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

Federal RegisterJul 1, 2015

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 87 and 1068

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

RIN 2060-AS31

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

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule and advance notice of proposed rulemaking.

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 CO

standard for aircraft at the International Civil Aviation Organization (ICAO), ICAO's progress in establishing global aircraft standards that achieve meaningful reductions in CO

emissions, and (provided the EPA promulgates final endangerment and cause and contribute findings for aircraft engine GHG emissions) the potential use of section 231 of the Clean Air Act to adopt and implement corresponding aircraft engine GHG emission standards domestically, ensuring transparency and the opportunity for public comment.

DATES:

Comments.

Comments must be received on or before August 31, 2015.

Public Hearing.

The EPA will hold a public hearing on August 11, 2015 in Washington, DC, at the William Jefferson Clinton East Building, Room 1153, 101 Constitution Avenue NW., Washington, DC 20004. If no one contacts the EPA requesting to speak at the hearing for this proposal by July 13, 2015 the public hearing will not take place and will be cancelled with no further notice. Speakers should contact Ms. JoNell Iffland (see

FOR FURTHER INFORMATION CONTACT

) to request to speak at the hearing. The last day to pre-register in advance to speak at the hearing will be August 6, 2015. The hearing will start at 10:00 a.m. local time and continue until everyone has had a chance to speak. Requests to speak will be taken the day of the hearing at the hearing registration desk, although preferences on speaking times may not be able to be fulfilled. If you require the service of a translator or special accommodations such as audio description, please let us know at the time of registration. For further information on the public hearing or to register to speak at the hearing,

please see

section I.B below or go to

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

ADDRESSES:

Comments.

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2014-0828, by one of the following methods:

•

Online: www.regulations.gov

Follow the on-line instructions for submitting comments.

•

Email: A-and-R-Docket@epamail.epa.gov

Attention Docket ID No. EPA-HQ-OAR-2014-0828.

•

Fax:

(202) 566-9744, Attention Docket ID No. EPA-HQ-OAR-2014-0828.

•

Mail:

U.S. Postal Service, send comments to Air and Radiation Docket and Information Center, Environmental Protection Agency, Mail Code: 28221T, 1200 Pennsylvania Ave. NW., Washington, DC 20460. Attention Docket ID No. EPA-HQ-OAR-2014-0828.

•

Hand Delivery:

U.S. Environmental Protection Agency, EPA West, EPA Docket Center, EPA West Building, Room 3334, 1301 Constitution Ave. NW., Washington, DC 20004. Attention Docket ID No. EPA-HQ-OAR-2014-0828. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for deliveries of boxed information.

Instructions:

Direct your comments to Docket ID No. EPA-HQ-OAR-2014-0828. See section I.B on “Public Participation” for more information about submitting written comments. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at

http://www.regulations.gov

, including any personal information provided, unless the comment includes information claimed to be confidential business information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through

http://www.regulations.gov

or email. The

http://www.regulations.gov

Web site is an “anonymous access” system, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through

http://www.regulations.gov,

your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should avoid the use of special characters, or any form of encryption, and be free of any defects or viruses. For additional information about the EPA's public docket visit the EPA Docket Center homepage at:

http://www.epa.gov/dockets

. For additional instructions on submitting comments, go to section I.B of this document.

Docket.

The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2014-0828. All documents in the docket are listed in the

www.regulations.gov

index. Although listed in the index, some information is not publicly available,

e.g.,

CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy in the EPA's docket. Publicly available docket materials are available either electronically in

www.regulations.gov

or in hard copy at the Air and Radiation Docket and Information Center, EPA/DC, EPA WJC West, Room 3334, 1301 Constitution Ave. NW., Washington, DC. The Public Reading Room is open

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 CO

Emissions Standard and Request for Comment

A. Purpose of the International Standard

B. Applicability of the International CO

Emissions Standard

C. CAEP Discussion on In-Production Aircraft Applicability

1. Applicability to In-Production Aircraft and Date of Implementation

2. Reporting Requirement for New In-Production Aircraft

D. Metric System, Applicability, and Certification Requirement

1. CO

Metric System

2. Applicability

3. Certification requirement

4. Regulating the Entire Aircraft Instead of the Engine

E. Stringency Options

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

1. Non-Recurring Costs (Engineering Development Costs)

2. Technology Responses

3. Cost Effectiveness Analysis

G. Request for Comment on the EPA's Domestic Implementation of International CO

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:

Category

NAICS

Code

SIC

Code

Examples of potentially affected entities

Industry

3364412

3724

Manufacturers of new aircraft engines.

