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

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Page **1** of **193 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 (E PA). **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 that together were defined a s the air pollution in the 2009 Endangerment F inding under section 202(a) of the Clean Air Act and that together constitute the primary cause of the climate change problem . The Administrator is also proposing to find that greenhouse gas emissions*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **2** of **193** 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 the EPA’s work supporting the United States’ efforts at the International Civil Aviation Organization (ICAO) to reduce greenhouse gas emissions from aircraft, IC AO’s progress in establishing global aircraft standards that achieve meaningful CO 2 reductions , and the potential use of section 2 31 of the Clean Air Act to implement corresponding aircraft engine standards domestically , e nsuring transparency and the opportunit y 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 advance 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 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **3** of **193** such as audio descriptio n, please let us know at the time of registration. If no one contacts the EPA requesting a public hearing 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. F or 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: 282 2 1 T, 1200 Pennsylvania Ave., NW, Washington, DC 20460. Attention Docket ID No. EPA
- HQ
OAR
- 2014
- 0828.

 Hand Delivery : U.S. Environmental Protection Agency , EPA West , EPA Docket Center, EPA West Building, Room 3334, 1301 Constitution Ave., NW., Washington ,*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **4** of **193** 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 avail able 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 otherwise protected through http://www.regulations.gov or e - mail. The http://www.regulations.gov website is an “anon y

mous 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 Internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD
- ROM you submit. I f the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should avoid the use of special*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **5** of **193** characters, or an y form of encryption, and be free of an y defects or viruses. For additional information about the EPA’s public docket visit the EPA Docket Center homepage at : http://www.epa.gov/dockets. For additional instruction s 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 Inte rnet and will be publicly available only

in hard copy in the EPA’s docket . Publicly available docket materials are available either electronically

in www.regulations.gov or in hard copy at the Air and Radiation Docket and In formation 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 Age ncy , 2000 Traverwood Drive, Ann Arbor , MI 48105; Telephone number: (734) 214
- 4454; Fax number: (734) 214
- 4816; E
- mail address: iffland.jonell@epa.gov
. Please use this contact*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **6** of **193** information for general questions about this rulemaking, to request a hearing, to determine if a hearing will be held, and to register to speak at the hearing, if one is held. **SUPPLEMENTARY INFORMATION: 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: OVERVI EW AND CONTEXT FOR THIS PROP OSAL A. Summary B. Background Information Helpful to Understanding This Proposal 1. Greenhouse Gases and Their Effects 2. Statutory

Basis for This Proposal C. The EPA’s Responsibilities under the Clean Air Act 1. The EPA’s Regulation of Greenhouse Gases 2. Background on the Ai rcraft Petition, 2008 ANPR, and U.S. District Court Decision D. The EPA’s Regulation of Aircraft Emissions E. U.S. Aircraft Regulations and International Community 1. International Regulations and U.S. Obligations*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **7** of **193**

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
. GREENHOUSE GASES ENDANGER PUB LIC HEALTH AND WELFARE

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 Welfare 1. More Recent Evidence That Elevated Atmos pheric Concentrations of the Six Greenhouse Gases Are the Root Cause of Observed Climate Change 2. More Recent Evidence that Greenhouse Gases Endanger Public Health 3. More Recent Evidence that Greenhouse Gases Endanger Public Welfare 4. Consideration of Other Clim ate 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. Proposed Definition of Air Pollutant 2. How the Defi nition 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 3. Proposed Contribution Finding for the Single Air Pollutant Comprised of the of Six Well
- Mixed Greenhouse Gases*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **8** of **193**

4. Additional Considerations VI
. ADVANCE NOT IC E OF PROPOSED RUL EMAKING: DI SCUSSION OF ONGOING IN TERNATIONAL PROCEEDINGS TO DEVELOP AIRCRAFT CO2 EMI SSI ONS STANDARD AND REQUEST FOR C OMMENT 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 O ptions, 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. Executive Order 13211: Actions Concerning Regulatio ns That Significantly Affect Energy Supply , Distribution or Use I. National Technology

Transfer and Advancement Act (NTTAA) J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and L ow - Income Populations*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **9** of **193** K. Determinatio n 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 en gine 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 propos ed 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 Code Examples of Potentially Affected Entities Industry 3364412 3724 Manufacturers of new aircraft engines. Industry 336411 3721 Manufacturers of new aircraft. a North American Industry Classification S ys tem (NAI CS). b Standard Industrial Classification (SIC) code.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **10** of **193** 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 have an interes t 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 applicable to greenho use 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
. Other ty pes of enti ties 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 part icipate 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **11** of **193** 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 Shou ld 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 endangerment 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 section number.

 Explain why

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

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Page **12** of **193**

 Describe an y assumptions and provide an y technical information and/or data that you used.

 If you estimate potential costs or burdens, expla in 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 personal 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 yo u 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
- ROM the specific information that is claimed as CBI. In addition to one complete version of the comment that includes information claimed as CBI, you must submit a copy of the comment that does not contain the information claimed as CBI for inclusion in the public*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **13** of **193** 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
accomm odate 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 acc ess 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 allow ed in the building, cameras may onl y be used outside of the building and demonstrations will not be allowed on federal property for security reasons. The EPA may

ask clarifying que stions during the oral presentations but will not respond to the presentati ons 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **14** of **193** presentations if we re ceive 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 statements will be included in the docket for the rulemaking. The EPA will make every effort to follow the schedule as closely

as possible on the day

of the hearing; however , please plan for the hearing to run either ahead of schedule or behind schedule . Information regarding the hearing (including information as to whether or not one will be held) will be available at [ insert website ] . Again, all requests for a public hear ing to be held must be received by **[insert date 10 days after publication in the Federal 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **15** of **193** 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 c ause or contribute finding, the EPA disaggregated the existing data in one area of the GHG Inventory (for the General Aviation Jet Fuel Category) and had the disaggregation methodology and results peer reviewed in accordance with the EPA’s Peer Review Hand book
. 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 and Sinks: 1990

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

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Page **16** of **193 Children’s Environmental 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 p ublished since 2009 strengthens these conclusions by providing more detailed findings regarding children’s vulnerabilities and projected impacts they may experience. The se studies co nclude that children will be disproportionately affected b y heat waves,
a ir pollution, infectious and waterborne illnesses, and mental health effects resulting from extreme weather events. In addition, these studies find that climate change will influence production of pollen that affects asthma and other allergic respiratory d iseases , to which children are among those especiall y susceptible
. A dditional health concerns may arise in low income households, especially those with children, if climate change reduces food availabilit y and increases prices, leading to food insecurity within households.

