******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **1** of **198 EO12866_GHG Emissions from Aircraft _2060**  **- AS31 NPRM_ANPRM_FRN_** 
**````````` 20152**  **7 .**  **docx ENVIRONMENTAL PROTECTION AGENCY**  **40 CFR Parts 87 and 1068**  **[EPA -**  **HQ -**  **OAR -**  **20 14**  **- 0828**  **; FRL_XXXX -**  **X] RIN 2060**  **- A**  **S31 Proposed**  **Finding th at**  **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 i s 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, m ethane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride
-- that together were defined as the air pollution in the 2009 Endangerment F inding under section 202(a) of the Clean Air Act and that together constitute the primary******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **2** of **1 98**  cau se 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 this mix of greenhouse gases in the atmosphere. Thus, she proposes to find that greenhouse gas emissions from those classes of engines are contributing to air pollution which endanger s 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 t o provide an overview of and seek input on a variet y of issues related to setting an international CO 2 standard for aircraft at the International Civil Aviation Organization (I CAO) , ICAO’s progress in establishing global aircraft standards that achieve meaningful reductions in CO 2 emissions , and (provided the EPA promulgates final endangerment and cause and contribute findings for aircraft engine GHG emission s ) the potential use of section 2 31 of the Clean Air Act to adopt and implement corresponding aircraft engine GHG emission standards domestically , e nsuring transparency and the opportunity

for public comment. **DATES:** Comments. Comments must be received on or before **[ I**  **nsert date 60 days after**  **publication in the Federal Register ]** 
. Public Hearing
. If an yo ne contacts the EPA requesting a public hearing by **[insert date**  **10 days after publication in the Federal Register ]**  , w e will hold a public hearing on [DATE and PLACE ]. If a hearing is requested, the last day to pre - register in adv ance to speak at the hearing will be [ insert date ]
. The hearing will start at 9:30 am local time and continue until everyone has had a chance to speak. Requests to speak will be taken the day of******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **3** of **198** 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. If no one contacts the EPA requesting a public hearin g to be held concerning this proposed rule by **[insert date 10 days after publication in the Federal Register**  **]** , a public hearing will not take place. For further information on the public hearing or to register to speak at the hearing, please see section I .B below or go to [ ADD WEBSI TE ADDRESS ]. **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 In formation Center, Environmental Protection Agency , Mail C ode: 2822 1 T, 1200 Pennsylvania Ave., NW, Washington, DC 20460. Attention Docket ID No. EPA
- HQ
OAR
- 201 4
- 0828.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **4** of **198**  Hand Delivery : U.S. Environmental Protection Agency , EPA West , EPA Docket Center, EPA West Building, Room 3334, 1301 Constitution Ave., NW., Washington, DC 20 004
. 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 an y personal information provided, unless the comment includes information claimed to be c onfidential b usiness i nformation (CBI) or other information whose disclosure is restricted b y statute. Do not submit information that you consider to be CBI or other wise protected through http://www.regulations.gov or e - mail. The http://www.regulations.gov website is an “anon ym ous access” s ys tem, 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 e
mail comment directly

to the EPA without going through http://www.regulations.gov , your e mail address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Intern et. 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. I f the EPA cannot read your******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **5** of **198** 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 an y form of encryption, and be free of an y defects or viruses. For additional information about the EP A’s public docket visit the EPA Docket Center homepage at : http://www.epa.gov/dockets. For additional instructions on submitting comments, go to
s ection I.B o f 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 b y statute. Certain other material, such as copy righted material, is not placed on the Internet and will be pu blicly 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 In formati on 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 holiday s. 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 I ffland, Office of Transportation and Air Qualit y, Assessment and Standards Division (ASD), Environmental Protection Agency , 2000 Traverwood Drive, Ann Arbor , MI 48105; Telephone number: (734) 214
- 4454;******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **6** of **198** Fax number: (734) 214
- 4816; E
- mail address: iffland.jonell@epa.gov
. Please use this contact information for general questions about this rulemakin g, 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: Acronyms and Abbreviations**  **.** We use multiple acrony ms and terms in the preamble. While this list may not be exhaustive, to ease the reading of the preamble and for refere nce purposes, the EPA defines the following terms and acron ym s here: [ IN SERT ]
**TABLE OF CONTENTS** I. GENERAL INFORMATION A. Does this Action Apply to Me? B. Public Participation

1. What Should IConsider as I Prepare M y 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. IN TRODUCTION: OVERVIEW AND CONTEXT FOR THIS PROPOSAL A. Summary B. B ackground 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 Petitio n, 2008 ANPR, and U.S. District Court Decision D. The EPA’s Regulation of Aircraft Emissions******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **7** of **198** E. U.S. Aircraft Regulations and International Community 1. International Regulations and U.S. Obligations 2. Why is the International Community Currently

Addressing Aircraft CO2 Emissions? 3. Relationship of the EPA’s Proposed Endangerment and Cause or Contribute Finding and International Aircraft Standards III. LEGAL FRAMEWORK FOR THIS ACTION

A. Section 231(a)(2)(A)

—Endangerment and Cause or Contribute 1. The Statutory

L anguage 2. How the Origin of the Current Statutory L anguage Informs the EPA’s Interpretation of Section 231(a)(2)(A) 3. Additional Considerations for the Cause or Contribute Anal ys is B. Air Pollutant, Public Health and Welfare IV
. T HE P ROPOSED ENDANGERMENT F INDIN G 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 Administrator’s Judgment that the Six Well
Mixed Greenhouse Gases Endanger Public Health and Welf are 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 Endange r 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 THE SIX LONG
- LIVED, WELL
- MIXED GREENHOUSE GASES A. The Air Pollutant 1. Propo sed Definition of Air Pollutant 2. How the Definition of Air Pollutant in the Endangerment Determinatio n 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******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **8** of **198**

3. Proposed Contribution Finding for the Single Air Pollutant Comprised of the of Six Well
- Mixed Greenhouse Gases 4. Additional Considerations VI
. ADVANCE NOT IC E OF PROPOSED RULEMAKING: DI SCUSSION OF ONGOING IN TERNATIONAL PROCEEDINGS TO DEVELOP AIRCRAFT CO2 EMI SSI ONS STANDARD AND REQUEST FOR COMMENT A. Purpose of the International Standard B. Applicability

of the International Aircraft CO2 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 Sy stem, Applicability , and Certification Requirement 1. CO2 Metric Sy stem 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 Analy sis 1. Non
- Recurring Costs (engineering development costs) 2. Technology

Responses 3. Cost Effectiveness Analysis G. Request for Comment on Potential for a Different EPA Standard than International CO2 Standard VII. STATUTORY AUTHORTY EXECUTIVE ORDER REVI EWS

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 Safet y Risks H. Exec utive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply , Distribution or Use I. National Technology

Transfer and Advancement Act (NTTAA)******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **9** of **198** J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Popu lations and L ow - Income Populations K. Determination Under Section 307(d) VIII. STATUTORY PROVI SIONS AND LEGAL AUTHORITY 

## I. **General Information Does this Action Apply to Me?**  A. 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 g as emissions from certain classes of engines
-- those used in certain aircraft
-- cause or contribute to air pollution which endanger s 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 NAI CS a Code SI C b Cod e Examples of Potentially Affected Entities Industry 3364412 3724 Manufacturers of new aircraft engines. Industry 336411 3721 Manufacturers of new aircraft. a North American Industry Classification S ys tem (NAI CS). b Standard Industrial Classification (SI C) code.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **10** of **198** This table is not intended to be exhaustive, but rather provides a guide for readers regarding entities likely

to be interested in today ’s proposed action. This table lists the ty pes of entities that the EPA is now aware could potentially hav e an interest in this proposed action. I f 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 applicabl e 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 enforce these emissions standards in such aircraft per section 232 of the Clean Air Act
. Othe r ty pes 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.

**Public Participation** B. The EPA request s comment on all aspects of th e proposed aircraft endangerment and cause or contribute findings and the A dvance N otice of P roposed R ulemaking (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******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **11** of **198** 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
- 0 8 28) b y the deadline if you want them to be considered.

1. What Should IConsider as I Prepare M y Comments for the EPA? We are opening a formal comment period b y publishing this document. We will accept comments during the period indicated in the **DATES** section. If yo u have an interest in the proposed aircraft end angerment and cause or contribut e finding s and/or the ANPR described in this document, we encourage you to comment on an y aspect of this rulemaking.

Tips for Preparing Your Comments. When submitting comments, remember to:

 Id entify

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 s ection number.

 Explain why

you agree or disagree, suggest alternatives, and substitute language for your requested changes.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **12** of **198**

 Describe an y assumptions and provide an y 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 clearl y as possible, avoiding the use of profanity or p ersonal threats.

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

a. Submitting CBI Do not submit information to the EPA containing CBI through http://www.regulations.gov or e - mail. Clearl y mark the part or all of the information that you claim to be CBI. For CBI information o n 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
- R OM 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 th e public******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **13** of **198** 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 . In addition, you will need to obtain a property pass for an y person al belong ing s you bring with you. Upon leaving the building, you will be required to return this property pass to the securit y desk. No large signs will be allowed in the building, cameras may onl y be used outside of the building and d emonstrations will not be allowed on federal property for securit y reasons. The EPA may

ask clarifying que stions 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 notify

Ms
. JoNell Iffland if they will need specific equipment, or if there are other special needs related to providing comments at the hearing. The EPA will provide equipment for commenters to show overhead slides or make computerized slide******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **14** of **198** presentations if we receive special requests at least 3 business days in advance of the public hearing
. Oral testimony

will be limited to 5 minutes for each commenter. The EPA requests that commenters provide the EPA with at least 2 copies of their oral testimony in hard cop y form or a cop y electronically . Verbatim transcripts of the hearings and written s tatements 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
. In formation regarding the hearing (including information as to whether or not one will be held) will be available at [ insert website ] . Again, all requests for a public hearing to be held must be received by **[insert date 10 days after publication in the Fe**  **deral Register]**
.

**Did the**  **EPA Conduct a Peer Review before Issuing this Notice?** C. As outlined in s ection 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 pub lic health and welfare was to rel y primarily upon the recent, major assessments by the U.S. Global Change Research Program (USGCRP), the I

ntergovernmental Panel on Climate Change (I PCC), and the National Research Council (NRC) of the National Academies. T hese assessments draw s ynthesis 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 emplo yed b y the USGCRP, IP CC, and the NRC, and has******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **15** of **198** determined that these assessments have been adequately peer reviewed in a manner commensurate with the EPA’s Peer Review Policy 1 and the guidelines in O ffice of M anagement and B udget ’s (OMB) Final Information Quality Bulletin for Peer Review (“OMB Bulletin”) for highl y influential scientific assessments
. According to guidelines in the EPA's Peer Review Handbook, if the Agency has determined that information has already been subject to adequate peer review, then it is not necessary to have further peer review of that information. 2 The EPA also cites data from its annual Inventory of U.S. Greenhouse Gas Emissions and Sinks report , 3 which the Agency has determined to have been adequately reviewed in accordance with the OMB Bulletin and the EPA’s Peer Review Handbook. For the presentation of emissions inventory information to support the cause or contribute finding, the EPA disaggregated the existing data in one area of the GHG Inventory (for the General Aviation Jet Fu el Category) and had the disaggregation methodology and results peer reviewed in accordance with the EPA’s Peer Review Handbook
. All relevant peer review documentation is located in the docket for today 's action ( EPA
- HQ
- OAR
- 2014
- 0828 )
.

1 U.S. EPA, 2006: EPA Peer Review Policy . Available at http://www.epa.gov/peerreview/ (Last accessed February 5, 2015). 2 U.S. EPA, 2012: EPA Peer Review Handbook, Third Edition
. Available at http://www.epa.gov/peerreview/pdfs/peer_review_handbook_2012.pdf (Last accessed February 5, 2015). 3 U.S. EPA, 2014: Inventory of U.S. Greenhouse Gas Emissions a nd Sinks: 1990

- 2012 , 529 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport , (Last accessed February 5 , 2015)
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **16** of **198**

**Children’s Environm ental Health**  D. As described in detail in section IV of this preamble , the scientific evidence and conclusions in the USGCRP, IP CC, and the NRC assessment reports cited in the 2009 Endangerment Finding 4 indicate that children are uniquely vulnerable to climate change related health effects given behavioral , development al , and ph ys iologic al factors . The new assessment literature published since 2009 strengthens these conclusions by providing more detailed findings regarding children’s vulne rabilities and projected impacts they may experience. The se assessments describe how children’s unique physiological and developmental factors contribute to making them particularly vulnerable to climate change. Impacts to children are expected fro m heat waves, air pollution, infectious and waterborne illnesses, and mental health effects resulting from extreme weather events. In addition, the assessments find that climate chan ge will influence production of pollen that affects asthma and other allergic respiratory

diseases , to which children are among those especially susceptible
. A dditional health concerns may

arise in low income households, especially those with children, if climate

4 U.S. EPA, 2009: Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act ; Final Rule

, 74 FR 66496 (Dec ember 15, 2009) (“ 2009 Endangerment Finding”); 74 FR 18886 (April 24, 2009) (“Proposed 2009 Endangerment Finding”).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **17** of **198** change reduces food availability and increases prices, leading to food insecurity within households. **Environmental Justice** E. As described in detail in section IV below , the scientific assessment literature cited in the 2009 Endangerment Finding conc luded that certain populations are most vulnerable to the health and welfare effects of climate change , including the elderl y, the poo r, and indigenous peoples in the United States, particularly Alaska Natives. The new assessment literature strengthens the se conclusions b y providing more detailed findings regarding these populations’ vulnerabilities and projected impacts they may experience. In addition, the most recent assessment literature provides new information on how some communities of color may b e uniquel y vulnerable to climate change health impacts. These assessments find that certain climate change related impacts

— including heat waves, degraded air quality, and extreme weather events

—have disproportionate effects on low
- income and some c ommunities of color , raising environmental justice concerns. Existing health disparities and other inequities in these communities increase their vulnerability to the health effects of climate change. In addition , the studies also find that climate cha nge poses particular threats to i ndigenous p eoples’ health, wellbeing, and ways of life.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **18** of **198** 

## II. **Intr oduction: Overview and Context for**  **this Pr oposal**  **Summary** A. 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)
co ntribute to air pollution that endanger s public health and welfare. Covered aircraft would be those aircraft to which ICAO has agreed the international CO 2 standard would apply 5 : subsonic jet aircraft with a maximum takeoff mass (MTOM) greater than 5,700 kilograms , and subsonic propeller
- driven (e.g., turboprop) aircraft with a MTOM greater than 8,618 kilograms . Examples of covered aircraft would include small er jet aircraft such as the Cessna Citation CJ2+ and the Embraer E170 , up to and includin g the largest commercial jet aircraft such as the Airbus A380 and the Boeing 747. Other examples of covered aircraft would include larger turboprop aircraft, such as the ATR 72 and the Bombardier Q400
. In this proposed action, the EPA relies primarily o n the extensive scientific and technical evidence in the record supporting the Endangerment and Cause or Contribute

5 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Standards, Circular (Cir) 337, AN/192, Available at: http://www.icao.int/p ublications/catalogue/cat_2015

_ en.pdf . The ICAO Circular 337 is found on page 85 of the catalog and is copy right protected; Order No. CIR337 ( last accessed April 15, 2015
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **19** of **198** Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act ; Final Rule, 74 FR 66496 (collectivel y referred to as the 2009 Endangerment Finding in today ’s action). This includ es 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 anal yt ical 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 compellingl y supports an endangerment finding under CAA section 231(a). Furthermore, this proposed findi ng under section 231 reflects the EPA’s careful consideration not only of the scientific and technical record for the 2009 Endangerment F i nding, 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 anal ys es 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 sec tion 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. T he 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 GHG s : CO 2 , methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. This is the same******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **20** of **198** definition that was used for the finding for purposes o f section 202(a). It is the Administrator’s judgment that the total body of scientific evidence compellingl y supports a positive endangerment finding that elevated concentrations of the six well
- mixed GHG s constitute air pollution that endanger s 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 c lasses of aircraft engines cause or contribute to the air pollution that may reasonabl y 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 GHG s . B ased 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 endanger s 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******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **21** of **198** EPA anticipates that ICAO will adopt a final CO 2 emissions standard in February 2016. This proposal, and an y 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 ar e of at least equivalent stringency as the anticipated IC AO CO 2 standards. Once an international standard is finalized by ICAO, member s tates are then required to adopt standards that are equivalent to those set by I CAO , or they

may ad opt standards that are more stringent than those agreed upon by ICAO once proper notification is given. Section II. D provides additional discussion of the international aircraft standard
setting process. **Background Information Helpful to Understanding This Proposal**  B. 1. Greenhouse Gases and Their Effects GHGs in the atmosphere effectivel y trap some of the Earth’s heat that would otherwise escape to space. GHGs are both naturally occurring and anthropogenic. The primary GHGs directl y emitted by human activities include CO 2 , methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. Of these six gases, two ( CO 2 and nitrous oxide) are emitted by aircraft engines
. These six gases, once emitte d, 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******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **22** of **198** atmosphere. O bservations of the Earth’s globall y averaged combined land and ocean surface temperature over the period 1880 to 2012 show a warming of 0.85 [0.65 to 1.06] degrees Celsius or 1.53 [1.17 to 1.91] degrees Fahrenheit
. 6 The heating effect caused by the human
induced buildup of these and other GHGs in the atmosphere , plus other human activities (e.g., land use change and aerosol emissions), is extremely likel y (>95 percent likelihood) to be the cause of most of the observed global warming since the mid
- 20 th century . 7 A detailed explanation of climate change and its impact on health, society , and the environment is included in the record for the 2009 Endangerment Finding . The relevant scientific information from that record has also been included in the docket for this proposed determination under CAA section 231 (EPA
- HQ
- OAR
- 02914
- 0828 )
. Section IV of this preamble discusses this information, as well as information from the most recent scientific assessment s , in the context of the Administrator’s proposed endangerment finding under CAA section 231. The U.S. transportation sector is a significant contributor to total U.S. and global anthropogenic GHG emissions. In 2012, aircraft remained the single largest GHG
- e mitting transportation source not yet subject to an y GHG regulations . Aircraft constitute a significant part of U.S. transportation emissions, accounting for 11 percent of all U.S transportation GHG

6 “ IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.
- K. Plattner, M. Tignor , S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, 29 pp. 7 Ibid
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **23** of **198** emissions and representing more than 3 percent of total U.S. GHG emissions in 2012
. 8 Globally , U.S. aircraft GHG emissions represent 29 percent of all global aircraft emissions and 0.5 percent of total global GHG emissions. Section V of this preamble provides detailed information on aircraft GHG emissions in the context of the Administrator’s proposed cause or contribute finding under CAA section 231.

2. Statutory

Basis for This Proposal Section 231(a) (2)(A) of the CAA states that “ The Administrator shall, from time to time, issue proposed emission standards applicable to the emission of an y 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 reasonabl y be anticipated to endanger public health or welfare. Second, the Administrator must decide whether, in her judgment, emissions of an air po llutant from certain classes of aircraft engines

8 U.S. EPA, 2014: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

- 2012 , 529 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html# fullreport , (Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **24** of **198** cause or contribute to this air pollution. 9 If the Administrator answers both questions in the affirmative, she must issue standards under section 231. See Massachusetts v. EPA , 549 U.S. 497, 533 (20 0 7) (int erpreting analogous provision in CAA section 202 ) . Section I II of this preamble summarizes the legal framework for this proposed action under CAA section 231. Ty pically , past endangerment and cause or contribute findings have been proposed concurrently

wi th 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 58 FR 28809, 28813

– 14 (May 17, 1993), Final Rule 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 65 FR 35430 (June 2, 2000), Final Rule 66 FR 5002 (Jan. 18, 2001). However, there is no requirement that the Administrator propose the endangerment and cause or contribute findings concurrentl y with proposed standards. See 74 FR 66501
- 6 6502 (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

9 To clarify the distinction between air pollution and air pollutant, the air pollution is the atmospheric concentrations and can be thought of as the total, cumulative stock of GHGs in the atmosphere. The ai r 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.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **25** of **198** anal ys is 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 fin dings in response to a 2007 citizen s’ petition
. 10 The Administrator is applying the rulemaking provisions of CAA section 307(d) to this action, pursuant to CAA section 307(d)(1)(V), which provides that the provisions of 307(d) appl y to “such other actions as the Administrator may determine.” 11 Any

standard setting rulemaking under section 231 will also be subject to the notice and comment rulemaking procedures under 307(d), as provided in CAA section 307(d)(1)(F) (appl yi ng the provisio ns of 307(d) to the promulgation or revision of an y aircraft emission standard under section 231). Thus, these proposed findings will be subject to the same rulemaking
r equirements that would apply if the proposed findings were part of a standard
- setting rulemaking.

10 Center for Biological Diversity, Center for Food Safety, Friends of the Earth, International Center for Technology Asse ssment, and Oceana, 2007: Petition for Rulemaking Under the Clean A ir 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 February 5, 2015). 11 As the Administrator is applying the provisions of section 307(d) to this rulemaking under section 307(d)(1)(V), w e need not determine whether those provisions would apply to this action under section 307(d)(1)(F).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **26** of **198**

**The EPA’s Responsibilities under the Clean Air Act** C. 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 electri c generation, industrial, commercial and other facilities, are subject to various CAA programs. Implementation of the Act over the past four decades has resulted in significant reductions in air pollution while the nation’s economy has continued to grow.

1. The EPA’s Regulation of Greenhouse Gases In Massachusetts v. EPA , 549 U.S. 497 (2007), the Supreme Court found that GHGs are air pollutants that can be regulated under the CAA. The Court held that the Administrator must determine whether emissions of GHGs from new motor vehicles cause or contribute to air pollution which may

reasonabl y 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 wa s bound by the provisions of s ection 202(a) of the CAA
. The Supreme Court decision resulted from a petition for rulemaking under s ection 202(a) filed by more than a dozen environmental, renewable energy, and other organizations. Followi ng 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:******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **27** of **198**  **Endangerment Finding:** The Administrator f ound that the then
- current and projected concentrations of the six key well
- mixed GHG s
— CO 2 , methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride

— in the atmosphere threaten the public health and welfare of current and future generatio ns .
 **Cause or Contribute Finding:** The Administrator f ound 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 d id 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 un der s ection 202(a). Subsequently , in May of 2010 the EPA, i n collaboration with the National Highway Traffic Safet y Administration (NHTSA), finalized Phase 1 GHG emission standards for light
- dut y vehicles (2012
- 2016 model years)
. 14 This was followed in August 2011 by adoption of the first
- ever GHG emission standards for heav y duty engines and vehicles (2014
- 2018 model years)
. 15 On August 29, 2012, the second phase

14 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)
. 15 US EPA, 2011: Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium

- and Heavy

Duty Engines and Vehicles; Final Rule, 76 FR 57106 (September 15, 2011).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **28** of **198** of the GHG emission standards for light
- dut y vehicles (2017
- 2025 model years ) w as finalized further reducing GHG emissions from light
- duty vehicles
. 16 In2014 , 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 f rom m edium
- and h eavy - d ut y v ehicles
. 17 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 em issions, and over the lifetime of these vehicles GHG emissions will have be en reduced b y more than 6.2 billion metric tons
. 18 , 19 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

16 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). 17 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 (L ast a ccessed February 5, 2015). 18 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/otaq/climate/documents/420r12016.pdf (L ast accessed February 5 , 2015)
. 19 76 FR 57106 (September 15, 2011).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **29** of **1 98**  change , and lead international efforts to address global climate change
. 20 As part of the Climate Action Plan, the President issued a Presidential Memorandum directing the EPA to
wor k expeditiously

to complete carbon pollution standards for the power sector. 21 In response, in January 201 4 , the EPA proposed carbon pol lution standards for new electric utility generating units
. 22 This was followed in June 2014, by proposed standards to address carbon pollution from modified and reconstructed power plants 23 and from existing power plants. 24 Inthe Climate Action Plan, the President also indicated that the U.S. was working internationally

to make progress in a variet y of areas and specificall y noted the progress being made b y ICAO to develop global CO 2 emission standards for aircraft. 25 The proposed endangerment and cause o r 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

20 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 (L ast accessed February 5 , 2015)
. 21 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 ( L ast accessed February 5 , 2015). 22 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)
. 23 U.S. EPA, 2014: Carbon Pollution Standards for Modified and Recons tructed Stationary Sources: Electric Utility Generating Units; Proposed Rules , 79 FR 34960 (June 18, 2014 ). 24 U.S. EPA, 2014: Carbon Pollution Emission Guidelines for Existing Stationary Sources: Electric Utility Generating Units; Proposed Rule , 79 FR 34830 (June 18, 2014)
. 25 Executive Office of the President, 2013: The President’s Climate Action Plan at 21 , June
. Available at: http://www. whitehouse.go v/sites/default/files/image/president27sclimateactionplan.pdf (L ast accessed February 5 , 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **30** of **198** emissions from the aviation sector, the highest
- emitting category of transportation sources that the E PA has not y et addressed. As presented in more detail in Section V of this preamble, total U.S. aircraft GHG emissions in 2012 represented 11 percent of GHG emissions from the U.S. transportation sector , 26 and in 2010, the latest y ear with complete global emissions data, U.S. aircraft GHG emissions represented 2 9 percent of global aircraft GHG emissions
. 27 , 28 U.S. aircraft GHG emissions are p rojected to increase b y almost 50 percent over the next two decades. 29 S ee s ection V of this preamble for more information about the data sources that compose the aircraft GHG emissions inventory
.

26 U.S. EPA, 2014: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

- 2012 , 529 pp. Available at http://www.epa.gov/ climatechange /ghgemissions/usinventoryreport.html#fullreport (Last accessed February 5, 2015). 27 Ibid. 28 IPCC, 2014: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs
- Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J
. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, pp. 599
- 670. 29 As discussed in s ection V.B.2.c ., fuel burn growth rates for air carriers and general aviation aircraft operating on jet fuel are projec ted to grow by 47 percent from 2010 to 2034 , and this provides a scaling factor for growth in GHG emissions which would increase at a similar rate as the fuel burn by 2030, 2034, and 2040. FAA, 2013: FAA Aerospace Forecast Fiscal Years 2014
- 2034 , 62 pp . Available at https://www.faa.gov/about/office_org/headquarters_offices/ apl/aviation_forecasts/aerospace_forecasts/2014
- 2034/media/2014_FAA_Aerospace_Forecast.pdf (Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **31** of **198**

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 engi nes which in her judgment causes or contributes to air pollution which may

reasonabl y 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 (P etitioners) sent a letter to the EPA petitioning the Agency to undertake rulemaking regarding GHG emissions from aircraft. 30 Specifically , Petitioners
re quested that the EPA make a finding that GHG emissions from aircraft engines “ may rea sonab ly be anticipated to endanger public health and welfare ” and that the E PA promulgate standards for GHG emissions from aircraft
. Following the Supreme Court’s decision in Massachusetts v. EPA in 2007 , the EPA issued an ANPR in 2008 presenting information relevant to potentially regulating GHGs under the Act, and soliciting public comment on how to respond to the Court’s ruling and the potential ramifications of the Agency ’s decision to regulate GHG s under the CAA. This

30 Center for Biological Diversity, Center for Food Safety, Friends of the Earth, International Center for Technology Assessment, and Oceana, 2007: Petition for Rulemaking Under the Clean air Act to Reduce the Emissions of Air Pollutants from Aircraft the Co ntribute to Global Climate Change, December 5. Available at http://www.epa.gov/otaq/aviation.htm (Last accessed February 5 , 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **32** of **198** 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 Fed. Reg. 4435 4, 44468
- 44473 (July 30, 2008)
. With regard t o 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 st akeholders 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 ince ntive 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 2 engine emissions standards, these commenters felt that international CO 2 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 2 emissions standards were based on aircraft cruise conditions instead of landing and takeoff operations (L TO) . 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 23 1 of the CAA. Finall y ,******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **33** of **198** industry commenters noted that an y 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 endange rment 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 pre empted 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 IC AO’s standard for oxides of nitrogen (NO x ) 31 and should also include provisions for an averaging, banking, and trading (ABT) program . 32 Some commenters also stated their su

pport for fleet
- wide (in
- use fleet) emission reductions through a cap
- and
- trade sy stem. Finally , these stakeholders stated that, absent the EPA rulemaking, quick

31 Sections II.D.1 and II.E provide an overview of the history ICAO’s r egulation of aircraft engine NOx emissions from 1981 through 2012 and the EPA’s adoption of equivalent aircraft engine NOx standards under the CAA
. 32 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 com ply 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.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **34** of **198** international actions were unlikely and that the EPA should engage internationally to push for action on reducing CO 2 emissions from aircraft. On July 31, 2008, Earthjustice, on behalf of Petitioners, notified the EPA of its intent to file suit under CAA section 304(a) against the EPA for the Agency ’s alleged unr easonable delay in responding to its aircraft petition and in making an endangerment finding under section 231
. On June 11, 2010, Petitioners filed a c omplaint against the EPA in the U.S. District Court for the District of Columbia claiming that, among other things, the EPA had unreasonabl y 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 reasonabl y be anticipated to endanger public health and/or welfare
. The District Court found that while CAA s ection 231 generall y confers broad discretion to the EPA in determin ing what standards to promulgate , s ection 231(a)(2)(A) impose d a nondiscretionary dut y on the EPA to make a finding with respect to endangerment from aircraft GHG emissions
. Center for Biological Diversity, et al. v. EPA , 794 F. Supp. 2d 151 (D.D.C
. 2011)
. This ruling was issued in response to EPA’s motion to dismiss the case on jurisdictional grounds and did not address the merits of the Plaintiffs’ claims regarding the Agency ’s alleged unreasonable delay
. Therefore, it did not include an order for the EPA to make such a finding b y a certain date. In a subsequent ruling on the merits , the Court found that the Plaintiffs had not shown that EPA had unreasonabl y dela ye d in making an******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **35** of **198** endangerment determination regarding GHG emissions from aircraft. Center for Biological Diversity, et al. v. EPA , No. 1:10
- 985 (D.D.C. March, 20, 2012). Thus, the Court did not find the EPA to be liable based on the Plaintiffs’ claims and did not place the Agency under a remedial order to make an endangerment finding or to issue standards. The Plaintiffs did not appeal this ruling to the U.S. Court of Appeals for the D.C. Circuit. The EPA issued a Response to the Aircraft Petition 33 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 A gency significant time to complete this action
. The EPA explained that the A gency 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 co nducting future GHG endangerment findings. The EPA further explained that after receiving the Court of Appeal’s ruling, it would take at least 22 months from that point for the Agency

to conduct an additional finding regarding aircraft GHG emissions
. Meanwhile, the Court upheld EPA’s section 202 findings in a decision of a three
judge panel on June 26, 2012, and denied petitions for rehearing of that decision on December 20, 2012. Coalition for Responsible Regulation, Inc., v. EPA , 684 F.3d 102 (D.C. Cir. 2012),

33 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 February 5, 2015) and Doc ket EPA
HQ
- OAR
- 2014
- 0828.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **36** of **198** reh’g denied 2012 U.S. App. LEXI S 26315, 25997 (D.C. Cir 2012). 34 Given these rulings, we are proceeding with today’s proposed findings regarding aircraft engine GHG emissions as a further step toward responding to th e Petition for Rulemaking
.