Industry

336411

3721

Manufacturers of new aircraft.

North American Industry Classification System (NAICS).

Standard Industrial Classification (SIC) code.

This table is not intended to be exhaustive, but rather provides a guide for readers regarding entities likely to be interested in this proposed action. This table lists the types of entities that the EPA is now aware could potentially have an interest in this proposed action. If the EPA issues final affirmative findings under section 231(a) regarding greenhouse gases, the EPA would then be required to undertake a separate notice and comment rulemaking to issue emission standards applicable to greenhouse gas emissions from the classes of aircraft engines that the EPA finds cause or contribute in such a finding, and the FAA would be required to Prescribe regulations to insure compliance with these emissions standards pursuant to section 232 of the Clean Air Act. Other types of entities not listed in the table could also be interested and potentially affected by subsequent actions at some future time. If you have any questions regarding the scope of this proposed action, consult the person listed in the preceding

FOR FURTHER INFORMATION CONTACT

section.

B. Public Participation

The EPA requests comment on all aspects of the proposed aircraft endangerment and cause or contribute findings and the Advance Notice of Proposed Rulemaking (ANPR). This section describes how you can participate in this process.

If you submitted comments on the issues raised by this proposal in dockets for other, earlier Agency efforts (

e.g.,

the 2009 Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202 of the Clean Air Act or the Advance Notice of Proposed Rulemaking on Regulating Greenhouse Gases under the Clean Air Act), you must still submit your comments to the docket for this action (EPA-HQ-OAR-2014-0828) by the deadline if you want them to be considered.

1. What should I consider as I prepare my comments for the EPA?

We are opening a formal comment period by publishing this document. We will accept comments during the period indicated in the

DATES

section. If you have an interest in the proposed aircraft endangerment and cause or contribute findings and/or the ANPR described in this document, we encourage you to comment on any aspect of this rulemaking.

Tips for Preparing Your Comments

When submitting comments, remember to:

• Identify the rulemaking by docket number and other identifying information (subject heading,

Federal Register

date and page number).

• Follow directions—The agency may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number.

• Explain why you agree or disagree, suggest alternatives, and substitute language for your requested changes.

• Describe any assumptions and provide any technical information and/or data that you used.

• If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced.

• Provide specific examples to illustrate your concerns, and suggest alternatives.

• Explain your views as clearly as possible, avoiding the use of profanity or personal threats.

• Make sure to submit your comments by the comment period deadline identified.

Do not submit information to the EPA containing CBI through

http://www.regulations.gov

or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CD-ROM the specific information that is claimed as CBI. In addition to one complete version of the comment that includes information claimed as CBI, you must submit a copy of the comment that does not contain the information claimed as CBI for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.

2. Public Hearing

If a hearing is held, it will provide interested parties the opportunity to present data, views or arguments concerning the proposed action. The EPA will make every effort to accommodate all speakers who arrive and register. Because this hearing, if held, will be at a U.S. government facility, individuals planning to attend the hearing should be prepared to show valid picture identification to the security staff in order to gain access to the meeting room. Please note that the REAL ID Act, passed by Congress in 2005, established new requirements for entering federal facilities. These requirements took effect July 21, 2014. If your driver's license is issued by Alaska, American Samoa, Arizona, Kentucky, Louisiana, Maine, Massachusetts, Minnesota, Montana, New York, Oklahoma, or the state of Washington, you must present an additional form of identification to enter the federal buildings where the public hearings will be held. Acceptable alternative forms of identification include: Federal employee badges, passports, enhanced driver's licenses and military identification cards. In addition, you will need to obtain a property pass for any personal belongings you bring with you. Upon leaving the building, you will be required to return this property pass to the security desk. No large signs will be allowed in the building, cameras may only be used outside of the building and demonstrations will not be allowed on federal property for security reasons. The EPA may ask clarifying questions during the oral presentations but will not respond to the presentations at that time. Written statements and supporting information submitted during the comment period will be considered with the same weight as oral comments and supporting information presented at the public hearings.