4 U.S. EPA, 2009: Endangerment and Cause o r 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”).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **17** of **193 Environmental Justice**  E. As described in detail in section IV below , the scientific assessment literature cited in the 2009 Endangerment Finding concluded 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 these conclusions b y providing more detailed findings regarding these populations’ vuln erabilities and projected impacts they may experience. In addition, the most recent assessment literature provides new information on how some communities of color may be uniquel y vulnerable to climate change health impacts. These studies 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 communities 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 change poses particular threats to i ndigenous p eoples’ health, wellbeing, and ways of life.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **18** of **193** 

## II. **Intr oductio**  **n: 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) contribute 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 : subsonic jet aircraft w ith 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 II and the Embraer E170 , up to the largest jet aircraft in passenger service
-- 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
. [ Consider breaking the paragraph here. ] In this proposed action, the EPA relies primarily o n the extensive scientific and technical evidence in the record supporting the 2009 Endangerment Finding under CAA section 202 , including the major, peer
- reviewed scientific assessm ents regarding 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **19** of **193** Administrator’s view is that the body of scientifi c 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 finding under section 231 rests on careful consideration not o nly

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 more recent information or anal ys es suggest that it would be reasonable for the EPA to now reach a different or contrary conclusion for purposes of CAA section 231(a)(2)(A) than the Agency reached for purposes of section 202(a) in 2009. However, as explained below, in proposing this finding for purposes of section 231, we are not reopeni ng 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 : c arbon dioxide (CO 2 ), methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. This is the same definition that was used for the finding for purposes of section 202(a). It is the Administrator’s judgment that the total body of scientific evide nce 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
.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **20** of **193** Under section 231 of the CAA, the Administrator must also determine whether emissions of any

air pollutant from a class or classes of aircraft engines cause or contribute to the air pollution that may 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 pr oposing 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 pr oposed findings come in response to the U.S. District Court for the District of Columbia’s ruling that section 231(a)(2)(A) of the CAA imposes a non
discretionary

dut y to issue such findings
. Center for Biological Diversity, et al. v. EPA , 794 F. Supp. 2d 151 (D.D.C. July 5, 2011)
. This case involved a citizen petition submitted by Friends of the Earth, Oceana, the Center for Biological Diversit y, and Earthjustice (Petitioners) requesting that the EPA issue standards under section 231(a)(2)(A) of the A ct for the GHG emissions from aircraft. The proposed findings are in response to this petition and are for purposes of section 231(a)(2)(A). The EPA is not proposing or taking action under any other provision of the CAA. Further, the EPA anticipates that ICAO will adopt a final CO 2 emissions standard in February 2016. This proposal, and an y final endangerment and*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **21** of **193** cause or contribute findings for aircraft engine GHG emissions, are also part of preparing for
a possible subsequent domestic rulemaking pr ocess to adopt standards that are of at least equivalent stringency as the anticipated ICAO CO 2 standards. **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, perfluoroc arbons, and sulfur hexafluoride. Of these six gases, two ( CO 2 and nitrous oxide) are emitted by aircraft engines
. These six gases, once emitted, remain in the atmosphere for decades to centuries. Thus, they

become well mixed globally in the atmosphere an d their concentrations accumulate when emissions exceed the rate at which natural processes remove them from the atmosphere. The heating effect caused by the human
- induced buildup of these and other GHGs in the atmosphere is extremely likely (>95 percent likelihood) to be the cause of most of the observed global warming since 1950. 5 A detailed explanation of climate change and its

5 “ 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 Chang e [Stocker,*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **22** of **193** impact on health, societ y, and the environment is included in the record for the EPA’s 2009 Endangerment Finding under CAA section 202 . 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 anthropog enic GHG emissions. In 2012, aircraft remained the single largest GHG
- emitting 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 emissions and representing more than 3 percent of total U.S. GHG emissions in 2012
. 6 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.

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. 6 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).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **23** of **193**

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

re asonably

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 h er 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 pollutant from certain classes of aircraft engines
c ause or contribute to this air pollution. 7 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) (interpreting 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

with proposed standards under various sections of th e CAA, including section

7 To clarify the distincti on between air pollution and air pollutant, the air pollution is the atmospheric concentrations and can be thought of as the total, cumulative stock of GHGs in the atmosphere. The air pollutants, on the other hand, are the emissions of GHGs and can be tho ught of as the flow that changes the size of the total stock.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **24** of **193** 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, Propo sed 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), Fin al 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
- 66502 (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 anal ys is applies to section 231 (a)(2)(A) , which is analogous to section 202(a). 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 oth er actions as the Administrator may determine.” 8 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

8 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).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **25** of **193** provisions of 307( d) to the promulgation or revision of any aircraft emission standard under section 231). Thus, these proposed findings will be subject to the same rulemaking
r equirements that would apply if the proposed findings were part of a standard
- setting rulemaking
. **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 electric generatio n, 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 R egulation 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 or not 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 b y 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 b y more than a dozen environmental, renewable energy, and other organizations.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **26** of **193** On April 17, 2009, the A dministrator signed proposed findings under section 202(a) that GHGs in the atmosphere endanger public health and welfare ( the “ endangerment finding”) and that the combined emissions of these GHGs from new motor vehicles and new motor vehicle engines cause or contribute to that GHG air pollution (“cause or contribute” finding). 9 On December 7, 2009 , the Administrator signed a notice that finalized two di stinct findings regarding GHGs under s ection 202(a) of the CAA :

 **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 generations
.
 **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. 10 These findings ( collectively referred to as the 2009 Endangerment Finding in today ’s action ) d id not themselves impose any requirements on industry or other entities. However,

9 74 FR 18886 ( Apr il 24, 2009 ). 10 74 FR 66496 (December 15, 2009).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **27** of **193** these findings compelled the EPA to promulgate GHG emission standards for new motor vehicles under s ection 202(a). Subsequentl y, 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)
. 11 This was followed in August 2011 by

adoption of the first
- ever GHG emission standards for heavy
- dut y engines and vehicles (2014
- 2018 model years)
. 12 On August 29, 2012, the second phase of the GHG emission standards for light
- dut y vehicles (2017
- 2025 model years ) w as finalized further red ucing GHG emissions from light
- dut y vehicles
. 13 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 eav y - d uty v ehicles
. 14 These three historic GHG rules 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

11 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)
. 12 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). 13 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). 14 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, Feb ruary 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 accessed February 5, 2015).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **28** of **193** reductions in GHG emissions, and over the lifetime of these vehicles GHG emissions will be reduced b y more than 6.2 billion metric tons. 15 , 16 On June 25, 2013, President Obama ann ounced a Climate Action Plan that set forth a series of executive actions to further reduce carbon pollution, prepare the U.S. for the impacts of climate change , and lead international efforts to address global climate change
. 17 As part of the Climate Acti on Plan, the President issued a Presidential Memorandum directing the EPA to work expeditiously to complete carbon pollution standards for the power sector. 18 In response, in January 201 4 , the EPA proposed carbon pollution standards for new electric utility generating units
. 19 This was followed in June 2014, by proposed standards to address carbon pollution from modified and reconstructed power plants 20 and from existing power plants. 21

15 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)
. 16 76 FR 57106 (September 15, 2011 ). 17 Executive Office of the President, 2013: The President’s Climate Action Plan , June 25. Available at: http://www. whitehouse.gov/sites/default/files/i mage/president27sclimateactionplan.pdf (L ast accessed February 5 , 2015)
. 18 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). 19 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)
. 20 U.S. EPA, 2014: Carbon Pollution Standards for Modifie d and Reconstructed Stationary Sources: Electric Utility Generating Units; Proposed Rules , 79 FR 34960 (June 18, 2014 ). 21 U.S. EPA, 2014: Carbon Pollution Emission Guidelines for Existing Stationary Sources:*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **29** of **193** 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. 22 The proposed endangerment and cause or contribute findings for aircraft GHG emissions under section 231(a)(2)(A) of the CAA are a preliminary but necessary

first step to begin to address GHG emissio ns from the aviation sector, the highest
- emitting category of transportation sources that the EPA 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 emi ssions from the U.S. transportation sector , 23 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
. 24 , 25 U.S. aircraft GHG emissions are projected to increase b y almost 50

Electric Utility Generating Units; Proposed Rule , 79 FR 34830 (June 18, 2014)
. 22 Executive Office of the President, 2013: The President’s Climate Action Plan at 21 , June
. Available at: http://www. whit ehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf (L ast accessed February 5 , 2015). 23 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). 24 Ibid. 25 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **30** of **193** percent over the next two decades. 26 S ee s ection V of this preamble for more information about the data sources that compose the aircraft GHG emissions inventory
.