**U.S. Aircraft Regulations and the International Community** D. The EPA and the Federal Aviation Administration (FAA) traditionally work within the standard
- setting process of I CAO’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 I CAO, and subsequently the EPA has initiated rulemakings under CAA section 231 to establish domestic standards equivalent to ICAO’s standards where appropriate
. This approach has been affirmed as reasonable by the U.S. Court of Appeals for the D.C. Circuit. NACAA v. EPA , 489 F .3d 12 21, 1230
- 32 (D.C. Cir. 2007). After EPA promulgates aircraft engine emissions standards, CAA section 232 requires the FAA to issue subsequent regulations to e nsure compliance with these standards when issuing certificates u nder its United States Code Title 49 authority
. In exerc ising the EPA’s standard
- setting and FAA’s enforcement authorities ,

34 Petitions for certiorari were filed in the Supreme Court, and the Supreme Court granted six of those petitions but “agreed to decide only one question: ‘Whether EPA permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouse gases”
. Utility Air Reg. Group v. EPA , 134 S. Ct. 2427, 2438 (2014); see also Virginia v. EPA , 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA , 134 S. Ct. 418 (2013), and CRR , 134 S. Ct. 468 (2013) (all denying cert.) . Thus, the Supreme Court did not disturb the D.C. Circuit’s holding that affirmed the 2009 E ndangerment F inding.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **37** of **198** w e 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 2 standard), provided the EPA issues final positive endangerment and cause or contribute findings under CAA section 231. This approach is contingent on I CAO’s adoption of an international aircraft CO 2 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 aircr aft engine emissions. IC AO is a United Nations (UN) specialized agency , established in 1944 by the Convention on International Civil Aviation ( Chic ago Convention ) , “ in order that international civil aviation may be developed in a safe and orderl y manner and that international air transport services may be established on the basis of equality of opportunit y and operated soundly

and economicall y.” 35 IC AO sets standards an d regulations necessary for aviation safet y, security, efficiency, capacit y and environmental protection, and serves as the forum for cooperation in all fields of international civil aviation. IC AO works with the Chicago Convention’s member States and global aviation organizations to develop international Standards and Recommended Practices (SARPs ) , which member States

35 ICAO, 2006: Convention on International Civil Aviation, Ninth Edition , Document 7300/9. Available at www.icao.int (Last accessed February 5, 2015)
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **38** of **198** reference when developing their legally
- enforceable national civil aviation regulations
. The U
. S
. is currentl y one of 19 1 participating IC AO member States. 36 , 37 In the interest of global harmonization and international air commerce, t he 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 I CAO. Any

member State which finds it impracticable to comply in all respects with an y i nternational standard or procedure, or which deems it necessary to adopt regulations or practices differing in an y particular respect from those established by an international standard, is required to give immediate no tification to I CAO of the differences between its own practice and that established b y the international standard
. 38 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 certific ation of aircraft noise and aircraft engine emissions are covered b y Annex 16 of the Chicago

36 Mem bers of ICAO’s Assembly are generally termed member States or contracting States. These terms are used interchangeably throughout this preamble. 37 There are currently 191 Contracting States according to ICAO’s website: www.icao.int (Last accessed February 5, 2015)
. 38 ICAO, 2006: Convention on International Civil Aviation, Ninth Edition , Document 7300/9. Available at www.icao.int (Last accessed February 5, 2015)
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **39** of **198** Convention. To continue to address aviation environmental issues, in 2004, I CAO established three environmental goals: (1) limit or reduce the number of people af fected 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 IC AO ’s standards . Member States may ban the use of an y aircraft within their airspace that does not meet I CAO standards. 39 Second, member States are required to recognize the airworthiness certificates of an y State whose standards are at least as stringent as ICAO ’s standards , thereby assuring that aircraft of any member State will be pe rmitted to operate in any other member State. 40 Third, t o ensure that international commerce is not unreasonabl y constraine d , a member State which elects to adopt more stringent domestic emission standards is obligated to notify I CAO of the differences between its standards and ICAO standards. 41

39 ICAO, 2006: Convention on International Civil Aviation , Article 87 , Ninth Edition, Document 7300/9. Available at http://www.icao.int/publications/pages/doc7300.aspx (Last accessed February 5, 2015). 40 ICAO, 2006: Convention on International Civil Aviation , Article 33, Ninth Edition, Document 7300/9. Available at http://www.icao.int/publications/pages/doc7300.aspx (Last accessed February 5, 2015). 41 ICAO, 2006: Convention on International Civil Aviation, Article 38 , Ninth Edition, Document 7300/9. Available at http://www.icao.int/publications/pages/doc7300.aspx (Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **40** of **198** 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 C ommittee is responsible for evaluating, researching, and recommending measures to the ICAO Council that address th e environmental impact s 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. ” 42 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 I CAO Council reviews and adopts the recommendations made by CAEP. It then reports to the I CAO Assembly , the highest body of the Organization, where the main policies on aviation environmental protection are adopted and translated into Assembly Resolutions.

42 CAEP’s terms of reference are available at http://www.icao.int/environmental
protection/Pages/Caep.aspx#ToR
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **41** of **198** At CAEP meetings, the U
. S
. is represented b y the FAA and play s an active role
. 43 The EPA has historicall y been a principal participant in various IC AO/CAEP working groups and other international venues, assisting and adv ising 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). 44 , 45 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 b y ICAO in 1981
. 46 These standards limited aircraft engine emissions of hydrocar

bons, carbon monoxide, and NO x . 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 199 3 , I CAO adopted a CAEP /2 proposal to

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 (IG IA) 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. 44 ICAO, 2 008: Aircraft Engine Emissions , International Standards and Recommended Practices, Environmental Protection, Annex 16, Volume II, Second Edition, July. Available at www.icao.int (Last accessed February 5, 2015)
. 45 CAEP develops new

emission standards based on an assessment of the technical feasibility, cost, and environmental benefit of potential requirements. 46 ICAO, 2008: Aircraft Engine Emissions: Foreword, International Standards and Recommended Practices, Environmental Protection, Annex 16, Volume II, Third Edition, July. Available at www.icao.int (Last accessed February 5, 2015)
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **42** of **198** t ighten the original NO x standard b y 20 percent and amend the test procedures. 47 These 199 3 standards applied both to newly
- certified turbofan engines, which are those engine models that received their initial ty pe certificate after the effective date of the regulations
- also referred to as newl y - certified engines or new engine designs
-- and to in
- production engines , but with different effective dates for newl y - certified engines and in
- production engines
. In 1995, CAEP/3 recommended a further tighte ning of the NO x standards by 16 percent and additional test procedure amendments, but in 1997 the I CAO 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 x reduction proposal, which I CAO approved in 1998. The CAEP/4 standard s applied onl y 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 a

pply to in
- production engines ). In 2004, CAEP/6 recommend ed a 12 percent NO x reduction , which I CAO approved in 200 5
. 48 , 49 The CAEP/6 standard s applied to new engine designs certified after December 31, 2007. In2010, CAEP/8 recommended a further tightening of the NO x standards by 15 percent for new engine designs certified after

47 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. 48 CAEP/5 did not address new aircraft engine emission standards. 49 ICAO, 2008: Aircraft Engine Emissions , Annex 16, Volume II, Third Edition, July 2008, Amendment 4 e ffective on July 20, 2008. Available at www.icao.int (Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **43** of **198** December 31, 2013
. 50 , 51 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. 52 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 IC AO CO 2 emissions s tandard
. 53 Also, Resolution A37
- 19 provided a framework towards the achievement of an environmentally sustainable future for international aviation. With th is Resolution, the I CAO Assembly agreed to a global aspirational goal for international aviation of improving annual fuel efficiency by two percent and stabilizing CO 2

50 CAEP/7 did not address new aircraft engine emission standards. 51 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. 52 ICAO, 2011: Aircraft Engine Emissions , Annex 16, Volume II, Third Edition, July 2008, Amendment 7 effective on July 18, 2011. Available at www.icao.int (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). 53 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.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **44** of **198** emissions at 2020 levels. 54 The Resolution included the following statements rega rding ICAO policies and practices related to climate change. “
- ... I CAO 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 climat e 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 2 emissions, are projected to grow as a result of the continued development of the sector.”

54 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 tonn e 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 April 17, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **45** of **198** As the above statements indicate, r educing climate impacts of int ernational aviation is a critical element of ICAO’s strategic objective of achieving environmental protection and sustainabl e development of air transport. IC AO is currentl y pursuing a comprehensive set of measures to reduce aviation’s climate impact , inc luding alternative fuels, CO 2 emissions technology
- based standards, operational improvements, and market based measures . The development and adoption of a CO 2 emissions s tandard is an important part of I CAO’s comprehensive set of measures.

3. Relationship of the EPA’s Proposed Endangerment and Cause or Contribute Finding s to International Aircraft Standards As described earlier, the EPA and the FAA work within the I CAO/CAEP standard setting process to establish international emission standards and related requirements. Under this approach international emission standards have first been adopted b y ICAO (with U.S. participation and agreement), and subsequently the EPA has initiated rulemakings under CAA section 231 to establish domestic aircraft engine emis sion standards that are of at least equivalent stringency

as ICAO’s standards. This approach has been affirmed as reasonable by the U.S. Court of Appeals for the D.C. Circuit. NACAA v. EPA , 489 F.3d 12 21, 1230
- 32 (D.C. Cir. 2007). In exercising the EPA’s standard
- setting authorit y, provided the EPA makes positive endangerment and cause or contribute findings under CAA section 231 and ICAO adopts an international aircraft CO 2 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******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **46** of **198** similar approach for the future CAA section 231 aircraft GHG standard (or aircraft CO 2 standard)
. We anticipate that I CAO/CAEP will adopt a final aircraft CO 2 emissions standard in February 2 016. This proposal, and any final e ndangerment 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 2 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 we lfare. 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 c au se or contribute findin g. 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 diligentl y over the past four years within the ICAO/CAEP process on a range of technical issues regarding aircraft CO 2 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 2 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******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **47** of **198** regard to these issues and the aircraft engine GHG emission standards that it may potentiall y adopt under the CAA
. **The EPA’s Regulation of Aircraft Emissions** E. As required b y 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. 55 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 I CAO requirements are generally referred t o as CAEP/2 standards. 56 That action included new NO x emission standards for newly manufactured commercial turbofan engine s ( as described earlier, those engines built after the effective date of the regulations that were alread y certified to pre - existing s tandards

– also referred to as in
- production engines ) 57 and for newl y - certified commercial turbofan engines ( as described earlier, those engine models that received their initial ty pe certificate after the effective date of the regulations

– also referred to as new

55 U.S. EPA , 1 973: Emission Standards and Test Procedures for Aircraft; Final Rule , 38 FR 19088 (July 17, 1973)
. 56 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. 57 This does not mean that in 1997 we promulgated requirements for the re
- certification or retrofit of existing in
use engines.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **48** of **198** engine designs ). 58 Italso included a carbon monoxide emission standard for in
- production commercial turbofan engines. 59 In2005, we promulgated more stringent NO x emission stand ards for newl y - certi fied commerc ial turbofan engines
. 60 That final rule brought the U.S. standards closer to alignment with IC AO CAEP/4 requirements that became effective in 2004
. In 2012, we issued more stringent two
- tiered NO x emission standards for newly
- certified and in
- production c ommercial and non
- commercial turbofan aircraft engines , and these NO x standards align with IC AO’s CAEP/6 and CAEP/8 requirements that became effective in 2013 and 2014, respectively
. 61 , 62 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 b y IC AO. In addressing CO 2 emissions, however,

58 In the existing EPA regulations, 40 CFR part 87, newly
- certified aircraft engines are described as engines of a ty pe or model of which the date of manufacture of the first individual production model was after the im plementation 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. 59 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)
. 60 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 )
. 61 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)
. 62 While IC AO’s standards were not limited to “commercial” aircraft engines, our 1997 standards w ere explicitly limited to commercial engines, as our finding that NO x and carbon monoxide emissions from aircraft engines cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare wa s so limited
. See 62 FR 25358. In the 2012 rulemaking, we expand ed the scope of that finding and of our standards pursuant to S ection 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 br ing our standards into full alignment with ICAO’s.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **49** of **198** ICAO has moved to regulating a whole aircraft
. This I C AO extension beyond pollutant emissions from engines to the whole aircraft was described in a 2013 IC AO circular
. 63 Several factors are considered when addressing whole
- aircraft CO 2 emissions, as the CO 2 emissions are influenced by aerodynamics, weight, an d engine
- specific fuel consumption
. Since each of these factors may affect aircraft engine fuel consumption, they ultimatel y affect CO 2 emissions. Rather than viewing CO 2 as a measurable emission from engines, therefore, ICAO now addresses CO 2 emissions as a characteristic applicable to the entirety of the aircraft based on fuel consumption. Inthis proposed action, we are giving advance notice that the EPA may propose to adopt domestic GHG emission standards (which m ay take the form of CO 2 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 se ctions 231(a)(2)(A) and 231(a)(3), if triggered b y final positive endangerment and cause or contribute findings, to

“ issue propose d emission standards applicable to the emission of” GHG from aircraft engines and to issue final “regulations with such modifi cations as [she] deems appropriate.”

63 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192, Available at www.icao.int (Last accessed Feb ruary 5, 2015)
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **50** of **198** 

## III. **Legal Fram ework for**  **T his**  **Action** The EPA has previousl y made an endangerment finding for GHG s under Title II of the CAA, in the 2009 E ndangerment F inding 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 (79 FR 18886, 18890
- 94 (Apr. 24, 2009), and 79 FR 66496, 66505
- 10 (Dec. 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 o r 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) concern s “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 reasonabl y be anticipated to endanger public health or welfare.” Thus, the text o f the CAA section concerning aircraft emissions in section 231(a)(2)(A) mirrors the text of CAA section 202(a) that was the basis for the 2009 Endangerment Finding
. The EPA’s approach in the 2009 Endangerment Finding (described below in Sections III .A and III.B) was affirmed by the U.S. Court of Appeals for the D.C. Circuit in Coalition for Responsible Regulation, Inc. v. EPA , 684 F.3d 102 (D.C. Cir. 2012), reh’g denied 2012 U.S. App. LEXI S 26313, 26315, 25997 (D.C. Cir 2012) ( CRR ) . In particular, the D.C. Circuit******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **51** of **198** ruled that the 2009 E ndangerment F inding ( 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 Massa chusetts v. EPA and the text and structure of the CAA, and was adequatel y 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 onl y one question: ‘Whether EPA permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouse gases.’” Utility Air Reg. Group v. EPA , 134 S. Ct. 2427, 2438 (2014); see also Virginia v. EPA , 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA , 134 S. Ct. 418 (2013), and CRR , 134 S. Ct. 468 (2013) (all den yi ng cert.). Thus, the Supreme Court did not disturb the D.C. Circuit’s holding that affirmed the 2009 Endangerment F inding. Accordingl y, 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 follow ing discussion, is acting consistentl y with that judicially sanctioned framework for purposes of this proposed section 231 finding. Two provisions of the CAA govern today ’s proposal. Section 231(a)(2)(A) sets forth a two - part predicate for regulatory a ction under that provision: endangerment and cause or******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **52** of **198** 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
. **Section 231(a)(2)(A)**

**— Endangerment and Cause or Contribute**  A. 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. 83
T he Administrator interprets the two
- part test required under section 231(a)(2)(A) as being the same as that explained in the 2009 Endangerment F inding. ( See 74 FR 66505
- 06.) As in the section 202(a) context, this anal ys is 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. 84

83 See CRR , 684 F.3d at 117 (explaining two
- part analysis under section 202(a)). 84 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).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **53** of **198** In making this scientific judgment, the Administrator is guided b y 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. 85 The Administrator is thus to consider both current and future risks. Second, the Administrator is to exercise judgment by weighing risks, assessing potential harms, and making reasonable projections of future trends and possibilities. It follows that when exercising her judgment the Administrator balances the likelihood and severit y 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 severit y ma y be less significant, but the likelihood high. 86 At different points along this scale , the Administrator is permitted to find endangerment. Accordingl y, 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 . . . o r a greater risk of lesser harm’ or an y combination in between.” CRR , 684 F.3d at 123 (quoting Ethyl Corp. v. EPA , 541 F.2d, 1, 18 (D.C. Cir. 1976)).

85 See id. at 121
- 122. 86 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. v. EPA , 541 F.2d, 1, 18 (D.C. Cir. 1976)).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **54** of **198** Third, because scientific knowledge is constantl y 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. 87 At the same time, the Administrator must exercise reasoned decision making, and avoid s peculative inquiries. Fourth , the Administrator is to consider the cumulative impact of sources of a pollutant in assessing the risks from air pollution, and is not to look only at the risks attributable to a single source or class of sources. We additionally note that i n 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 GHG s emitted by the subject source classes
. Suc h an approach would collapse the two prongs of the test by requiring that an y climate change impacts upon which an endangerment determination is made result solel y from the GHG emissions of aircraft. See 74 FR at 66542 (explaining the same point in the co ntext of analogous language in section 202(a)). Similarly , the Administrator is not, in making the endangerment and cause or contribute finding s , to consider the effect of emissions reductions from the resulting standards. 88 The threshold

87 See id. at 121
- 122. 88 As the D.C. Circuit explained in reviewing the 2009 Endangerment F inding under analogous language in section 202(a): “At bottom , § 202(a)(1) requires EPA to answer only two questions: whether particular ‘air******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **55** of **198** endangerment an d cause or contribute criteria are separate and distinct from the standard setting criteria that appl y if the threshold findings are met, and they serve a different purpose. Indeed, the more serious the endangerment to public health and welfare, the more important it may be that action be taken to address the actual or potential harm even if no one action alone can solve the problem, and a series of actions is called for
. Fifth , the Administrator is to consider the risks to all parts of our population, including those who are at greater risk for reasons such as increased susceptibility to adverse health effects. If vulnerable subpopulations are especially at risk, the Administrator is entitled to take that point into account in deciding the question of endangerment. Here too, both likelihood and severit y of adverse effects are relevant. As explained previously in the 2009 Endangerment F inding and as reiterated below for this proposed section 231 finding , vulnerable subpopulations face serio us health risks as a result of climate change. As the Supreme Court recognized in Massachusetts v. EPA , 549 U.S. at 534, the EPA may make an endangerment finding despite the existence of “some residual uncertainty” in the scientific record. See also CRR, 6 84 F. 2d at 122. Thus, this framework recognizes that regulatory

agencies such as the EPA must be able to deal with the realit y that “ [m]an’s ability

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.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **56** of **198** to alter his environment has developed far more rapidly than his ability

to foresee with certaint y the ef

fects of his alterations. ” See Ethyl Corp v. EPA, 541 F.2d 1, 6 (D.C. Cir.), cert. denied 426 U.S. 941 (1976). Both “ the Clean Air Act ‘and common sense * * * demand regulatory

action to prevent harm, even if the regulator is less than certain that harm is otherwise inevitable.’ ” See Massachusetts v. EPA , 549 U.S. at 506, n.7 (citing Ethyl Corp .) ; see also CRR , 684 F.3d at 121
- 122
. In the 2009 Endangerment F inding, the Administrator recognize d that the scientific context for an action addressing climate change wa s unique at that time because there was a very large and comprehensive base of scientific information that ha d been developed over many years through a global consensus process involving numerous scientists from many countries and representing man y disciplines . 74 FR at 66506. T hat informational base has since grown
. T he Administrator also previousl y recognize d that there are varying degrees of uncertaint y across man y of these scientific issues , which remains true
. It is in this context that she is exercising her judgment and appl yi ng the statutory framework in this proposed section 231 finding
. Further discussion of the language in section 231(a)(2)(A), and parallel language in 202(a), is provided below to explain more fully the basis for this interpretation , which the D.C. Circuit upheld in the 202(a) context
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **57** of **198**

1. The Statutory

L anguage The interpretation described above flows from the statutory language itself. The phrase “ may

reasonabl y be anticipated ” and the term “ endanger” in section 231(a)(2)(A) (as in section 202(a)) authorize, if not require, the Administrator to act to prevent harm and to act in conditions of uncertainty
. They do not limit her to merel y reacting to harm or to ac ting only when certainty has been achieved; indeed, the references to anticipation and to endangerment imply

that to fail to look to the future or to less than certain risks would be to abjure the Administrator’s statutory responsibilities. As the D.C. Ci rcuit explained, the language “may

reasonably

be anticipated to endanger public health or welfare” in CAA § 202(a) requires a “precautionary , forward
- looking scientific judgment about the risks of a particular air pollutant, consistent with the CAA’s preca utionary and preventive orientation.” CRR, 684 F.3d at 122 (internal citations omitted)
. The court determined that “[r]equiring that EPA find ‘certain’ endangerment of public health or welfare before regulating greenhouse gases would effectivel y prevent E PA from doing the job that Congress gave it in § 202(a)

— utilizing emission standards to prevent reasonabl y anticipated endangerment from maturing into concrete harm.” Id. The same language appears in section 231(a)(2)(A ) , and the same interpretation applies in that context. Moreover, b y instructing the Administrator to consider whether emissions of an air pollutant cause or contribute to air pollution in the second part of the two
- part test , the Act makes clear that she need not find that emissions from any one sector or class of sources are******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **58** of **198** the sole or even the major part of an air pollution problem. The use of the term “ contribute ” clearl y indicates that such emissi ons need not be the sole or major cause of the pollution
. Finally , the phrase “ in [her] judgment ” authorizes the Administrator to weigh risks and to consider projections of future possibilities, while also recognizing uncertainties and extrapolating from existing data. Finally , when exercising her judgment in making both the endangerment and cause
- or contribute findings, the Administrator balances the likelihood and severity of effects. Notably , the phrase “ in [her] judgment ” modifies both “ may reasonabl y be anticipated ” and

“ cause or contribute. ”

2. How the Origin of the Current Statutory Language Informs the EPA’s Interpretation of Section 231(a)(2)(A) In the proposed and final 2009 Endangerment F i nding, the EPA explained that when Congress revised the section 202(a) language that governed that finding, along with other provisions , as part of the 1977 amendments to the CAA, it was responding to decisions issued by the D.C. Circuit in Ethyl Corp. v. EPA regarding the pre
- 1977 version of section 211(c) of the Act. 74 FR at 18891; see also 74 FR at 66506. Section 231 was one of those other CAA provisions included in the 1977 amendments; therefore, the Agency ’s discussion for the 2009 Endangerment Find ing regarding the history of section 202 and how it supports the EPA’s approach is also relevant for section 231. The legislative history of those amendments,******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **59** of **198** particularl y the report b y the House Committee on Interstate and Foreign Commerce, demonstrates that the EPA’s interpretation of the s ection 231(a)(2)(A) language as set forth here in support of the Agency ’s section 231 finding ( which is the same as its interpretation of the parallel language in section 202(a) as explained in the 2009 Endangerment F inding ) , is fully consistent with Congress’ intention in crafting these provisions. See H.R. Rep. 95
- 294 (1977), as reprinted in 4 A Legislative History of the Clean Air Act Amendments of 1977 (1978) at 2465 (hereinafter LH). 90 The legislative history

cl earl y indicates that the House Committee believed the Ethyl Corp . decisions posed several “crucial policy questions” regarding the protection of public health and welfare. H.R. Rep. 95
- 294 at 48, 4 LH at 2515
. 91 The following paragraphs summarize the en b anc decision in Ethyl Corp. v. EPA and describe how the House Committee revised the endangerment language in the 1977 amendments to the CAA to serve several purposes consistent with that decision . In particular, the language: (1) emphasizes the preventive or precautionary nature of the CAA 92 ; (2) authorizes the Administrator to

90 The committee explained that its action addressed not only section 211(c)(1)(A) but rather the entire proposal, and would thus apply its interpretation to all other sections of the Act relating to public health protection. 4 LH at 2516. It also noted that it had used the same basic formulation in section 202 and section 231, as well as in other sections. Id. at 2517. 91 The Supreme Court recognized that the c urrent language in section 202(a)(1), which uses the same formulation as that in section 231(a)(2)(A), is “more protective” than the 1970 version that was similar to the section 211 language before the D.C. Circuit in Ethyl Corp
. Massachusetts v. EPA , 549 U.S. at 506, fn 7. 92 See H.R. Rep. 95
- 294 at 49, 4 LH at 2516 (“To emphasize the preventive or precautionary nature of the Act, i.e. to assure that regulatory action can effectively prevent harm before it occurs”).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **60** of **198** reasonabl y project into the future and weigh risks; (3) assures the consideration of the cumulative impact of all sources; (4) instructs that the health of susceptible individuals, a s well as health y adults, should be part of the anal ys is; and (5) indicates an awareness of the uncertainties and limitations in information available to the Administrator. H.R. rep. 95
- 294 at 49
- 50, 4 LH 2516
- 17. 93 In revising the statutory

language, Con gress relied heavily on the en banc decision in Ethyl Corp. v. EPA , which reversed a 3
- judge panel opinion regarding an EPA rule restricting the content of lead in leaded gasoline. 94 After reviewing the relevant facts and law, the full court evaluated the statutory language at issue to see what level of “certainty [was] required by the Clean Air Act before EPA may act.” 541 F.2d at 7. The petitioners argued that the statutory language “will endanger” required proof of actual harm, and that the actual harm had to come from emissions from the fuels in and of themselves. Id

. at 12, 29. The en banc court rejected this approach, finding that the term “endanger” allowed the Administrator to act when harm is threatened, and did not require

93 Congress also standardized this lang uage across the various sections of the CAA which address emissions from both stationary and mobile sources. H.R. Rep. 95
- 294 at 50, 4 LH at 2517; section 401 of the CAA Amendments of 1977. 94 At the time of the 1973 rules requiring the reduction of lead i n leaded gasoline, section 211(c)(1)(A) of the CAA stated that the Administrator may promulgate regulations that: “control or prohibit the manufacture, introduction into commerce, offering for sale, or sale of any fuel or fuel additive for use in a motor v ehicle or mo tor vehicle engine (A) if any emissions product of such fuel or fuel additive will endanger the public health or welfare * * *.” CAA 211(c)(1)(A) (1970).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **61** of **198** proof of actual harm. Id

. at 13. “A statute allowing for regulation in the face of danger is, necessarily , a precautionary statute.” Id

. Optimally , the court held, regulatory action would not only precede, but prevent, a perceived threat. Id
. The court also rejected peti tioner’s argument that any threatened harm must be “probable” before regulation was authorized. Specificall y, the court recognized that danger “is set not by

a fixed probability

of harm, but rather is composed of reciprocal elements of risk and harm, or p robability and severity .” Id

. at 18. Next, the court held that the EPA’s evaluation of risk is necessarily an exercise of judgment, and that the statute did not require a factual finding. Id

. at 24. Thus, ultimately , the Administrator must “act, in part on ‘factual issues,’ but largel y ‘on choices of policy, on an assessment of risks, [and] on predictions dealing with matters on the frontiers of scientific knowledge * * *.” Id
. at 29 (citations omitted). Finally , the en banc court agreed with the EPA that even without the language in section 202(a) (which is also in section 231(a)(2)(A)) regarding “cause or contribute to,” it was appropriate for the EPA to consider the cumulative impact of lead from numerous sources, not just the fuels being regulated under section 211(c). Id
. at 29
- 31. The dissent in the original Ethyl Corp. decision and the en banc opinion were of “critical importance” to the House Committee which proposed the revisions to the endangerment language in the 1977 amendments to the CAA. H.R. Rep. 95
- 294 at 48, 4 LH at 2515. The Committee addressed those questions with the language that now appears in section 231(a)(2)(A) and several other CAA provisions

— “emission of any air pollutant * * ******** **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **62** of **198** which in [the A dministrator’s] judgment causes, or contributes to, air pollution which may reasonabl y be anticipated to endanger public health or welfare.” As noted above in s ection I I I.A.1, the phrase “in [her] judgment” calls for the Administrator to make a comparative assessment of risks and projections of future possibilities, consider uncertainties, and extrapolate from limited data. Thus, the Administrator must balance the likelihood of effects with the severity of the effects in reaching her judgment. The Committ ee emphasized that the Administrator’s exercise of “judgment” 95 may

include making projections, assessments and estimates that are reasonable, as opposed to a speculative or “ ‘ crys tal ball’ inquiry .” Moreover, procedural safeguards apply to the exercise o f judgment, and final decisions are subject to judicial review. Also, the phrase “in [her] judgment” modifies both the phrases “cause and contribute” and “may reasonabl y be anticipated,” as discussed above. H.R. Rep. 95
- 294 at 50
- 51, 4 LH at 2517
- 18. As the Committee further explained, the phrase “may reasonably

be anticipated” points the Administrator in the direction of assessing current and future risks rather than waiting for proof of actual harm. This phrase is also intended to instruct the Administrator to

95 Throughout this Notice under CAA section 231, as throughout the previous Notices concerning the 2009 Endangerment Finding under section 202, the judgments on endangerment and cause or contribute are descr ibed as a finding or findings. This is for ease of reference only, and is not intended to imply that the Administrator’s judgment is solely a fact finding exercise; rather, the Administrator’s exercise of judgment is to consider and weigh multiple factors when applying the scientific information to the statutory criteria.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **63** of **198** consider the limitations and difficulties inherent in information on public health and welfare. H.R. Rep. 95
- 294 at 51, 4 LH at 2518. 96 Finally , the phrase “cause or contribute” ensures that all sources of the contaminant which contribute to air pollution are considered in the endangerment anal ys is (e.g., not a single source or category of sources). It is also intended to require the Admi nistrator to consider all sources of exposure to a pollutant (for example, food, water, and air) when determining risk. Id

. 3. Additional Considerations for the Cause or Contribute Anal ys is By instructing the Administrator to consider whether emissions of an air pollutant cause or contribute to air pollution, the statute is clear that she need not find that emissions from an y one sector or class of sources are the sole or even the major part of an air pollution problem. The use of the term contribute clearl y indicates a lower threshold than the sole or major cause. Moreover, like the section 202(a) language that governed the 2009 Endangerment Finding , the statutory

language in section 2 31 (a)(2)(A) does not contain a modifier on its use of the term “ contribute
. ” Unlike other CAA provisions, it does not require “ significant ”