Speakers should contact Ms. JoNell Iffland (see

FOR FURTHER INFORMATION CONTACT

) if they will need specific equipment, or if there are other special needs related to providing comments at the hearing. Oral testimony will be limited to no more than 10 minutes for each commenter, although we may need to adjust the time for each speaker if there is a large turnout. The EPA requests that commenters provide the EPA with three copies of their oral testimony in hard copy form the day of the hearing or an electronic copy in advance of the hearing date. Verbatim transcripts of the hearings and written

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

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.

U.S. EPA, 2006:

EPA Peer Review Policy.

Available at

http://www.epa.gov/peerreview/

(Last accessed May 12, 2015).

U.S. EPA, 2012:

EPA Peer Review Handbook, Third Edition.

Available at

http://www.epa.gov/peerreview/pdfs/peer_review_handbook_2012.pdf

(Last accessed May 12, 2015).

The EPA also cites data from its annual Inventory of U.S. Greenhouse Gas Emissions and Sinks report,

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).

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).

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

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.

U.S. EPA, 2009:

Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act; Final Rule,

74 FR 66496 (December 15, 2009) (“2009 Endangerment Finding”); 74 FR 18886 (April 24, 2009) (“Proposed 2009 Endangerment Finding”).

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 CO

standard would apply:

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.

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.

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

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: CO

, 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 CO

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 CO

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 CO

, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. Of these six gases, two (CO

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.

The heating effect caused by the human-induced buildup of these and other GHGs in the atmosphere, plus other human activities (

e.g.,

land use change and aerosol emissions), is extremely likely (>95 percent likelihood) to be the cause of most of the observed global warming since the mid-20th century.

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.

“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.

Ibid.

The U.S. transportation sector constitutes a meaningful part of total U.S. and global anthropogenic GHG emissions. In 2013, aircraft remained the single largest GHG-emitting transportation source not yet subject to any GHG regulations. Aircraft clearly contribute to U.S. transportation emissions, accounting for 11 percent of all U.S transportation GHG emissions and representing more than 3 percent of total U.S. GHG emissions in 2013.

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.

U.S. EPA, 2015:

Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2013,

564 pp. Available at

http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport,

(last accessed May 12, 2015).

2. Statutory Basis for This Proposal

Section 231(a)(2)(A) of the CAA states that “The Administrator shall, from time to time, issue proposed emission standards applicable to the emission of any air pollutant from any class or classes of aircraft engines which in [her] judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare.”

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.

If the Administrator answers both questions in the affirmative, she must issue standards under section 231.

See Massachusetts

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.

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

Center for Biological Diversity, Center for Food Safety, Friends of the Earth, International Center for Technology Assessment, and Oceana, 2007: Petition for Rulemaking Under the Clean Air Act to Reduce the Emissions of Air Pollutants from Aircraft the Contribute to Global Climate Change, December 5. Available at

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

(last accessed May 12, 2015).

The Administrator is applying the rulemaking provisions of CAA section 307(d) to this action, pursuant to CAA section 307(d)(1)(V), which provides that the provisions of 307(d) apply to “such other actions as the Administrator may determine.”

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.

As the Administrator is applying the provisions of section 307(d) to this rulemaking under section 307(d)(1)(V), we need not determine whether those provisions would apply to this action under section 307(d)(1)(F).