2. Background on the Aircraft Petition, 2008 ANPR, and D.C. District Court Decision Section 231(a)(2)(A) of the CAA directs the Administrator of the EPA to, from time to time, propose aircraft engine emissions standards applicable to the emission of an y air pollutant from any classes of aircraft engines 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, Friend s of the Earth, Oceana, the Center for Biological Diversity , Earthjustice , and others (Petitioners) sent a letter to the EPA petitioning the Agency to undertake rulemaking regarding GHG emissions from aircraft. 27 Specifically , Petitioners
re quested that the EPA make a finding that GHG emissions from aircraft engines “ may

26 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). 27 Center for Biological Diversity, Center for Food Safety, Friends of the Earth, International Center for Technology Assessment, and Oceana, 2007: Petition for Rulemaking Under the Clean air Act to Reduce the Emissions of Air Pollutants from Aircraft the Contribute to Global Climate Change, December 5. Available at http://www.epa. gov/otaq/aviation.htm (Last accessed February 5 , 2015).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **31** of **193** 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 , 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 2007 ruling and the potential ramifications of the Agency ’s de cision to regulate GHGs under the CAA. This ANPR described and solicited comment on numerous petitions the Agency had received to regulate GHG emissions from both stationary and mobile sources, including aircraft. 73 Fed. Reg. 4435 4, 44468
- 44473 (July 30, 2008)
. With regard to aircraft, the Agency sought comment on the impact of aircraft operations on GHG emissions and the potential for reductions in GHG emissions from these operations. In response to the ANPR, the EPA received comments from a wide range of aviation sector stakeholders including industry trade groups, individual manufacturers, states and local governments, and nongovernmental organizations (NGOs). Industry groups and individual manufacturers stressed that fuel costs (and market forces) cr eated an economic incentive to reduce fuel consumption and thus GHG emissions. One industry association indicated its commitment to achieve an additional 30 percent fuel efficiency improvement by

2025. Another commenter identified engine technologies that were improving fuel consumption by more than 15 percent. With regard to CO 2 engine emissions standards, these commenters felt*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **32** of **193** 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 . Industry

commenters also argued that other potential approaches to reducing aircraft related emissions, such as averaging of GHGs among existing aircraft fleets and cap
and
- trade schemes as existed in the European Union, were beyond the scope of the EPA ’s authority under section 231 of the CAA. Finall y i ndustry commenters noted that any program developed b y the EPA should incentivize market forces and provide for flexibility
. State/local governments and NGO commenters felt strongly that the EPA had cle ar authority to find endangerment under section 231 and that there were multiple options to reduce aircraft emissions, so that the Agency must set a GHG emissions standard for aircraft engines as states were 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 G HG standard could be set as a function of thrust similar to IC AO’s standard for oxides of nitrogen (NO x ) and should also include provisions for averaging, banking, and trading (ABT). Some commenters also stated their
su pport for fleet
- wide (in
- use fleet) emission reductions through a cap and trade s ys tem. Finally , these stakeholders stated that, absent the EPA rulemaking, quick international actions were unlikel y and that the EPA should engage internationall y to push for action on reducing CO 2 emissions from aircraft.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **33** of **193** On July 31, 2008, Earthjustice, on behalf of Petitioners, notified the EPA of its intent to file suit under CAA section 304(a) against the EPA for the Agency ’s alleged unreasonable delay in responding to its aircr aft 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 dela yed 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 ground s 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 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **34** of **193** remedial order to make an endangerment finding or to issue standards. The Plaintiffs did not appeal this ruling to the U.S. Court of App eals for the D.C. Circuit. The EPA issued a Response to the Aircraft Petition 28 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 a m inimum of 22 months to complete this action following the then
- awaited ruling of the U.S. Court of Appeals regarding the previous section 202 finding
. We also stated that our rulemaking action would begin once the U.S. Court of Appeals for the D.C. Cir cuit decided pending cases regarding the CAA section 202 Endangerment Finding
. Meanwhile, the Court upheld EPA’s section 202 findings in a decision of a three
judge panel on June 26, 2012, and denied petitions for rehearing of that decision on December 20, 2012. Coalition for Responsible Regulation, Inc., v. EPA , 684 F.3d 102 (D.C. Cir. 2012), reh’g denied 2012 U.S. App. L EXI S 26315, 25997 (D.C. Cir 2012). 29 Given these rulings, we

28 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 Docket EPA
HQ
- OAR
- 2014
- 0828. 29 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **35** of **193** are proceeding with today’s proposed findings regarding aircraft engine GHG emissions in furtherance of our prior r esponse to th e Petition for Rulemaking
.

**The EPA’s Regulation of Aircraft Emissions** D. 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. 30 We have occasionally revised these regulations
. In a 1997 rulemaking, for example, we made our emission sta ndards and test procedures more consistent with those of ICAO’s Committee on Aviation Environmental Protection (CAEP) for turbofan engines used in commercial aviation with rated thrusts greater than 26.7 kilonewtons . These ICAO requirements are general ly referred to as CAEP/2 standards. 31 That action included new NO x emission standards for newl y manufactured commercial turbofan engines (those engines built after the effective date of the regulations that were already certified to pre
- existing standards

– also referred to as in
- production engines ) 32 and for newl y - certified commercial turbofan engines (those engine models that

30 U.S. EPA , 1 973: Emission Standards and Test Procedures for Aircraft; Final Rule, 38 FR 19088 (July 17, 1973)
. 31 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. 32 This does not mean that in 1997 we promulgated requirements for the re
- certification or retrofit of existing in
use engines.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **36** of **193** received their initial ty

pe certificate after the effective date of the regulations). 33 Italso included a carbon monoxide emission standard for newly
- manufactured commercial turbofan engines. 34 In 2005, we promulgated more stringent NO x emission stand ards for newl y certi fied commercial turbofan engines
. 35 That final rule brought the U.S. s tandards closer to alignment with ICAO CAEP/4 requirements that became effective in 2004
. In2012, we issued more stringent two
- tiered NO x emission standards for newl y - certified and in
production commercial and non
- commercial turbofan aircraft engines , an d these NO x standards align with IC AO’s CAEP/6 and CAEP/8 requirements that became effective in 2013 and 2014, respectively
. 36 , 37 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

33 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 individu al 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. 34 U.S. EPA, 1997: Con trol of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test Procedures; Final Rule, 62 FR 25355 (May 8, 1997)
. 35 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 )
. 36 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)
. 37 While ICAO’s standards were not limited to “commer cial” aircraft engines, our 1997 standards were 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 publi c 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 bring our standards into full alignment with ICAO’s.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **37** of **193** requirements with those promulgated b y IC AO. In addressing CO 2 emissions, however, ICAO has moved to regulating a whole aircraft
. This I CAO extension beyond pollutant emissions from engines to the whol e aircraft was described in a 2013 IC AO circular
. 38 Several factors are considered when addressing whole
- aircraft CO 2 emissions, as the CO 2 emissions are influenced by aerodynamics, weight, and 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 CO2 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 CO 2 (or GHG) standards for aircraft engines used in covered aircraft as an outgrowth of the international negotiations that commenced in 2010 under the auspices ICAO/CAEP. **U.S. Aircraft Regulations and the**  **International Community** E. The EPA and the Federal Aviation Administration (FAA) traditionally work within the ICAO/CAEP standard
- setting process to establish international emission standards and related requirements. Historically , u nder this approach , international emission standards have first been adopted b y IC AO, and subsequently the EPA has initiated rulemakings under CAA