96 Thus, the statutory language does not require that the EPA prov e the effects of climate change “beyond a reasonable doubt.” Indeed, such an approach is inconsistent with the concepts of reasonable anticipation and endangerment embedded in the statute. See also CRR , 684 F.3d at 121
- 122.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **64** of **198** contribution. Compare , e.g., CAA sections 111(b); 213(a)(2), (4). Congress made it clear that the Administrator is to exercise her judgment in determining contribution, and authorized regulatory

controls to address air pollution even if the air pollution problem results from a wide variet y of sources. While the endangerment test looks at the entire air pollution problem and the risks it poses, the cause or contribute test is designed t o authorize the EPA to identify and then address what may well be many different sectors , classes, or groups of sources that are each part of the problem. As explained for the 2009 Endangerment Finding , the D.C. Circuit has discussed the concept of contrib ution in the CAA , and its case law supports the EPA’s interpretation that the level of contribution need not be significant. 74 FR at 66542. In Catawba County v. EPA , 571 F.3d 20 (D.C. Cir. 2009), the court upheld EPA ’ s PM[2.5] attainment and nonattainment designation decisions, analyzing CAA section 107(d), which requires EPA to designate an area as nonattainment if it “ contributes to ambient air quality in a nearby

area ” not attaining the national ambient air quality standards. Id

. at 35. The court noted that it had previousl y held that the term “ contributes ” is ambiguous in the context of CAA language. See EDF v. EPA , 82 F.3d 451, 459 (DC Cir. 1996). “ [A]mbiguities in statutes within an agency ’ s jurisdiction to administer are delegations of authority to the agency

to fill the statutory

gap in reasonable fashion. ” 571 F.3d at 35 (citing Nat' l Cable & Telecomms. Ass'c v. Brand X Internet Servs , 545 U.S. 967, 980 (2005)). The court then proceeded to consider and reject petitioners' argument that the verb “ contributes ” in CAA section 107(d) necessarily connotes******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **65** of **198** a significant causal relationship. Specifically , the D
. C
. Circuit again noted that the term is ambiguous, leaving it to EPA to interpret in a reasonable manner. In the context of thi s discussion, the court noted that “ a contribution may simply exacerbate a problem rather than cause it * * *
. ” 571 F.3d at 39. This is consistent with the D
. C
. Circuit ’s discuss ion of the concept of contribution in the context of CAA section 213 and rules for nonroad vehicles i n Bluewater Network v. EPA , 370 F.3d 1 (D
. C
. Cir. 2004) . In that case, industry argued that section 213(a)(3) requires a finding of a significant contribution before the EPA can regulate, while the EPA ’s view was that the CAA requires a finding only of contribution. Id

. at 13. Section 213(a)(3), like section 2 31 (a)(2)(A) , is triggered by a finding that certain sources “ cause, or contribute to, ” air pollution, while an adjacent provision, section 213(a)(2), is triggered b y a fin ding of a

“ significant ” contribution. The court looked at the “ ordinary meaning of ‘contribute’ ” when upholding the EPA ’s reading. After referencing dictionary definitions of “ contribute, ” the court also noted that “ [s]tanding alone, the term has no inhe rent connotation as to the magnitude or importance of the relevant ‘share’ in the effect; certainly it does not incorporate any ‘significance’ requirement. ” 370 F.3d at 13. 97 The court found that the bare “ contribute ” language invests the Administrator with discretion to exercise judgment regarding what

97 Specifically, the decision no ted that “ ‘contribute’ means simply ‘to have a share in any act or effect,’ W ebster’s T hird N ew I nternational D ictionary 496 (1993), or ‘to have a part or share in producing,’ 3 O xford E nglish D ictionary 849 (2d ed. 1989). ” Id. at 13.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **66** of **198** constitutes a sufficient contribution for the purpose of making a cause or contribute finding
. Id
. at 14. 98 Like the statutory

language considered in Catawba County and Bluewater Networ k, as well as the section 202(a) language that governed the Agency ’s previous findings for GHGs emitted by

other ty pes of mobile sources , section 2 31 (a)(2)(A) refers to contribution and does not specify

that the contribution must be significant before an a ffirmative finding can be made. To be sure, an y finding of a “ contribution ” requires some threshold to be met; a truly trivial or de minimis “ contribution ” might not count as such. The Administrator therefore has ample discretion in exercising her reasonable judgment and determining whether, under the circumstances presented, the cause or contribute criterion has been met. 99 As noted above, in addressing provisions in section 202(a), the D.C. Circuit has explained that the Act at the endangerment fi nding step did not require the EPA to identify a precise numerical value or “a minimum threshold of risk or harm before determining whether an air pollutant endangers.” CRR , 684 F.3d at 122
- 123. Accordingl y, EPA “may base an endangerment finding on ‘a lesser risk of greater harm . . . or a greater risk of lesser harm’ or any combination in

98 The court explained, “ [t]he repeated use of the term ‘significant’ to modify the contribution required for all nonroad vehicles, coupled with the omission of this modifier from the ‘cause, or contribute to’ finding required for individual categories of ne w nonroad vehicles, indicates that Congress did not intend to require a finding of ‘significant contribution’ for individual vehicle categories. ” Id. at 13. 99 Section V discusses the evidence in this case that supports the proposed finding of contribution. The EPA need not determine at this time the circumstances in which emissions would be trivial or de minimis and would not warrant a finding of contribution.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **67** of **198** between.” Id. (quoting Ethyl Corp ., 541 F.2d at 18). Recognizing the substantial record of empirical data and scientific evidence that the EPA relied upon in the 20 09 Endangerment Finding , the court determined that its “failure to distill this ocean of evidence into a specific number at which greenhouse gases cause ‘dangerous’ climate change is a function of the precautionary

thrust of the CAA and the multivariate an d sometimes uncertain nature of climate science, not a sign of arbitrary or capricious decision
- making.” Id. at 123. As the language in section 231(a)(2)(A) is analogous to that in section 202(a), it is clearl y reasonable to apply this interpretation to the endangerment determination under section 231(a)(2)(A). Moreover, the logic underlying this interpretation supports the general principle that under CAA section 231 the EPA is not required to identify a specific minimum threshold of contribution from potentially subject source categories in determining whether their emissions “cause or contribute” to the endangering air pollution. Th e reasonableness of this principle is further supported b y the fact that section 231 do es not impose on the EPA a requirement to find that such contribution is “significant,” let alone the sole or major cause of the endangering air pollution. This context further supports the EPA’s interpretation that section 231(a)(2)(A) requires some level of contribution that, while exceeding de minimis or trivial thresholds, does not need to rise to a pre - determined numerical level of significance. In addition, when exercising her judgment in making a cause or contribute determination , the Administr ator not only considers the cumulative impact, but also looks at the totality

of the circumstances (e.g., the air pollutant, the air pollution, the nature of the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **68** of **198** endangerment, the ty

pe or classes of source s at issue , the number of sources in the source sec tor or class , and the number and ty pe of other source sectors or categories that may emit the air pollutant) when determining whether the emissions “ justify regulation ” under the CAA. See Catawba County , 571 F.3d at 39 ( discussing EPA’s interpretation of the term “contribute” under CAA § 107(d) and finding it reasonable for the agency to adopt a totality of the circumstances approach); see also 74 FR at 66542
. Further discussion of this issue can be found in s ection s IV and V of this preamble
.

**Air Pollutant, Public Health and Welfare** B. The CAA defines both “ air pollutant ” and “ welfare. ” Air pollutant is de fined as: “ any air pollution agent or combination of such agents, including an y ph ys ical, chemical, biological, radioactive (including source material, special nuclear material, and by product material) substance or matter which is emitted into or otherwise enters the ambient air. Such term includes any precursors to the formation of any air pollutant, to the extent the Administrator has identified such precursor or precursors for the particular purpose for which the term ‘air pollutant’ is used. ” CAA secti on 302(g). Greenhouse gases fit well within this capacious definition. See Massachusetts v. EPA , 549 U.S. at 532. They are “ without a doubt ” phy sical chemical substances emitted into the ambient air. Id
. at 529. Section V below contains further discuss ion of the “ air pollutant ” for purposes of today ’s section 231 proposed******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **69** of **198** contribution finding, which uses the same definition of air pollutant as the EPA adopted for purposes of the 2009 Endangerment Finding
. Regarding “ welfare , ” the CAA states that “ [a]ll language referring to effects on welfare includes, but is not limited to, effects on soils, water, crops, vegetation, man
- made materials, animals, wildlife, weather, visibility , and climate, damage to and deterioration of propert y, and hazards to transportation, as well as effects on economic values and on personal comfort and well
- being, whether caused by transformation, conversion, or combination with other air pollutants. ” CAA section 302(h). This definition is quite broad. Importantly , it is not an exclusive list due to the use of the term “ includes, but is not limited to, * * *. ” Effects other than those listed here may also be considered effects on welfare. Moreover, the terms contained within the definition are themselves expansive. For example, deterioration to propert y could include damage caused b y extreme weather events. Effects on vegetation could include impacts from changes in temperature and precipitation as well as from the spreading of invasive species or insects. Prior welfare effects evaluated b y the EPA in other contexts include impacts on vegetation, as well as reduced visibility , changes in nutrient balance and acidity of the environment, soiling of buildings and statues, and erosion of building materials. See, e.g., Final Secondary National Ambient Air Quality Standard s for Oxides of Nitrogen and Sulfur , 7 7 FR 20218 (20 12 ); Control of Emissions from Nonroad Large Spark Ig nition Engines and Recreational Engines (Marine and Land
- Based),******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **70** of **198** 67 FR 68242 (2002); Final Heav y - Dut y Engine and Vehicle Standards and Highway Diesel Sulfur Control Requirements, 66 FR 5002 (2001). Although the CAA defines “effects on welfare” as discussed above, there are no definition s of “public health ” or “public welfare” in the Clean Air Act. The Supreme Court has discussed the concept of “public health” in the context of whether costs can be considered when setting National Ambient Air Quality Standards. Whitman v. American Trucking Ass’n , 531 U.S. 457 (2001). In Whitman , the Court imbued the term with its most natural meaning:

“ the health of the public. ” Id . at 466. When considering public health, the EPA has looked at morbidity , such as impairment of lung function, aggravation of respiratory and cardiovascular disease, and other a cute and chronic health effects, as well as mortality
. See, e.g., Final National Ambient Air Quality Standard for Ozone, 73 FR 16436 (200 8 ). 

## IV. **The Proposed Endangerment Finding under CAA**  **section 231** 
This section describes the Administrator’s proposed endangerment finding under CAA section 231(a)(2) and its basis
. Beginning w ith the air pollution under consideration, the Administrator is proposing to use the same definition of the “ air pollution” under CAA section 231(a)(2) as that used under CAA section 202(a)(1), namel y the mix of six well
mixed GHGs mentioned above : CO 2 , methane , nitrous oxide, hydrofluorocarbons, perfluorocarbons , and sulfur h exafluoride. As described in section IV.A below, i t is the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **71** of **198** Administrator’s view that the reasons d etailed in the 2009 Endangerment Finding for defining the scope and nature of the air pollution to be these six well
- mixed GHGs remain valid and well
- supported by the current science and are therefore reasonable bases for adopting the same definition of “air pollution” in this section 231(a)(2)(A) finding
. In formation from the new scientific assessments described in s ection IV. B below provide s further support that the six well
- mixed GHGs are the primary cause and driver of climate change. The Administrator considered other climate
- forcing agents both in the 2009 Endangerment Finding and in today ’s action; however, these substances are not included in the air pollution definition proposed today for the reasons discussed below in s ection IV.B .4
. The Administrator is proposing to find, for purposes of CAA section 231(a)(2)(A), that elevated concentrations of the six well
- mixed GHGs constitute air pollution that endanger s both the public health and the public welfare of current and future generations. T h e Administrator’s view is that the body of scientific evidence amassed in the record for the 2009 Endangerment Finding compellingl y supports an endangerment finding under CAA section 231(a). Information from the new scientific assessments described in s ection IV .B below provides further support and justification for this proposed finding. S ection IV.A below summarizes the 2009 Endangerment F inding under CAA section 202 , e xplains the approach EPA took in compiling an extensive record to inform the Administrator’s judgment on that f inding, and describes the recent judicial affirmation of the 2009 Endangerment Finding
. S ection IV.B provides a summary of new scientific******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **72** of **198** assessments that strengthen or provide further scientific evidence, in addition to that which the Administrator relied upon in making her prior judgment , for a finding that GHGs endanger public health and welfare. 101 Fi nally , s ection IV.C summarizes the Administrator’s conclusion for purposes of section 231, in light of the evidence , anal ys is, and conclusions that led to the 2009 Endangerment Finding as well as more recent evidence, that emissions of the six well
- mixed G HGs in the atmosphere endanger public health and welfare
. **Scientific Basis of the 2009 Endangerment Finding**  **under CAA section**  A. **202(a)(1)** In the 2009 Endangerment Finding, the Administrator found that elevated concentrations of the well
- mixed GHGs in the atmosphere may reasonably

be anticipated to endanger public health and welfare of current and future generations. See, e.g., 74 FR 66516. The Administrator reached this judgment by carefull y considering a significant body of scientific evidence and public comments submitted to the Agency
. The sections below summarize the scope and nature of the relevant air pollution for the 2009 E ndangerment F inding , as well as the public health and welfare considerations within the finding
.

101 While the EPA is providing a summary of newer scientific assessments below , the EPA is also relying on the same scientific and technical evidence discussed in the notices for the 2009 Endangerment Finding in this proposed finding for pu

rposes of CAA section 231. See s ection s III of the 2009 Proposed Endangerment Finding and s ections III and IV of the 200 9 Endangerment Finding.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **73** of **198**

1. The Definition of Air Pollution in the 2009 Endangerment Finding The Administrator defined the scope and nature of the relevant air pollution as the aggregate group of six key , well
- mixed GHGs : CO 2 , methane, nitrous oxide, hydrofluorocarbons , perfluorocarbons , and sulfur hexafluoride
. 102 T he Administrator considered five primary

reasons for focusing on this aggregate group as the air pollution in the 2009 Endangerment Finding: (1) they share common phy sical properties that influence their climate effects ; (2) on the basis of these common phy sical properties, they have been determined to be the primary cause of human
- induced climate change, are the best
understood driver of climate change, and are expected to remain the key driver of future climate change; (3) they are the c ommon focus of climate change science research and policy anal ys es and discussions; (4) using the combined mix of these gases as the definition (versus an individual gas - by
- gas approach) is consistent with the science, because risks and impacts associated with GHG
- induced climate change are not assessed on an individual gas
- by
- gas basis ; and (5) using the combined mix of these gases is consistent with past EPA practice, where separate substances from different sources, but with common properties, may be tre ated as a class (e.g., oxides of nitrogen , particulate matter, volatile organic compounds ). 103

102 74 FR 66516. 103 74 FR 66517 to 66519.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **74** of **198** The common phy sical properties these six GHGs share that are relevant to the climate change problem include the following: all are long
- lived in the atmosphere; 105 all become globall y well mixed in the atmosphere , resulting in similar GHG concentrations around the globe regardless of geographic location of emissions ; all trap outgoing heat that would otherwise escap e to space; and all are directl y emitted as GHGs rather than becoming a GHG in the atmosphere after emission of a precursor gas. The Administrator acknowledged that other anthropogenic climate forcers also play a role in climate change but for various scientific and policy

reasons, these substances were not included in the air pollution definition
. 107 As explained in more detail in the 2009 Endangerment Finding, the EPA made the judgment that the scientific evidence is compelling that ele vated concentrations of heat
trapping GHGs are the root cause of re cently observed climate change and that the scientific record showed that most of the observed increase in global average temperatures since the mid
- 20th century is very

likely due to the observed increase in anthropogenic GHG

105 We use ‘‘long
- lived’’ here to mean that the gas has a lifetime in the atmosphere sufficient to become globally well
- mixed throughout the entire atmosphere, which requires a minimum atmospheric lifetime of about one year. IPCC also refers to these six gree nhouse gases as long
- lived. According to the most recent IPCC Fifth Assessment Report (2014), m ethane has an atmospheric lifetime of about 12 years . One of the most commonly used hydrofluorocarbons (HFC

– 134a) has a lifetime of about 1 3 years. Nitrous oxide has a lifetime of around 1 30 years; sulfur hexafluoride over 3,000 years; and some perfluorocarbons up to 10,000 to 50,000 years. CO 2 is sometimes approximated as having a lifetime of roughly 100 years, but for a given amount of CO 2 emitted a better descr iption is that s om e fraction of the atmospheric increase in concentration is quickly absorbed by the oceans and terrestri al vegetation, some fraction of the atmospheric inc rease will only slowly decrease over a number of ye ars, and a small portion of the i ncrease will remain for many centuries or more. 107 74 FR 66519 to 66521
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Page **75** of **198** concentrations. The attribution of observed climate chang e to anthropogenic activities was based on multiple lines of evidence. 108 The first line of evidence arises from our basic phy sical un derstanding of the effects of changing concentrations of GHGs , natural factors, and other human impacts on the climate sy stem. The second line of evidence arises from indirect, historical estimates of past climate changes that suggest that the changes in global surface temperature over the last several decades are unusual. The third line of evidence arises from the use of computer
- based climate models to simulate the likely patterns of response of the climate sy stem to different forcing mechanisms (both n atural and anthropogenic ).

2. Public Health Impacts Detailed in the 2009 Endangerment Finding Climate change resulting from anthropogenic GHG emissions threatens multiple aspects of public health. 109 Indetermining that the well
- mixed GHG air pollution is reasonabl y anticipated to endanger public health for current and future generations, the Administrator noted her view that climate change can increase the risk of morbidity and mortality. 110 In making that public health finding, the Administrator considered direct temperature effects, air quality

effects, the potential for changes in vector
- borne diseases, and the potential for

108 74 FR 66518. 109 74 FR 66524 to 66530
. 110 74 FR 6 6524
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Page **76** of **198** changes in the severit y and frequency of extreme weather events. In addition, the Administrator considered whether and how susceptible populations may be particularl y at risk. As explained in more detail in the 2009 Endangerment Finding, with respect to direct temperature effects, b y raising average temperatures, climate change increases the likelihood of heat waves, which are ass ociated with increased deaths and illnesses. Climate change is also expected to lead to reductions in cold
- related mortality
. The 2009 Endangerment Finding, while noting uncertaint y about how heat and cold related mortality would change in the future, al so pointed to a USGCRP assessment report discussion that increases in heat
related mortalit y due to global warming in the United S tates was unlikely to be compensated for b y decreases in cold
- related mortality
. With regard to air qualit y effects, c limate change is expected to increase ozone pollution over broad areas of the country , including large metropolitan population centers , and thereb y increase the risks of respiratory infection, aggravation of asthma, and premature death. Other public health threats stem from the potential for increased deaths, injuries, infectious and waterborne diseases, stress
- related disorders , and other adverse effects associated with increased hurricane intensity and increased frequency

of intense storms and heav y precipit ation associated with climate change. In addition, climate change is expected to be associated with an increase in the spread of food
- , water - , and vector
- borne diseases in susceptible populations. Climate change also has the potential to change aeroalle rgen production (for example, through lengthening the growing season for allergen
- producing plants), and subsequent human******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **77** of **198** exposures could increase allergenic illnesses. Children, the elderly , and the poor are among the most vulnerable to climate
- related h ealth effects.

3. Public Welfare Impacts Detailed in the 2009 Endangerment Finding Climate change resulting from anthropogenic GHG emissions also threatens multiple aspects of public welfare. 111 Indetermining that the well
- mixed GHG air pollution is reasonabl y anticipated to endanger public welfare for current and future generations, the Administrator considered the multiple pathway s by which GHG air pollution and resultant climate change affect public welfare b y evaluating the numerous and far
- ran ging risks to food production and agriculture; forestry ; water resources; sea level rise and coastal areas; energy , infrastructure, and settlements; and ecos ys tems and wildlife. The Administrator also considered impacts on the U.S. population from climate change effects occurring outside of the United States. As explained in more detail in the 2009 Endangerment Finding, the potential serious adverse impacts of extreme events, such as wildfires, flooding, drought, and extreme weather conditions provided strong support for the determination. Climate change is expected to place large areas of the country at serious risk of reduced water supplies, increased water pollution, and increased occurrence of extreme events such as floods and droughts. Coastal areas are expected to face increased risks from storm and flooding damage

111 74 FR 66530 to 66536
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **78** of **198** to propert y, as well as adverse impacts from rising sea level such as land loss due to inundation, erosion, wetland submergence and habitat loss. Climate change is expected to result in an increase in peak electricity demand, and extreme weather from climate change threatens energy , transportation, and water resource infrastructure. Climate change may exacerbate existing environmental pressures in certain settlements, particularly in Ala skan indigenous communities. Climate change is also very likely to fundamentally

change U.S.
ecos ys tems over the 21st century and to lead to predominantly negative consequences for biodiversity , ecosy stem goods and services, and wildlife. Though there may be some benefits for agriculture and forestry in the next few decades, the body of evidence points towards increasing risks of net adverse impacts on U.S. food production, agriculture and forest productivit y as average temperature continues to rise. Loo king across all sectors discussed above, the risk and the severi ty of adverse impacts on public welfar e are expected to increase over time. Lastly , these impacts are global and may exacerbate problems outside the United S tates that raise humanitarian, tra de, and national securit y issues for the United States.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **79** of **198**

4. The Science Upon Which the Agency Relied As outlined in s ection I II .A of the 2009 Endangerment Finding , 112 the EPA's approach to providing the technical and scientific information to inform the Administrator's judgment regarding the question of whether GHGs endanger public health and welfare was to rely primarily upon the recent, major assessments by the USGCRP, the IPCC, and the NRC. These assessments addressed the scientific issues that the EPA was re quired to examine, were comprehensive in their coverage of the GHG and climate change issues, and underwent rigorous and exacting peer review b y the expert community, as well as rigorous levels of U.S. government review , in which the EPA took part
. Primary reliance on the major scientific assessments provided assurance that the Administrator was basing her judgment on the best available, well
- vetted science that reflected the consensus of the climate science research community
. The major findings of the USGCRP, IPCC, and NRC assessments supported the Administrator’s determination that elevated concentrations of GHGs in the atmosphere may reasonably

be anticipated to endanger the public health and welfare of current and future gen erations. The EPA presented this scientific support at length in the comprehensive record for the 2009 Endangerment Finding
. R elevant sections of documents from th e 2009 Endangerment Finding record have been placed in the docket for this proposed finding under CAA section 231.

112 74 FR 66510 to 66512
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Page **80** of **198** The EPA then reviewed ten administrative petitions for reconsideration of the Endangerment Finding in 2010. 113 Inthe Reconsideration Denial, the Administrator denied those petitions on the basis of the Petitioners ’ failure to provid e substantial support for the ir argument that the EPA should revise the Endangerment Finding and their objections’ lack of “central relevance” to the Finding. The EPA prepared an accompanying thre e - volume Response to Petitions document to provide addition al information, often more technical in nature, in response to the arguments, claims, and assertions by the P etitioners to reconsider the Endangerment Finding. 114 The 2009 Endangerment Finding and the 2010 Reconsideration Denial were challenged in a lawsuit before the U.S. Court of Appeals for the D.C. Circuit. 115 On June 26, 2012, the Court upheld the Endangerment Finding and the Reconsideration Denial, ruling that the Finding (including the Reconsideration Denial) was not arbitrary or capricious, was consiste nt with the U.S. Supreme Court's decision in Massachusetts v. EPA ( which affirmed

113 Ad ministrative petitions are available from http://www.epa.gov/climatechange/endangerment/petitions.html (Last accessed Feb ruary 5, 2015) , and in the docket for the 2009 Endangerment Finding: EPA
- HQ
- OAR
- 2009
- 017. 114 U.S. EPA , 2010: Denial of the Petitions to Reconsider the Endangerment and Cause or Contribute Findings for Greenhouse Gases Under section 202(a) of the Clean Air Act , 75 FR 49557 (Aug ust 13, 2010) (“Reconsideration Denial”). In that notice, the EPA throughly considered the scientific and technical information relevant to the petitions. In additi on to the other information discussed in the present notice, the EPA is also relying on the scientific and technical evidence discussed in that prior notice for purposes of its proposed determinat ion under CAA section 231. See s ection III of the Reconsider ation Denial. 115 Coalition for Responsible Regulation, Inc. v. Environmental Protection Agency , 684 F.3d 102 (D.C. Cir. 2012),), reh'g en banc denied, 2012 U.S. App. LEXIS 25997, 26313, 26315 (D.C. Cir. 2012) ( CRR ).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **81** of **198** the EPA ’s authority

to regulate greenhouse gases) 116 and the text and structure of the CAA, and was adequately supported b y the administrative record. 117 The Court also agreed with the EPA that the Petitioners had “ not provided substantial support for their argument that the Endangerment Finding should be revised.” 118 The Court found that the EPA had based its decision on “substantial scientific evidence,” observing that “EPA’s scientific evidence of record included support for the proposition that greenhouse gases trap heat on earth that would otherwise dissipate into space; that this ‘greenhouse effect’ warms the climate; that human activity is contributing to increased atmospheric levels of greenhouse gases; and that the climate sy stem is warming,” as well as providing extens ive scientific evidence for EPA’s determination that anthropogenically induced climate change threatens both public health and welfare. 119 The court further noted that the EPA's reliance on assessments was consistent with the methods decision
- makers often u se to make a science
based judgment. 120 Moreover, the Court supported the EPA's reliance on the major scientific assessment reports conducted by USGCRP, IPCC, and NRC and found: The EPA evaluated the processes used to develop the various assessment reports, reviewed their contents, and considered the depth of the

116 549 U.S. 497 (2007). 117 CRR , 684 F.3d at 117
- 27. 118 Id. at 125 119 Id. at 120
- 121. 120 Id . at 121******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **82** of **198** scientific consensus the reports represented. Based on these evaluations, the EPA determined the assessments represented the best source material to use in deciding whether GHG emissions may be reas onably

anticipated to endanger public health or welfare. * * * Itmakes no difference that much of the scientific evidence in large part consisted of “ sy ntheses ” of individual studies and research. Even individual studies and research papers often s ynthesi ze past work in an area and then build upon it. This is how science works. The EPA is not required to re
- prove the existence of the atom every time it approaches a scientific question. 121 In addition, the EPA ’s reliance on the major assessments to inform the Administrator's judgment allowed for full and explicit recognition of scientific uncertainty regarding the endangerment posed by the atmospheric buildup of GHGs . T he Administrator considered the fact that “ some aspects of climate change science and the projected impacts are more certain than others.” 122 The D.C. Circuit subsequently noted that “the existence of some uncertaint y does not, without more, warrant invalidation of an endangerment finding.” 123

121 Id
. at 120. 122 74 FR at 66524 123 CRR , 684 F.3d at 121.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **83** of **198** As noted above the Supreme Court granted some of the petitions for certiorari that were filed, while denyi ng others, but agreed to decide only the question: “ Whether EPA permissibly

determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sourc es that emit greenhouse gases.” 124 Thus, the Supreme Court did not disturb the D.C. Circuit’s holding that affirmed the 2009 Endangerment F inding. **Recent Science**  **Further Supports**  **the Administrator’s Judgment that the Six**  B. **Well -**  **Mixed Greenhouse Gases Endanger Public Health and Welfare**  Since the closure of the administrative record concerning the 2009 Endangerment Finding (including the denial of petitions for reconsideration) , a number of new major , peer reviewed scientific assessments have been released. The EPA carefull y reviewed the updated scientific concl usions in these assessment s, largel y to evaluate whether they would lead the EPA in this CAA section 231(a)(2)(A) finding to propose a different interpretation of, or plac e more or less weight on, the major findings reflected in the previous assessment rep orts that underpinned the Administrator ’s judgment that the six well
- mixed GHGs endanger public health and welfare. From its review, the EPA finds that these new

124 Utility Air Reg. Group v. EPA , 134 S. Ct. 2427, 2438 (2014) (internal marks and citations omitted). See also Virginia v. EPA , 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA , 134 S. Ct. 418 (2013), and CRR , 134 S. Ct. 468 (2013) (all denying cert.)
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Page **84** of **198** assessments are largel y consistent with, and in many cases strengthen and add to , the already compelling and comprehensive scientific evidence detailing the role of the six well
- mixed GHGs in driving climate change, detailed in the 2009 Endangerment Finding. Therefore , the new scientific assessments do not provide any reasonable basis on which to propose under CAA section 231(a)(2)(A) a different conclusion than the one the EPA reached in 2009 under CAA section 202(a). Rather, they provide further support for today ’s proposed finding under section 231
. Inparticular, the new assessments discusse d in this preamble provide additional detail regarding public health impacts , particularl y on groups and people at certain lifestages especially vulnerable to climate change including children, the elderl y , low
- income communities and individuals, indigenous groups, and communities of color. The subsections below present brief summaries of the relevant key findings from the new major peer
- reviewed scientific assessments , which include the following:

 IPCC's 2013
- 2014 Fifth Assessment Report (AR5) 125

125 IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.
- K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University Press, 1535 pp, doi:10.1017/CBO9781107415324; IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mac h, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, 1132 pp; IPCC, 2014: Climate Change 2014: Impacts, A daptation, and Vulnerability. Part B: Regional Aspects . Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada,******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **85** of **198**  IPCC’s 2012 “Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation” (SREX) 126

 USGCRP's 2014 “Climate Change Impacts in the United States : the Third National Climate Assessment” (NCA3 ) 127

 NRC ’ s 2010 “Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean” (Ocean Acidification) 128

 NRC ’ s 2011 “Climate Change, the Indoor Environment, and Health” (Indoor Environment) 129

 NRC ’ s 2011 “Report on Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia” (Climate Stabilization Targets) 130

R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, 688 pp; and IPCC, 2014: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs
- Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, 1435 pp. 126 IPCC, 2012: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation . A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.
- K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.) ]. Cambridge University Press, 582 pp. 127 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, 841 pp. 128 NRC, 2010: Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean
. The National Academies Press , 188 pp
. 129 NRC Institute of Medicine , 2011 : Climate Change, the Indoor Environment, and Health. Washington, DC: The National Academies Press , 272 pp
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Page **86** of **198**  NRC ’ s 2011 “National Securit y Implications for U.S. Naval Forces” (National Security Implications) 131

 NRC ’ s 2011 “Understanding Earth's Deep Past: Lessons for Our Climate Future” (Understanding Earth's Deep Past) 132

 NRC ’ s 2012 “Sea Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future” (Sea Level Rise) 133

 NRC ’ s 201 3 “Climate and Social Stress: Implications for Securit y Anal ys is” (Climate and Social Stress) 134

 NRC ’ s 2013 “Abrupt Impacts of Climate Change” (Abrupt Impacts) 135

 NRC ’ s 2014 “ The Arctic in the Anthropocene: Emerging Research Questions ” (Arctic) 136

.