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

Massachusetts

EPA,

549 U.S. 497 (2007), the Supreme Court found that GHGs are air pollutants that can be regulated under the CAA. The Court held that the Administrator must determine whether emissions of GHGs from new motor vehicles cause or contribute to air pollution which may reasonably be anticipated to endanger public health and/or welfare, or whether the science is too uncertain to make a reasoned decision. In making these decisions, the Administrator was bound by the provisions of section 202(a) of the CAA. The Supreme Court decision resulted from a petition for rulemaking under section 202(a) filed by more than a dozen environmental, renewable energy, and other organizations.

Following the Supreme Court decision, the EPA proposed (74 FR 18886, April 24, 2009) and then finalized (74 FR 66496, December 15, 2009) the 2009 Endangerment Finding, which can be summarized as follows:

• Endangerment Finding: The Administrator found that the then-current and projected concentrations of the six key well-mixed GHGs—CO

, 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).

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).

On August 29, 2012, the second phase of the GHG emission standards for light-duty vehicles (2017-2025 model years) was finalized further reducing GHG emissions from light-duty vehicles.

In 2014, the President directed the EPA and the Department of Transportation to set standards by March 2016 that further increase fuel efficiency and reduce GHG emissions from medium- and heavy-duty vehicles.

U.S. EPA, 2010:

Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards; Final Rule,

75 FR 25324 (May 7, 2010).

US EPA, 2011:

Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles; Final Rule,

Federal Register

57106 (September 15, 2011).

U.S. EPA, 2012:

2017 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards; Final Rule,

77 FR 62623 (October 15, 2012).

Executive Office of the President, 2014:

Remarks by the President on Fuel Efficiency Standards of Medium and Heavy-Duty Vehicles,

Office of the Press Secretary, February 18. Available at:

http://www.whitehouse.gov/the-press-office/

2014/02/18/remarks-president-fuel-efficiency-standards-medium-and-heavy-duty-vehicl

(last accessed May 12, 2015).

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

U.S. EPA. “EPA and NHTSA Set Standards to Reduce Greenhouse Gases and

Improve Fuel Economy for Model Years 2017-2025 Cars and Light Trucks

.” Office of Transportation and Air Quality Document No. EPA-420-F-12-051, August 2012. Available at

http://www.epa.gov/otaq/climate/documents/420f12051.pdf

(last accessed May 26, 2015). See also US EPA, 2012:

Regulatory Impact Analysis: Final Rulemaking for 2017-2025 Light-Duty Vehicle Greenhouse Gas Emissions Standards and Corporation Average Fuel Economy Standards,

August, Document No. EPA-420-R-12-016, Table 7.4-2. Available at:

http://www.epa.gov/oms/climate/documents/420r12016.pdf

(last accessed May 12, 2015).

76 FR 57106 (September 15, 2011).

On June 25, 2013, President Obama announced a Climate Action Plan that set forth a series of executive actions to further reduce GHGs, prepare the U.S. for the impacts of climate change, and lead international efforts to address global climate change.

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.

In response, in January 2014, the EPA proposed carbon pollution standards for new electric utility generating units.

This was followed in June 2014, by proposed standards to address carbon pollution from modified and reconstructed power plants

and from existing power plants.

Executive Office of the President, 2013:

The President's Climate Action Plan,

June 25. Available at:

http://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf

(last accessed May 26, 2015).

Executive Office of the President, 2013:

Presidential Memorandum—Power Sector Carbon Pollution Standards,

Office of the Press Secretary, June 25. Available at:

http://www.whitehouse.gov/the-press-office/2013/06/25/presidential-memorandum-power-sector-carbon-pollution-standards

(last accessed May 12, 2015).

U.S. EPA, 2014:

Standards of Performance for Greenhouse Gas Emissions From New Stationary Sources: Electric Utility Generating Units; Proposed Rule,

79 FR 1430 (January 8, 2014).

U.S. EPA, 2014:

Carbon Pollution Standards for Modified and Reconstructed Stationary Sources: Electric Utility Generating Units; Proposed Rules,

79 FR 34960 (June 18, 2014).

U.S. EPA, 2014:

Carbon Pollution Emission Guidelines for Existing Stationary Sources: Electric Utility Generating Units; Proposed Rule,

79 FR 34830 (June 18, 2014).

In the Climate Action Plan, the President also indicated that the U.S. was working internationally to make progress in a variety of areas and specifically noted the progress being made by ICAO to develop global CO

emission standards for aircraft.

