (June 18, 

2012)). 

239EPA’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. 

240An aircraft manufacturer reporting 

requirement for in-production aircraft CO2 emission 

rates would require the reporting of aircraft CO2

emissions during the cruise phase of operation to 

the EPA. The majority of aircraft CO2 emissions 

occurs in the cruise phase of operation, and thus, 

reporting CO2 emission rates from this phase will 

improve our ability to track full-flight aircraft CO2

emission rates over time (in addition to reporting 

the aircraft engine CO2 emissions during the 

landing and takeoff cycle). Also, the aircraft test 

procedure that was agreed upon at CAEP/9 now 

enables us to measure aircraft CO2 emissions during 

cruise. 

241This GHG or CO2 emissions rate data will help 

to track trends, raise awareness, better understand 

the technology in the fleet, etc. 

Another study funded by the EPA 

corroborates this analysis.234 The EPA 

requests comments on whether applying 

the international CO2 aircraft standard 

only to new aircraft types would be 

consistent with the accepted purpose of 

the international standard (the purpose 

of the standard that has been accepted 

by the CAEP Steering Group). Lastly, the 

EPA requests comment on the 

appropriateness of a possible EPA 

regulation following either of these 

approaches (applicability to only new 

aircraft types or applicability to both 

new types and in-production aircraft) 

which are under consideration at CAEP. 

Also, there have been concerns raised 

in CAEP about applying the 

international CO2 standard to inproduction 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 inproduction 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 inproduction aircraft. 

2. Reporting Requirement for New InProduction Aircraft 

CAEP is working to define mandatory 

in-production aircraft options, and one 

possible option is a reporting 

requirement 236 237 238 for in-production 

aircraft CO2 emissions rates (measured 

according to the aircraft test procedure 

that was agreed upon at CAEP/9) as an 

alternative to establishing an aircraft 

CO2 standard for in-production aircraft. 

Although a reporting requirement 

provides policy relevant information, it 

does not necessarily translate into 

specific emissions reductions. The EPA 

recognizes that only a mandatory 

standard for in-production aircraft 

would ensure that the aircraft CO2

standard reduces per-aircraft CO2

emissions rates. However, a reporting 

requirement could be an important 

component of an in-production aircraft 

CO2 standard, especially if it is 

implemented shortly after an inproduction 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 inproduction aircraft CO2 standard. 

In 2009 the EPA promulgated a final 

GHG reporting rule that applies to many 

sectors in the United States, including 

manufacturers of heavy-duty and 

offroad vehicles and engines, and 

manufacturers of aircraft engines.239 240

The EPA’s experience with reporting 

programs indicates that the EPA and the 

public would be able to track CO2

emissions rates trends (i.e., trends of 

aircraft cruise fuel burn rates) from 

aircraft over time. Requiring the 

reporting of aircraft CO2 emissions rates 

trends from aircraft over time is 

appropriate and feasible. Requiring 

aircraft manufacturers to report aircraft 

CO2 emissions rates shortly after an inproduction 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. 

Independent of action that CAEP may 

or may not take in February 2016, the 

EPA could under its CAA section 114(a) 

authority pursue a reporting 

requirement for aircraft cruise GHG or 

CO2 emissions rates—to ensure we have 

GHG or CO2 emissions rates data on all 

in-production aircraft (and any new 

aircraft types that enter service).241 The 

EPA could use the same metric agreed 

to at CAEP/9 (and in ICAO circular 337). 

This will be described in detail in 


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242 In this case, manufacturers would need to 

report the GHG or CO2 emission rates for inproduction 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. 

243By applying a reporting requirement to inproduction aircraft after a certain implementation 

date, this reporting requirement also includes new 

aircraft types that are produced after this 

implementation date. 

244As 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. 

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. 

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. 

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 inproduction 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. 

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. 

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. 