130 NRC 2011: Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia . The National Academies Press, 298 pp
. 131 NRC, 2011: National Security Implications of Climate Change for U.S. Naval Forces
. Th e National Academies Press, 226 pp
. 132 NRC, 2011: Understanding Earth's Deep Past: Lessons for Our Climate Future . The National Academies Press, 2 1 2 pp. 133 NRC, 2012: Sea
-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future
. The National Academies Press, 201 pp. 134 NRC, 2013: Climate and Social Stress: Implications for Security Analysis. The National Academies Press , 280 pp
. 135 NRC, 2013: Abrupt Impacts of Climate Change: Anticipating Surprises . The National Academies Press, 250 pp. 136 NRC, 2014: The Arctic in the Anthropocene: Emerging Research Questions. The National Academies Press, 220 pp
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Page **87** of **198**

1. More Recent Evidence That Elevated Atmospheric Concentrations of the Six Greenhouse Gases Are the Root Cause of Observed Climate Change The EPA has carefully

reviewed the recent assessments regarding elevated concentrations of the six well
- mixed GHGs in the atmosphere. The EPA finds that the new assessments of the IPCC, USGCRP, and NRC support and strengthen the science underl yi ng the 2009 Endangerment Finding that the six well
- mixed GHGs are the root cause of recently observed climate change. Key findings are described briefl y here. According to the IPCC AR5 , observations of the Earth’s globally averaged combined land and ocean surface temperature over the period 1880 to 2012 show a warming of 0.85 [0.65 to 1.06] degrees Celsius or 1.53 [1.17 to 1.91] degrees Fahrenheit. 137 The IPCC AR5 concludes that the global average net effect of the increase in atmospheric GHG concentrations, plus other human activities (e.g., land use change and aer osol emissions), on the global energy balance since 1750 has been one of warming. This total net heating effect, referred to as “ forcing, ” is estimated to be 2
. 3 Watts per square meter (W/m2), which has increased from the previous 2007 IPCC Fourth Assessment Report (AR4) total net estimate of 1 .6 Watts per square meter (W/m2) that was referred to in the record for the 2009

137 “ 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 Unive rsity Press, 29 pp.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **88** of **198** Endangerment Finding. The reasons for this increase i nclude continued i ncreases in GHG concentrations, as well as reductions in the estimated negative forcing due to aerosols. The IPCC AR5 rates the level of confidence 138 in their radiative forcing estimates as “high” for methane and “very

high” for CO 2 and nitrous oxid e . The new assessments also have greater confidence in attributing recent warming to human causes. The IPCC AR5 stated that it is extremely likel y (>95 percent likelihood) that human influences have been the dominant cause of warming since the mid
- 20 th c entury , which is a stronger statement than the AR4 conclusion that it is very likely (>90 percent likelihood) that most of the increase in temperature since the mid
- 20 th century was due to the increase in GHG concentrations. The AR4 conclusion was referred to in the record for the 2009 Endangerment Finding
. In addition, the IPCC AR5 found that concentrations of CO 2 and several other of the major GHGs are higher than they have been in at least 800,000 years. This is an increase from what was reported in IPCC AR4, which found higher concentrations than in at least 650,000 years.

138 The IPCC expresses levels of confidence using five qualifiers: very low, low, medium, high, and very high. These levels are based on a qualitative evaluation of the robustness of the evidence (considering the type, amount, quality, an d consistency of evidence such as data, mechanistic understanding, theory, models, and expert judgment) and the degree of agreement among the findings
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **89** of **198** The USGCRP NCA3 states that there is very high confidence 139 that the global climate change of the past 50 y ears is primaril y due to human activities. Human activities are affecting climate through increasing atmospheric levels of heat
- trapping gases , through changing levels of various particles that can have either a heating or c ooling influence on the atmosphere , and through a ctivities such as land use changes that alter the reflectivity of the Earth’s surface and caus e climatic warming and cooling effects
. The USGCRP concludes that “c onsidering all known natural and human drive rs of climate since 1750, a strong net warming from long
- lived greenhouse gases produced b y human activities dominates the recent climate record.” 140 These recent and strong conclusions attributing recent observed global warming to human influence have been made despite what some have termed a warming slowdown or “hiatus” over the past 15 y ears or so. The IPCC AR5 notes that global mean surface temperature exhibits substantial natural decadal and interannual variability , such that trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long
- term climate trends. As an example, the IPCC AR5 notes that the rate of warming over the 15 ye ar period from 1998
- 2012 was less than that ov er the period 1951
-

139 The NCA expresses levels of confidence using four qualifiers: low , medium, high, and very high. These levels are based on the strength and consistency of the observed evidence; the skill, range, and consistency of mo del projections; and insights from peer
- reviewed sources. 140 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Progr am , p. 741******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **90** of **198** 2012. This short term variability does not alter the long
- term climate trend that the IPCC AR5 finds after its review of independently verified observational records: “E ach of the past three decades has been successivel y warmer at the E arth’s surface than all the previous decades in the instrumental record, and the first decade of the 21st century has been the warmest .” 141 , 142 The NRC Climate Stabilization Targets assessment c oncludes that CO 2 emissions are currentl y altering the atmosphe re's composition and will continue to alter Earth’s climate for thousands of years . The NRC Understanding Earth’s Deep Past assessment finds that “the magnitude and rate of the present greenhouse gas increase place the climate sy stem in what could be one of the most severe increases in radiative forcing of the global climate system in Earth history .” 143 This assessment finds that if no emissions reductions are made CO 2 concentrations by

the end of the century

are projected to increase to levels that Earth has not experienced for more than 30 million ye ars .

141 IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.
- K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University Press, p. 161. 142 Furthermore, we would note that according to both NOAA and NASA, 2014 was the warmest year in the mo dern instrumental record for globally averaged surface temperature, and that the ten warmest years, with the exception of 1998, have now occurred since 200 0. Available at http://www.giss.nasa.gov/research/news/20150116/ (Last accessed February 5, 2015). 143 NRC, 2011: Understanding Earth's Deep Past: Lessons for Our Climate Future . The National Academies Press, p. 138
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Page **91** of **198**

2. More Recent Evi dence that Greenhouse Gases Endanger Public Health The EPA has carefully

reviewed the key

conclusions in the recent assessments regarding human
- induced climate change risks and impacts on public health. The EPA finds that the new assessments are consistent with or strengthen the underl yi ng science considered in the 2009 Endangerment Finding regarding public health effects from changes in temperature, air qualit y, extreme weather, and climate
- sensitive d iseases and a eroallergens
. These key

findings are described briefl y here. Regarding temperature effects, the conclusions of the assessment literature cited in the 2009 Endangerment Finding were uncertain with respect to the exact balance of how heat
versus cold
- related mortality will ch ange in the future, but noted that the available evidence suggested that the increased risk from heat would exceed the decreased risk from cold in a warming climate. The most recent assessments now have greater confidence that increases in heat
- related mortalit y will b e larger than the decreases in cold
- related mortality
. The USGCRP NCA3 concludes that, “ While deaths and injuries related to extreme cold events are projected to decline due to climate change, these reductions are not expected to compensate for the increa se in heat
- related deaths .” 144 The IPCC AR5 also notes a potential benefit of climate change could include “ modest reductions in cold
- related mortality and morbidity

in

144 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 224
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Page **92** of **198** some areas due to fewer cold extremes (low confidence) ,” 145 but that, “[o] verall, we conclude that the increase in heat
- related mortality by mid
- century

will outweigh gains due to fewer cold periods .” 146 Regarding air qualit y effects, the assessment literature cited in the 2009 Endangerment Finding concluded that c limate change is expected to inc rease regional ozone pollution, with associated risks in respiratory illnesses and premature death, but that the directional effect of climate change on ambient particulate matter levels was less certain. The USGCRP NCA3 similarly concludes that, “ Climate change is projected to harm human health by increasing ground
- level ozone and/or particulate matter air pollution in some locations
. ... There is less certaint y in the responses of airborne particles to climate change than there is about the response of ozone. ” 147 The IPCC AR5 finds that o zone and particulate matter have been associated with adverse health effects in man y locations in North America , and that o zone concentrations could increase under future climate change scenarios if emissions of precursors were held con s tant . For particulate matter, both the USGCRP NCA3 and IPCC AR5 discuss increasing wildfire risk under climate change, and explain that wildfire smoke exposure can

145 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, p. 713. 146 Ibid. at p. 721
. 147 Melillo, Jerry M., T erese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 222.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **93** of **198** lead to various respiratory and cardiovascular impacts. The NRC Indoor Environment assessment identifies potential adverse health risks associated with climate
- change induced alterations in the indoor environment, including possible exposure to air pollutants like ozone via changes in outdoor air quality . Other risks include potential for alterations in indoor allergens due to climate change
- related increases in outdoor pollen levels , potential chemical exposures due to greater use of pesticides to address changes in geographic ranges of pest species , and dampness/mold associated s ymptoms and illness due to potential flooding and water damage in buildings from climate change
- related increases in storm intensity and extreme precipitation events
. Regarding extreme weather events (e.g., storms, heav y precipitation, and, in some regions of the United States, floods and droughts), the conclusions of the assessment literature cited in the 2009 Endangerment Finding found potential for increased deaths, injuries, infectious and waterborne diseases, and stress
- related disorders. Similarly , the USGCRP NCA3 discusses elevated waterborne disease outbreaks and the potential for mold contamination and degraded indoor air qualit y following heav y precipitation. Other impacts include mortality

associated with flooding and impacts on mental health, such as anxiety and post - traumatic stress disorder. The IP CC AR5 also discusses death and injury in coastal zones and regions vulnerable to inland flooding. The USGC RP NCA3 and the IPCC AR5 both find that climate change may increase exposure to and health risks associated with drought conditions, which includes impacts from wildfires, dust storms, extreme heat events,******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **94** of **198** flash flooding, degraded water qualit y, reduced water quantit y, and water
- related diseases. The IPCC SREX assessment projects further increases in some extreme weather and climate events during this century, and specifically notes that changes in extreme weather events have implications for disaster risk in the health sector. The e ffects of climate change on climate
- sensitive d iseases were also cited in the 2009 Endangerment Finding, including a likel y increase in the spread of several food and water
borne pathogens among susceptible populations , and the potential for range expansion of some zoonotic disease carriers such as the Ly me disease
- carrying tick
. T he new assessment literature similarly

focuses on increased exposure risk for some diseases under climate change, finding that i ncreasing temperatures may expand or shift the ranges of some disease vectors like mosquitoes, ticks, and rodents
. The IP CC AR5 notes that climate change may influence the “ growth, survival, persistence, transmission, or virulence of pathogens ” 148 that
cause food and water - borne disease
. T he USGCRP NCA3 notes that uncertainty remains regarding future projections of i ncrease d human burden of vector
- borne disease, given complex interacting factors such as “ local, small
- scale differences in weather, human

148 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, p. 726
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **95** of **198** modification o f the landscape, the diversity of animal hosts, and human behavior that affects vector - human contact, among other factors.” 149 Regarding a eroallergens , the assessment literature cited in the 2009 Endangerment Finding found potential for climate change to a ffect the prevalence and severity of allergy sy mptoms, but that definitive data or conclusions were lacking on how climate change might impact aeroallergens in the United States. The most recent assessments now have greater confidence that climate change will influence production of pollen that affects asthma and other allergic respiratory

diseases such as allergic rhinitis, as well as effects on conjunctivitis and dermatitis
. Both the USGCRP NCA3 and the IPCC AR5 found that increasing temperature has len gthened the allergenic pollen season for ragweed, and that increased CO 2 by itself can elevate production of plant
- based allergens. The IPCC AR5 concludes that in North America, “warming will lead to further changes in the seasonal timing of pollen release (high confidence). ” 150 The assessment literature cited in the 2009 Endangerment Finding concluded that certain populations, including children, the elderly, and the poo r, are most vulnerable to

149 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 225. 150 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects
. Contribution of Working Group II to the Fifth Assess me nt Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, p. 1465
- 1466.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **96** of **198** climate
- related health effects
. The 2009 Endangerment F inding also described climate change impacts facing indigenous peoples in the United States, particularly Alaska Natives. The new assessment literature strengthens these conclusions by providing more detailed findings regarding these populations’ vulnerab ilities and projected impacts they may experience. In addition, the most recent assessment literature provides new information on how some communities of color may be uniquely vulnerable to climate change health impacts. T he USGCRP NCA3 finds that, “ C limate change will, absent other changes, amplify some of the existing health threats the nation now faces. Certain people and communities are especiall y vulnerable, including children, the elderly , the sick, the poor, and some communities of color. ” 151 Ac cording to the USGCRP NCA3, certain c limate change related impacts

—including heat waves, degraded air quality , and extreme weather events

— have disproportionate e ffect s on low
- income and some communities of color , raising environmental justice concern s. Existing health disparities and other inequities in these communities increase their vulnerability to the health effects of climate change. The USGCRP NCA3 also finds that climate change, in addition to c hronic stresses such as extreme povert y , is affecti ng i ndigenous p eoples ’ health in the United States through

151 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 221.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **97** of **198** impacts such as reduc ed acces s to traditional foods, decreased water quality , and increasing exposure to health and safety hazards
. The IP CC AR5 finds that climate change
- induced warming in the Ar ctic and resultant changes in environment (e.g., permafrost thaw, effects on traditional food sources) have significant observed and projected impacts on the health and well
- being of Arctic residents, especially i ndigenous peoples. S mall, remote, predomin antly
- i ndigenous communities are especially vulnerable given their “ strong dependence on the environment for food, culture, and way of life; their political and economic marginalization; existing social, health, and poverty disparities; as well as their fr equent close proximity

to exposed locations along ocean, lake, or river shorelines .” 152 In addition, increasing temperatures and loss of Arctic sea ice increases the risk of drowning for those engaged in traditional hunting and fishing. The USGCRP NCA3 con cludes that c hildren will suffer disproportionately from climate change given the unique phy siological and developmental factors that occur during this lifestage
. Impacts on children are expected from heat waves, air pollution, infectious and waterborne illness es , and mental health effects resulting from extreme weather events. The IPCC AR5 indicates that c hildren are among those especially susceptible to most

152 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects
. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R ., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, p. 15 81.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **98** of **198** allergic diseases , as well as health effects associated with heat waves, storms, and floods
. The IPCC finds that a dditional health concerns may arise in low income households , especiall y those with children , if climate change reduces food availability and increases prices, leading to fo od insecurit y within households. Both the USGCRP and IPCC conc lude that climate change will increase health risks facing the elderl y. Older people are at much higher risk of mortalit y during extreme heat events. Pre
- existing health conditions also make older adults susceptible to cardiac and respiratory

impacts of air pollution and to more severe consequences from infectious and waterborne diseases. L imited mobility among older adults can also increase health risks associated with extreme weather and floods.

3. More Recent Evidence that Greenhouse Gases Endanger Publi c Welfare The EPA has carefully

reviewed the recent scientific conclusions in the assessments regarding human
- induced climate change impacts on public welfare. 153 The EPA finds that they are largel y consistent with or strengthen the underlying science suppo rting the 2009

153 The CAA stat es that ‘‘[a]ll language referring to effects on welfare includes, but is not limited to, effects on soils, water, crops, vegetation, man
- made materials, animals, wildlife, weather, visibility, and climate, damage to and deterioration of property, and hazards to transportation, as w ell as effects on economic values and on personal comfort and well
- being, whether caused by transformation, conversion, or combination with other air pollutants.’’ CAA section 302(h). This language is quite broa d. Importantly, it is not an exclusive list due to the use of the term ‘‘includes, but is not limited to, * * *.’’ Effects other than those listed here may also be considered effects on welfare.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **99** of **198** Endangerment Finding regarding public welfare effects on food production and agriculture; forestry ; water resources; sea level rise and coastal areas; energy , infrastructure, and settlements; ecosy stems and wildlife; and impacts on the U.S. population from climate change effects occurring outside of the United States
. These key findings are described briefl y here. Regarding agriculture, the assessment literature cited in the 2009 Endangerment Finding found potential for increased CO 2 levels to benefit yi elds of certain crops in the short
term, but with considerable uncertainty. The body of evidence pointed towards increasing risk of net adverse impacts on U.S. food production and agriculture over time, with the potential for significant dis ruptions and crop failure in the future. The most recent assessments now have greater confidence that climate change will negatively affect U.S. agriculture over this century
. Specificall y, the USGCRP NCA3 concludes, “ While some U.S. regions and some t yp es of agricultural production will be relativel y resilient to climate change over the next 25 years or so, others will increasingly suffer from stresses due to extreme heat, drought, disease, and heavy downpours. From mid
- century on, climate change is pro jected to have more negative impacts on crops and livestock across the country
. ” 154 The IPCC AR5 concludes, “ Overall yields of major crops in North America are projected to decline modestly by mid
- century

and more steeply

by 2100 among studies that do not c onsider adaptation (very

154 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe , Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 16.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **100** of **198** high confidence). ” 155 The IPCC AR5 notes that in the absence of extreme events , climate change may

benefit ce rtain regions and crops , but that in North America significant harvest losses have been observed due to recent extreme weather events
. In addition, the IPCC SREX assessment specifically

notes that projected changes in extreme weather events will increase disaster risk in the agriculture sector. Regarding forestry , the assessment literature cited in the 2009 Endangerment Finding found that near term benefits to forest growth and productivity in certain parts of the country from elevated CO 2 concentrations and temperature increases to date are offset by longer term risk s from wildfires and the spread o f destructive pests and disease that present serious adverse risks for forest productivity
. The most recent assessments provide further support for this conclusion. Both the USGCRP NCA3 and the IPCC AR5 conclude that climate change is increasing risks to forest health from fire, tree disease and insect infestations, and drought. The IPCC AR5 also notes risks to forested ecosy stems associated with c hanges in temperature, precipitation amount, and CO 2 concentrations , which can affect species and ecological communities, lea ding to ecos ys tem disruption, reorganization, movement or loss. The NRC Arctic assessment states that climate change is likely to hav e a large negative

155 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects
. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, p. 1462.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **101** of **198** impact on forested ecos ystems in the high northern latitudes due to the effects of permafrost thaw and greater wildfire frequency , extent, and severity
. The NRC Climate Stabilization Targets assessment found that for an increase in globa l average temperature of 1 to 2 °C above pre - industrial levels, the area burnt by wildfires in western North America will likely more than double. Regarding water resources, the assessment literature cited in the 2009 Endangerment Finding concluded that increasing temperatures and increased variability in precipitation associated with climate change will impact wat er quality and quantity

through changes in snowpack, increased risk of floods , drought, and other concerns such as water pollution. Similarly , the new assessments further support projections of water resource impacts associated with increased fl oods and short
- term drought in most U.S. regions. The USGCRP NCA3 also finds that, “ [c] limate change is expected to affect water demand, groundwater withdrawals, and aquifer recharge, reducing groundwater availability in some areas. ” 156 The IPCC AR 5 finds that in part of the western United States, “ water supplies are projected to be further stressed b y climate change, resulting in less water availability and increased drought conditions .” 157 The IPCC AR5 also projects that climate change will degrade surface water

156 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National C limate Assessment. U.S. Global Change Research Program, p. 70. 157 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects
. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Pan el on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **102** of **198** quality , including the Great Lakes, and will negatively aff ect drinking water treatment/ distribution and sewage collection sy stems . The assessment literature cited in the 2009 Endangerment Finding found that the most serious potential adverse effects to coastal areas are the increased risk of storm surge and flooding in coastal areas from sea level rise and more intense storms. C oastal areas also face other adverse impacts from sea level rise such as land loss due to inundation, erosio n, wetland submergence, and habitat loss
. The most recent assessments provide further evidence in line with the science supporting the 2009 Endangerment Finding. The USGCRP NCA3 finds that, “S ea level rise, combined with coastal storms, has increased the risk of erosion, storm surge damage, and flooding for coastal communities, especially along the Gulf Coast, the Atlantic seaboard, and in Alaska. ” 158
T he IPCC AR5, the USGCRP NCA3 , and three of the new NRC assessments provide estimates of projected global s ea level rise. These estimates, while not alway s directl y comparable as they

assume different emissions scenarios and baselines, are at least 40 percent larger than, and in some cases more than twice as large as, the projected rise estimated in the

Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, p. 1456
- 1457. 158 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 9.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **103** of **198** IPCC A R4 assessment , which was referred to in the 2009 Endangerment Finding. 159 The NRC Sea Level Rise assessment projects a global sea level rise of 0.5 to 1.4 meters by 2100, which is sufficient to lead to a relative rise in sea level even around the northern c oasts of Washington State , where the land is still rebounding from the disappearance of the great ice sheets
. The NRC National Security Implications assessment suggests th at “the Department of the Nav y should expect roughl y 0.4 to 2 meters global average sea
- level rise by 2100. ” 160 The NRC Climate Stabilization Targets assessment states that an increase of 3 °C will lead to a sea level rise of 0.5 to 1 meter b y 2100. While these NRC and IPCC assessments continue to recognize and chara cterize the uncertainty inherent in accounting for ice sheet processes, these revised estimates are consistent with the assessments underl yi ng the 2009 Endangerment Finding. Regarding climate impacts on energy , infrastructure, and settlements , the 2009 End angerment Finding cited the assessment literature’s findings that temperature increases will change heating and cooling demand ; that declining water quantit y ma y adversel y impact the availability

of cooling water and h ydropower in the energy sector; and th at changes in extreme weather events will threaten energy , transportation, water, and other key societal

159 The 2007 IPCC AR4 assessment cited in 2009 Endangerment Finding estimated a projected sea level rise of between 0.18 and 0.59 meters by the end of the century, relative to 1990. It should be noted that in 2007, the IPCC stated that including poorly unders tood ice sheet processes could lead to an increase in the projections. 160 NRC, 2011: National Security Implications of Climate Change for U.S. Naval Forces
. Th e National Academies Press, p. 28.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **104** of **198** infrastructure, particularly on the coast. The most recent assessments provide further evidence in line with the science supporting the 2009 Endangerm ent Finding. For example, the USGCRP NCA3 finds that, “ Coastal infrastructure, including roads, rail lines, energy infrastructure, airports, port facilities, and military bases, are increasingly at risk from sea level rise and damaging storm surges. ” 161 Th e NRC Arctic assessment identifies threats to human infrastructure in the Arctic from increased flooding, erosion, and shoreline ice pile
up, or ivu , associated with summer sea ice loss and the increasing frequency and severit y of storms . Regarding ecos ys tems and wildlife, the assessment literature cited in the 2009 Endangerment Finding found that climate change will predominantly adversely impact both terrestrial and marine biodiversity and the ability of these ecosy stems to provide goods and services
. The NRC Arctic assessment states that majo r marine and terrestrial biomes will likely shift pole ward , with significant implications for changing species composition, food web structures , and ecosy stem function. The NRC Climate Stabilizatio n Targets assessment found that coral bleaching will increase due both to warming and ocean acidification. The NRC Understanding Earth's Deep Past assessment notes four of the five major coral reef crises of the past 500 million years were caused by acidi fication and warming that followed

161 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program , p. 9.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **105** of **198** GHG increases of similar magnitude to the emissions increases expected over the next hundred years . Similarly, the NRC Ocean Acidification assessment finds that “[t]he chemistry of the ocean is changing at an unprecedent ed rate and magnitude due to anthropogenic CO 2 emissions; the rate of change exceeds any known to have occurred for at least the past hundreds of thousands of y ears.” 162 The assessment notes that the full range of consequences is still unknown, but the risks “threaten coral reefs, fisheries, protected species, and other natural resources of value to societ y. ” 163 The IP CC AR5 also projects biodiversity losses in marine ecos ys tems, especiall y in the Arctic and tropics
. Ingeneral, climate change impacts related to public welfare are expected to be unevenl y distributed across different regions of the United States and have a greater impact
on certain populations, such as indigenous peoples and the poor. The USGCRP NCA3 finds climate change impacts such as the rapid pace of temperature rise, coastal erosion and inundati on related to sea level rise and storms, ice and snow melt, and permafrost thaw are affecting indigenous people in the United States. Particularl y in Alaska, critical infrastructure and traditional livelihoods are threatened b y climate change and, “[i] n p arts of Alaska, Louisiana, the Pacific Islands, and other coastal locations, climate change impacts (through erosion and inundation) are so severe that some communities are already relocating

162 NRC, 2010: Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean
. The National Academ ies Press , p. 5. 163 Ibid.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **106** of **198** from historical homelands to which their traditions and cultural identities are tied. ” 164 The IPCC AR5 notes, “ Climate
- related hazards exacerbate other stressors, often with negative outcomes for livelihoods, especiall y for people living in poverty (high confidence). Climate
related hazards affect poor people’s lives directly through impacts on livelihoods, reductions in crop yields, or destruction of homes and indirectly through, for example, increased food prices and food insecurity
. ” 165
In the 2009 Endangerment Finding , the Administrator considered impacts on the U.S. population from climate change effects occurring outside of the United States, such as national securit y concerns that may arise as a result of climate change impacts in other regions of the world. The most recent assessments provide further evidence in line with the science supporting the 2009 Endangerment Finding. The NRC Climate and Social Stress assessment found that it would be “prudent for securit y anal ys ts to expect climate surprises in the c oming decade . . . and for them to become progressivel y more serious and more frequent thereafter. ” 166 The NRC National Security Implications assessment recommends preparing

164 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 17. 165 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mas trandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, p. 796. 166 NRC, 2013: Climate and Social Stress: Implications fo r Security Analysis. The National Academies Press , p. 18.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **107** of **198** for increased needs for humanitarian aid; responding to the effects of climate chan ge in geopolitical hotspots, including possible mass migrations; and addressing changing security needs in the Arctic as sea ice retreats. In addition, the NRC Abrupt Impacts report examines the potential for tipping points, thresholds beyond which major and rapid changes occur in the Earth’s climate sy stem , as well as in natural and human sy stems that are impacted by the changing climate. The Abrupt Impacts report did find less cause for concern than some previous assessments regarding some abrupt events within the next century such as disruption of the oceanic Atlantic Meridional Overturning Circulation (AMOC) and sudden releases of high
- latitude methane from hydrates and permafrost
. But, the same report found that the potential for abrupt changes in ec os ys tems, weather and climate extremes, and groundwater supplies critical for agriculture now seem more likely , severe, and imminent. The assessment found that some abrupt changes were already underway

( e.g., Arctic sea ice retreat and increases in extinc tion risk due to the speed of climate change), and cautioned that even abrupt changes such as the AMOC disruption that are not expected in this century can have severe impacts if/when they happen. 4. Consideration of Other Climate Forcers Both in the 2 009 Endangerment Finding and in this action, the Administrator recognizes that there are other substances in addition to the six well
- mixed GHGs that are******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **108** of **198** emitted from human activities and affect Earth’s climate (referred to as climate forcers). These can b e grouped into two categories: (1) other substances with similar phy sical properties to the six well
- mixed GHGs

—these include the ozone
- depleting substances of chlorofluorocarbons, h ydrochlorofluorocarbons, and halons, as well as nitrogen trifluoride and s imilar recently

identified substances ; and (2) short
- lived substances

—tropospheric ozone and its precursor gases, water vapor, and aerosol particles and precursors. For s ome short
lived substances

— namely , water vapor ; NO x ; and aerosol particles including black carbon

— their phy sical properties result in the se substances hav ing different, and often larger, climate effects when emitted at high altitudes
. However, the very properties that lead to differential climate effects depending on the altitude of emission

— properties that are different from those of the six well
- mixed, long
- lived GHGs

—l ead to more uncertainty in the scientific understanding of these short
- lived substances’ total effect on Earth’s climate . Mor e de tail is provided below. As described in s ection III.B of the 2009 E ndangerment Finding and in section IV.A.1 of this preamble , the primary reasons for defining the air pollution as the aggregate group of the six well
- mixed GHG s include their common phy sical properties relevant to climate change (i.e., long
- lived, well
- mixed, directly emitted), the fact that these gases are considered the primary

drivers of climate change , and the fact that these gases remain the best understood drivers of anthropogen ic climate change. The common phy sical properties of the six well
mixed GHGs not only

support grouping them together as a class, but also contribute to their******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **109** of **198** higher degree of scientific understanding related to climate change, relative to short
- lived subs tances that are not well
- mixed, or substances that are formed indirectly rather than being directly emitted. After considering additional information in the new assessments regarding the climate
- relevant substances outside the basket of the six well
- mixed GHGs , it is the Administrator’s view that the reasons originall y stated for not including these substances in the scope of the GHG air pollution still apply at this time. For example, nitrogen triflouride and some other recentl y discovered substances are not as well studied or understood as the six well
- mixed GHG s . Similarly , for tropospheric ozone

— a short
- lived gas in the atmosphere that is not directly

emitted (it forms from emissi ons of various precursor gases)

—the understanding and quantification of the link between precursor emissions and climate change is not as strong as for the six well
- mixed GHGs
. Regarding the short
- lived substances with different climate effects when emitted at high altitudes , the Aircraft Petition (see s ecti on I I of this preamble ) mentions the effects of water vapor and NO x on clouds and atmospheric chemistry
. The major peer
- reviewed scientific assessments of the IPCC and NRC provide the current state of scientific understanding of these effects; the USGCRP assessments have not dealt specificall y with emissions at high altitude. The EPA considered the following assessment reports to obtain the best estimates of these substances’ net impact on the climate s ys tem, which is generall y******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **110** of **198** discussed in terms of radiative forcing: the IPCC AR5, the IPCC 2007 Fourth Assessment Report (AR4), 167 the IPCC Special Report: Aviation and the Global Atmosphere (IPCC 1999), 168 the NRC’s Advancing the Science of Climate Change (NRC 2010), 169 and the NRC’s Atmospheric Effects of Aviatio n: A Review of NASA's Subsonic Assessment Project (NRC 1999). 170 In addition to high altitude water vapor and NO x , the literature indicates that aerosol particles, including black carbon, emitted at high altitudes have more interactions with clouds and therefore have different effects on the global energy balance than do particles emitted at the surface. The state of the science as represented in the assessment literature highlights significant scientific uncertaint ies regarding the total net forcing effect of water vapor , NO x , and aerosol particles when emitted at high altitudes
. Given these uncertainties, the Agency is not including them in the proposed definition of air pollution for purposes of the endange rment finding under section 231 of the CAA. The short
- lived nature of these substances means that, unlike the long
- lived GHGs, the climatic impact of the substance is