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,

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.

See section V of this preamble for more information about the data sources that compose the aircraft GHG emissions inventory.

Executive Office of the President, 2013:

The President's Climate Action Plan

at 21, June. Available at:

http://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf

(last accessed May 12, 2015).

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).

Ibid.

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. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, pp. 599-670.

As discussed in section V.B.2.c., fuel burn growth rates for air carriers and general aviation aircraft operating on jet fuel are projected to grow by 49 percent from 2010 to 2035, and this provides a scaling factor for growth in GHG emissions which would increase at a similar rate as the fuel burn by 2030, 2035, and 2040. FAA, 2015:

FAA Aerospace Forecast Fiscal Years 2015-2035,

134 pp. Available at

https://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_forecasts/2015-2035/media/2015_National_Forecast_Report.pdf

(last accessed May 12, 2015).

2. Background on the Aircraft Petition, 2008 ANPR, and D.C. District Court Decision

Section 231(a)(2)(A) of the CAA directs the Administrator of the EPA to, from time to time, propose aircraft engine emissions standards applicable to the emission of any air pollutant from any classes of aircraft engines which in her judgment causes or contributes to air pollution which may reasonably be anticipated to endanger public health or welfare.

On December 5, 2007, Friends of the Earth, Oceana, the Center for Biological Diversity, Earthjustice, and others (Petitioners) sent a letter to the EPA petitioning the Agency to undertake rulemaking regarding GHG emissions from aircraft.

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.

Center for Biological Diversity, Center for Food Safety, Friends of the Earth, International Center for Technology Assessment, and Oceana, 2007:

Petition for Rulemaking Under the Clean air Act to Reduce the Emissions of Air Pollutants from Aircraft the Contribute to Global Climate Change,

December 5. Available at

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

(last accessed May 12, 2015).

Following the Supreme Court's decision in

Massachusetts

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 CO

engine emissions standards, these commenters felt that

international CO

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 CO

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 (NO

)

and should also include provisions for an averaging, banking, and trading (ABT) program.

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 CO

emissions from aircraft.

Sections II.D.1 and II.E provide an overview of the history ICAO's regulation of aircraft engine NO

emissions from 1981 through 2012 and the EPA's adoption of equivalent aircraft engine NO

standards under the CAA.

ABT programs have been utilized in a number of Clean Air Act programs to provide greater flexibilities that lower overall costs by allowing a manufacturer to comply with performance standards through averaging emissions among the vehicles it manufactures. Companies that achieve extra pollution reductions can bank these as `credits” and then `trade or sell' emission credits to other companies, typically those that face higher costs to control pollution. Well-designed ABT programs can sometimes achieve greater emissions reductions at less cost and provide incentives for technology innovation.

On July 31, 2008, Earthjustice, on behalf of Petitioners, notified the EPA of its intent to file suit under CAA section 304(a) against the EPA for the Agency's alleged unreasonable delay in responding to its aircraft petition and in making an endangerment finding under section 231. On June 11, 2010, Petitioners filed a complaint against the EPA in the U.S. District Court for the District of Columbia claiming that, among other things, the EPA had unreasonably delayed because it had failed to answer the 2007 Petition and to determine whether or not GHG emissions from aircraft cause or contribute to air pollution which may reasonably be anticipated to endanger public health and/or welfare.

The District Court found that while CAA section 231 generally confers broad discretion to the EPA in determining what standards to promulgate, section 231(a)(2)(A) imposed a nondiscretionary duty on the EPA to make a finding with respect to endangerment from aircraft GHG emissions.

Center for Biological Diversity, et al.

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.