38 ICAO , 2013: CAEP/9 Agreed Certification Requirement for the Aeroplane CO 2 Emissions Standard, Circular (Cir) 337, AN/192, Available at www.icao.int (Last accessed February 5, 2015)
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Page **38** of **193** sect ion 231 to establish domestic standards equivalent to I CAO’s standards where appropriate
. This approach has been affirmed as reasonable b y 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 p romulgates aircraft engine emissions standards, CAA section 232 requires the FAA to issue subsequent regulations to e nsure compliance with these standards when issuing certificates under its United States Code Title 49 authority
. In exerc ising the EPA’s standard
- setting and FAA’s enforcement authorities , w e expect to proceed using a similar approach for the future CAA section 231 aircraft engine CO 2 standard (or GHG standard ), provided the EPA issues final positive endangerment and cause or contribute findings under CAA section 231
. This approach is contingent on IC AO ’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 ( Chicago 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **39** of **193** and operated soundly

and economicall y.” 40 IC AO sets standards and 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 memb er States and global aviation organizations to develop international Standards and Recommended Practices (SARPs) , which member States reference when developing their legally
- enforceable national civil aviation regulations
. The U
. S
. is currentl y one of 1 9 1 participating IC AO member States. 41 , 42 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, stan dards, 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 nt ernational 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 notification to I CAO of the differenc es between its own practice and that established b y the international standard
.

40 ICAO, 2006: Convention on International Civil Aviation, Ninth Edition , Document 7300/9. Available at www.icao.int (Last accessed February 5, 2015)
. 41 Mem bers of ICAO’s Assembly are generally termed member States or contracting States. These terms are used interchangeably throughout this pream ble. 42 There are currently 191 Contracting States according to ICAO’s website: www.icao.int (Last accessed February 5, 2015)
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Page **40** of **193** ICAO’s work on the environment focuses primarily on those problems that benefit most from a common and coordinated approach on a worldwide basis, namely aircraft noise and engine emissions
. Standards and Recommended Practices ( SARPs ) for the certification of aircraft noise and aircraft engine emissions are covered b y Annex 16 of the Chicago Convention. To continue to address aviation environmental issues, in 2004, I CAO e stablished three environmental goals: (1) limit or reduce the number of people affected by significant aircraft noise; (2) limit or reduce the impact of aviation emissions on local air quality ; and (3) limit or reduce the impact of aviation greenhouse gas emissions on the global climate. The Convention has a number of other features that govern international commerce. First, member States that wish to use aircraft in international transportation must adopt emissions standards and other recommended practi ces 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. 43 Second, member States are required to recognize the airworthiness certificates of an y State wh ose 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. 44 Third, t o ensure that international commerce is not unreasonabl y constraine d , a

43 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). 44 ICAO, 2006: Convention on International Civil Aviatio n , Article 33, Ninth Edition, Document 7300/9. Available at http://www.icao.int/publications/pages/doc7300.aspx (Last accessed February 5, 2015).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **41** of **193** 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. 45
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 the 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 feasibi lity ; 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. ” 46 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 Counci l 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.

45 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). 46 CAEP’s terms of reference are available at http://www.icao.int/environmental
protection/Pages/Caep.aspx#ToR
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Page **42** of **193** At CAEP meetings, the U
. S
. is represented b y the FAA and play s an active role
. 47 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 em issions, 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 recommende d practices (Annex 16 to the Chicago Convention). 48 , 49
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 i n 1981
. 50 These standards limited aircraft engine emissions of hydrocarbons, carbon monoxide , and NO x . In 1994, ICAO adopted a CAEP /2 proposal to tighten the original NO x standard b y 20 percent and amend the test procedures. 51

47 Pursuant to the President’s memorandum of August 11, 1960 (and related Executive Order No. 10883 from 1960), the Interagency Group on International Aviation (IGIA ) was established to facilitate coordinated recommendations to the Secretary of State on issues pertaining to international aviation. The DOT/FAA is the chair of IGIA, and as such, the FAA represents the U.S. on environmental matters at CAEP. 48 ICAO, 2008: 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)
. 49 CAEP develops new

emission standards based on an assessment of the technical feasibility, cost, and environmental benefit of potential requirements. 50 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)
. 51 CAEP condu cts 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **43** of **193** In 1995, CAEP/3 recommended a further tightening 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 after December 31, 2003 (i.e., unlike the CAEP/2 standards, the CAEP/4 requirements did not apply to previously

certified, newly
- manufactured engines , also referred to as in
- production engines ). In 2004, CAEP/6 recommend ed a 12 percent NO x reduction , which IC AO approved in 200 5
. 52 , 53 The CAEP/6 standard s applied to new engine designs (newl y - certified mode ls) certified after December 31, 2007. In2010, CAEP/8 recommended a further tightening of the NO x standards by

15 percent for newl y - certified engines. 54 , 55 The Committee also recommended that the CAEP/6 standards be applied to newl y - manufactured engines o r 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

aircraft emission standards was CAEP’s successor , i.e., CAEE. The first meeting of CAEP, therefore, is referred to as CAEP/2. 52 CAEP/5 did not address new aircraft engine emission standards. 53 ICAO, 2008: Aircraft Engine Emissions , Annex 16, Volume II, Third Edition, July 2008, Amendment 4 effective on July 20, 2008. Available at www.icao.int (Last accessed February 5, 2015). 54 CAEP/7 did not address new aircraft engine emission standards. 55 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
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Page **44** of **193** standards (to CAEP/6 and CAEP/8 standards) were promulgated domestically in 2012 by

the EPA in consultation with FAA
. 56

2. T he International Community ’s Reasons for Addressing Aircraft CO 2 Emissions In October 2010 , the 37th Assembly (Resolution A37
- 19) of ICAO requested the development of an IC AO CO 2 emissions s tandard
. 57 Also, Resolution A37
- 19 provided a framework towards the achievement of an environmentally sustainable future for international aviation. With this Resolution, the I CAO Assembly agreed to a global aspirational goal for international aviation of improving annual fuel efficiency by 2 percent and stabilizing CO 2 emissions at 2020 levels. The Resolution included the following statements regarding ICAO policies and practices related to climate change. “

- ... I CAO and its member States recognize th e importance of providing continuous leadership to international civil aviation in limiting or reducing its emissions that contribute to global climate change;

56 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 o f Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test Procedures; Final Rule , 77 FR 36342 (June 18, 2012). 57 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **45** of **193** - Reemphasizing the vital role which international aviation plays in global economic and social d evelopment 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 emissi ons, are projected to grow as a result of the continued development of the sector . ” As the above statements indicate, r educing climate impacts of international 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 , including alternative fuels, CO 2 emissions technology
- based standards, operational impr ovements , 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **46** of **193**

3. Relationship of the EPA’s Proposed Endangerment and Cause or Contribute Finding 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 a dopted 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 emission standards that are of at least equivalent stringency

as ICAO’s standards. This approach has been affirmed as reasonable by the U.S. Court of Appeals for the D.C. Circuit. NACAA v. EPA , 489 F.3d 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 o r 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 expect s to proceed along a similar approach for the future CAA section 231 aircraft GHG standard (or aircraft CO2 standard)
. We anticipate that I CAO/CAEP will adopt a final aircraft CO 2 emissions standard in February 2016. 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. Thes e findings, which are factual and science
- based,*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **47** of **193** encompass a determination of whether GHG emissions from aircraft cause or contribute to air pollution which may

reasonably

be anticipated to endanger public health or welfare. If positive findings are made, the EPA is 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 has not trigg ered 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 discusses the issues arising in the ongoing international proceedings and U.S. input at CAEP regarding the international CO 2 standard , which is expected to be finalize d in February 2016 . T o e nsure transparency and to assist the Agency

in developing its position with regard to these issues and the aircraft CO 2 emission standard s that it may potentially

adopt under the CAA, the EPA requests public comments on a variet y of issues in Section V I
. 