167 IPCC, 2007: Climate Change 2007: The Physical Scientific Basis . Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qi n, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)] Cambridge University Press, 996 pp. 168 IPCC , 1999: Aviation and the Global Atmosphere, Special Report to the Intergovernmental Panel on Climate Change [ Penner, J.E. , D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland ( e ds.) ] Cambridge University Press, 373 pp. 169 NRC, 2010: Advancing the Science of Climate Change
. The National Academies Press , 528 pp
. 170 NRC, 1999: Atmospheric Effects of Aviation: A Review of NASA’s Subsonic Assessment Project. The National Academies Press, 54 pp.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **111** of **198** dependent on a number of factors such as the location and time of its emission. The
m agnitude, and often the direction (positive/warming or negative/cooling), of the globally averaged climate impact will differ depending on the location of the emission due to the local atmospheric conditions (e.g., due to differing concentrations of other compounds with which the emissions can react, background humidity levels, or the presence or absence of clouds). In addition, for emissions at an y given location, the spatial and temporal pattern of the climate forcing will be heterogeneous, again often differing in direction (for example, in the case of NOx emissions, the near term effect in the hemisphere in which the emissions occur is usuall y warming due to increased ozone concentrations, but the longer term effects, and effects in the other hemisphere , are often cooling due to increased destruction of methane). As the climatic effects of these substances when emitted at high altitudes were not addressed at length in the 2009 Endangerment Finding, the following subsections briefly summarize the finding s of the major scientific assessments regarding these substances’ climatic effects at altitude and the various sources of uncertainty surrounding these estimates.
a. Changes in Clouds from High Altitude Emissions of Water Vapor and Particles Aviation
- induced cloudiness (sometimes called AIC) refers to all changes in cloudiness assoc iated with aviation operations, which are primarily due to the effects of high altitude emissions of water vapor and particles (primarily sulfates and black carbon )
. Changes in cloudiness affect the climate b y both reflecting solar radiation (cooling) and trapping outgoing longwave radiation (warming). Unlike the warming effects associated with******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **112** of **198** the six long
- lived, well
- mixed GHG s , the warming effects associated wi th changes in cloud cover are more regional and temporal in nature
. The three key components of aviation
induced cloudiness are persistent contrails, contrail
- induced cirrus, and induced cirrus. A ircraft engine emissions of water vapor at high altitudes during flight can lead to the formation of condensation trails , or contrails , under certain conditions such as ice
supersaturated air masses with specific humidity levels and temperature
. The NRC estimates that persistent contrails increased cloudiness ab ove the United S tates by two percent between 1950 and 1988, with similar results reported over Europe. 171 As stated above, clouds can have both warming and cooling effects, and persistent contrails were once considered to have significant net warming effec ts. However, m ore recent estimates suggest a smaller overall climate forcing effect of persistent contrails
. The IPCC AR5 best estimate for the global mean radiative forcing from contrails is 0.01 W/m2 ( medium confidence and with an uncertaint y range of 0.005 to 0.03 W/m2 ). 172 To put this number into context, some examples of other IPCC AR5 best estimates for global mean radiative forcing include: 1.68 W/m2 for CO 2 (very high confidence and with an uncertainty range of 1.33 to 2.03 W/m2 ), 0.97 W/m2 for methane (high confidence and with an uncertainty range of 0.74 to 1.20 W/m2 ), and 0.17

171 NRC, 1999: Atmospheric Effects of Aviation: A Review of NASA’s Subsonic Assessment Project . The National Academies Press, 54 pp. 172 IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contr ibution 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 P ress, 1535 pp.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **113** of **198** W/m2 for nitrous oxide (very high confidence and with an uncertaint y range of .013 to 0.21 W/m2 ). 173 Inaddition, the NRC (2010) assessment suggested that contrails may a ffe ct regional diurnal temperature differences , but this has been called into question by the recent findings presented in the IPCC AR5 , which suggests that aviation contrails do not have an effect on mean or diurnal range of surface temperatures (medium conf idence)
. Persistent contrails also sometimes lose their linear form and develop into cirrus clouds, an effect referred to as contrail
- induced cirrus. S tudies to date have been unable to isolate this climate forcing effect, but the IP CC AR5 provides a combined contrail and contrail
- induced cirrus best estimate of 0.05 W/m 2 (low confidence and with an uncertaint y range of 0.02 and 0.15 W/m 2 )
. 174
P articles emitted or formed in the atmosphere as a result of aircraft emissions may also act as ice nuclei and modify naturall y forming cirrus cloud s, an effect referred to as “induced cirrus
. ” The two primary aviation
- induced particles are sulfates and black carbon, and their effects on cirrus cloud modification is an area of active research
. Th ere are sign ificant

173 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 174 IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.
- K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University Press, 1535 pp.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **114** of **198** challenges in estimating the climatic impacts of induced cirrus; f or example, the 2007 IPCC AR4 characterizes our k

nowledge of the natural freezing modes in cirrus conditions as “poor,” and notes that cirrus cloud processes are not well represented in global models. 175 Neither IPCC AR4 nor AR5 provide d g lobal or regional estimates related to this forcing. Given differences in scientific understanding of the three components of aviation
induced cloudiness, the more recent assessments have not provide d estimates of the net climate fo rcing effect of changes in clouds from high altitude emissions of water vapor and particles. Going back to the 1999 IPCC assessment, the science is characterized as “very uncertain” with a range for the best estimate between 0 to 0.040 W/m 2

. 176 b. Direct Radiative Forcing Effects of High Altitude Particle Emissions The 2009 Endangerment Finding noted that mu ch of the uncertainty range surrounding the estimate of total net forcing due to all human activities was due to uncertainties about the cooling and warming effects of aerosols 177 (though from all sources, not just aircraft). The Finding noted that the magnitude of aerosol effects can vary immensel y with location and

175 IPCC, 2007: Climate Change 2007: The Physical Scientific Basis . Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)] Cambridge Unive rsity Press, 996 pp. 176 IPCC, 1999: Aviation and the Global Atmosphere, Special Report to the Intergovernmental Panel on Climate Change [Penner, J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] Cambridge University Press, 373 pp. 177 74 FR 6651 7******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **115** of **198** season of emissions , and also discussed black carbon as a specific ty pe of aerosol particle, noting that estimates of its total climate forcing effect have a large uncertainty range. 178 Here, we discuss the direct radiative forcing effects of high altitude emissions of the two primary aviation
- induced particles, sulfates and black carbon
. Aircraft emit precursor gases that convert to sulfate particles in the atmosphere , such
as sulfur dioxide. S ulfate particles have direct effects on the climate by scattering solar radiation, which result s in cooling. The more recent assessments have not quantif ied this effect from aviation. Going back to the 1999 IPCC assessment, the direct effect of sulfate aerosols from av iation for the year 1992 is estimated at
- 0.003 W/m 2 with an uncertaint y range between
- 0.001 and
- 0.009 W/m 2

. 179 Black carbon emissions from aviation, which are produced b y the incomplete combustion of jet fuel, primarily absorb solar radiation and heat the surrounding air, resulting in a warming effect
. The more recent assessments have not quantif ied this effect from aviation. The 1999 IPCC assessment estimates the global mean radiative forcing of black carbon emissions to be 0.003 W/m2 w ith uncertainty spanning 0.001 to 0.009 W/m2

. 180 The IPCC 1999 assessment suggests that because the contribution of black carbon in the

178 74 FR 66520 179 IPCC, 1999: Aviation and the Global Atmosphere, Special Report to the Intergovernmental Panel on Climate Change [Penner, J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] Cambridge University Press, 373 pp. 180 Ibid.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **116** of **198** stratosphere (which actually contribute to cooling of the surface rather than warming) w as not included in its calculatio ns, its estimates of radiative forcing were likel y to be too high
.
c. Changes in Atmospheric Chemistry from High Altitude Nitrogen Oxides Emissions Emissions of NO x do not themselves have warming or cooling effects, but affect the climate through catal yz ing changes in the chemical equilibrium of the atmosphere
. High altitude e missions of NO x increase the concentration of ozone , which has a warming effect in the short term . Elevated NOx concentrations also lead to an increased rate of destruction of methane , which has a cooling effect in the long
- term . The reduced methane concentrations eventuall y contribute to decreases in ozone, which also decreases the long
- term net warming effect
. Thus, the net radiative impact of NO x emissions depends on the balance between the reductions in methane versus the production of ozone , which in turn depends on the time scale under consideration. Q uantifying these impacts is an area of active study with large uncertainties. The quantification of the net global effect of NO x is difficult because the atmospheric chemistry effects are heavily dependent on highly

localized atmos pheric properties and mixing ratios. Because the background atmospheric concentration of NO x is important for quantifying the impact of aviation NO x emissions on ozone and methane concentrations, the location of aircraft emissions would be an important additional factor
. In addition, NO x has different residence times in the atmosphere depending on the altitude at which it is emitted. T he residence time of NO x in the upper troposphere, or roughl y the cruise******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **117** of **198** altitude for jet aircra ft, is on the order of several day s. Going back to the IPCC 1999 assessment, the globally

averaged radiative forcing estimates for aircraft emissions of NO x in 1992 were 0.023 W/m 2 for O 3 - induced changes (uncertaint y range of 0. 0 11 to 0. 0 46 W/m2 ), and
- 0. 0 14 W/m 2 for methane

- induced changes (uncertaint y range of
- 0.005 to
- 0. 0 42 W/m2 )
. 181 The IP CC AR5 presents the impact of aviation NO x emissions using a different metric, global warming potential ( GWP ), which is a measure of the warming impact of a pulse of emissions of a given substance over 100 years relative to the same mass of CO 2 . The AR5 presents a range from
- 21 to +75 for GWP of aviation NO x . 182 The uncertainty in sign indicates uncertainty

whether the net effect is one of warming or cooling. This report further suggests that at cruise altitude there is strong regional sensitivity of ozone and methane to NO x , particularl y notable at low latitudes
. The Administrator notes that NO x emissions are already regulated under the EPA’s rules implementing CAA section 231, at 40 CFR part 87. The prerequisite endangerment and cause or contribute findings that formed the basis for these standards, however, did not rel y

181 IPCC, 1999: Aviation and the Global Atmosphere, Special Report to the Intergovernmental Panel on Climate Change [Penner, J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] Cambridge University Press, 373 pp. 182 IPCC, 2013: Climate Change 2013: The Ph ysical 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 (ed s.)].Cambridge University Press, 1535 pp.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **118** of **198** upon any conclusions re garding the climate forcing impacts of NO x , but rather the role of NO x emissions as a precursor to ozone formation in areas that did not meet the National Ambient Air Quality

Standard (NAAQS) for ozone
. 184 The continuing significant uncertainties regarding NO x as a climate forcer do not undermine the Agency ’s prior conclusion under CAA section 231 that emissions of NO x from aircraft engines cause or contribute to air pollution which may

reasonably

be anticipated to endanger public health or welfare due to th eir contribution to ozone concentrations that exceed the NAAQS. d. Summary Overall, the state of the science as represented in the assessment literature highlights significant scientific uncertainties regarding the total net forcing effect of water vapor , N O x , and aerosol particles, when emitted at high altitudes. The dependence of the effects on where the substance is emitted, and the complex temporal and spatial patterns that result, mean that the current level of understanding regarding these short
- lived substances is much lower than for the six long
- lived, well
- mixed GHG s . Given the aforementioned scientific uncertainties at present , the Agency

is not including these constituents in the proposed definition of air pollution for purposes of the endangerment finding under section 231 of the CAA
.

184 U.S. EPA, “Control of Air Pollution from Aircraft and Aircraft Engines, Emission Standards and Test Procedures for Aircraft
. ” Final Rule, 38 FR 19088, July 17, 1973.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **119** of **198 Summary of the Administrator’s Proposed Endangerment Finding**  **u nder CAA**  C. **S ection 231**  In sum, the Administrator proposes to find, for purposes of CAA section 231(a)(2)(A), that elevated atmospheric concentrations of the six well
- mixed GHG s constitute air pollution that endanger s both the public health and the public welfare of current and f uture generations
. In this proposed action under CAA section 231(a)(2)(A), the EPA rel ies primarily on the extensive scientific and technical evidence in the record supporting the 2009 Endangerment F inding , including the major , peer - reviewed scientific as sessments used to address the question of whether GHGs in the atmosphere endanger public health and welfare , and on the anal yt ical framework and conclusions upon which the EPA relied in making that finding
. This proposed finding under section 231 accounts for the EPA’s careful consideration not only

of the scientific and technical record for the 2009 Endangerment Finding, but a l s o of new, major scientific assessments issued since closing the administrative record for the 2009 Endangerment Findi ng. N o recent information or anal yses 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 2 02(a)
. In proposing this finding for purposes of section 231, we are not reopening or revisiting our 2009 Endangerment F inding
. To the contrary , in light of the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **120** of **198** recent judicial decisions upholding those findings, the EPA believes the 2009 Endange rment Finding is firml y established and well settled. 185 Moreover, there is no need for the EPA to reopen or revisit that finding for purposes of making an additional finding under section 231 of the CAA. Therefore, public comments addressing this finding for purposes of section 231(a)(2)(A) should be limited to the section 231 context; the EPA will not consider or respond to comments on this proposal that seek a reevaluation of our 2009 Endangerment F inding for purposes of section 202(a). 

## V. **The Proposed Cause or** **Contribute Finding for Greenhouse Gases**  **under CAA**  **Section 231** As noted above, the Administrator has proposed to define the air pollution for purposes of the endangerment finding under CAA section 231 to be the aggregate of six well
mixed GHGs in the atmosphere. The second step of the two
- part endangerment test for this proposed finding is for the Administrator to determine whether the emission of any air pollutant from certain classes of aircraft engines causes or contributes to this air pollution. This is referred to as the cause or contribute finding, and is the second proposed finding b y the Administrator in this action.

185 CRR , 684 F.3d at 117 (D.C. Cir. 2012), reh'g en banc denied, 2012 U.S. App. LEXIS 25997, 26313, 26315 (D.C. Cir. 2012); see also Utility Air Reg. Group v. EPA , 134 S. Ct. at 2438 (2014).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **121** of **198** Section V. A of this proposal desc ribes the Administrator’s reasoning for using the same definition and scope of the GHG air pollutant that was used in the 2009 Endangerment Finding. Section V. B put s forth the Administrator’s proposed finding that emissions of well
mixed GHGs from classes of aircraft engines used in covered aircraft contribute to the air pollution which endanger s public health and welfare. **The Air Pollutant** A. 1. Proposed Definition of Ai r Pollutant Under section 231, the Administrator is to determine whether emissions of any air pollutant from any

class or classes of aircraft engines cause or contribute to air pollution which may

reasonabl y be anticipated to endanger public health or welfare. As with the 2009 Endangerment Finding that the EPA conducted for purposes of CAA section 202(a), when making a cause or contribute finding under section 231(a)(2), the Administrator must first define the air pollutant being evaluated. T he Administrator has reasonably and logically considered the relationship between the GHG air pollution and air pollutant : while the air pollution is the concentra tion ( e.g., stock) of the well
- mixed GHGs in the atmosphere, the air pollutant is the same combined grouping of the well
- mixed GHGs , the emissions of which are anal yz ed for contribution ( e.g., the flow into the stock). See 74 FR at 66537 (similar discussio n with respect to the finding for section 202)
. Thus, for purposes of s ection 231, the Administrator is proposing to use the same definition of the air pollutant that was used in the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **122** of **198** 2009 Endangerment Finding , name ly , the aggregate group of the same six GH Gs : CO 2 , methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. See 74 FR at 66536
- 66537 (discussing the definition of the GHG air pollutant with respect to the finding for section 202)
. That is, as for the 2009 Endangerment Finding, the Administrator is proposing to define a single air pollutant made up of these six GHGs. To reiterate what the Agency has previousl y stated on this subject, this collective approach for the contribution t est is consistent with the treatment of GHGs by those studying climate change science and policy , where it is common prac t ice to evaluate GHGs on a collective, CO 2 - equivalent basis. 186 This collective approach to defining the air pollutant is not unique; grouping of many substances with common attributes as a single pollutant is common practice under the CAA, for example with particulate matter and volatile organic compounds (VOC)
. As noted in section IV , these substances share common attributes that support their grouping as the air pollution for purposes of the endangerment finding. These same common attributes also support the Administrator grouping the six GHGs for purposes

186 As detailed in the 2009 Endangerment Finding proposal (74 FR 18904 (April 24, 2009) and continuing today, the UNF CCC, the U.S. and other Parties report their annual emissions of the six GHGs in CO 2 - equivalent units. This facilitates comparisons of the multiple GHGs from different sources and from different countries, and provides a measure of the collective warming p otential of multiple GHGs. Emissions of different GHGs are compared using GWPs , which as described in section IV.B of this preamble are measures of the warming impact of a pulse of emissions of a given substance over 100 years relative to the same mass of CO 2 . T herefore, GWP
weighted emissions are measured in teragrams of CO 2 equivalent ( Tg CO 2 eq ). The EPA’s Greenhouse Gas Reporting Program ( http://www.epa.gov/ghgreporting/index.html , (L ast accessed February 5 , 2015 )) also reports GHG emissions on a CO 2 - equivalent basis , recognizing the common and collective treatment of the six GHGs.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **123** of **198** of defining the air pollutant for the proposed cause or contribute finding under CAA section 231. The Administrator recognizes that in this case, the aircraft engines covered by this notice emit two of the six gases , but not the other four gases. Nonetheless, it is entirely appropriate, and in keeping with the 2009 Endangerment Find ing and past EPA practice, for the Administrator to define the air pollutant in a manner that recognizes the shared relevant properties of all these six gases, even though they are not all emitted from the classes of
source s before her. 187 For example, a so urce may emit only

20 of the possible 200
- plus chemical s that meet the definition of VOC in the EPA’s regulations, but that source is evaluated based on its emissions of VOC and not on its emissions of the 20 chemicals by name. The fact that these six sub stances within the definition of GHG s share common, relevant attributes is true regardless of the ty pe of source s being evaluated for contribution. By proposing to use the defini tion of the air pollutant as comprised of the six GHGs with common attributes, the Administrator is taking account of these shared attributes and how they are relevant to the air pollution that endanger s public health and welfare.

187 In the 2009 Endangerment Finding, the Administrator found that four of the six gases that were include d in the definition of the air pollutant were emitted by section 202 sources. 74 FR 66496, 66537 (December 15, 2009).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **124** of **198**

2. How the Definition of Air Pollutant in the Endangerment Determination Affects S ection 231 Standards. Under section 231(a), the Administrator is required to set “emission standards applicable to the emission of an y air pollutant” from classes of aircraft engines that the Administrator determines causes or contributes to air pollution that endangers public health or welfare
. If the Administrator makes a final determination under s ection 231 that the emissions of the GHG air pollutant from certain classes of aircraft engines contribute to the air pollution that may

reasonably

be anticip ated to endanger public health and welfare , then she is called on to set standards applicable to the emissions of this air pollutant. The term “standards applicable to the emissions of any air pollutant” is not defined, and the Administrator has the discr etion to interpret it in a reasonable manner to effectuate the purposes of section 231 to set standards that either control the emissions of the group of s i x well
- mixed gases as a whole and/or control emissions of individual gases , as constituents of the c lass. For example, it might be appropriate to set a standard that measures and controls the aggregate emissions of the group of GHGs, weighted b y CO 2 equivalent. Depending on the circumstances, however, it may be appropriate to set standards for certain individual gases, or some combination of group and individual standards. These and other similar approaches could appropriately be considered in setting a standard or standards applicable to the emission s of the group of GHGs that are defined as the air p ollutant. The Administrator would consider a variet y of factors in determining what approach to take in setting the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **125** of **198** standard or standards; for example , she would consider the characteristics of the aircraft emissions, such as rate and variability, the kin d and availability of control technology , and other matters relevant to setting standards under section 231. 188 **Proposed Cause or Contribute Finding** B. 1. The Administrator’s Approach in Making this Proposed Finding As it did for the 2009 Endangerment Finding, and consistent with prior practice and current science, the EPA uses annual emissions as a reasonable prox y for contributions to the air pollution, i.e., elevated atmospheric concentrations of GHG s . Cumulative anthropogenic emissions are primaril y responsible for the observed change in concentrations in the atmosphere (i.e., the fraction of a country ’s or an economic sector’s cumulative emissions compared to the world’s GHG emissions over a long time period will be roughly equal to the fraction of the change in concentrations attributable to that country or economic sector); likewise, annual emissions are a reasonable proxy for annual incremental changes in atmospheric conce ntrations.

188 In setting GHG emissions standards for model years 2012
- 2016 light
- duty vehicles, the EPA set fleet
- wide average CO 2 equivalent standards for cars and trucks based on a technology assessment analysis which indicated that there was a wide range of technologies available for manufacturers to use when upgrading vehicles to reduce CO 2 emissions and improve fuel economy. The final stan dards were based on CO 2 emissions
- footprint curves, where each vehicle has a different CO 2 emissions compliance target depending on its footprint value (related to the size of the vehicle). The EPA also set standards to cap tailpipe nitrous oxide, methane emissions, and provided compliance credits to manufacturers who improved air conditioning systems, such as through reduced refrigerant leakage (hydrofluorocarbons) and indirect CO 2 emissions related to the increased load on the engine. 75 FR 25324 (May 7, 2010).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **126** of **1 98**  There are a number of possible way s of assessing whether air pollutants cause or contribute to the air pollution which may reasonabl y be anticipated to endanger public health and welfare , and no single approach is required or has been use d exclusively in previous determinations under the CAA
. Because the air pollution against which the contribution is being evaluated is the six well
- mixed GHGs, the logical starting point for any contribution anal ys is is a comparison of the emissions of th e air pollutant from the section 231 category to the total U.S. and total global emissions of the six GHGs. The Administrator recognizes that there are other valid comparisons that can be considered in evaluating whether emissions of the air pollutant cau se or contribute to the combined concentration of the six GHGs . To inform the Administrator’s assessment, section V.B.2 presents the following t ypes of simple and straightforward comparisons of U.S. aircraft GHG emissions :

 As a share of current total U.S. GHG emissions;

 As a share of current U.S. transportation GHG emissions;

 As a share of current total global GHG emissions; and

 As a share of the current global tran sportation GHG emissions. All annual GHG emissions data are reported on a CO 2 - equivalent (CO 2 eq) basis, which as described above is a commonly accepted metric for comparing different GHGs. This approach is consistent with how EPA determined contribution for GHGs under section 202 of the CAA in 2009
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **127** of **198**

2. Overview of Greenhouse Gas Emissions Atmospheric concentrations of CO 2 and other GHGs are now at essentiall y unprecedented levels compared to the distant and recent past. 189 This is the unambiguous result of human emissions of these gases. Global emissions of well
- mixed GHGs have been increasing, and are projected to continue increasing for the foreseeable future
. According to IPCC AR5 , t otal global (from all major emitting sources including forestry and other land use) emissions of GHGs in 201 0 were about 49 , 000 teragrams 190 o f CO 2 equivalent ( Tg CO 2 eq)
. 191 This represents an increase in global GHG emissions of about 29 percent since 1990 and 23 percent since 2000
. In 201 0 , total U.S. GHG emissions were responsible for about 14 percent of global GHG emissions (and about 12 percent when factoring in the effect of carbon sinks from U.S. land use and forestry)
. Because 2010 is the most recent ye ar for which IP CC emissions data are available, we provide 2011 estimates from another widel y used and recognized glob al dataset, the World

189 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. T ignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, p. 11. 190 One teragram (Tg) = 1 million metric tons = 1 megatonne (Mt). 1 metric ton = 1,000 kg = 1.102 short tons = 2,205 lbs. 191 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, 1435 pp.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **128** of **198** Resources Institute ’s (WRI) Climate Analy sis Indicators Tool (CAIT), 192 for comparison. According to WRI/CAIT, the t otal global GHG emissions in 2011 were 43 , 816 Tg of CO 2 eq , represent ing an increase in global GHG emissions of about 42 percent since 1990 and 30 percent since 2000 (excluding land use, land use change and forestry). These estimates are generall y consistent with those of IPCC. In 2011 , WRI/CAIT data indicate that total U.S. GHG emissions were responsible for almost 15.5 percent of global emissions , which is also generall y in line with the percentages using IPCC’s 2010 estimate described above. According to WRI/CAIT, current U.S. GHG emissions rank only behind Chin a’s, which was responsible for 24 percent of total global GHG emissions
. The Inventory of U.S. Greenhouse Gas Emissions and Sinks Report 193 (hereinafter “U.S. Inventory”), in which 2012 is the most recent year for which data are available , indicates that t otal U.S. GHG emissions increased by 4.7 percent from 1990 to 2012 (or by about 2. 7 percent when including the effects of carbon sinks) , while emissions decreased from 2011 to 2012 by

3.4 percent. This decrease was attributable to multiple factors including reduced carbon intensity

of fuels for electricity

generation, i mprovements in vehicle fuel efficiency with reductions in miles travel e d, and a warmer winter leading to a decrease in

192 World Resources Institute (WRI) Climate Analysis Indicators Tool (CAIT) Data Explorer (Vers ion 2.0). Available at http://cait.wri.org (Last accessed February 5, 2015 ). 193 U.S. EPA, 2014: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

- 2012 , 529 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullreport , (Last accessed February 5, 2015)
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **129** of **198** heating requirements
. The U.S. Inventory also shows that while overall U.S. GHG emissions grew between 1990 and 2012 , transportation GHG emissions grew at a significantly higher rate , 1 7 percent , more rapidly than an y other U.S. sector . Within the transportation sector,
a ircraft remain the single largest source of GHG emissions not yet subject to any GHG regulations.

Section V.B.2. a which follows describes U.S. aircraft GHG emissions within the domestic context, while section V.B.2. b describes these same GHG emissions in the global context. Section V.B.2. c addresses future projec tions of aircraft GHG emissions.

a. U
. S
. Aircraft GHG Emissions Relative to U
. S
. GHG Transportation and Total U
. S
. GHG Inventory Relying on data from the U.S. Inventory , w e compare U.S. aircraft GHG emissions to the transportation sector and to total U.S. GHG emissions as an indication of the role th is source play s in the total domestic contribution to the air pollution that is causing climate change. In 2012 , total U.S. GHG emissions from all sources were 6,526 Tg CO 2 eq. As stated above, t otal U.S. GHG emissions have increased by almost 5 percent between 1990 and 2012 , while U.S. transportation GHG emissions from all categories have grown 17 percent since 1990. The U.S. transportation sector was the second largest GHG emitting sector (behind electricit y generation), contributing 1,948 Tg CO 2 eq or about 30 percent of total U.S. GHG******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **130** of **198** emissions in 2012. This sectoral total include s emissions from combustion of U.S. international bunker fuels , which are fuels used for transport activities , from aviation (both commercial and military

) and marine sources
. Consistent with IPCC guidelines for common and consistent accounting and reporting of GHGs under the UNFCCC, the “ U.S. international aviation bunker fuels ” category include s emissions from combustion of fuel p urchased in and used by aircraft departing from the U nited S tates , regardless of whether t hey are a U.S. flagged carrier. Total U.S. aircraft emissions constitute a significant part of the U.S. transportation sector’s emissions, accounting for 212 Tg CO 2 eq or 11 percent of such emissions ( s ee .)
. In 2012, emissions from aircraft (212 Tg CO 2 eq) were the third

Table V
. 1 largest transportation source of GHGs within the United Stat es, behind light
- duty v ehicles and medium
- and heav y - duty trucks ( totaling 1,535.6 Tg CO 2 eq )
. For purposes of making this cause or contribute finding, the EPA is focused on, and proposes to include , a set of aircraft engine classes used in ty pes of aircraft as described below , which corresponds to the scope of the international CO 2 emissions standard contemplated b y ICAO. As mentioned earlier in section I I
. D , traditionally the EPA (and FAA) participates at ICAO in the development of international standards, and then where appropriate, the EPA establishes domestic aircraft engine emission standards under CAA section 231 of at least equivalent stringency to ICAO’s standards
. An international CO 2 emissions standard i s******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **131** of **198** anticipated in February

2016, and provided that the EPA makes a positive endangerment finding and IC AO adopts an international CO 2 emissions standard that is both consistent with CAA section 231 and appropriate for domestic needs, we would expect to proc eed with promulgating a CO 2 emissions standard (or GHG standard) of at least equivalent stringency domestically . As described later in section V I .D, the thresholds of applicability for the international CO 2 emissions standard are based on gross weight as follows: for subsonic jet aircraft, a maximum takeoff mass (MTOM) greater than 5,700 kilograms; and for subsonic propeller driven (e.g., turboprop ) aircraft , a MTOM greater than 8 , 618 kilograms. 195 Applying these gross weight thresh olds, our proposed cause or contribute finding applies to GHG emissions from classes of engines used in covered aircraft
. Examples of covered aircraft would include small er jet aircraft such as the Cessna Citation CJ2+ and the Embraer E170 , up to the l argest commercial jet aircraft
-- the Airbus A380 and the Boeing 747. Other examples of covered aircraft would include larger turboprop aircraft, such as the ATR 72 and the Bombardier Q400
. Our intention is for the scope of the contribution finding to correspond to the aircraft engine GHG emissions that are from aircraft that match the applicability thresholds for the international aircraft CO2 standard. As such we have also identified aircraft that are not covered aircraft for purposes of our proposed contribution finding. That includes aircraft that fall below the international applicability thresholds : smaller turboprop aircraft,

195 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Stan dard, Circular (Cir) 337, AN/192, Available at www.icao.int (Last accessed February 5, 2015)
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Page **132** of **198** such as the Beechcraft King Air 350i , and smaller jet aircraft, such as the Cessna Citation M2
. In addition, I CAO (with U.S. participation) has agreed to exclude “ piston
- engine aircraft, ”

“ helicopters, ” and “ military aircraft ” 196 from the ty

pes of aircraft that would be covered b y the anticipated ICAO standards. 197 These aircraft would not be covered aircraft and consequentl y , we are also not including GHG emissions from classes of engines used in these ty pes of aircraft in our proposed cause or contribute finding. Thus, for the purposes of the cause or contribute finding, the EPA proposes to include GHG emissions from aircraft engines used in covered aircraft in the scope of this proposed cause or contribute finding. This is an equivalent scope of applicability as that contemplated by ICAO. T he majority o f the GHG emissions from all classes of aircraft engines w ould be covered b y this scope of applicability. Below we describe the contribution of these U.S. covered aircraft GHG emissions to U.S. GHG emissions, and later in section V.B.2.b we discuss the contribution of these U.S. covered aircraft emissions to glo bal GHG emissions. In 2012, GHG emissions from U.S. covered aircraft (which includes U.S. international aviation bunker fuels in certain cases ) comprised 9 0 percent ( 19 0 Tg CO 2 eq ) of total U.S.