(1/SAR)avg is calculated at 3 gross weight 

fractions of Maximum Takeoff Mass 

(MTOM): 

High gross mass: 92% MTOM 

Mid gross mass: Average of high gross mass 

and low gross mass 

Low gross mass: (0.45 * MTOM) + (0.63 * 

(MTOM¥0.924)) 

The Reference Geometric Factor (RGF) 

is a measure of the fuselage size on a 

given aircraft. In analyzing various 

metric system options it was found that 

in some instances, namely stretch 

aircraft, changes in aircraft size, and 

thus capability, were not reflected in 

changes to the aircraft’s gross weight 

(MTOM). To account for these 

occurrences, and the variety of methods 

that manufacturers may use to make 

such a change, an adjustment factor was 

added (the RGF with a 0.24 exponent 

used in the metric system). 

2. Applicability 

CAEP has decided the scope of 

applicability for a future international 

CO2 standard should be subsonic jet and 

propeller-driven aircraft meeting the 

following criteria: 

All subsonic jet aircraft over 12,566 

lbs (5,700 kg) MTOM. 

All subsonic propeller driven (e.g., 

turboprop) aircraft over 19,000 lbs (8618 

kg) MTOM, except amphibious 

airplanes and those designed and used 

for fire-fighting operations. 

No military aircraft will be subject to 

this international standard. 

3. Certification Requirement 

CAEP has developed a mature 

certification requirement 246 that would 

allow for the determination of an 

aircraft CO2 metric value for any aircraft 

meeting the applicability criteria set 

forth above. This certification 

requirement incudes the metric system 

and test procedure. The test procedure 

was based upon industry’s current best 

practices for establishing the cruise 

performance of their aircraft, and input 

from certification authorities. These 

procedures include specifications for 

aircraft conformity, weighing, fuel 

specifications, test condition stability 

criteria, required confidence intervals, 

measurement instrumentation required, 

and corrections to reference conditions. 

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 


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247 ICAO, 2013: CAEP/9 Agreed Certification 

Requirement for the Aeroplane CO2 Emissions 

Standard. Available at http://www.icao.int/

publications/catalogue/cat_2015_en.pdf (last 

accessed May 12, 2015). The ICAO Circular 337 is 

found on page 85 of the ICAO Products & Services 

2015 catalog and is copyright protected; Order No. 

CIR33. 248 ICAO, Environmental Report 2010—Aviation 

and Climate Change, 2010, which is located at 

http://www.icao.int/environmental-protection/

Pages/EnvReport10.aspx (last accessed May 12, 

2015). 

249 Ibid. 

250Fly-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). 

251 ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, March 17, 

2015. 

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). 

253The 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. 

254The aircraft shown in these charts are inproduction and current in-development. These 

aircraft could be impacted by an in-production 

standard in that, if they were above the standard, 

they would need to either implement a technology 

response or go out of production. For a new type 

only standard there will be no regulatory 

requirement for these aircraft to respond. 

255Aircraft that are currently in-development but 

will be in production by the applicability dates. 

These could be new types or significant partial 

redesigned aircraft. 

256PIANO (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. 

257Metric values were generated using PIANO. 

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. 

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. flyby-wire).249 250

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. 

For aerodynamics, friction and liftdependent 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. 

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 inproduction and in-development around 

the world (within the applicable weight 

thresholds and categories), and this 

includes the wide range of technology 

that is currently in the aircraft fleet.253

Generally, the stringency options that 

are being evaluated fall into three 

categories as follows: (1) CO2 stringency 

levels that could impact 254 only the 

oldest, least efficient aircraft inproduction around the world, (2) 

middle range CO2 stringency levels that 

could impact many aircraft currently inproduction 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. 

The figures below are intended to 

show the range of stringency levels 

under consideration at CAEP and CO2

metric value levels of today’s inproduction 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 manufacturerprovided estimates of the aircraft metric 

value performance. 

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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37798 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

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. 

BILLING CODE 6560–50–P 


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Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 37799 

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 


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37800 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

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 in-production and indevelopment fleet, and Figure 4 projects 

out to the 2023 fleet. In addition, these 

figures allow one to compare the 

technology level and efficiency of 

aircraft with differing MTOMs. 