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

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Page **48** of **193** 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 ai r pollutant from any

class or classes of new motor vehicles or new motor vehicle engines, which in [the Administrator’s] judgment cause, or contribute to, air pollution which may reasonably

be anticipated to endanger public health or welfare.” Similarly , section 231(a)(2)(A) concerns “the emission of any air pollutant from any

class or classes of aircraft engines which in [the Administrator’s] judgment causes, or contributes to, air pollution which may reasonabl y be anticipated to endanger public health or welfare.” Thus, the text of the CAA section concerning aircraft emissions in section 231(a)(2)(A) mirrors the text of CAA section 202(a) that was the basis for the 2009 Endangerment Finding
. The EPA’s approach in the 2009 Endangerment Finding was aff irmed b y 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 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 adequately supported by the administrative record. CRR , 684 F.3d at 116
- 128. The D.C. Circuit found that the EPA had based its decision on “substantial scientific evidence” and noted that the EPA’s reliance on major scientific assessments was consistent with the methods that decision
- makers often*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **49** of **193** use to make a science
- based judgment. Id. at 120
- 121. Petitions for certiorari were filed in the Supreme Court, and the Supreme Court granted six of those petitions but “agreed to decide only one question: ‘Whether EPA permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary

sources that emit greenhouse gases.’” Utility Air Reg. Group v. EPA , 134 S. Ct. 2427, 2438 (2014); see also Virginia v. EPA , 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA , 134 S. Ct. 418 (2013), and CRR , 134 S. Ct. 468 (2013) (all denyi 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 consistently 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 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **50** of **193** 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. 58
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 or welfare. See CRR , 684 F.3d at 117
- 118. 59 In making this scientific judgment, the Administrator is guided b y five principles. F irst, the Administrator is required to protect public health and welfare. She is not asked to wait until harm has occurred but instead must be read y to take regulatory action to prevent harm before it occurs. 60 The Administrator is thus to consider both current and future risks.

58 See CRR , 684 F.3d at 117 (explaining two
- part analysis under section 202(a)). 59 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 bas is for it is presented.” CRR , 684 F.3d at 120 (internal citations and marks omitted). 60 See id. at 121
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Page **51** of **193** 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. 61 Under either scenario , 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)). 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. 62 At the same time, the Administrator must exercise reasoned decision making, and avoid speculative inquiries.

61 See id. at 122
- 123 (noting that the § 202(a)(1) inquiry “necessarily entails a case
- by
- case, sliding scale approach” because endangerment is “‘ com posed 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)). 62 See id. at 121
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Page **52** of **193** Fourth , the Administrator is to consider the cumulative impact of sources of a particular t ype of pollution in assessing the risks from that pollution, and is not to look only at the risks attributable to a single source or class of sources. Fifth , the Administrator is to consider the risks to all parts of our population, including those who are at greater risk for reaso ns 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 section 231 finding , vulnerable subpopulations face serious health risks as a result of climate change. As the Supreme Court recognized in Massachusetts v. EPA , 549 U.S. at 534, the EPA may make an endangerment finding despite the existence of “some residual uncertainty” in the scientific record. See also CRR, 684 F. 2d at 122. Thus, this framework recognizes that regulatory agencies such as the EPA must be able to deal with the realit y that “ [m]an’s ability to alter his environment has developed far more rapidly than his ability

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

action to prevent harm, even if the regulator is less than certain that harm is otherwise inevitable.’ ” See Massachusetts v. EPA , 549 U.S. at 506, n.7 (citing Ethyl Corp .) ; see also CRR , 684 F.3d at 121
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Page **53** of **193** In the 2009 Endangerment F inding, the Administrator recognize d that the context for
an action addressing climate change is unique
. 74 FR at 66906. At that time there was a v ery large and comprehensive base of scientific information that ha d been developed over many ye ars through a global consensus process involving numerous scientists from many countries and representing man y disciplines , and that informational base has since grown . She also previously recognize d that there are varying degrees of uncertainty across many of these scientific issues , which remains true
. It is in this context that she is exercising her judgment and 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) cont ext . 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 Admi nistrator 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 acting only when certainty has been achieved; indeed, the references to anticipation and to endangerment imply

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

reasonably

be anticipated to endanger public health or welfare” in CAA §*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **54** of **193** 202(a) requires a “precautionary , forward
- looking scientific judgment about the risks of a particular air pollutant, consistent with the CAA’s precautionary and preventive orientation.” CRR, 684 F.3d at 122 (internal citations omitted)
. The court determined that “[r]equi ring that EPA find ‘certain’ endangerment of public health or welfare before regulating greenhouse gases would effectivel y prevent EPA from doing the job that Congress gave it in § 202(a)

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

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Page **55** of **193**

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 inding, the EPA explained that when Congress revised the section 202(a) language that governed that finding, al ong 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 Finding regarding the history of section 202 and how it supports the EPA’s approach is also re levant for section 231. The legislative history of those amendments, 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 su pport 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **56** of **193** (1977), as reprinted in 4 A Legislative History of the Clean Air Act Amendments of 1977 (1978) at 2465 (hereinafter LH). 63 The legislative history

clearl y indicates that the House Committee believed the Ethyl Corp . decisions posed several “c rucial policy questions” regarding the protection of public health and welfare. H.R. Rep. 95
- 294 at 48, 4 LH at 2515
. 64 The following paragraphs summarize the en banc decision in Ethyl Corp. v. EPA and describe how the House Committee revised the endanger ment 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 65 ; (2) authorizes the Administrator to 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, as well as health y adults, should be part of the anal ys is; and (5) indicates an awareness of the

63 The committee explained that its action addressed not only section 211(c)(1)(A) but rath er 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 oth er sections. Id. at 2517. 64 The Supreme Court recognized that the current language in section 202(a)(1), which uses the same formulation as that in section 231(a)(2)(A), is “more protective” than the 1970 version that was similar to the section 211 lang uage before the D.C. Circuit in Ethyl Corp
. Massachusetts v. EPA , 549 U.S. at 506, fn 7. 65 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 p revent harm before it occurs”).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **57** of **193** uncertainties and limitations in information available to the Administrator. H.R. rep. 95
- 294 at 49
- 50, 4 LH 2516
- 17. 66 In revising the statutory

language, Congress relied heavily on the en banc decision in Ethyl Corp. v. EPA , which reversed a 3
- judge panel opinion regarding an EPA rule restricting the content of lead in leaded gasoline. 67 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 ban c court rejected this approach, finding that the term “endanger” allowed the Administrator to act when harm is threatened, and did not require proof of actual harm. Id

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

. Optimally , the court held, regulatory action would not only precede, but prevent, a perceived threat. Id

.