196 ICAO regulations only apply to civil aviation (aircraft and aircraft engines), and consequently, ICAO regulations do not apply to military aircraft. 197 The applicability of the anticipated international CO 2 standard would be limited to subso nic aircraft, and wo uld not extend to supersonic aircraft. Since space vehicles (or spacecraft) w ill be operated at supersonic speeds, space vehicles would not be covered by the anticipated international CO2 standard.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **133** of **198** aircraft GHG emissions 198 and 1 0 percent of total U.S. transportation sector GHG emissions (See .)
. Overall , U.S. covered a ircraft comprised the third largest source of GHG Table V
. 1 emissions in the U.S. transportation sector behind only the light
- duty v ehicle and medium
and heav y - dut y truck sector s , which is the same ranking as total U.S. aircraft
. 199 The U.S. covered aircraft also represent 3 percent of total U.S. GHG emissions , which is approximately equal to the contribution from total U.S. aircraft of 3.2 p ercent (Table V.1)
. 200 It is important to note that in regard to the six well
- mixed GHGs (CO 2 , methane, nitrous oxide, hydrofluorocarbons , perfluorocarbons , and sulfur hexafluoride ), only two of these gases
-- CO 2 and nitrous oxide
-- are reported as non
- zer o emissions for total aircraft and

198 [INSERT REFERENCE f or ERG analysis of covered aircraft (or the general aviation jet fuel breakout) after it is completed.] 199 Com pared independently, total U.S. aircraft GHG emissions and U.S. covered aircraft GHG emissions are both ranked the third largest source in the U.S. transportations sector, behind only light
- duty vehicle and medium
- and heavy
- duty truck sectors. 200 Total U.S. aircraft GHG emissions and U.S. covered aircraft GHG emissions were from 11 to 30 percent greater in 2000 and 2005 than in 1990. These increases in aircraft GHG emissions are primarily because aircraft operations (or number of flights) grew by similar amounts during this time period. Also, total U.S. aircraft GHG emissions and U.S. covered aircraft GHG emissions were from 13 to 19 percent greater in 2000 and 2005 than in 2012. These decreases in aircraft GHG emissions are partly because aircraft operations decreased by similar amounts during this time period. In addition, the decreases in aircraft emissions are due in part to improved operationa l efficiency that results in more direct flight routing, improvements in aircraft and engine technologies to reduce fuel burn and emissions, and the accelerated retirement of older, less fuel efficient aircraft. Also, the U.S. transportation GHG emissions were changing at similar rates as total U.S. aircraft GHG emissions and U.S. covered aircraft GHG emissions for these same time periods, and thus, the aircraft GHG emissions share of U.S. Transportation remains approximately constant (over these time per iods). (U.S. EPA, 2014: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

- 2012 . Available at http://www.epa.gov/climatechange/ghgemissions/usinventor yreport.html#fullreport , Last accessed February 5, 2015; U.S. FAA. 2015, APO Terminal Area Forecast Summary Report

- Forecast Issued January 2015 , http://aspm.faa.gov/apow taf/ .).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **134** of **198** covered aircraft. 201 CO 2 represents 99 percent of all GHGs from both total aircraft (210 Tg CO 2 eq) and U.S. covered aircraft (1 88 Tg CO 2 eq), and nitrous oxide represents about one percent from total aircraft (2 Tg CO 2 eq) and covered aircraft (1.8 Tg CO 2 eq). M odern aircraft do not emit methane, 202 and hydrofluorocarbons , perfluorocarbons , and sulfur hexafluoride are not products of aircraft engine combustion. **Table V**  **. 1**  COMPARI SON S OF U.S. AIRCRAFT GHG EMISSIONS TO TOTAL U.S. TRANSPORTATION AND TOTAL U.S. GHG EMI SSI ONS

1990 2000 2005 2010 2011 2012 Total U.S. Aircraft GHG emissions (Tg CO2 e q) Share of U.S. Transportation 228 14% 26 2

12% 254

12% 216

11% 215

11% 212 11%

201 U.S. EPA, 2014: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990

- 2012 , 529 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullrepor t , (Last accessed February 5, 2015)
. 202 Emissions of methane from jet fuels are no longer considered to be emitted (based on the latest studies) across the time series from aircraft gas turbine engines burning jet fuel A at higher pow er settings (EPA, Recom mended Best Practice for Quantifying Speciated Organic Gas Emissions from Aircraft Equipped with Turbofan, Turbojet and Turboprop Engines , EPA
- 420
- R
- 09
- 901, May 27, 2009 (see http: //www.epa.gov/otaq/regs/nonroad/aviation/420r09901.pdf ). Based on this data, methane emissions factors for jet aircraft were reported as zero to reflect the latest emissions testing data. Also, the 2006 IPCC Guidelines indicate the following: “Methane (CH 4 ) may be emitted by gas turbines during idle and by older technology engines, but recent data suggest that little or no CH 4 is emitted by modern engines.” ( IPCC, 2006 : IPCC Guidelines for National Greenhouse Gas Inventories , The National Greenhouse Gas In ventories Programme, The Intergovernmental Panel on Climate Change, H.S. Eggleston, L. Buendia, K. Miwa, T Ngara, and K. Tanabe (eds.). Hayama, Kanagawa, Japan.) The EPA uses an emissions factor of zero to maintain consistency with the IPCC reporting guid elines, while continuing to stay abreast of the evolving research in this area. For example, one r ecent study has indicate d that modern aircraft jet engines operating at higher power modes consume rather than emit methane (Santoni et al. , 2011: Aircraft Em issions of Methane and Nitrous Oxide during the Alternative Aviation Fuel Experiment, Environ. Sci. Technol., 45, pp. 7075
- 7082).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **135** of **198** Share of total U.S. Inventory 3.7% 3.7% 3.5% 3.1% 3.2% 3.2% U.S. Covered Aircraft GHG emissions (Tg CO2 e q) Share of U.S. aircraft GHG emissions Share of U.S. Transportation Share of total U.S. Inventory 171 75 % 10 % 2.7 % 223

85 % 10 % 3.1 % 2 1 8

86 % 10 % 3 % 1 91

88 % 9.5 % 2.8 % 193

90 % 9.8 % 3 % 190 90 % 9.7 % 3 % Transportation Sector emissions (Tg CO2 e q) Share of total U.S. Inventory 1,661 27% 2,136

30% 2,136

30% 1,999

29% 1,969

29% 1,948 30%
Total U.S. GHG emissions 6,233 7,107 7,254 6,875 6,753 6,526
b. U
. S
. Aircraft GHG Emissions Relative to Global Aircraft GHG Inventory and the Total Global GHG Inventory For background information and context, we first provide information on the contribution of GHG emissions from global aircraft and the global transportation sector to total global GHG emissions , and describe how this compares to the emissions from aircraft that would be covered by the anticipated ICAO CO 2 standard
. We then compare U.S. aircraft GHG emissions to the gl obal aircraft sector , to the global transport sector, and to total global GHG emissions as an indication of the role th is source play s in the total global contribution to the air pollution that is causing climate change. As in the preceding section, we present comparisons from both total U.S. aircraft and U.S. covered aircraft.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **136** of **198** A ccording to IPCC AR5, global aircraft GHG emissions in 2010 we re 11 percent of global transport GHG emissions and 2 percent of total global GHG emissions. Data from ICAO’s 2013 Environmental Report indicate that the vast majority of global emissions from the aircraft sector are emitted by the t ypes of aircraft that would be covered by the anticipated ICAO CO 2 standard (“I CAO covered aircraft”). 203 When compared to global data from IPCC AR5 , worldwide GHG emissions from I CAO covered aircraft represented about 93 percent (688 Tg CO 2 eq) of global aircraft GHG emissions , 204 10 percent of global tr ansport GHG emissions, and 1.5 percent of total global GHG emissions in 2010
. Comparing data from the U.S. Inventory to IPCC AR5, we find that total U.S. aircraft GHG emissions represented about 29 percent of global aircraft GHG emissions, about 3.1 percent of global transport GHG emissions , and about 0.5 p ercent of total global GHG emissions in 2010 (see Table V. 2 ). For U.S. covered aircraft in 2010 GHG emissions represented about 2 6 percent of global aircraft GHG emissions, 2. 7 percent of globa l transport GHG emissions , and 0.5 percent of total global GHG emissions (see Table V.2 ). Because 2010 is the most recent year for which IPCC emissions data are available, we also made

203 ICAO CAEP , 2013 : ICAO Environmental Report 2013, Aviation and Climate Change , 224 pp . Available at http://cfapp.icao.int/Environmental
- Report
- 2013/ (Last accessed February 5, 2015)
. 204 Worldwide GHG emissions from ICAO covered aircraft include emissions from both international and domestic aircraft operations arou nd the world.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **137** of **198** comparisons using 2011 estimates from WRI /CAIT and the International Ener gy Agency (IEA) 205 and found that they yi eld very similar results. 206
**Table V**  **. 2**  COMPARI SONS OF U.S. AIRCRAFT GHG EMISSIONS TO TOTAL GLOBAL

GREENHOUSE GAS EMI SSI ONS IN 2010 2010 ( Tg CO 2 e q) Total U.S.

Aircraft Share ( % ) U.S. Covered

Aircraft Share (%) Global Aircraft

Share ( % )
Global Aircraft GHG emissions 7 4 3 29 26
-- Global Transport GHG emissions 7 , 000 3.1 2
. 7 11 Total G lobal GHG emissions 49 , 000 0.5 0.5 2

For a ddition al background information and context , we used 2011 WRI /CAIT and IE A data to make comparisons between the aircraft sector and the emissions inventories of entire countries and regions
. W hen compared to entire countries , total global aircraft GHG emissions in 2011 ranked 9 th overall , behind only China, United States, I

ndia, Russian Federation, Japan, Brazil, German y, and Indonesia , and ahead of about 175 other countries.

205 International Energy Agency, Data Services. Available at http://data.iea.org (Last accessed February 5, 2015). 206 Data from WRI/CAIT and IEA show that, i n 2011, total U.S. aircraft emission s represented about 28 percent of gl obal aircraft GHG emissions, about 3.7 percent of g lobal transport GHG emissions, and about 0.5 percent of total global GHG emissions
. U.S. covered aircraft represented about 2 5 percent of global aircraft GHG emissions, 3. 3 percent of global transport GHG emissions, and 0.5 percent of total global GHG emissions in 2011
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **138** of **198** Total U.S. aircraft GHG emissions have historically been and continue to be by far the largest contributor to global aircraft GHG emissions. Total U.S. aircraft GHG emissions are about 7 tim es higher than aircraft GHG emissions from China, which globally is the second ranked country for aircraft GHG emissions, and about 5 times higher than aircraft GHG emissions from all of Asia. U.S. covered aircraft GHG emissions are about 6 times more than aircraft GHG emissions from China, and about 4 times more than aircraft GHG emissions from all of Asia. If U.S. covered aircraft emissions of GHGs were ranked against total GHG emissions for entire countries, these covered aircraft emissions would rank ahead of Belgium , Czech Republic, Ireland, Sweden and about 150 other countries in the world.

c. Aircraft GHG Emissions Are Projected to Increase in the Future While overall GHG emissions from U.S. covered aircraft increased b y about 12 percent from 1990 to 2010 , the portion attributable to U.S. international aviation bunker fuels 207 increased b y about 1 00 percent. 208 During this same time period, g lobal aircraft GHG

207 The U.S. inte rnational aviation bunker fuels category includes emissions from combustion of fuel purchased in and used by aircraft departing from the United States, regardless of whether they are a U.S. flagged carrier. GHG emissions from U.S. international aviation bunker fuels are a subset of GHG emissions from U.S. covered aircraft. From 1990 to 2010, GHG emissions from U.S. covered aircraft increased from 171 to 191 Tg CO2eq , and GHG emissions from U.S. international aviation bunker fuels grew from 30 to 57 Tg CO2eq during this same time period . From 1990 to 2011, GHG emissions from U.S. covered aircraft increased from 171 to 193 Tg CO2eq (about 13 percent), and GHG emissions from U.S. international aviation bunker fuels grew from 30 to 62 Tg CO2eq (about 110 percent). 208 U.S. EPA, 2014: Inventor y of U.S. Greenhouse Gas Emissions and Sinks: 1990

- 2012 , 529 pp. Available at http://www.epa.gov/climatechange/ghgemissions/usinventoryreport.html#fullrepo rt , (Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **139** of **198** emissions grew b y about 4 0 percent, and the portion attributable to global international aviati on bunker fuels increased b y 80 percent
. 209 , 210 Notwithstanding the substantial growth in GHG emissions from U.S. international aviation bunker fuels, U.S. covered aircraft emissions have not increased as much as global aircraft emissions primarily because the U.S. aviation market was relatively mature compared to the markets in Europe and other emergent markets , and because during this time period the U.S. commercial air carrier s suffered several major shocks that reduced demand for air travel. 211 , 212 After consolidation and restructuring in recent ye ars, the U.S. commercial air carriers have regain ed profitability and are forecasted by the FAA to grow more over the next 20 to 30 years . 213 With regard to global aircraft GHG emissions, the aviation market s in Asia/Pacific , Europe (where airline deregulation has stimulated significant new demands in this period) , and the Middle East (and other emerging

209 IPCC, 2014: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs
- Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, pp. 599
- 670. 210 According to IEA, from 1990 to 2 011 , global aircra ft GHG emissions grew by about 50 percent, and global international aviation bunker fuels increased by 80 percent
. International Energy Agency Data Services, Available at http://data.iea.org (Last accessed February 5, 2015). 211 FAA, 2013: FAA Aerospace Forecast Fiscal Years 2014

- 2034 , 62 pp. Available at https://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_forecasts/2014
- 2034/media/2014_FAA_Aerospace_Forecast.pdf (Last accessed February 5, 2015). 212 These shocks include the September 11 terro r attacks , significant increases in fuel prices , debt restructuring in Europe and U.S. , and a global recession. 213 According to the FAA Aerospace Forecast , in 2013 U.S. air carriers w ere profitable for the fourth consecutive year.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **140** of **198** markets) have been growing rapidl y, and the global market is expected to continue to grow significantl y ov er the next 20 to 30 years. 214
R ecent studies estimate that both IC AO covered aircraft and U.S. covered aircraft will experience substantial growth over the next 20 to 30 years in the ir absolute fuel burn, and that this will translate into increase d GHG emissions. ICAO estimates that the global fuel burn from I CAO covered aircraft will increase b y about 120 percent from 2010 to 2030 and by about 210 percent from 2010 to 2040 (for a scenario with moderate technology and operational improve ments). 215 T he FAA projects that the fuel consumption from U.S. air carriers and general aviation aircraft operating on jet fuel w ill grow b y 47 percent from 2010 to 2034, correspond ing to an average annual increase rate in fuel consumption of 1.9 percent. 216 These aircraft groups ( U.S. air carriers and general aviation aircraft operating on jet fuel) are of similar scope to the U.S. covered aircraft whose engine GHG emissions are the subject of this proposed finding . Using fuel burn growth rates provided ab ove as a scaling factor for growth in GHG emissions ( globall y and nationally) , it is estimated that GHG

214 According to the FAA Aerospace Forecast , the International Air Transport Association (IATA) reports that world air carriers (including U.S. airlines) are expected to register an operating profit for 2013. Based on financial data compiled by ICAO and IATA, between 2004 and 2013 wo rld airlines produced cumulative operating profits (with nine years out of ten posting gains) and net profits (with six years out of ten posting gains). 215 ICAO CAEP , 2013 : ICAO Environmental Report 2013, Aviation and Climate Change , 224 pp . Available at http://cfapp.icao.int/Environmental
- Report
- 2013/ (Last accessed February 5, 2015)
. 216 FAA, 2013: FAA Aerospace Forecast Fiscal Years 2014

- 2034 , 62 pp. Available at https://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_fo recasts/2014
- 2034/media/2014_FAA_Aerospace_Forecast.pdf (Last accessed February 5, 2015)
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **141** of **198** emissions from IC AO covered aircraft and U.S. covered aircraft would increase at a similar rate as the fuel burn by

2030, 2034, and 2040
. 3. Proposed Contribution Finding for the Single Air Pollutant Comprised of the of Six Well
- Mixed Greenhouse Gases Taking into consideration the data summarized in section 2 above, the A dministrator proposes to find that GHG emissions from classes of engines used in U.S. covered aircraft , which are subsonic jet aircraft with a maximum takeoff mass (MTOM) greater than 5,700 kilogram s and subsonic propeller driven (e.g., turboprop) aircraft with a MTOM greater than 8,618 kilograms, contribute to the air pollution that endanger s public health and welfare. The Administrator is not at this time proposing a contributio n finding for GHG emissions from engines not used in covered aircraft (i.e., those used in small er turboprops, small er jet aircraft , piston
- engine aircraft, helicopters and military aircraft)
. We solicit comment on the scope of the proposed contribution finding, whether a broader contribution finding ( e.g. , including all engines used in aircraft certified b y the FAA ) would be appropriate , and the extent to which EPA has discretion to establish standards pursuant to a contribution finding that do not impose requirements on every engine or class of engines within the scope of that f i nding. It is the Administrator’s judgment that the collective GHG emissions from the classes
o f engines used in U.S. covered aircraft are significant, whether the comparison is domestic (10 percent of all U.S. transportation GHG emissions , representing 3 percent of total U.S.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **142** of **198** emissions) or global (2 6 percent of total global aircraft GHG emissions representing 2. 7 percent of total global transportation emissions and 0.5 percent of all global GHG emissions). The proposed scope of GHG emissions from engines used in U.S. covered aircraft under this cause or contribute finding would result in the vast majority ( 9 0 percent) of U.S. aircraft GHG emissions being included in this determination. The Administrator believes that consideration of the global context is important for the cause or contribute test , but that the anal ys is should not solely consider the global context. GHG emissions from engines used in U.S. covered aircraft will become globally well
- mixed in the atmosphere, and thus will have an effect not only on the U.S. regional climate but also on the global climate as a whole, for years and indeed man y decades to come. It is the Administrator’s view that the cause or contribute test used here under CAA s ection 231 can follow the same reasoning that was used in the 2009 GHG cause or contribute finding under CAA section 202; that is, the Administrator believes a positive cause or contribute finding for GHG emissions from engines used in U.S. covered aircraft is justified whether only the domestic context is considered, only the global context is considered, or both the domestic and global GHG emission s comparisons are viewed in combination. As was the case in 2009 , n o single GHG source category dominates on the global scale, and man y (if not all) individual GHG source categories could appear small in comparison to the total, when, in fact, they could be very

important contributors in terms of both absolute emissions or in comparison to other source categories, globally or within the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **143** of **198** United States. If the United S tates and the rest of the world are to combat the risks associated with global climate change, contributors must do their p art even if their contributions to the global problem, measured in terms of percentage, are smaller than typicall y encountered when tackling solel y regional or local environmental issues .” 217 Moreover, as the Supreme Court explained in Massachusetts v. EPA , agencies commonly take an incremental approach to resolving large issues, stating that, “[a]gencies, like legislatures, do not generall y resolve massive problems in one fell regulatory swoop. ... They

instead whittle away

at them over time, refining their p referred approach as circumstances change and as they develop a more nuanced understanding of how best to proceed.” 549 U.S. 497, 524 (2007) (citations omitted). The Administrator continues to believe that these unique, global aspects of the climate chan ge problem

—including that f rom a percentage perspective there are no dominating sources emitting GHGs and few sources that would even be considered to be close to dominating

—tend to support consideration of contribution to the air pollution at lower perc entage levels than EPA ty pically encounters when anal yz ing contribution towards a more localized air pollution problem
. Thus, th e Administrator, similar to the approach taken in the 2009 GHG cause or contribute finding under CAA s ection 202 , is placing si gnificant weight on the fact that engines used in U.S. covered aircraft contribute 3 percent of total U.S.

217 74 FR 66543 (December 15, 2009).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **144** of **198** GHG emissions for the proposed contribution finding and comprise the single largest transportation source in the United S tates that has not yet be en regulated for GHG emissions.

4. Additional Considerations The Administrator is also concerned that reasonable estimates of GHG emissions from engines used in U.S. covered aircraft are projected to grow over the next 20 to 30 years. Given the projected growth in aircraft emissions compared to other sectors, it is reasonable for the Administrator to consider future emissions projections as adding weight to her primary reliance on annual emissions. Recent projections reveal that by 2034 GHG emissions from all aircraft and U.S. covered aircraft engines are likely to increase by

almost 50 percent. 218 By contrast, it is estimated that by 2034 the light duty

vehicle sector will see a 30 percent reduction in GHG emissions from the 2010 baseline , while the heavy duty vehicle sector will experience a 35 percent increase in GHG emissions from the 2010 baseline (this projected increase does not reflect the impact of GHG reductions anticipated from the Phase 2 heav y duty GHG standards th at have not yet been promulgated). In addition, by 2034 the rail sector is projected to experience a 6 percent reduction in GHG emissions from 2010 baseline
. 219

218 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 47 percent from 2010 to 2034 and this provides a scaling factor for growth in GHG emissions which would increase at a similar rate as the fuel burn by 2030, 2034, and 2040. 219 U.S. Energy Information Administration ( EIA), 2014: Annual Energy Outlook (AEO) 2014 with projections to 2040 , DOE/EIA
- 0383, 269 pp. EIA’s reference case ( used as the baseline in this com parison) assumes fuel economy levels for light duty vehicles required to meet federal light duty GHG standards for years 2012
- 20 25,******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **145** of **198** Because the projected growth in aircraft engine GHG emissions from U.S. covered aircraft appears to be greater in percentage terms than other transportation sources, this future consideration adds weight to the Administrator’s proposed positive contribution finding
. 

## VI. **A dvance**  **N otice of**  **P ro**  **posed R** **ulemaking : Discussion of**  **Ongoing International Proceedings to Develop**  **Air craft**  **CO 2**  

## Em **issions Standard and Request for Comment** 
For more than four ye ars, the EPA and FAA have been engaged with the IC AO ’s Committee on Aviation Environmental Protection (I CAO/CAEP) to establish an international CO 2 e missions standard which the EPA could then consider proposing for adoption under its section 231 authority

of the CAA. Th is section of today ’s notice serves as an ANPR to discuss the key

issues of the ongoing international proceedings prior to February 20 16, when ICAO/CAEP is expected to finalize an international aircraft CO 2 standard. An ANPR is intended to solicit comments and/or information from the public prior to an agency determining whether to propose a rulemaking. As such, an ANPR does not propose or impose any regulatory

requirements. The EPA may choose to develop an ANPR for actions ( such as
and for heavy duty trucks GHG standards for years 2014
- 2018, plus improvements in vehicles and engines for all subsectors due to availability of fuel
- saving technologies and fuel price effects. EIA counts biofuels as zero tailpipe GHG emissions. Becaus e the com parison in this section focuses on tailpipe emissions, we include them here, at volumes as forecast in the AEO 2014 reference case. Available at http://www.eia.gov/forecasts/aeo/ (Last accessed Jan

uary 13, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **146** of **198** the promulgation of standards pursuant to CAA section 231 to implement an international aircraft CO 2 standard domestically) which are still in the earl y stages of development and for which public input may

be particularly

helpful. This also helps e nsure transparency , while assisting the EPA in obtaining input from a wide range of stakeholders as we continue work within CAEP t o establish an international CO 2 aircraft standard. The EPA is seeking comments for all interested parties, including small businesses, on a variety of issues related to setting an international CO 2 standard for aircraft , including whether such standards should apply to in
- production aircraft instead of new aircraft ty pes onl y , the appropriate effective dates for the potential international CO 2 standard , as well as the appropriate stringency levels
. CAEP met an important milestone at its 9 th meeti ng (CAEP/9) in 2013 in reaching an agreement on the appropriate metric to be used in ass essing fuel efficiency (or CO 2 emissions) 220 of an engine/ aircraft combination
. They also reached agreement on a mature certification requirement 221 to evaluate CO 2 emissions for new aircraft t ypes and also agreed on certain aspects of the scope of applicability of the CO 2 emissions standard ; however, work on applicability

options for in
- production aircraft continues.

220 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192 , Available at www.icao.int (Last accessed February 5, 2015). Section 3.2 of this Circular states the following: “An important Phase 1 milestone in the development of the CO 2 Standard was reached on 11 July 2012, when the CAEP Steering Group agreed unanimously on a CO 2 me tric system to measure the aeroplane fuel burn performance and therefore the CO 2 emissions produced.” 221 ICAO defines a certification requirement as a com bination of metric, procedures, instrumentation and measurement methodology, and compliance requirements
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **147** of **198** At the CAEP Steering Group meeting in November 20 13, there was agreement on a set of stringency

options to be used for the cost
- effectiveness anal ys is, and at the Steering Group meeting in September 2014 there was a decision on the associated inputs for costs and technology

responses to be utilized in th e cost - effectiveness anal ys is of these stringency options. This analy sis, and work on the applicability of the standard to in
- production aircraft and the certification requirement are scheduled to be completed prior to the 10 th CAEP meeting (CAEP/10) in F ebruary 2016. As described in section II. 0 , the EPA and the FAA traditionally

work within the I CAO/CAEP standard
- setting process to establish international emissi on standards and related requirements. Under this approach, international emission standards have first been adopted b y ICAO, and subsequently the EPA has initiated rulemakings under CAA section 231 to establish domestic standards that are of at least equa l stringency

as ICAO’s standards. This approach has been affirmed as reasonable by the U.S. Court of Appeals for the D.C. Circuit. Provided the EPA makes a positive endangerment finding 222 under CAA section 231 and I CAO adopts an international aircraft CO 2 standard that is consistent with CAA section 231 and U.S. domestic needs, we would expect to proceed with a similar approach promulgating a CO 2 emissions standard (or GHG standard) of at least equivalent stringency

domestically
.

222 As shorthand throughout today’s action , we will use the term “endangerment finding” for both endangerment and cause or contribute findings.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **148** of **198 Purpose of the**  **International Standard** A. At the CAEP Steering Group meeting in 2011, the U.S provided a paper recommending that CAEP agree that the purpose of the international CO 2 emissions standard be “to achieve CO 2 emissions reductions from the aviation sector beyond expected ‘ business as usual ’

– i.e., a standard that achieves CO 2 emissions reductions from the aviation sector beyond what would be achieved in the absence of a standard. This would be anal yz ed using ICAO criteria of technical feasibility, environmental benefit, cost effectiveness, and impacts of interdependencies .” 223 T he Steering Group accepted the U.S. proposal for the purpose of the international CO 2 standard , and it is expected to be included in the s tandard setting process . The metric s ys tem, stringency options, costs, technology responses (inputs to be utilized in the cost
- effectiveness anal ys is ), and applicability ultimately chosen will all have an effect on whether the international CO 2 emissions standard adheres to this stated purpose of the standard. The U.S. continues to support the adoption of an international CO 2 emissions standard that meets this stated purpose , and the EPA request s comment on this continued support . T he EPA reque sts comment on how to achieve the purpose of the standard
.

223 CAEP (U.S. Working Paper), “U.S. Position on the Development of ICAO’S Aircraft CO 2 Standard,” CAEP
SG/20112
- WP/25 , Presented by the United States, U.S. Working Paper for CAEP Steering Group meeting, Beijing, China, 12 to 16 September 2011
..******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **149** of **198** B. **Applicability of the International CO 2**  **Emissions Standard**  We are requesting comment on whether the aircraft CO 2 standard should apply to in
production aircraft, including aircraft with an y engineered fuel efficiency improvements (e.g. , different engines, redesigned wings , or engine performance improvement packages , etc. ) or whether the aircraft CO 2 standard should appl y only to completel y new aircraft t ype designs. In
- production aircraft and new aircraft t ypes are defined as follows:

- In
- production aircraft : those aircraft ty pes which have already received a Type C ertificate, and for which manufacturers either have existing undelivered sales orders or would be willing and able to accept new sales orders
. 224 , 225 , 226

- New aircraft ty

pes : aircraft ty

pes that have applied for a Ty pe C ertificate 227 after the effective date of a standard and that have never been manufactured prior to the effective date of a standard.