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37802 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

BILLING CODE 6560–50–C 

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. 


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200000 300000 400000 

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--Lines of Constant 

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t:::. In Production 

500000 600000 

Figure 4 - Percent from least efficient line of constant technology for the predicted 2023 

in-production fleet 
Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 37803 

258 ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, March 17, 

2015. 

259The 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. 

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 inproduction 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 

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

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 nonrecurring 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 topdown approach would not be the best 

approach for minor changes or 

incremental improvements because the 

significant design efforts include many 

changes that would not be required for 

smaller CO2 reductions. The EPA used 

the information gathered by ICF 

International to provide input on the 

cost for individual technologies which 

were used to build up non-recurring 

costs for these incremental 

improvements (a bottom-up approach). 

The technologies available to make 

incremental improvements to aircraft is 

wide ranging and aircraft specific. Some 

examples of technologies that could be 

integrated into an aircraft for 

incremental improvements include 

improved fan blade design or reduction 

in turbine clearances in the engine, 

reducing the gap between control 

surfaces, carbon brake pads, or 

advanced wing tip devices. As an 

example, ICF International estimated 

that depending on the additive nature of 

specific technologies and the magnitude 

improvement required, the cost to 

incrementally improve the Boeing 767 

could range from approximately 230 


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37804 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

260 ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, March 17, 

2015. 

261TRL is a measure of Technology Readiness 

Level. CAEP has defined TRL8 as the ‘‘actual 

system completed and ‘flight qualified’ through test 

and demonstration.’’ TRL is a scale from 1 to 9, 

TRL1 is the conceptual principle, and TRL9 is the 

‘‘actual system ‘flight proven’ on operational 

flight.’’ The TRL scale was originally developed by 

NASA. ICF International, CO2 Analysis of CO2- 

Reducing Technologies for Aircraft, Final Report, 

EPA Contract Number EP–C–12–011, see page 40, 

March 17, 2015. 

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. 

263According 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. 

264U.S. EPA, ‘‘Control of Air Pollution from 

Aircraft and Aircraft Engines; Emission Standards 

and Test Procedures;’’ Final Rule, 70 FR 2521, 

November 17, 2005. 

million to 1.3 billion US dollars (3.5% 

to 11% metric value improvement).260

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 inproduction, 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. 

3. Cost Effectiveness Analysis 

CAEP is currently conducting the cost 

effectiveness analysis for new-type and 

in-production aircraft. With rare 

exceptions CAEP has historically 

developed new type only standards. To 

model cost impacts of a new type 

standard, CAEP has historically used an 

assumption that the in-production 

aircraft will respond to the new type 

standard, even though the standard 

would not apply to them and has 

assumed that the aviation sector is 

competitive enough that market forces 

will drive manufacturers to voluntarily 

upgrade their fleet to meet any new type 

aircraft standard. This scenario is 

modeled no differently from a 

mandatory in-production standard. The 

EPA requests comment on modeling 

cost and environmental impacts of newtype standards based on the assumed 

attainment of such emissions levels by 

in-production aircraft. 

Because CAEP has modeled all inproduction aircraft as responding by the 

implementation date of the new-type 

standard, CAEP has by definition, 

performed an in-production analysis. 

More stringent options for new-type 

aircraft may be restricted due to the 

assumed in-production impacts. 

CAEP has recognized that its past 

methods for modeling a new-type only 

standard (by assuming in-production 

aircraft comply) may not be sufficient 

for the CO2 standard analysis. Thus, 

CAEP developed new methods to model 

what cost and environmental impacts 

would result from only new types being 

regulated under a new-type emission 

standard. CAEP is still determining the 

best way to conduct an analysis of 

impacts only on new types using the 

agreed upon technology responses and 

cost estimates. The EPA requests 

comments on how to model cost 

impacts for only new types for the 

future international CO2 standard, if it 

were to apply only to new types. The 

EPA also requests comment on how the 

modeling should be conducted to 

differentiate in-production and new 

type scenarios. 