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

on June 27, 2012 stating our intention to move forward with a proposed endangerment finding for aircraft GHG emissions under section 231, while explaining that it would take the Agency significant time to complete this action. The EPA explained that the Agency would not begin this effort until after the U.S. Court of Appeals completed its then-pending review of the previous section 202 Endangerment Finding, since the then-awaited ruling might provide important guidance for the EPA in conducting future GHG endangerment findings. The EPA further explained that after receiving the Court of Appeal's ruling, it would take at least 22 months from that point for the Agency to conduct an additional finding regarding aircraft GHG emissions.

U.S. EPA, 2012:

Memorandum in Response to Petition Regarding Greenhouse Gas Emissions from Aircraft,

June 14. Available at

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

(last accessed May 12, 2015) and Docket EPA-HQ-OAR-2014-0828.

Meanwhile, the Court upheld EPA's section 202 findings in a decision of a three-judge panel on June 26, 2012, and denied petitions for rehearing of that decision on December 20, 2012.

Coalition for Responsible Regulation, Inc.,

EPA,

684 F.3d 102 (D.C. Cir. 2012), reh'g denied 2012 U.S. App. LEXIS 26315, 25997 (D.C. Cir. 2012).

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.

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

EPA,

134 S. Ct. 2427, 2438 (2014);

see also Virginia

EPA,

134 S. Ct. 418 (2013),

Pac. Legal Found.

EPA,

134 S. Ct. 418 (2013), and

CRR,

134 S. Ct. 468 (2013) (all denying cert.). Thus, the Supreme Court did not disturb the D.C. Circuit's holding that affirmed the 2009 Endangerment Finding.

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

The EPA and the Federal Aviation Administration (FAA) traditionally work within the standard-setting process of ICAO's Committee on Aviation Environmental Protection (CAEP) to establish international emission standards and related requirements. Historically, under this approach, international emission standards have first been adopted by ICAO, and subsequently the EPA has initiated rulemakings under CAA section 231 to establish domestic standards equivalent to ICAO's standards where appropriate. This approach has been affirmed as reasonable by the U.S. Court of Appeals for the D.C. Circuit.

NACAA

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

GHG standard (which may take the form of a CO

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 CO

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.”

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

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.

Members of ICAO's Assembly are generally termed member States or contracting States. These terms are used interchangeably throughout this preamble.

There are currently 191 Contracting States according to ICAO's Web site:

www.icao.int

(last accessed May 12, 2015).

In the interest of global harmonization and international air commerce, the Chicago Convention urges its member States to collaborate in securing the highest practicable degree of uniformity in regulations, standards, procedures and organization. The Chicago Convention also recognizes that member States may adopt standards that are more stringent than those agreed upon by ICAO. Any member State which finds it impracticable to comply in all respects with any international standard or procedure, or which deems it necessary to adopt regulations or practices differing in any particular respect from those established by an international standard, is required to give immediate notification to ICAO of the differences between its own practice and that established by the international standard.

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.

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.

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.

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.

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.

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.

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.

ICAO's CAEP, which consists of Members and Observers from States, intergovernmental and non-governmental organizations representing aviation industry and environmental interests, undertakes ICAO's technical work in the environmental field. The Committee is responsible for evaluating, researching, and recommending measures to the ICAO Council that address the environmental impacts of international civil aviation. CAEP's terms of reference indicate that “CAEP's assessments and proposals are pursued taking into account: technical feasibility; environmental benefit; economic reasonableness; interdependencies of measures (for example, among others, measures taken to minimize noise and emissions); developments in other fields; and international and national programs.”

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.

CAEP's terms of reference are available at

http://www.icao.int/environmental-protection/Pages/Caep.aspx#ToR

(last accessed May 12, 2015).

At CAEP meetings, the U.S. is represented by the FAA and plays an active role.

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

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

Pursuant to the President's memorandum of August 11, 1960 (and related Executive Order No. 10883 from 1960), the Interagency Group on International Aviation (IGIA) was established to facilitate coordinated recommendations to the Secretary of State on issues pertaining to international aviation. The DOT/FAA is the chair of IGIA, and as such, the FAA represents the U.S. on environmental matters at CAEP.

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.