224 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192 , Available at www.icao.int (Last accessed February 5, 2015). 225 As described earlier in section D , in existing U.S. aviation emissions regulations, in
- production means newly
manufactured or built after the effective date of the regulations
-- and already cert ified to pre
- existing standards (if emission standards w ere established previously).). This is similar to the current CAEP definition for in
production aircraft ty

pes for purposes of the CO 2 standard. 226 According to ICAO Cir 337, a Type Certificate is “[a] document issued by a Contracting State to define the design of an aircraft type and to certify that this design meets the appropriate airworthiness requirements o f that State”.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **150** of **198** In addition, for context, o ut of production aircraft are those aircraft t ypes which have already received a T yp e Certificate, but for which manufacturers either have no existing undelivered sales orders or would not be willing and able to accept new sales orders. These aircraft are aircraft ty

pes that are no longer in active producti on . 228 As described earlier in section II.E , CAEP ’s Steering Group meeting in 2010 agreed that the scope of applicability for the international airc raft CO 2 standard will be subsonic jets with an applicability

weight threshold of maximum takeoff mass ( MTOM ) greater than 5 , 700kg (12 , 566lb) and turboprop aircraft with a MTOM greater than 8 , 618kg (19 , 000lb)
. CAEP also agreed that the international CO 2 standard will apply to new aircraft t ypes, but not apply to out of production aircraft ty pes , and that applying the standard to in
- productio n aircraft ty pes should not be ruled out. 230

227 A Type Certificate is a design approval process whereby the FAA ensures the manufacturer’s designs meet the minimum requirements for aircraft safety and environmental regulations. This is typically issued only once for each aircraft, and mo dified as needed as an aircraft is modified over the course of its production life. This Ty pe Certificate (for new aircraft types) would be the initial or new T ype Certificate for this aircraft. 228 Out of production aircraft that are still in operational use would become subject to the international standard only if the standard applied to “in
- use” aircraft , which it will not since CAEP has agreed that the international aircraft CO 2 standard should not apply to out of production aircraft types
. Note, the EPA ’s CAA section 231 aircraft engine standards have applied to in
- use aircraft only in very limited situations, such as the prohibition against fuel venting at 40 CFR 87.11 and smoke number standards at 40 CFR 87.31. Note, however, that unlike the EPA’s authority to promulgate emission standards for motor vehicles under CAA section 202(a) or for nonroad engines and vehicles under section 213(a), section 231 of the CAA does not restrict the EPA’s authority to set standards for only ne w aircraft. 230 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192 , Available at www.icao.int (Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **151** of **198** It is important to further describe the difference between new aircraft ty pes and in
production aircraft. There are three categories of aircraft under consideration when describing a CO 2 standard: new aircraft t ypes submitted for certification (known as clean sheet designs), those with lesser levels of design change, such as a new series in an established ty pe and model ( considered to be significant partial redesigns), or an aircraft with incremental improvements. 231 New aircraft ty pe s or new t ype designs are significant investments for manufacturers and are used for new and significantly different designs ( also characterized as complete redesigns )
. Significant partial redesigns may b e characterized as a new or later series of an established model that may incorporate newl y designed wings and give purchasers more choice s of engines
. In cremental improvements are less extensive changes to an aircraft such as performance improvement pack ages that may be added to an aircraft or engine at some point during the production cycle
. New aircraft ty

pes or new ty

pe designs are infrequent
. The most recent new ty pe designs introduced in service, such as the Airbus A380 in 2007, the Boeing 787 in 2011, and the original Boeing 777 in 1995 , 232 , 233 , 234 indicate that it is un likely a new t ype de sign will

231 New aircraft types fall under the initial or new Type Certificate, and significant partial redesigns and incremental improvements fall under an amended Type Certificate. Significant partial redesigns would be a new or later series of an established model, and incremental improvements would be a part of the same series as the established model. 232 Boeing, 2011: Boeing Unveils First 787 to Enter Service for Japan Airlines , December 14. Available at http://boeing.mediaroom.com/index.php?s=20295&item=2075 ( Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **152** of **198** seek certification in the next 10 to 15 years . 235 (New aircraft ty pes (and similarly

for significant partial redesigns) ty pically yi eld large fuel burn reductions

– 10 percent to 20 percent over the prior generation they replace, and a s one might expect, the se significant fuel burn reductions do not happen frequently
. Also, a ircraft development programs are expensive. Itis not unusual for new ty pe designs to take 8
- 10 years to develop, from preliminary

design to entry

into service. 236 , 237 ) S ignificant partial redesigns do not occur often, but are slightly

more frequent than new ty pe designs. For example, after the current significant partial redesign wave 238 has passed ( which includes the Boeing 747
- 8, Boeing 737 Max, Airbus 320 Neo, and Boeing 777
- X), we do not currentl y have knowledge of man y additional significant partial redesigns anticipated over the next decade ( as the previous wave of significant partial redesigns included the Boeing 777
- 200LR in 2004, 777
- 300ER in 2006,

233 The Independent, 2012: BA reveals Airbus A380 superjumbo flight plans , by Peter Woodman, December 11. Available at http://www.independent.co.uk/travel/news
- and
- advice/ba
- reveals
- airbus
- a380
- superjumbo
- flight
plans
- 8405961.html ( Last accessed February 5, 2015). 234 ICF International , CO 2 Analysis of CO2 -Reducing Technologies for Aircraft , Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015
. 235 Ibid. 236 Ibid. 237 Analysts estimate a ne w single aisle would have cost $10
- 12 billion to develop. The A380 and 787 are estimated to each have cost around $20 billion to develop; the A350 is estimated to have cost $15 billion , excluding engine development. Due to the large development cost of a totally new aircraft design, manufacturers are opting to re
- wing or just re
- engine their aircraft (significant partial redesigns) . Boeing is said to have budgete d $5 billion for the re
- wing of the 777 and Airbus and Boeing have budgeted $1
- 2 billion each for the re
- engine of the A320 and the 737, r espectively (excluding engine development costs). Embraer has publically stated they will need to spend $1
- 2 billion to re - wing the EMB
- 175 and variants. (ICF International, CO2 Analysis of CO2 -Reducing Technologies for Aircraft, Final Report, EPA Contrac t Number EP
- C
- 12
- 011, March 17, 2015.) 238 In general, design waves are prompted by the combination of market demand for new aircraft performance needs (e.g., more seats for longer range) and the age of existing aircraft, and design waves are typically enabl ed by advances in propulsion technology.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **153** of **198** 737NG in 1998, Airbus 319 in 1996, and Airbus 330
- 200 in 1998). 239 , 240 In cremental improvements will likely be frequent and occur in the near term. O ne approach CAEP is considering would be to limit the applicability of any international CO 2 standard to only new ty pe designs (or new aircraft t ypes). Under this approach the international CO 2 standard would not apply

to s ignificant partial redesigned aircraft and incremental improvements
. Under another approach CAEP is considering, CAEP would also apply the international CO 2 standard to in
- production aircraft (in addition to new aircraft t ypes) . S ignificant partial redesigned aircraft and incremental improvement s would be characterized as changes made to in
- production aircraft; thus, these categories of aircraft (or these changes) would need to meet the international CO 2 standard under this approach (or they would need to meet the standard if it also applied to in
- production aircraft)
. 241 The EPA requests comments on the applicability approaches that CAEP is considering. Another approach for applicability of the international CO 2 standard that CAEP could adopt (or CAEP is considering) would be an approach based on criteria addressing significant

239 ICF International, CO 2 Analysis of CO2 -Reducing Technologies for Aircraft , Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015. 240 Insofar as we are going through a wave of major redesign and service entry now , prospects for further step
function improvements will be low in the coming 10
- 15 y ears. (ICF International, CO2 Analysis of CO 2 - Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015.) 241 As described earlier, CAEP has not ruled out applying the international CO 2 standard to in
- production aircraft ty pes, which are aircraft types that have already received a Type Certificate and are produced after the effective date of the standard. In
- production aircra ft types would include significant partial redesigned aircraft and incremental improvements. CAEP is currently considering and analyzing in
- production applicability.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **154** of **198** changes to aircraft designs , which could be considered an applicability requirement different than that for new aircraft ty pes onl y and in
- production aircraft. This alternative approach could redefine a n ew aircraft t ype for CO 2 purposes to include in
- production aircraft that have a significant change in CO 2 emissions, thus including in
- production aircraft in the applicability

of the CO 2 standard. The alternative approach could even cover significant partial redesigned aircraft , depending upon the definition
. CAEP’s current mature certification requirement for the international CO 2 standard 242 provides further detail on technology change s to aircraft that would affect the aircraft’s CO 2 metric value
. A changed version of an aircraft could be defined as follows: an aircraft which incorporates changes in ty pe design that may

adversel y affect243 its CO 2 emissions. This possible definition could also note the following: (1) where the proposed change in design, configuration, power or mass is so extensive that a substantially new investigation of compliance with the applicable airworthiness regulations is required, the aircraft should be considered to be a new typ e design rather than a changed version, and (2) “adversely” refers to an increase in CO 2 emissions of more than an amount (or percentage) that has yet to be determined (this amount or criteri on is still being considered b y CAEP). The EPA requests comment on this change
- based criteria

242 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Sta ndard, Circular (Cir) 337, AN/192, Available at www.icao.int (Last accessed February 5, 2015) . See Chapter 1. 243 Due to substantial market forces to alleviate any adverse effects on aircraft fuel burn or CO 2 emissions, a dverse changes are rare.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **155** of **198** approach , including how to identify those changes that would result in treating in
- production aircraft as new ty

pes subject to the standard
. If CAEP were to limit the scope of applicability to new aircraft types onl y ( and without the significant change criteri a approach described above), the international CO 2 standard would not appl y to later series aircraft with redesigned wings, aircraft that are available with different engines , or aircraft that undergo incremental improvements. Following are several e xamples that illustrate this situation. The re
- engined Boeing 737 Max is an example of a significant partial redesigned aircraft that is expected to enter into service in 2017. 244 This aircraft would fall under the original Boeing 737 Ty pe Certificate that w as issued in 1967 (and entered into service in 1968)
-- or more specificall y it would fall under an amended T ype Certificate, and it would not be considered a new aircraft type as defined by CAEP. The current in
- production 737s (Next Generation 737s or commonly abbreviated as 737 NGs) feature newer engines , have redesigned wings, and entered service in 1998 under the original 737 Ty

pe Certificate that was issued in 1967, and these also were not considered a new ty pe aircraft when they

were introduced in 1998
. 245 Another example of an aircraft that

244 Boeing, 737 Max Program “LEAPS” into Engine Testing , Article by Eric Olson, http://www.boeing.com/boeing/Features/2014/07/bca_737max_leap_07_11_14.page , July 11, 2014. 245 The original 737 entered service in 1968. The 737 Classic entered service in 1984, and it had new high bypass engines, an updated wing, and other aerodynamic imp rovements. The 737 NGs entered service in 1998, and they featured a new wing and updated engines. Several mid
- life upgrades were produced for the 737 NGs, offering improved range, payload, and efficiency. (ICF International, CO2 Analysis of CO 2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015.)******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **156** of **198** does not qualify

as a new ty

pe is the Boeing 747
- 8 aircraft, that entered into service in 2011, and which included a new wing, new engi nes, and a lengthened fuselage but fell under an amended T ype Certificate for the original Boeing 747 that was certified in 1969 (and entered into service in 1969). An example of incremental improvements to in
- production aircraft, is the Boeing Next Gener ation 737 performance improvement package which was implemented between 2011 and 2013 and the Boeing 767
- 300 winglets that entered into service in 2008, both of which improve aircraft fuel efficiency
. There are man y other examples that exist for different manufacturers and aircraft around the world as well, but for conciseness, we are limiting our discussion to these above examples. These examples illustrate the ty pical certification for significant partial redesigns and incremental improvements by variou s aircraft certificating or certifying authorities (or national airworthiness authorities) around the world. Using CAEP’s current definition of new aircraft t ypes (clean sheet designs, which are completely

new aircraft) we cannot today identify the first aircraft to which the new standard would apply
. As the examples above illustrate, new aircraft t ypes are infrequent , 246 and there are no currentl y announced new t ype designs that are expected to be introduced after the implementation dates being anal y zed by CAEP

– 2020 and 2023. Furthermore, based on

246 ICF International , CO 2 Analysis of CO2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **157** of **198** provisions to which CAEP has already agreed , 247 new aircraft t ypes subject to the CO 2 standard would be aircraft that submit an application for a T ype C ertificate after the implementation dates of 2020 and 2023 (dates for the stringency analy sis) which would likely result in entry

into service dates of about 2025 or 2028. 248 If the international CO 2 standard is applied only

to new aircraft ty

pes, then CO 2 emissions would not be expected to begin to deviate fr om business
- as - usual ( in comparison to CO 2 emissions reductions that would be achieved in the absence of a standard) before 2025
. Therefore, an international standard developed for only

new aircraft t ypes may

not actually

appl y to an y new aircraft for at least a decade
. E ven if a few new ty pe aircraft are introduced in th is timeframe , it will take even longer for these aircraft to comprise any significant portion of the fleet. Therefore, appl yi ng an international standard which applies only to new aircra ft t ypes will likely result in no additional CO 2 reductions beyond what would have occurred absent a CO 2 standard, either for

247 ICAO , 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192, Available at www.icao.int (Last accessed February 5, 2015) . Section 1.5 states that that the date to be used in determining th e applicability of the CO 2 standard is the date the application for a Type Certificate was submitted to the certificating authority having jurisdiction over the manufacturer responsible for the aircraft design. Section 1.6 specifi es that an application shall be effective for the period specified in the designation of the airworthiness regulations appropriate to the aircraft ty pe . An application for a Type Certificate is valid for 5 years. 248 These dates assum e 5 y ears from applicat ion for the aircraft Type Certificate to entry into service, which is how long an application is valid for a Type Certificate
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **158** of **198** the near
- and mid
- term, about 5 to 1 0 years from 2016, or even in the longer
- term of 20 ye ars plus
. 249 , 250 The EPA requests comments on the timeframes for introducing new aircraft ty pes and their subsequent penetration into the fleet. Are there an y aircraft manufacturer announcements that we missed in regard to new aircraft ty pes that will be introduced or appl y for a T ype Certificate after 2020 and 2023 (or new aircraft t ypes that w i ll be introduced or apply for a Ty pe Certificate five ye ars after these dates )? 251 If so, what are these new aircraft ty pes? How many

new ty pes are projected to enter the fleet in this timeframe and what portion of the fleet will they represent ? T he alternative approach described earlier ( addressing change s in design of in
production aircraft) may

offer an opportunity

to cover more aircraft in an earlier timeframe (includ ing significant partial redesigns), but it is unclear what effect this approach would have

249 Approximate time
- scales are considered to be 5 years for near
- term , 10 y ears for mid
- term, and 20 years or mo re for long
- term. 250 ICF International , CO 2 Analysis of CO2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015. 251 In November 2014, Boeing indicated that it would replace the 737 with a new aircraft typ e in 2030. E arlier this decade , Boeing was assessing an all new clean sheet 737 replacement, but eventually they decided to re engine the 737 (the 737 Max) instead
. (Flight Club, Paul Thompson, Here's The Skinny On What's Next For Boeing, November 16, 2014. Available at http://flightclub.jalopnik.com/heres
- the
- skinny
- on - whats
- next - for
boeing
- 1656206527 , Also, Wichita Business Journal, Danie l McCoy, Boeing planning 737 MAX replacement by 2030

— What it could mean for Spirit AeroSystems , November 5, 2014. Available at http://www.bizjournals.com/wichita/blog/2014/11/boeing
- planning
- 737
- ma x - replacement
- by
- 2030
- what.html ). We would consider th is as a Boeing projection or sketching out of plans for a new aircraft type, but it is not a commitment from Boeing.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **159** of **198** on additional CO 2 emissions reductions compared to a standard for only new aircraft t ypes. The EPA requests comments on the timeframe for CO 2 emissions reduc tions and the likely share of annual aircraft production (or share of in
- production aircraft built annually) that would be affected under the alternative approach. Applying an emission standard to in
- production aircraft (if the EPA makes a positive endangerment finding), means that all aircraft that are built (in
- production) after the effective date of the regulation would need to certify and comply

with the standard to remain in produc tion
. This includes (as described earlier) in
- production aircraft with incremental improvements (though we reiterate this would not include in
- use aircraft) . As an example of in
- production aircraft, the Gulfstream G650, which is currentl y in pro duction and expected to remain so after 2020, would need to certify and comply with the new CO 2 standard. In the next section we discuss in more detail how applicability to in
- production aircraft could work
. C. **CAEP Discussion on In -**  **Production Aircraft Appl icability**  At the request of the CAEP Steering Group meeting in November 2013 , CAEP began work on defining potential options to implement applicability requirements for in
- production aircraft
. Subsequentl y, based on the options provided to the 2014 Steerin g Group meeting, CAEP decided that it should continue to investigate potential in
- production aircraft applicability options, and that these should be presented at the July 2015 Steering Group meeting, so that a decision can be taken at the 10th meeting of CAEP (CAEP/10) in February******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **160** of **198** 2016 regarding whether the international CO 2 standard will apply to in
- production aircraft. There are a wide range of options under consideration, including both mandatory and voluntary options for reporting and certification pr ocesses for in
- production aircraft applicability , but the 2014 Steering Group meeting requested that CAEP focus on defining the mandatory

options (in contrast to options such as voluntary reporting and certification)
. 1. Applicability

to In
- Production Aircraft and Date of Implementation At the 2014 Steering Group meeting, CAEP also agreed that 2023 represented the earliest possible date for an in
- production aircraft standard to allow time to promulgate domestic regulations and process manufacturer certi fication applications. CAEP did not rule out later dates though and could consider implementation dates for an in
- production aircraft CO 2 standard later than 2023 ( CAEP could consider applicabilit y date s for in
- production aircraft that are five ye ars foll owing the new aircraft ty pe applicabilit y date, i.e. dates ranging from 2023 to 2028). The EPA seeks comments on both a 2023 implementation date and on possible later implementation dates for an in
- production domestic CO 2 (or GHG) aircraft engi ne emissions standard that would be adopted under CAA section 231 , 252 the impact the date of

252 Traditionally, international emission standards have first been adopted by ICAO, and subsequently the EPA had initiated rulemakings und er CAA section 231 to establish domestic standards equivalent to ICAO’s standards where appropriate. Provided ICAO adopts an international aircraft CO 2 standard that is consistent with******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **161** of **198** implementation might have on per - aircraft GHG or CO 2 emissions rates and the ability of a domestic GHG or CO 2 standard to achieve aircraft emission reductions beyond what would occur in the absence of such a standard. Would the dates of applicability ( e.g., 2023 to 2028) be consistent with the purpose of the standard as agreed to by CAEP ? As described in section VI .F. 2 , the technologies considered for the CAEP anal ys es are those technologies that will be widely used on in
- production aircraft b y 2016 or shortly thereafter. 253 The EPA request s comments regardi ng whether appl yi ng an international CO 2 standard to in
- production aircraft is consistent with the purpose of the standard as agreed to by the CAEP Steering Group meeting in 2011 : “ to achieve CO 2 emission reductions from the aviation sector b eyond expected ‘ business as usual ’
... anal yz ed using IC AO criteria of technical feasibility , environmental benefit, cost effectiveness, and impacts of interdependencies.” 254 The International Coalition for Sustainable Aviation (ICSA) , 255 which

CAA section 231 and it is appropriate for domestic needs in the United States, we expect to proceed along a similar approach for the future CAA section 231 aircraft engine CO 2 standard (or aircraft engine GHG standard), provided the EPA issues final positive endangerment and cause or contribute findings under CAA section 231
. 253 CAEP determined in 2012 that all technology responses would have to be based on technology that would be in common use by the time the standard was to be decided upon in 2016 or shortly thereafter. This generation of technology was defined within CAEP as a Technology Readiness Level (TRL) 8

– an a ctual system completed and qualified through test and demonstration

– by 2016 or shortly thereafter. 254 CAEP (U.S. Working Paper), “U.S. Position on the Development of ICAO’S Aircraft CO 2 Standard,” CAEP
SG/20112
- WP/25 , Presented by the United States, U.S. Working Paper for CAEP Steering Group meeting, Beijing, China, 12 to 16 September 2011 . Available at http://www.epa.gov/otaq/aviation.htm
. Inte rnational Coalition for Sustainable Aviation (ICSA), “ ICAO’S CO2 Standard as Part of a Basket of Measures to Meet Emission Reduction Goals ” , ICAO Assembly
- 38th Session, Executive Committee, Agenda Item 17
- Environmental Protection, A38
- WP/297 , EX/99 , Se ptem ber 19, 20 13
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **162** of **198** is a CAEP Observer organization, submitted papers to CAEP that analy zed this issue. Also, a member of ICSA 256 has developed similar anal ys es which indicate that a ppl ying the international standard only to new aircraft types would likely result in no additional CO 2 reductions beyond what would have occurred absent a CO 2 standard, either for the near
- and mid
- term, about 5 to 1 0 years from 2016, or even in the longer
- term of 20 years plus . This occurs, the ICCT state s , because the development cycle s f or new aircraft are very

lengthy and it is not unusual for new aircraft to take 8 to 10 ye ars to develop from preliminary design to entry into service and once in service it takes significant time for new aircraf t ty pes to penetrate the fleet. 257 , 258 Another s tudy funded by

the EPA corroborates this analy sis
. 259 The EPA requests comments on whether applying the international CO 2 aircraft standard onl y to new aircraft t ypes woul d be consistent with the agreed purpose of the international standard (the purpose of the standard that has been agreed to by the CAEP Steering Group) . Lastl y, the EPA requests comment on the appropriateness of following either of th e s e approach es

255 The International Coalition for Sustainable Aviation (ICSA) is a structured network of enviro nmental non
governmental organiz ations (NGOs) who share a common concern with civil aviation’s contribution to air quality issues, climate chan ge and noise, and who are committed to developing and providing technical expertise, common policy positions and strategies with a view to reducing emissions an d noise from aviation
. See http://www.icsa
- aviati on.org/
. 256 The International Council on Clean Transportation (ICCT) is a member of ICSA, and ICCT is an independent nonprofit organization founded to provide research and technical and scientific analysis to environmental regulators. See http://www.theicct.org/
. 257 ICCT, Efficiency Trends for New Commercial Jet Aircraft 1960 to 2008, November 2009. 258 ICCT, “ Could ICAO’s CO2 Standard Not Actually Cover Any Aircraft? Yes, If Nobody’s Watching”. Blog, December 9, 2014. Available at http://www.theicct.org/blogs/staff/could
- icaos
- co2
- standard
- not - cover - any aircraft
. 259 ICF International , CO 2 Analy sis of CO2 -Reducing Technologies for Aircraft , Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **163** of **198** (applicability

to onl y new aircraft t ypes or both new aircraft t ypes and in
- p roduction aircraft) in any future CAA section 231 aircraft engine CO 2 or GHG emissions standard ( if either approach is adopted b y ICAO, and the EPA make s a positive endangerment finding). Also, there have been concerns raised in CAEP about applying the int ernational CO 2 standard to in
- production aircraft. These concerns include (a) the added resource burden on certificating authorities to process manufacturers’ certification applications, which will be more numerous compared to new aircraft t ypes; and (b) the potential added costs to manufacturers to certify

in
- production aircraft. The EPA requests comment on these two concerns, including providing supporting documentation on the extent of these concerns and any other issues the commenters may identify with applying the international CO 2 standard to in
- production aircraft
.

2. Reporting Requirement for New In
- Production Aircraft CAEP is working to define mandatory in
- production aircraft options , and one possible option is a reporting requirement260 , 261 , 262 for in
- production aircraft CO 2 emissions rates

260 Currently, CAEP is developing a publicly available database for aircraft CO 2 emissions (CAEP is now considering format, parameters, etc. for the database), but submissions to this database by aircraft manufacturers wo uld be voluntary. There will not be a CAEP mandatory reporting requirement associated with this potential CO 2 database . In addition, i f the international aircraft CO2 standard applies to only new aircraft types, it could be many years before any data exists in this database. 261 For many years, ICAO has maintained an Aircraft Engine Emissions Databank for landing and takeoff certificated emissions values of NO x , hydrocarbon, carbon monoxide, and smoke number (ICAO and the EPA******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **164** of **198** (measured according to the aircraft test procedure that was agreed upon at CAEP/9) as an alternative to establishing an aircraft CO 2 standard for in
- production aircraft
. A lthough a reporting requirement provides policy relevant information, it does not necessarily translate into specific emissions reductions
. T he EPA recognizes that only a mandatory

standard for in
- production aircraft would ensure that the aircraft CO 2 standard reduces per
- aircraft CO 2 emissions rates. However, a reporting requirement could be an important component of an in
production aircraft CO 2 standard , especiall y if it is implemented shortly after an in
- production aircraft standard is adopted. It would ensure that CO 2 emissions rates data are gathered quickly prior to an effective date for the final standard (tracking CO 2 emissions rates is beneficial for the reasons discussed later in this section and for potentiall y assisting with the assessment of a future CO 2 standard)
. The EPA request s comment on an aircraft manufacturer reporting requirement that is implemented soon after the adoption of an in
production international aircraft CO 2 standard, as a component of the in
- production aircraft CO 2 standard
.

also have aircraft engine emission standards for these pollutants). It contains certified emissions data voluntarily reported from each aircraft engine manufacturer . This databank is available at https://easa.europa.eu/document
library/icao
- aircraft
- engine
- emissions
- databank
. 262 In 2012, the EPA promulgated annual reporting requirements for aircraft engine emissions of NO x , hydrocarbon, carbon monoxide, and smoke number and related parameters. One of the reasons that the EPA issued these reporting requirements was due to the varying amount of voluntary data reported by aircraft engine manufacturers. ( U.S. EPA, “Control of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test Procedures”. Final Rule, 77 FR 36342, June 18 , 2012).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **165** of **198** In 2009 the EPA promulgated a final GHG reporting rule that applies to many sectors in the United S tates , including manufacturers of heav y - dut y and offroad vehicles and engines , and manufacturers of aircraft engine s . 263 , 264 The EPA’s experience with reporting programs indicates that the E PA and the public would be able to track CO 2 emissions rates trends (i.e., trends of aircraft cruise fuel burn rates) from aircraft over time. Requiring the reporting of aircraft CO 2 emissions rates trends from aircraft over time is appropriate and feasible. Requiring aircraft manufacturers to report aircraft CO 2 emissions rates shortly after an in
production international aircraft standard is adopted would enable and expedite the tracking and understanding of these emission trends. In addition, reporting programs ty picall y raise awareness of emissions and can improve the understanding of the factors that influence emission rates as well as the actions that can be taken to reduce emissions. Wh en similar methods for monitoring, measurement, and reporting are applied across an industry , it can

263 EPA’s 2009 rule on Mandat ory Reporting of Greenhouse Gases included engine manufacturers for the following mobile source sectors: highway h eavy - duty (engine and vehicle) , non - road, aircraft, locomotive, marine , snowmobiles, and motorcycles. Manufacturers of aircraft jet engines o f rated output (or thrust) greater than 26.7 kilonewtons are required under this program to report annually to the EPA CO 2 and NO x emissions from aircraft engines during the landing and takeoff cycle. Manufacturers of these engines wer e already measuring and recording CO 2 emissions as part of existing criteria air pollutant emission requirements fo r the landing and takeoff cycle, but prior to this 2009 rule, these data w ere not reported to the EPA . M anufacturers voluntarily report ed the data to ICAO, but there was no assurance that the EPA would receive this information, and thus, the 2009 rule required reporting of the aircraft engine CO 2 and NO x emissions during the landing and takeoff cycle to the EPA. 264 An aircraft manufacturer rep orting require ment for in
- production aircraft CO 2 emission rates wo uld require the reporting of aircraft CO 2 emissions during the cruise phase of operation to the EPA. The majority of aircraft CO 2 emissions occur s i n the cruise phase of operation , and thus , reporting CO 2 emission rates from this phase will improve our ability to track full
- flight aircraft CO 2 emission rates over time (in addition to reporting the aircraft engine CO 2 emissions during the landing and takeoff cycle)
. Also, the aircraft test procedure that was agreed upon at CAEP/9 now enables us to measure aircraft CO 2 emissions during cruise.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **166** of **198** lead to more consistent, accurate, and timel y data to inform decision
- making for individual manufacturers and the EPA (including a comparison of the CO 2 em issions rates from aircraft of various manufacturers) . Thus, a reporting requirement could potentially contribute to efforts to identify

and implement future aircraft CO 2 emission reduction opportunities. Independent of action that CAEP may or may not t ake in February

2016, the EPA could under its CAA section 114(a) authorit y pursue a reporting requirement for aircraft cruise GHG or CO 2 emissions rates

– to ensure we have GHG or CO 2 emissions rates data on all in
- production aircraft (and an y new aircraft types that enter service). 265 The EPA could use the same metric agreed to at CAEP/9 (and in ICAO circular 337). This will be described in detail in VI .D. 1 below. In general, the EPA asks for comment on a mandatory reporting requirement for in
- production aircraft GHG or CO 2 emissions rates

– either as part of the CAEP international standard or as an independent domestic require ment to be adopted by the EPA. If the EPA were to pursue this requirement independentl y from CAEP, what lead time would be appropriate for manufacturers to report the GHG or CO 2 emissions rates from all of their in
- production aircraft266 (after we pr omulgate such a requirement)? Additionally , if we

265 This GHG or CO 2 emissions rate data will help to track trends, raise awareness, better understand the technology in the fleet, etc. 266 In this case, manufacturer s would need to report the GHG or CO 2 emission rates for in
- production aircraft (aircraft types which have already received a Type Certificate, and for which manufacturers either have existing undelivered sales order or would be willing and able to accept new sales orders) that are built after a certain date, which has yet to be determined but would likely be a date that occurs shortly after we promulgate the requirement.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **167** of **198** were to pursue such an independent reporting requirement, should we require the annual reporting of the GHG or CO 2 emissions rates from in
- production aircraft ( and an y new t yp e aircraft) 267 to enable us to track an y updates? We are not at this time proposing to promulgate such a requirement in advance of IC AO’s decision. Due to the possibility of I CAO’s adoption of a reporting requirement, we believe it is reasonable to await the outcome of that decision in order to determine whether to strictl y follow I CAO’s possible reporting requirement or make changes to it in the form of an additional U.S. domestic requirement, as appropriate. D. **Metric System, Applicability, and Certification Requirement** T he CO 2 metric sy stem and mature certification procedure were agreed upon by CAEP in 2013. 268 This section describes the metric sy stem that was developed, the scope of aircraft to be covered b y the international CO 2 standard, the certification test procedures that would be used to demonstrate compliance with the international CO 2 standard, and CAEP’s decision to focus on the entire aircraft for the international CO 2 standard
.

267 By applying a reporting requirement to in
- production aircraft after a certain implem entation date, this reporting requirement also includes ne w aircraft types that are produced after this implementation date. 268 As described earlier, the certification requirement is the combination of metric, procedures, instrumentation and measurement methodology, and compliance requirements. We are using the terms metric system and certification test procedures to describe these elements of the certification requirement.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **168** of **198**

1. CO 2 Metric Sy stem The metric s ys tem was developed to cover a wide range of aircraft t ypes, des igns, technology , and uses. To do this, the metric sy stem was designed to differentiate between generations of aircraft and to equitably capture improvements in aerospace technology (structural, propulsion, and aerodynamic) that contribute to a reduction in the airplane CO 2 emissions. In addition, the metric s ys tem accommodates a wide range of technologies and designs which manufacturers may choose to implement to reduce CO 2 emissions from their aircraft. The metric s ys tem agreed to at CAEP uses multiple Specific Air Range (SAR) test points to represent cruise fuel burn. SAR is a traditional measure of aircraft cruise performance which measures the distance an aircraft can travel for a unit of fuel. This i s similar to the instantaneous “miles per gallon” readings in many cars today
. However, here the invers e of SAR is used (1/SAR); therefore a lower metric value represents a better fuel efficiency . The SAR data are gathered at three gross weight points. The three equally weighted points are used to represent a range of day to day aircraft operations. 269 The functional form of the metric s ys tem is provided below.

269 ICAO Circular 337
- AT /192.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **169** of **198** = 1

. **Equation 1**  **: CO**  **2 Metric**  (1/SAR) avg is calculated at 3 gross weight fractions of Maximum Take o ff Mass (MTOM): High gross mass: 92% MTOM Mid gross mass: Average of high gross mass and low gross mass Low gross mass: (0.45 * MTOM) + (0. 63 * (MTOM ^ 0.924 ) ) The Reference Geometric Factor (RGF) is a measure of the fuselage size on a given aircraft. In anal yz ing various metric sy stem options it was found that in some instances, namely stretch aircraft, changes in aircraft size, and thus capability , were not ref lected in changes to the aircraft’s gross weight (MTOM). To account for these occurrences, and the variet y of methods that manufacturers may use to make such a change, an adjustment factor was added (the RGF with a 0.24 exponent used in the metric s ys tem)
.