G. Request for Comment on EPA’s 

Domestic Implementation of 

International CO2 Standards 

As described earlier in section II.E, 

traditionally international emission 

standards for aircraft engines have first 

been adopted by ICAO, and 

subsequently the EPA has initiated 

rulemakings to establish domestic 

standards that are of at least equal 

stringency as ICAO’s engine standards. 

However, the Chicago Convention,262

which established ICAO, recognizes that 

ICAO member states may adopt their 

own unique standards that are more 

stringent than ICAO standards. A 

participating member state (or nation) 

that adopts more stringent standards is 

obligated to notify ICAO of the 

differences between its standards and 

ICAO’s standards.263

Section 231(b) of the CAA requires 

that any emission standards ‘‘take effect 

after such period as the Administrator 

finds necessary (after consultation with 

the Secretary of Transportation) to 

permit the development and application 

of the requisite technology, giving 

appropriate consideration to the cost of 

compliance during such period.’’ 42 

U.S.C. 7571(b). Section 231(a)(2)(B) 

provides that the Administrator shall 

consult with the Administrator of the 

FAA on standards, and ‘‘shall not 

change the aircraft engine emission 

standards if such change would 

significantly increase noise and 

adversely affect safety.’’ 42 U.S.C. 

7571(a)(2)(B). 

As discussed in the 2005 rule (CAEP/ 

4 aircraft engine NOX standard),264 the 

EPA needs to have a technical basis for 

expecting the standards will be 

achievable in a specific period of time. 

While the statutory language of section 

231 is not identical to other provisions 

in title II of the CAA that direct the EPA 

to establish technology-based standards 

for various types of mobile sources, the 

EPA interprets its authority under 

section 231 to be similar to those 

provisions that grant us significant 

discretion to identify a reasonable 

balance of specified emissions 

reduction, and cost without adversely 

affecting safety or increasing noise. See, 

e.g., Husqvarna AB v. EPA, 254 F.3d 195 

(D.C. Cir. 2001) (upholding the EPA’s 

promulgation of technology-based 

standards for small non-road engines 

under section 213(a)(3) of the CAA). In 

this regard, we note CAEP’s intent for 

the purpose of the international CO2

standard (as accepted by the CAEP 

Steering Group in 2011), which is to 

achieve aircraft CO2 emissions 

reductions beyond that which would 


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Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 37805 

265 Ibid. 

have occurred in the absence of a 

standard. 

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. 

Although the EPA has traditionally 

established domestic standards that 

track the ICAO standards, for purposes 

of having a robust ANPR process, we 

ask for comment on the possibility of 

the EPA adopting a more stringent 

aircraft engine emissions standard than 

ICAO, provided ICAO/CAEP 

promulgates a standard in 2016 and the 

EPA makes a positive endangerment 

finding. In the same vein, the EPA 

requests that commenters consider the 

following factors (among others): The 

potential to reflect the CO2 emissions 

performance of products from U.S. 

manufacturers, competitive advantages 

and disadvantages for U.S. 

manufacturers, certification reciprocity 

with certificating authorities of other 

nations, and the EPA’s role in the 

ongoing ICAO negotiations. In addition, 

the EPA asks for comment on what 

action the EPA should take if the ICAO/ 

CAEP process fails to result in the 

adoption of an aircraft CO2 emissions 

standard. 

VII. Statutory Authority and Executive 

Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This action is a significant regulatory 

action because it raises novel policy 

issues. Accordingly, it was submitted to 

the Office of Management and Budget 

(OMB) for review. This action proposes 

a finding that GHG emissions from 

aircraft cause or contribute to air 

pollution that may be reasonably 

anticipated to endanger public health 

and welfare along with an ANPR which 

provides an overview of the 

international efforts to reduce GHG 

emissions, progress to date in 

establishing global aircraft standards 

that achieve meaningful CO2 reductions 

and, if the EPA finds that aircraft GHG 

emissions do cause or contribute to 

endangerment, the potential use of CAA 

section 231 to implement these 

standards domestically ensuring 

transparency and the opportunity for 

public comment. Any changes made in 

response to OMB recommendations 

have been documented in the docket. 