CAEP develops new emission standards based on an assessment of the technical feasibility, cost, and environmental benefit of potential requirements.

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.

These standards limited aircraft engine emissions of hydrocarbons, carbon monoxide, and NO

. The 1981 standards applied to newly manufactured engines, which are those engines built after the effective date of the regulations—also referred to as in-production engines. In 1993, ICAO adopted a CAEP/2 proposal to tighten the original NO

standard by 20 percent and amend the test procedures.

These 1993 standards applied both to newly-certified turbofan engines, which are those engine models that received their initial type certificate after the effective date of the regulations—also referred to as newly-certified engines or new engine designs—and to in-production engines, but with different effective dates for newly-certified engines and in-production engines. In 1995, CAEP/3 recommended a further tightening of the NO

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 NO

reduction proposal, which ICAO approved in 1998. The CAEP/4 standards applied only to new engine designs certified (or newly-certified engines) after December 31, 2003 (

i.e.,

unlike the CAEP/2 standards, the CAEP/4 requirements did not apply to in-production engines). In 2004, CAEP/6 recommended a 12 percent NO

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 NO

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.

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.

CAEP conducts its work over a period of years. Each work cycle is numbered sequentially and that identifier is used to differentiate the results from one CAEP to another by convention. The first technical meeting on aircraft emission standards was CAEP's successor,

i.e.,

CAEE. The first meeting of CAEP, therefore, is referred to as CAEP/2.

CAEP/5 did not address new aircraft engine emission standards.

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.

CAEP/7 did not address new aircraft engine emission standards.

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.

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).

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 CO

emissions standard.

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 CO

emissions at 2020 levels.

The Resolution included the following statements regarding ICAO policies and practices related to climate change.

A consolidated statement of continuing policies and practices related to environmental protection (known as Assembly Resolutions) is revised and updated by the Council every three years for adoption by the ICAO Assembly. ICAO, 2010:

Resolutions Adopted by the Assembly, 37th Session, Montreal, September 29-October 8, 2010,

Provisional Edition, November.

The global aspirational goal for international aviation of improving annual fuel efficiency by 2 percent is for the annual international civil aviation in-service fleet. Fuel efficiency is measured on the basis of the volume of fuel used per revenue tonne kilometer performed. (ICAO, CAEP,

Aspirational Goals and Implementation Options,

HLM-ENV/09-WP/5, High-Level Meeting on International Aviation and Climate Change, Presented by the Secretariat, Montreal, October 7 to 9, 2009. Available at

http://www.icao.int/Meetings/AMC/MA/High%20Level%202009/hlmenv_wp005_en.pdf

(last accessed May 12, 2015).

—. . . ICAO and its member States recognize the importance of providing continuous leadership to international civil aviation in limiting or reducing its emissions that contribute to global climate change;

—Reemphasizing the vital role which international aviation plays in global economic and social development and the need to ensure that international aviation continues to develop in a sustainable manner;

—. . . the ultimate objective of the United Nations Framework Convention on Climate Change (UNFCCC) is to achieve stabilization of greenhouse gas (GHG) concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system; and

—Acknowledging that international aviation emissions, currently accounting for less than 2 per cent of total global CO

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, CO

emissions technology-based standards, operational improvements, and market based measures. The development and adoption of a CO

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

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

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 CO

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 CO

standard).

We anticipate that ICAO/CAEP will adopt a final aircraft CO

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 CO

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 CO

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 CO

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.

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.

That action included new NO

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)

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).

It also included a carbon monoxide emission standard for in-production commercial turbofan engines.

In 2005, we promulgated more stringent NO

emission standards for newly-certified commercial turbofan engines.

That final rule brought the U.S. standards closer to alignment with ICAO CAEP/4 requirements that became effective in 2004. In 2012, we issued more stringent two-tiered NO

emission standards for newly-certified and in-production commercial and non-commercial turbofan aircraft engines, and these NO

standards align with ICAO's CAEP/6 and CAEP/8 requirements that became effective in 2013 and 2014, respectively.