66 Congress also standardized this language across the various sections of the CAA which address emissions from both stationary and mobile sources. H.R. Rep. 95
- 294 at 50, 4 LH at 2517; section 401 of the CAA Amendments of 1 977. 67 At the time of the 1973 rules requiring the reduction of lead in leaded gasoline, section 211(c)(1)(A) of the CAA stated that the Administrator may promulgate regulations that: “control or prohibit the manufacture, introduction into commerce, offeri ng for sale, or sale of any fuel or fuel additive for use in a motor vehicle 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).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **58** of **193** The court also rejected petitioner’s argument that any threatened harm must be “probable” before regulation was authoriz ed. 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 probability and severity .” Id

. at 18. Next, the court held that the EPA’s evaluation of ris k 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] o n 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)) reg arding “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 questi ons with the language that now appears in section 231(a)(2)(A) and several other CAA provisions

— “emission of any air pollutant * * * which in [the Administrator’s] judgment causes, or contributes to, air pollution which may reasonabl y be anticipated to end anger public health or welfare.”*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **59** of **193** 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 l imited data. Thus, the Administrator must balance the likelihood of effects with the severity of the effects in reaching her judgment. The Committee emphasized that the Administrator’s exercise of “judgment” 68 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 of judgment, and final decisions are subject to judicial review. Also, the phrase “in [her] judgment” modifi es 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

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

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Page **60** of **193** consider the limitations and difficulties inherent in information on public health and welfare. H. R. Rep. 95
- 294 at 51, 4 LH at 2518. 69 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 Administrator to consider all sources of exposure to a pollutant (for example, food, water, and air) when determining risk. Id

. 3. Additional Considerations for the Cause or Contribute Anal ys is By instructing the Administrato r 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. T he 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 modifi er on its use of the term “ contribute. ” Unlike other CAA provisions, it does not require “ significant ”

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

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Page **61** of **193** 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 to authorize the EPA to identify and then address what may well be many different sectors , classes, or groups of sources that are each part of the problem. As explained for the 2009 Endangerment Finding , the D.C. Cir cuit has discussed the concept of contribution in the CAA , and its case law supports the EPA’s interpretation that the level of contribution need not be significant. 74 FR at 66542. In Catawba County v. EPA , 571 F.3d 20 (D.C. Cir. 2009), the court uph eld 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **62** of **193** a significant causal relationship. Specifically , the D
. C
. Circuit again noted that the term is ambiguous, leaving it to EPA to interpret in a reasonable manner. In the context of this discussion, the court noted that “ a contribution may simply exacerbate a problem rather than cause it * * *
. ” 571 F.3d at 39. This is consistent with the D
. C
. Circuit ’s 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 pro vision, section 213(a)(2), is triggered b y a finding of a

“ significant ” contribution. The court looked at the “ ordinary meaning of ‘contribute’ ” when upholding the EPA ’s reading. After referencing dictionary definitions of “ contribute, ” the court also no ted that “ [s]tanding alone, the term has no inherent connotation as to the magnitude or importance of the relevant ‘share’ in the effect; certainly it does not incorporate any ‘significance’ requirement. ” 370 F.3d at 13. 70 The court found that the bare “ co ntribute ” language invests the Administrator with discretion to exercise judgment regarding what

70 Specifically, the decision noted 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 ngli sh D ictionary 849 (2d ed. 1989). ” Id. at 13.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **63** of **193** constitutes a sufficient contribution for the purpose of making an endangerment finding
. Id

. at 14. 71
Like the statutory

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

other 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 affirmative 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 discreti on in exercising her reasonable judgment and determining whether, under the circumstances presented, the cause or contribute criterion has been met. 72 As noted above, in addressing provisions in section 202(a), the D.C. Circuit has explained that the Act d id 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 an y combination in between.” Id. (quoting Ethyl Corp ., 541

71 The court explained, “ [t]he repeated use of the term ‘significant’ to modify the contribution required for all nonroad vehicles, coupled with the omission of this modifier from the ‘cause, or contribute to’ finding required for individual categories of new nonroad vehicles, indicates that Congress did not intend to require a finding of ‘significant contribution’ for individual vehicle categories. ” Id. at 13. 72 Section V discusses the evidence in this case tha t 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **64** of **193** F.2d at 18). Recognizing the substantial record of empirical data and scientific evidence that the EPA relied upon in the 2009 Endangerment Finding , the court determined that its “failure to distill this ocean of evidence into a specific number at which greenhouse gases cause ‘dangerous’ climate change is a function of the precautionary thrust of the CAA and the multivariate and sometimes uncertain nature of climate science, not a sign of arbitrary or capricious decision
- making.” Id. at 123. As the language in section 231(a)(2)(A) is analogous to that in section 202(a), this interpretation applies with equal weight to determinations under section 231(a)(2)(A). This context further supports the EPA’s interpretation that section 231(a)(2)(A) requires some level of contribution that, while exceeding de mi nimis or trivial thresholds, does not need to rise to the level of significance. In addition, when exercising her judgment, the Administrator not only considers the cumulative impact, but also looks at the totality of the circumstances (e.g., the air pol lutant, the air pollution, the nature of the endangerment, the ty pe or classes of source s at issue , the number of sources in the source sector or class , and the number and ty pe of other source sectors or categories that may emit the air pollutant) when det ermining whether the emissions

“ justify regulation ” under the CAA. See Catawba County , 571 F.3d at 39 (finding it reasonable for the agency to adopt a totalit y of the circumstances approach); see also 74 FR at 66542
. Further discussion of this issue can b e found in s ection s IV and V of this preamble
. In making an endangerment finding, the Administrator is not limited to considering only those impacts that can be traced to the amount of air pollution directly attributable to the*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **65** of **193** GHG s emitted b y the subject source classes
. Such an approach would collapse the two prongs of the test b y requiring that any climate change impacts upon which an endangerment determination is made result solely from the GHG emissions of aircraft. See 74 FR at 66542 (explaining the same point in the context of analogous language in section 202(a)). Similarly , the Administrator is not, in the endangerment finding itself, to consider the effect of emissions reductions from the resulting standards. 73 The thresh old endangerment and 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. **Air Pollutant, Public Health and Welfare** B. The CAA defines both “ air pollutant ” and “ welfare. ” Air pollutant is defined 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

73 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 pollution’
-- here, greenhouse gases
— ‘may reasona bly 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **66** of **193** material) substan ce or matter which is emitted into or otherwise enters the ambient air. Such term includes an y precursors to the formation of any air pollutant, to the extent the Administrator has identified such precursor or precursors for the particular purpose for whi ch the term ‘air pollutant’ is used. ” CAA section 302(g). Greenhouse gases fit well within this capacious definition. See Massachusetts v. EPA , 549 U.S. at 532. They are “ without a doubt ” phy sical chemical substances emitted into the ambient air. Id

. at 529. Section V below contains further discussion of the “ air pollutant ” for purposes of today ’s section 231 proposed contribution finding, which uses the same definition of air pollutant as the EPA adopted for purposes of the 2009 Endangerment Finding
. Regarding “ welfare , ” the CAA states that “ [a]ll language referring to effects on welfare includes, but is not limited to, effects on soils, water, crops, vegetation, man
- made materials, animals, wildlife, weather, visibility , and climate, damage to and deterioration of 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **67** of **193** well as from the spread ing 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,
an d 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), 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. 4 57 (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 c ardiovascular disease, and other acute and chronic health effects, as well as mortality
. See, e.g., Final National Ambient Air Quality Standard for Ozone, 73 FR 16436 (200 8 ).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **68** of **193** 

## 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” unde r 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 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 reas onable 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 cau se 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **69** of **193** 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). Info rmation 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 , explains 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 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. 74 Finally , 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 GHGs in the atmosphere endanger public health and welfare
.