B. Paperwork Reduction Act (PRA) 

This action does not impose an 

information collection burden under the 

PRA. The proposed endangerment and 

cause or contribute findings under CAA 

section 231 do not contain any 

information collection activities. 

C. Regulatory Flexibility Act (RFA) 

I certify that this action will not have 

a significant economic impact on a 

substantial number of small entities 

under the RFA. This action will not 

impose any requirements on small 

entities. The proposed endangerment 

and cause or contribute findings under 

CAA section 231 do not in-and-ofthemselves impose any new 

requirements but rather set forth the 

Administrator’s proposed determination 

that GHG emissions from certain classes 

of aircraft engines—those used in U.S. 

covered aircraft—cause or contribute to 

air pollution that may be reasonably 

anticipated to endanger public health 

and welfare. Accordingly, this action 

affords no opportunity for the EPA to 

fashion for small entities less 

burdensome compliance or reporting 

requirements or timetables or 

exemptions from all or part of the 

proposal. 

D. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain any 

unfunded mandate as described in 

UMRA, 2 U.S.C. 1531–1538, and does 

not significantly or uniquely affect small 

governments. The action imposes no 

enforceable duty on any state, local or 

tribal governments or the private sector. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. It will not have substantial 

direct effects on the states, on the 

relationship between the national 

government and the states, or on the 

distribution of power and 

responsibilities among the various 

levels of government. 

F. Executive Order 13175: Consultation 

and Coordination with Indian Tribal 

Governments 

This action does not have tribal 

implications as specified in Executive 

Order 13175. The proposed 

endangerment and cause or contribute 

findings under CAA section 231 do not 

in-and-of-themselves impose any new 

requirements but rather set forth the 

Administrator’s proposed determination 

that GHG emissions from certain classes 

of aircraft engines—those used in U.S. 

covered aircraft—cause or contribute to 

air pollution that may be reasonably 

anticipated to endanger public health 

and welfare. Thus, Executive Order 

13175 does not apply to this action. 

G. Executive Order 13045: Protection of 

Children from Environmental Health 

Risks and Safety Risks 

This action is not subject to Executive 

Order 13045 because it is not 

economically significant as defined in 

Executive Order 12866. The 

Administrator considered climate 

change risks to children as part of this 

proposed endangerment finding under 

CAA section 231. This action’s 

discussion of climate change impacts on 

public health and welfare is found in 

section IV of this preamble. Specific 

discussion with regard to children are 

contained in sections IV and I.D of the 

preamble titled ‘‘Children’s 

Environmental Health.’’ A copy of all 

documents pertaining to the impacts on 

children’s health from climate change 

have been placed in the public docket 

for this action. 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution or Use 

This action is not a ‘‘significant 

energy action’’ because it is not likely to 

have a significant adverse effect on the 

supply, distribution or use of energy. 

Further, we have concluded that this 

action is not likely to have any adverse 

energy effects because the proposed 

endangerment and cause or contribute 

findings under section 231 do not inand-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, lowVerDate Sep<11>2014 19:14 Jun 30, 2015 Jkt 235001 PO 00000 Frm 00049 Fmt 4701 Sfmt 4702 E:\FR\FM\01JYP2.SGM 01JYP2

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37806 Federal Register / Vol. 80, No. 126 / Wednesday, July 1, 2015 / Proposed Rules 

income, or indigenous populations 

because this action does not affect the 

level of protection provided to human 

health or the environment. The 

Administrator considered climate 

change risks to minority, low-income, 

and indigenous populations as part of 

this proposed endangerment finding 

under CAA section 231. This action’s 

discussion of climate change impacts on 

public health and welfare is found in 

section IV of the preamble. Specific 

discussion with regard to minority, 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). 

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] 

BILLING CODE 6560–50–P 


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