59 60

U.S. EPA, 1973:

Emission Standards and Test Procedures for Aircraft; Final Rule,

38 FR 19088 (July 17, 1973).

The full CAEP membership meets every three years and each session is denoted by a numerical identifier. For example, the second meeting of CAEP is referred to as CAEP/2, and CAEP/2 occurred in 1994.

This does not mean that in 1997 we promulgated requirements for the re-certification or retrofit of existing in-use engines.

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.

U.S. EPA, 1997:

Control of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test Procedures; Final Rule,

62 FR 25355 (May 8, 1997).

U.S. EPA, 2005:

Control of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test Procedures; Final Rule,

70 FR 2521 (November 17, 2005).

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).

While ICAO's standards were not limited to “commercial” aircraft engines, our 1997 standards were explicitly limited to commercial engines, as our finding that NO

and carbon monoxide emissions from aircraft engines cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare was so limited. See 62 FR 25358 (May 8, 1997). In the 2012 rulemaking, we expanded the scope of that finding and of our standards pursuant to Section 231(a)(2)(A) of the Clean Air Act to include such emissions from both commercial and non-commercial aircraft engines based on the physical and operational similarities between commercial and noncommercial civilian aircraft and to bring our standards into full alignment with ICAO's.

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 CO

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.

Several factors are considered when addressing whole-aircraft CO

emissions, as the CO

emissions are influenced by aerodynamics, weight, and engine-specific fuel consumption. Since each of these factors may affect aircraft engine fuel consumption, they ultimately affect CO

emissions. Rather than viewing CO

as a measurable emission from engines, therefore, ICAO now addresses CO

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 CO

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

from aircraft engines and to issue final “regulations with such modifications as [she] deems appropriate.”

ICAO, 2013:

CAEP/9 Agreed Certification Requirement for the Aeroplane CO

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.

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.

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

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

EPA,

134 S. Ct. 2427, 2438 (2014); see also

Virginia

EPA,

134 S. Ct. 418 (2013),

Pac. Legal Found.

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.

See CRR,

684 F.3d at 117 (explaining two-part analysis under section 202(a)).

The Administrator interprets the two-part test required under section 231(a)(2)(A) as being the same as that explained in the 2009 Endangerment Finding. (

See

74 FR 66505-06, December 15, 2009.) As in the section 202(a) context, this analysis entails a scientific judgment by the Administrator about the potential risks posed by GHG emissions to public health and welfare.

See CRR,

684 F.3d at 117-118.

When agencies such as the EPA make determinations based on review of scientific data within their technical expertise, those decisions are given an “extreme degree of deference” by the D.C. Circuit, and as that court noted in reviewing the 2009 endangerment finding, “although we perform a searching and careful inquiry into the facts underlying the agency's decisions, we will presume the validity of the agency action as long as a rational basis for it is presented.”

CRR,

684 F.3d at 120 (internal citations and marks omitted).

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.

The Administrator is thus to consider both current and future risks.

See id.

at 121-122.

Second, the Administrator is to exercise judgment by weighing risks, assessing potential harms, and making reasonable projections of future trends and possibilities. It follows that when exercising her judgment the Administrator balances the likelihood and severity of effects. This balance involves a sliding scale: On one end the severity of the effects may be significant, but the likelihood low, while on the other end the severity may be less significant, but the likelihood high.

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.

EPA,

541 F.2d, 1, 18 (D.C. Cir. 1976)).

See 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.

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.

At the same time, the Administrator must exercise reasoned decision making, and avoid speculative inquiries.

See

id.

at 121-122.

Fourth, the Administrator is to consider the cumulative impact of sources of a pollutant in assessing the risks from air pollution, and is not to look only at the risks attributable to a single source or class of sources. We additionally note that in making an endangerment finding, the Administrator is not limited to

considering only those impacts that can be traced to the amount of air pollution directly attributable to the 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.

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.

As 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.

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

EPA,

549 U.S. at 534, the EPA may make an endangerment finding despite the existence of “some residual uncertainty” in the scientific record.