2. Applicability CAEP has decided the scope of applicabilit y for a future international CO 2 standard should be subsonic jet and propeller
- driven aircraft meeting the following criteria :******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **170** of **198** All subsonic jet aircraft over 12,566 lbs (5,700 kg) MTOM. All subsonic propeller driven (e.g. turboprop) aircraft over 19,000 lbs (8618 kg) MTOM, except amphibious airplanes and those designed and used for fire
- fighting operations. No military

aircraft will be subject to this international standard. 3. C ertification require ment CAEP has developed a mature certification requirement270 that would allow for the determination of an aircraft CO 2 metric value for any aircraft meeting the applicability criteria set forth above. This certification requirement incud es the metric s ys tem and test procedure. The test procedure was based upon industry ’s current best practices for establishing the cruise performance of their aircraft, and input from certification authorities. These procedures include specifications for a ircraft conformity , weighing, fuel specifications, test condition stability criteria, required confidence intervals, measurement instrumentation required, and corrections to reference conditions.

270 ICAO, 2013: CAEP/9 Agreed Certification Requirement fo r the Aeroplane CO 2 Emissions Standard, Circular (Cir) 337, AN/192 , Available at www.icao.int (Last accessed February 5, 2015).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **171** of **198** These CO 2 test procedures are based upon manufacturer’s exi sting practices when certifying new aircraft. This means that there is a very heav y reliance on dedicated flight testing of the aircraft. This potentially poses challenges for the certification of in
- production aircraft. Manufacturers have stated that ther e could be logistical challenges associated with the certification of aircraft for CO 2 that have previously been ty pe certificated (e.g. procuring and instrumenting an aircraft for flight testing). To address this, the EPA is currentl y working within CAEP to encourage the development of a modified or separate equivalent certification test procedure that would reduce this burden on manufacturers and allow for quicker/simpler certification of in
- production ty pes. 4. Regulating the Entire Aircraft Instead of the Engine The CO 2 metric sy stem intends to equitably reward improvements in aircraft technologies that reduce emissions, including advances in structures (aircraft weight), propulsion (engine specific fuel consumption), and aerodynamics
. T hese three fac tors are key to the overall aircraft CO 2 emissions. In addition, CAEP has indicated ( and EPA agrees ) that it is best to consider the aircraft as a whole instead of only the aircraft engine technology in addressing factors that influence CO 2 emissions, because of the effect s and interaction these******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **172** of **198** key factors have on the aircraft CO 2 emissions from engines
. 271 The three factors
-- and technology

categories that improve these factors
-- are des cribed as follows : 272 S tructures: reducing basic aircraft weight to increase the commercial payload or extend range for the same amount of thrust and fuel burn; P ropulsion (thermody

namic and propulsion efficiency) : advancing the overall specific performance of the engine, to reduce the fuel burn per unit of delivered thrust; and Aerod ynamics: advancing the aircraft aerodynamics, to reduce drag and its a ssociate impacts on thrust. Specific examples of technologies that affect these three factors help to furth er illustrate that it is best to consider the aircraft as a whole in addressing CO 2 emissions. For structural improvements, aircraft manufacturers have shown significant weight reduction results over time due to the progressive introduction of new technol ogies such as: advanced alloy s and composite materials, improved and new manufacturing processes and techniques

271 ICAO, 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192 , Available at www.icao.int (Last accessed February 5, 2015). 272 ICAO, Environmental Report 2010

– Aviation and Climate Change , 2010, which is located at http://www.icao.int/environmental
- protection/Pages/EnvReport10.aspx
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **173** of **198** (including integration and global evaluation simulation ), and new s ys tems ( e.g. fly
- by
wire ). 273 , 274 For propulsion improvements, technologies include enhanced compressors (e.g., i ntercooled compressors ) and r educed hub
- tip ratio fan s . 275 As another example, manufacturers seek higher operating pressure ratios (OPR) to improve combustion and engine cycle refinements. For aerodynam ics, friction and lift
- dependent drag are the biggest contributors to aerod ynamic drag. Advances in aerody namics enable significant lift
- dependent drag reduction b y maximizing effective wing span extension. For example, wing
- tip devices can give an inc rease in the effective aerodyn amic span of wings, particularl y where wing lengths are limited by

airport gate sizes. Manufacturers are also looking at way s of decreasing the drag caused b y skin friction. An example of a technology to improve aircraft local skin friction is to utilize riblets (which are micro
- grooves on the surface) to maintain laminar flow via Natural Laminar Flow and Hy brid Laminar Flow Control (HLFC) to reduce turbulent skin

273 Ibid. 274 Fly
- by
- wire refers to a system which transmits signals from the cockpit to the aircraft's control surfaces ele ctronic ally rather than mechanically (AirlineRatings.com, see http://www.airlineratings.com/did
- yo u know.php?id=18 . Last accessed on April 17, 2015). 275 ICF International , CO 2 Analysis of CO2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **174** of **198** friction. 276 The first production example of a HLFC sy stem went into service on the new Boeing 787
- 9 in 2014. E. **Stringency Options** At the Steering Group meeting in November 2013, CAEP agreed to analyze a range of CO 2 stringency

options that cover the full range of aircraft in
- production and in
- development around the world (within the applicable weight thresholds and categories), and this includes the wide range of technology that is currentl y in the aircraft fl eet. 277 Generally, the stringency opti ons that are being evaluated fall into three categories as follows: (1) CO 2 stringency levels that c ould impact 278 only the oldest, least effi cient aircraft in
- production around the world, (2) middle range CO 2 stringency levels that c ould impact many aircraft currentl y in
production and comprising much of the current operational fleet, and (3) CO 2 stringency levels that could impact aircraft that have either just entered production or are in final design phase but will be in
- production by the time the international CO 2 standard becomes effective. We are requesting comment on the level (s) at which the CO 2 stringency options should be set,

276 ICAO, Environmental Report 2010

– Aviation and Climate Change , 2010, which is located at http://www.icao.int/environmental
- protection/Pages/EnvReport10.aspx
. 277 The ICAO standard has the following applicability weight threshold s: ma ximum takeoff mass greater than 5,700 kilograms for subson ic jet a ircraft and ma ximum takeoff mass greater than 8 , 618 kilograms for turboprops
. 278 The aircraft shown in these charts are in
- production and current in
- development. These aircraft could be im pacted by an in
- production standard in that, if they were above the standard, they would need to either im plement a technology response or go out of production. For a new ty pe only standard there will be no regulatory requirement for these aircraft to respond.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **175** of **198** what factors should be considered in establishing the stringency of the CO 2 standard, and on their potential relationship to any future CAA section 231 standard. The figures below are intended to show the range of stringency levels under consideration at CAEP and CO 2 metric value levels of today ’s in
- production and in
developm ent 279 aircraft
. The data shown were generated by the EPA using a commerciall y available aircraft modeling tool called PIANO. 280 This model contains non
- manufacturer provided estimates of the performance of various aircraft. In contrast, CAEP is using manufacturer
- provided estimates of the aircraft metric value performance. The stringency

options under consideration at CAEP are functions of the aircraft CO 2 Metric Value and have a correlating parameter of MTOM. They are upwards sloping and have a “kink” at 60 ,000 kilograms MTOM . The “kink” was included in the stringency options as a technical approach to reflect the different behaviors observed between the larger and smaller aircraft. The official stringency

options under consideration at CAEP have not been cleared for release outside of the participating members since deliberations on the standard are still

279 Aircraft that are currently in
- development but will be in production by the applicability dates. These could be new types or significant p artial redesigned aircraft. 280 PIANO (Project Interactive Analysis and Optimization), Aircraft Design and Analysis Software by Dr. Dimitri Simos, Lissys Limited, UK, 1990
- present; www.piano.aero . This is a commercially available aircraft design and performance soft ware suite used across the industry, and academia******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **176** of **198** ongoing (proceedings are expected to be completed at CAEP/10 in February 2016). To show the relative efficiency

of the aircraft , Figure 1 and Figure 2 below show the aircraft metric values 281 v er s us MTOM . In place of the official stringency options under consideration, lines of constant technology are used to notionally show how the stringency options were set across the fleet. These lines reflect the three ranges of options discussed above. Lower metric values, for a given MTOM, represent an increased fuel efficiency
. Figure 1 shows the makeup of the current production fleet and the in
- development aircraft. This is what CAEP is using as the starting point for modeling the a ffect of the CO 2 s tandard . Figure 2 s hows what the EPA expect s the market to look like in 2023, considering the publicl y announced plans by industry to replace existing aircraft with new products.

281 Metric values were generated using PIANO.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **177** of **198 Figure**  **1**

**– Lines of constant technology level over the**  **2014 in -**  **production and in**  **development fleet**  0.0 0.5 1.0 1.5 2.0 2.5 3.0

0 100000 200000 300000 400000 500000 600000**A i** **r c** **r a** **f t** **M e** **t r** **i c** **V a** **l u** **e (** **l o** **w e** **r v** **a l** **u e** **r e** **f l** **e c** **t s** **l o** **w e** **r C** **O 2** **e m** **i s** **s i** **o n** **s )** 

**MTOM (kg)** Lines of Constant Technology Level In Production In Development******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **178** of **198 Figure**  **2**

**– Lines of constant technology level over the predicted 2023 in**  **- production fleet** 

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0 100000 200000 300000 400000 500000 600000**A i** **r c** **r a** **f t** **M e** **t r** **i c** **V a** **l u** **e (** **l o** **w e** **r v** **a l** **u e** **r e** **f l** **e c** **t s** **l o** **w e** **r C** **O 2** **e m** **i s** **s i** **o n** **s**

**MTOM (kg)** Lines of Constant Technology Level In Production******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **179** of **198** A standard set near the upper - most line of constant technology in Figures 1 and 2 would affect a very

modest number of aircraft, namely the oldest, least efficient ty pes. Many of the aircraft that would be affected b y such a stringency level are being produced in very li mited numbers and may not be eligible to operate in U.S. air spac e (e.g., Russian and Ukraine aircraft)
. Aircraft around the middle two lines of constant technology in Figures 1 and 2 reflect the performance of man y aircraft that are currentl y in production and compose much of the current operational fleet. The current generation of single aisle aircraft from Boeing and Airbus are in this middle range. Aircraft near the low est line of c onstant technology in Figures 1 and 2 reflect the most advanced aircraft currentl y for sale on the market. These are aircraft that have either just entered production or are still in
- development but will be in
- production by the effective date of a potential in
- production the standard. The replacement single aisle aircraft and new twin aisle aircraft from Boeing and Airbus are modeled to be clustered around the lowest line
. While Figure s 1 and 2 show the range s of stringency under consideration and how aircraft fall within those ranges , because of the scale , it is hard to see the range of technology present in the fleet. Therefore Figure 3 and 4 expand the view and sho w percent difference s between the four constant technology lines represented in Figure s 1 and 2 . This allows for a clearer view of best and worst performing aircra ft; Figure 3 provides the perspective from the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **180** of **198** current in
- production and in
- development fleet, and Figure 4 projects out to the 2023 fleet
. In addition, these figures allow one to compare the technology level and effi ciency

of aircraft with differing MTOMs.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **181** of **198 Figure**  **3**

**– Percent from least efficient line of constant technology for the 2014 in** 

**production and in development fleet** -35% -30% -25% -20% -15% -10% -5% 0% 5%

0 100000 200000 300000 400000 500000 600000**M a** **r g** **i n** **t o** **H i** **g h** **e s** **t L** **i n** **e o** **f C** **o n** **s t** **a n** **t T** **e c** **h n** **o l** **o g** **y**

**MTOM (kg)** Lines of Constant Technology Level In Production In Development******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **182** of **198 Figure**  **4 -**  **Percent from least efficient line of constant technology for the predicted 2023**  **in**

**– production fleet**  -35% -30% -25% -20% -15% -10% -5% 0% 5%

0 100000 200000 300000 400000 500000 600000**M a** **r g** **i n** **t o** **H i** **g h** **e s** **t L** **i n** **e o** **f C** **o n** **s t** **a n** **t T** **e c** **h n** **o l** **o g** **y**

**MTOM (kg)** Lines of Constant Technology Level In Production******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **183** of **198** The EPA requests comment on a range of stringency options within the constant technology

lines identified in Figure 1 and Figure 2 , on their potential impact, and on their potential relationship to any future CAA section 231 standard. CAEP is considering the possibility of adopting two separate CO 2 stringency levels, one for new ty

pe aircraft and one for in
- production aircraft. This would allow stringencies to be set for both new ty

pes and in
- production aircraft at a level closer to what could be achieved by each aircraft t ype. Issues surrounding the potential for in
- production standards are discussed in section VI .C. 1
. There is ongoing discussion on what appropriate levels of stringency may be for new ty pe and in
- production aircraft. An y final decisions will have to wait until the full anal ys is has been conducted at CAEP. As explained in sections VI
. B and VI .C. 1 , new ty pes are infrequentl y developed and typicall y represent a step change in technology. It may be possible to set a level of stringency that is reasonable for in
- production aircraft to meet, but at the same time provide an incentive for new type aircraft to improve. However, this is challenging to devel op because of the significant efficiency improvements ty

pically seen between in
production and new t ype aircraft . The EPA requests comment on the potential for developing a standard with two stringency levels at CAEP
. The development of a new aircraft ty pe standard must take into consideration the standard ’ s potential effect on any future t ype designs . Even the most stringent option under******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **184** of **198** consideration at CAEP is still based on technology available today . An y new ty pe aircraft that may be deve loped and certified 10 years or more from now would be expected to use more advanced fuel efficient technology that is not yet developed or tested. The implications for an in
- production standard are more significant in the near term for manufacturers. Air craft currentl y in
- production, and not meeting the level of an in
production standard, would need to be modified to meet the standard to remain in production; this would take time and resources from the manufacturers. The full implications of this have
no t yet been resolved in CAEP. However, we expect that the effect on aircraft CO 2 emissions would be minimal for less stringent options. The aircraft with the highest CO 2 metric values generall y rel y on older technolog y and were designed in the 1980’s to earl y 1990 ’s. Man y of these aircraft are also expected to be replaced with updated versions in the near future, before a CO 2 standard would be implemented and go into effect. The EPA requests comment on the levels at which in
- production and new ty pe standards might be set and on what factors should be considered in establishing the stringency
. F. **Costs, Technology Responses for Stringency Options, and Cost -**  **Effectiveness Analysis**  The EPA has been involved in CAEP’s effort to analyze the CO 2 stringency opti ons and the potential costs and environmental impacts that would result from both new ty pe only CO 2 standards and in
- production international CO 2 standards. CAEP is still determining the******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **185** of **198** best way to conduct portions of this analy sis. The inputs that hav e been developed b y the CAEP include non
- recurring costs data and technology responses for the various stringency options under consideration. This section describes the development of these inputs. The EPA requests comments on how the modeling should be conducted to differentiate in
production and new t ype scenarios.

1. Non
- Recurring Costs (engineering development costs) CAEP developed a single cost estimate that could be used for all aircraft as a function of MTOM and percent metric value improvement required. Based on past practice, industry provided estimates for developing clean sheet designs and significant partial redesigns, only including high level information that has been made available to the public. This was considered to be a top down est imate because it included all aircraft development costs (airworthiness certification, noise, etc.) not just those for CO 2 improvements. Since the initial dataset provided b y industry onl y included major changes (or major improvements) , the EPA saw the need to supplement this dataset with an estimate of CO 2 - only changes (or CO 2 - only improvements) , which was considered to be a bottom up estimate. These changes would be much smaller, on the order of a few percent, and could be applied to in
- production aircraft at a cost much lower than projected b y industry
. The EPA contracted with IC F International to develop an estimate of the cost to modify in production aircraft to comply with a CO 2 standard. ICF International conducted a de tailed literature search,******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **186** of **198** conducted a number of interviews with industry leaders, and did its own modeling to estimate the cost of making modifications to in production aircraft. 283 The results from this peer reviewed study (small changes) were then combined with inputs from the industry and the other CAEP participants (large changes) to develop the CO 2 technology response and cost estimation. For the cost estimation, the CAEP combined the two different methodologies to develop the final cost surface. 284 A top
- down approach i s being used to model large changes to aircraft design, such as what would be seen in significant partial redesigns or new types. For significant partial redesigns that result in new series of an es tablished model, these ty pes of changes may include : redesigned wings, new engine options, longer fuselages, improv ed aerod ynamics, or reduc ed weight. When making significant changes to an aircraft man y other changes and updates get wrapped into the proc ess that do not have an effect on the CO 2 emissions of the aircraft , and significant partial redesigns may not have been spurred by changes to fuel efficiency (CO 2 reductions)
. This confluence of changes led CAEP to agree that it was reasonable to use the full development cost for a new ty pe (clean sheet) or significant partial redesign for major changes. Total costs for past projects were used to estimate non
- recurring cost for the CAEP anal ys is. This ty pe of aircraft improvement/development program has

283 ICF International , CO 2 Analysis of CO2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015
. 284 The two datasets were merged together and a single cost surface was then generated to calculate the cost to mo dify any aircraft based on the MTOM, and percent metric value change needed.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **187** of **198** historically

ranged approximately

from 1 to 15 billion Dollars (U.S.) depending on the size of the aircraft and scope of the improvements desired. A bottom
- up approach was used , by CAEP, to model smaller incremental metric value changes to aircraft design. The CAEP agreed that the above top
- down approach would not be the best approach for minor changes or incremental improvements because the significant design efforts include many changes that would not be required for smaller CO 2 reductions. The E PA used the information gathered b y IC F International to provide input on the cost for individual technologies which were used to build up non
- recurring costs for these incremental improvements (a bottom
- up approach). The technologies available to make i ncremental improvements to aircraft is wide ranging and aircraft specific. Some examples of technologies that could be integrated into an aircraft for incremental improvements include improved fan blade design or reduction in turbine clearances in the engi ne, reducing the gap between control surfaces, carbon brake pads, or advanced wing tip devices. As an example, I CF International estimated that depending on the additive nature of specific technolog ies and the magnitude improvement required, the cost to i ncrementally improve the Boeing 767 could******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **188** of **198** range from approximately 230 million to 1.3 billion US dollars (3.5% to 11% metric value improvement)
. 285

2. Technology

Responses When CAEP started to develop the technology responses for the stringency options, a determination needed to be made on what level of technology could be considered as a response to the standard. At the outset, CAEP decided the international CO 2 standard would be a technology

following standard, rather than a technology forcing one. Thi s means that the international standard would reflect a level of emissions performance that is already achieved by some portion of current in
- production aircraft. Additionally , CAEP determined in 2012 that all technology

responses would have to be based o n technology that would be in common use by the time the standard was to be decided upon in 2016 or shortly thereafter
. This generation of technology was defined within CAEP as a Technology Readiness Level (TRL) 8 286

– an a ctual s ys tem completed and qualified through test and demonstration

– by 2016 or shortly thereafter. This means that the technology responses considered for the future international CO 2 standard, going into effect internationally in 2020 or 2023 for new types

285 ICF International , CO 2 Analysis of CO2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
- 12
- 011, March 17, 2015
. 286 TRL8 is a measure of Technology Readiness Level. “ Technology has been proven to work in its final form and under expected conditions. In almost all cases, this TRL represents the end of true system development. Examples include developmental test and evaluation of the system in its intended
... system to determine if it meets design specifications .” TRL is a scale of 1 to 9, 1 being conceptual design, and 9 being large scale commercial use. As defined by the US Department of Defense in: DOD Deskbook 5000.2

-R Appendix 6
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **189** of **198** and potentially

in 2023 or later for in
- production, are based on what will be in operation by 2016 or shortly

thereafter. EPA is requesting comment on the approach of establishing a new ty pe standard in 2020 or 2023 and in
- production standard for 2023 and later based on proven 2016 technologies
. In addition the EPA request s comment on how the purpose of the standard , to achieve reductions beyond what would have been achieved in the absence of a standard , can be attained considering the technology response assumptions agreed to at CAEP
. 3. Cost Effectiveness Analysis CAEP is currently

conducting the cost effectiveness analy sis for new
- ty pe and in
production aircraft. With rare exceptions CAEP has historically developed new ty

pe onl y standards. To model cost impacts o f a new t ype standard, CAEP has historically used an assumption that the in
- production aircraft will respond to the new ty pe standard, even though the standard would not apply to them and has assumed that the aviation sector is competitive enough that mark et forces will drive manufacturers to voluntarily upgrade their fleet to meet any new t ype aircraft standard. This scenario is modeled no differentl y from a mandatory in
production standard. The EPA requests comment on modeling cost and environmental impacts of new
- ty

pe standards based on the assumed attainment of such emissions levels by in
- production aircraft.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **190** of **1 98**  Because CAEP has modeled all in
- production aircraft as respond ing by the implementation date of the new - ty pe standard, CAEP has by definition , performed an in
production anal ys is. M ore stringent options for new
- ty pe aircraft may

be restricted due to the assumed in
- production impacts. CAEP has recognized that its past methods for modeling a new
- ty pe onl y standard (b y assuming in
- production airc raft comply) may not be sufficient for the CO 2 standard analy sis. Thus, CAEP developed new methods to model what cost and environmental impacts would result from only

new t yp es being regulated under a new
- ty pe emission standard. CAEP is still determin ing the best way to conduct an analy sis of impacts only on new t yp es using the agreed upon technology

responses and cost estimates . The EPA requests comments on how to model cost impacts for only new t yp es for the future international CO 2 standard , if it were to apply onl y to new t ypes. The EPA also requests comment on how the modeling should be conducted to differentiate in
- production and new ty pe scenarios. G. **Request for Comment on Potential for a Different EPA Standard than International CO**  **2 Stand**  **ard** As described earlier in section I I .E , traditionally international emission standards for aircraft have first been adopted by I CAO, and subsequently the EPA has initiated rulemakings******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **191** of **198** to establish domestic standards that are of at least equal stringency as IC AO’s engine standards. However, the Chicago Convention, 287 which established ICAO, recognizes that ICAO member s tates may adopt their own unique standards that are more stringent than ICAO standards
. A participating m ember s tate (or n ation) that adopt s more stringent standards is obligated to notify I CAO of the differences between its standards and I CAO ’s standards
. 288 S ection 231(b) of the CAA requires that an y emission standards “ take effect after such period as the Administrator fin ds necessary (after consultation with the Secretary of Transportation) to permit the development and application of the requisite technology , giving appropriate consideration to the cost of compliance during such period. ” 42 U.S.C. 7571(b). S ection 231(a) (2)(B) provides that the Administrator shall consult with the Administrator of the FAA on standards, and “ shall not change the aircraft engine emission standards if such change would significantly increase noise and adversel y affect safet y. ” 42 U.S.C. 7571 (a)(2)(B).

287 ICAO, “Convention on International Civil Aviation,” Ninth Edition, Document 7300/9, 2006. Copies of this document can be obtained from the ICAO website located at www.icao.int
. 288 According to the Chicago Convention, a participating membe r State that ado pt s regulations or practices differing in any particular respect from those established by an international standard is obligated to notify ICAO of the differences between its standards and ICAO’s standards. However, member States that wish to use aircraf t 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.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

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Page **192** of **198** As discussed in the 2005 rule (CAEP/4 aircraft engine NO x standard) , 289 the EPA needs to have a technical basis for expecting the standards will be achievable in a specific period of time. While the statutory language of section 231 is not identical to other provisions in title II of the CAA that direct the EPA to establish techno logy
- based standards for various ty pes of mobile sources , the EPA interprets its authority under section 231 to be similar to those provisions that grant us significant discretion to identify a reasonable balance of specified emissions reduction, cost, saf et y, noise, and other factors. See, e.g., Husqvarna AB v. EPA , 254 F.3d 195 (DC Cir. 2001) (upholding the EPA’s promulgation of technology
based standards for small non
- road engines under section 213(a)(3) of the CAA). The EPA has significant discretion under section 231 in determining what standard is most reasonable for aircraft engine emissions . In this regard, we note CAEP’s agreed policy for the purpose of the international CO 2 standard (as agreed to by the CAEP Steering Group in 2011) , which is to achieve emissions rate reductions beyond that which would have occurred in the absence of a standard. In ruling on a petition for judicial review of the 2005 rule , 290 the U.S. Court of Appeals for the D.C. Circuit held that the EPA’s approach in that action of tracking the ICAO standards was reasonable and permissible under the CAA. NACAA v. EPA , 489 F.3d 12 21,

289 U.S. EPA, “Control of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test Procedures;” Final Rule, 70 FR 2521, November 17, 2005. 290 Ibid
.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **193** of **198** 1230
- 32 (D.C. Cir. 2007). T he Court also held that section 231 of the CAA confers a broad degree of discretion on the EPA to adopt aircraft emission standards that the Agency determines are reasonable. Id
. The EPA requests comment on our traditional approach of establishing domestic standards of at least equivalent stringency to ICAO’s standards. Should we follow th is same approach, as we have in the past? Also, the EPA asks for comment on the possibility of the EPA adopting a different GHG standard than ICAO, provided ICAO/CAEP adopts a standard in 2016 and the EPA makes a positive endangerment finding. For this possibility, the EPA requests that commenters consider the following factors (among others) : the potential to reflect the GHG performance of products from U.S. manufacturers, competitive advantages and disadvantages for manufacturers , and certif ication reciprocity with certificating authorities of other nations
. Inaddition, the EPA asks for comment on what action the EPA should take if I CAO/CAEP fails to adopt a CO 2 standard in 2016. We also invite comment on any other topic in regard to the connection between the EPA and ICAO standards. 

## VII. **Statutory Authority and Executive Order**  **Reviews Executive Order 12866: Regulatory Planning and Review and Executive Order**  A. **13563: Improving Regulation and Regulatory Review** This action is a significant regu latory action because it raises novel policy issues. Accordingl y, it was submitted to the Office of Management and Budget (OMB) for review.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **194** of **198** This action proposes a finding that GHG emissions from aircraft cause or contribute to air pollution that may be reasonably anticipated to endanger public health an d welfare along with
an ANPR which provides an overview of the i nternational efforts to reduce GHG emissions, progress to date in establishing global aircraft standards that achieve meaningful CO 2 redu ctions and, if the EPA finds that aircraft GHG emissions do cause or contribute to endangerment, the potential use of CAA section 231 to implement these standards dom estically

e nsuring transparency

and the opportunity

for public comment. Any changes made in response to OMB recommendations have been documented in the docket. **B. Paperwork Reduction Act (PRA)**  This action does not impose an information collection burden under the PRA. The proposed endangerment and cause or contribute f inding s under CAA section 231 do not contain an y information collection activities. **C. Regulatory Flexibility Act (RFA)**  I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. This acti on will not impose any requirements on small entities . The proposed endangerment and cause or contribute f inding s under CAA section 231 do not in
- and
- of
- themselves impose any

new requirements but rather set forth the Administrator’s proposed determin ation that GHG emissions from certain classes of aircraft engines

—those used in U.S. covered aircraft

— cause or contribute to air pollution that may be******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **195** of **198** reasonabl y anticipated to endanger public health and welfare. Accordingl y, this action affords no opportunity

for the EPA to fashion for small entities less burdensome compliance or reporting requirements or timetables or exemptions from all or part of the proposal
. **D. F**  **unded Mandates Reform Act (UMRA)** This action does not contain an y unfunded mandate as described in UMRA, 2 U.S.C. 1531

– 1538, and does not significantl y or uniquel y affect small governments. The action imposes no enforceable duty on an y state, local or tribal governments or the private sector. **E. Executive Order 13132: Federalism**  This action does not have federalism implications
. Itwill not have substantial direct effects on the s tates, on the relationship between the national government and the s tates, or on the distribution of power and responsibilities among the various levels of government . **F. Executive Order 13175:**  **Consultation and Coordination with Indian Tribal Governments**  Thi s action does not have tribal implications as specified in Executive Order 13175
. The proposed endangerment and cause or contribute f inding s under CAA sectio n 231 do not in
- and
- of
- themselves impose an y new requirements but rather set forth the Administrator’s proposed determination **t**hat GHG emissions from certain classes of aircraft engines

—those used in U.S. covered aircraft

— cause or contribute to air pollut ion that may be reasonabl y anticipated to endanger public health and welfare. Thus, E xecutive O rder 13175 does not apply to this action.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **196** of **198 G.**  **Executive Order 13045: Protection of Children from Environmental Health Risks and Safety Risks**  This action is not subject to Executive Order 13045 because it is not economically significant as defined in Executive Order 12866. The Administrator considered climate change risks to children as part of this proposed endangerment finding under CAA section 231. This action’s discussion of climate change impacts on public health and welfare is found in s ection IV of th is preamble. Specific discussion with regard to children are contained in section s IV and I. D of the preamble titled “Children’s Environmental Health
. ” A cop y of all documents pertaining to the impacts on children’s health from climate change have been placed in the public docket for this action. **H. Executive Order 13211: Actions Concerning Regulations That Significantly**  **Affect Energy Supply, Distributio n or Use**  This action is not a “significant energy action” because it is not likely to have a significant adverse effect on the supply , distribution or use of energy
. Further, we have concluded that this action is not likely to have any

adverse energy

eff ects because the proposed endangerment and cause or contribute finding s under section 231 do no t in
- and
- of themselves impose an y new requirements but rather set forth the Administrator’s proposed determination that GHG emissions from certain classes of aircraft engines

—those used in U.S. covered aircraft

— cause or contribute to air pollution that may be reasonably

anticipated to endanger public health and welfare.******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **197** of **198 I.**  **National Technology Transfer and Advancement Act (NTTAA)**  This action does not involve technical standards. **J. Executive Order 12898: Federal Actions to Address Environmental Justice in**  **Minority Populations and Low -**  **Income Populations** The EPA believes this action will not have potential disp roportionately high and adverse human health or environmental effects on minority , low
- income , or indigenous populations because this action does not affect the level of protection provided to human health or the environment. The Administrator considered climate change risks to minority , low
- income , and indigenous populations as part of this proposed endangerment finding under CAA section 231. This action’s discussion of climate change impacts on public health and welfare is found in s ection IV of the preamble. Specific discussion with regard to minority , low
- income , and indigenous populations are found in section s IV and I.E of th is preamble titled “ Environmental Justice
. ” A cop y of all documents pertaining to the impacts on these communities f

rom climate change have been placed in the public docket for this action. **K. Determination Under Section 307(d)**  Section 307(d)(1)(V) of the CAA provides that the provisions of section 307(d) appl y to “such other actions as the administrator may determine.” Pursuant to section 307(d)(1)(V) , the Administrator determines that this action is subject to the provisions of section 307(d).******* **Response to** Interagency Working Comments on **Draft** Language under EO1 2866 and EO 1 3563 Interagency

Review. Subject to Further Policy Review. Draft, **Do Not Cite, Quote, or Release During Review ** ***

Page **198** of **198** 

## VIII. **Statutory Pr ovisions and Legal**  **Authority** Statutory authorit y for this action comes from 42 U.S.C. sections 7 571 , 7601 and 7607
. Dated: _______________________________

_____________________________________ Gina McCarth y, Administrator