74 While the EPA is providing a summary of newer scientific assessments below , the EPA is also relying on the same scientific and technical evidence discussed in the notices for the 2009 Endangerment Finding in this proposed finding for purposes of CAA section 231. See s ection s III of the 2009 Proposed Endangerment Finding and s ections III and IV o f the 2009 Endangerment Finding.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **70** of **193 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
.

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 hexafl uoride
. 75 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) 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

75 74 FR 66516.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **71** of **193** to remain the key

driver of future climate change; (3) they are the common focus of climate change science research and p olicy 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 treated as a class (e.g., oxides of nitrogen , particulate matter, volatile organic compounds ). 76
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; 78 all become globall y well mixed in the atmosphere , resulting in similar GHG concentrations around the globe and at all measured altitudes regardless of geographic location or altitude 79 of

76 74 FR 66517 to 66519. 78 We use ‘‘long
- lived’’ here to mean that the gas has a lifetime in the atmosphere sufficient to become globally well
- mixed throughout the entire atmosphere, which requires a minimum atmospheric lifetime of about one year. IPCC also refers to these six greenhouse gases as long
- lived. According to the most recent IPCC Fifth Assessment Report (2014), 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 som etimes approximated as having a lifetime of roughly 100 years, but for a given amount of CO 2 emitted a better description 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 increase will remain for many centuries or more. 79 In the Aircraft Petition (see s ection I I of this preamble ), petitioners describe how certain aircraft emissions have different climatic effects when emitted at high altitudes during some aircraft cruise operations. These differing clim atic effects are discussed in s ection IV.B .4, but do not apply to emissions of the six well
- mixed*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **72** of **193** emissions ; all trap outgoing heat that would otherwise escape to space; and all are directly emitted as GHGs rather than becoming a GHG in the atmosphere after emission of a precursor gas. The Administrator acknowledged that other anthropogenic climate forcers also play a role in climate change but for various scientific and policy reasons, these substances wer e not included in the air pollution definition
. 80 As explained in more detail in the 2009 Endangerment Finding, the EPA made the judgment that the scientific evidence is compelling that elevated concentrations of heat
trapping GHGs are the root cause of 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 concentrations. The attri bution of observed climate chang e to anthropogenic activities was based on multiple lines of evidence. The first line of evidence arises from our basic ph ys ical understanding 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 evi dence arises from

GHG s . Even when emitted at high altitudes, the six GHG s have essentially the same climatic effects as when emitted at ground level because of the physical and chemical properties that make them long
- lived and well
mixed in the atmosphere. 80 74 FR 66519 to 66521
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Page **73** of **193** the use of computer
- based climate models to simulate the likely patterns of response of the climate sy stem to different forcing mechanisms (both natural and anthropogenic ).

2. Public Health Impacts Detailed in the 2009 Endangerment Findin g Climate change resulting from anthropogenic GHG emissions threatens multiple aspects of public health. 81 Indetermining that the well
- mixed GHG air pollution is reasonabl y anticipated to endanger public health for current and future generations, the Admi nistrator noted her view that climate change can increase the risk of morbidity and mortality. 82 In making that public health finding, the Administrator considered direct temperature effects, air quality

effects, the potential for changes in vector
- borne d iseases, and the potential for 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 Endange rment Finding, with respect to direct temperature effects, b y raising average temperatures, climate change increases the likelihood of heat waves, which are associated with increased deaths and illnesses. Climate change is also expected to lead to reducti ons in cold
- related mortality
. The 2009 Endangerment Finding, while noting uncertaint y about how heat and cold related mortality would change in the future, also pointed to a USGCRP assessment report discussion that increases in heat
-

81 74 FR 66524 to 66530
. 82 74 FR 66524
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Page **74** of **193** 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 precipitation associated with climate change. In addition, climate change is expected to be associated wi th an increase in the spread of food
- , water - , and vector
- borne diseases in susceptible populations. Climate change also has the potential to change aeroallergen production (for example, through lengthening the growing season for allergen
- producing plants ), and subsequent human exposures could increase allergenic illnesses. Children, the elderly , and the poor are among the most vulnerable to climate
- related health effects.

3. Public Welfare Impacts Detailed in the 2009 Endangerment Finding Climate change res ulting from anthropogenic GHG emissions also threatens multiple aspects of public welfare. 83 Indetermining that the well
- mixed GHG air pollution is

83 74 FR 66530 to 66536
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Page **75** of **193** reasonabl y anticipated to endanger public welfare for current and future generations, the Administrator con sidered the multiple pathway s by which GHG air pollution and resultant climate change affect public welfare b y evaluating the numerous and far
- ranging risks to food production and agriculture; forestry ; water resources; sea level rise and coastal areas; energy , infrastructure, and settlements; and 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 Endangerme nt 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 seri ous risk of reduced water supplies, increased water pollution, and increased occurrence of extreme events such as floods and droughts. Coastal areas are expected to face increased risks from storm and flooding damage to propert y, as well as adverse impact s 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 , transport ation, and water resource infrastructure. Climate change may exacerbate existing environmental pressures in certain settlements, particularly in Alaskan indigenous communities. Climate change is also very likely to fundamentally

change U.S.
ecos ys tems ov er the 21st century and to lead to predominantly negative consequences for biodiversity , ecosy stem goods and services, and wildlife. Though there may be some*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **76** of **19 3**  benefits for agriculture and forestry in the next few decades, the body of evidence points toward s increasing risks of net adverse impacts on U.S. food production, agriculture and forest productivit y as average temperature continues to rise. Looking 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, trade, and national securit y issues for the United States. 4. The Science Upon Which the Agency Relied As outlined in s ection I II .A of the 2009 Endangerment Finding , 84 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 rel y primarily upon the recent, major assessments by the USGCRP, the IPCC, and the NRC. These assessments addressed the scientific issues that the EPA was required to examine, were comprehensive in their coverage of the GHG and climate change issues, and unde rwent 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 he r judgment on

84 74 FR 66510 to 66512
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Page **77** of **193** the best available, well
- vetted science that reflected the consensus of the climate science research communit y. The major findings of the USGCRP, IPCC, and NRC assessments supported the Administrator’s determination that elevated concentrati ons of GHGs in the atmosphere may

reasonably

be anticipated to endanger the public health and welfare of current and future generations. The EPA presented this scientific support at length in the comprehensive record for the 2009 Endangerment Finding
. R e levant sections of documents from th e 2009 Endangerment Finding record have been placed in the docket for this proposed finding under CAA section 231. The EPA then reviewed ten administrative petitions for reconsideration of the Endangerment Finding in 201 0. 85 Inthe Reconsideration Denial, the Administrator denied those petitions on the basis of the Petitioners ’ fail ure to provide 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 additional information, often more technical in nature, in response to the arguments, claims, and assertions by the P etitioners to reconsider the Endangerment Finding. 86

85 Ad ministrative petitions are available from http://www.epa.gov/climatechange/endangerment/petitions.html (Last accessed February 5, 2015) , and in the docket for the 2009 Endangerment Finding: EPA
- HQ
- OAR
- 2009
- 017. 86 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)*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **78** of **193** 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. 87 On June 26, 2012, the Court upheld the Endangerment Finding and the Reconsideration Denial, ruling that the Finding (including the Reconsideration Denial) was not arbitrary or capricious, was consistent with the U.S. Supreme Court's decision in Massachusetts v. EPA ( which affirmed the EPA ’s authority

to regulate greenh ouse gases) 88 and the text and structure of the CAA, and was a dequately supported by

the administrative record. 89 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.” 90 The Court found that the EPA had based its decision on “substantial scientific evidence,” observing that “EPA’s scientific evidence of record included support fo r 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 cli mate sy stem is warming,” as well as providing extensive scientific evidence for EPA’s determination that anthropogenically induced climate change threatens

(“Reconsideration Denial”). In that notice, the EPA throughly considered the scientific and technical information relevant to the petitions. In addition to the other information discussed in the present notice, the EPA is also relying on the s cientific 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 Reconsideration Denial. 87 Coalition for Responsible Regulation, Inc. v. Environmental Protection Agen cy , 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 ). 88 549 U.S. 497 (2007). 89 CRR , 684 F.3d at 117
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Page **79** of **193** both public health and welfare. 91 The court further noted that the EPA's reliance on assessments was consistent with the methods decision
- makers often use to make a science
based judgment. 92 Moreover, the Court supported the EPA's reliance on the major scientific assessment reports conducted by USGCRP, IPCC, and NRC and found: The EPA evaluated the processes used to develop the various assessment reports, reviewed their contents, and considered the depth of the scientific consensus the reports represented. Based on these evaluations, the EPA determined the assessments represented the best source mate rial to use in deciding whether GHG emissions may be reasonably

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. E ven individual studies and research papers often s ynthesize 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. 93

91 Id. at 120
- 121. 92 Id . at 121 93 Id
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Page **80** of **193** 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 greenhouse gases. T he Administrator consi dered the fact that “ some aspects of climate change science and the projected impacts are more certain than others.” 94 The D.C. Circuit subsequently noted that “the existence of some uncertaint y does not, without more, warrant invalidation of an endangerment finding.” 95 As noted above the Supreme Court granted some of the petitions for certiorari that were filed, while den yi n g 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.” 96 Thus, the Supreme Court did not disturb the D.C. Circuit’s holding that affirmed the 2009 Endangerment F inding.

94 74 FR at 66524 95 CRR , 684 F.3d at 121. 96 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 **81** of **193 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 car efull y reviewed the updated scientific conclusions 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 findi ngs reflected in the previous assessment reports that underpinned the Administrator ’s judgment that the six well
- mixed GHGs endanger public health and welfare. From its review, the EPA finds that these new assessments are largel y consistent with, and in m any 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 23 1
. Inparticular, the new assessments discussed in this preamble provide additional detail regarding public health impacts , particularl y on groups and lifestages especiall y vulnerable to climate change including children, the elderly , low
- income
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Page **82** of **193** The subsections below present brief summaries of the relevant key findings from the new major peer
- reviewed scientific assessments , which include the IPCC's 2013
- 2014 Fifth Assessment R eport (AR5) 97 ; IPCC’s 2012 “Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation” (SREX) : 98 the USGCRP's 2014 “Climate Change Impacts in the United States : the Third National Climate Assessment” (NCA3 ) ; 99 the NRC's 2010 “Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean” (Ocean Acidification) ; 100 2011 “Climate Change, the

97 IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.
- K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University Press, 1535 pp, doi:10.1017/CBO9781107415324; IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A. N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, 1132 pp; IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects . Contribution of Working Group II to the Fifth Assessme 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. Mastrandre a, 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. 98 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. 99 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. 100 NRC, 2010: Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean
. The National Academies Press , 188 pp
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Page **83** of **193** Indoor Environment, and Health” (Indoor Environment) ; 101 2011 “Report on Climate Stabilization Targets: Emis sions, Concentrations, and Impacts over Decades to Millennia” (Climate Stabilization Targets) , 102 2011 “National Security Implications for U.S. Naval Forces” (National Security Implications) , 103 2011 “Understanding Earth's Deep Past: Lessons for Our Climate Future” (Understanding Earth's Deep Past) , 104 2012 “Sea Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future” (Sea Level Rise), 105 201 3 “Climate and Social Stress: Implications for Security Analysis” (Climate and Social Stre ss) , 106 2013 “Abrupt Impacts of Climate Change” (Abrupt Impacts) , 107 and 2014 “ The Arctic in the Anthropocene: Emerging Research Questions ” (Arctic) 108 assessments .

101 NRC Institute of Medicine , 2011 : Climate C hange, the Indoor Environment, and Health. Washington, DC: The National Academies Press , 272 pp
. 102 NRC 2011: Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia . The National Academies Press, 298 pp
. 103 NRC, 2011: National Security Implications of Climate Change for U.S. Naval Forces
. Th e National Academies Press, 226 pp
. 104 NRC, 2011: Understanding Earth's Deep Past: Lessons for Our Climate Future . The National Academies Press, 2 1 2 pp. 105 NRC, 2012: Sea

-Level Rise f or the Coasts of California, Oregon, and Washington: Past, Present, and Future
. The National Academies Press, 201 pp. 106 NRC, 2013: Climate and Social Stress: Implications for Security Analysis. The National Academies Press , 280 pp
. 107 NRC, 2013: Abrupt Impa cts of Climate Change: Anticipating Surprises . The National Academies Press, 250 pp. 108 NRC, 2014: The Arctic in the Anthropocene: Emerging Research Questions. The National Academies Press, 220 pp
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Page **84** of **193**

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. The IPCC AR5 concludes that the global ave rage net effect of the increase in atmospheric GHG concentrations, plus other human activities (e.g., land use change and aerosol emissions), on the global energy balance since 1750 has been one of warming. This total net heating effect, referred to as “ forcing, ” is estimated to be 2
. 3 Watts per square meter (W/m2), which has increased from the previous 2007 IPCC Fourth Assessment Report (AR4) total net estimate of 1 .6 Watts per square meter (W/m2) that was referred to in the record for the 2009 Endangerm ent Finding. The reasons for this increase i nclude continued i ncreases in GHG concentrations, as well as reductions in the estimated negative forcing due*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **85** of **193** to aerosols. The IPCC AR5 rates the level of confidence 109 in their radiative forcing estimates as “high” for methane and “very high” for CO 2 and nitrous oxide
. The new assessments also have greater confidence in attributing recent warming to human causes
. T he IPCC AR5 stated that it is extremely likel y (>95 percent likelihood) that human influences have been the dominant cause of warming since 1950 , 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 1950 was due to the increase in greenhouse gas
conce ntrations. 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 y ears . This is an increase from what was reported in IPCC AR4, which found higher concentrations than in at least 65 0,000 years
. The USGCRP NCA3 states that there is very high confidence 110 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

109 The IPCC expresses levels of confidence using five qualifiers: very low, low, medium, high, and very high. These levels are based on the type, amount, quality, and consistency of evidence (e.g., data, mechanistic understanding, theory, models, and expert judgment) and the degree of agreement. 110 The NCA expresses levels of confidence using four qualifiers: low , medium, high, and very high. These levels are based on the strength and consistency of the observed evidence; the skill, range, and consistency of model projections; and insights from peer
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Page **86** of **193** changing levels of various particles that can have either a heating or cooling influence on the atmosphere , and through a ctivitie s 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 drivers of climate since 1750, a strong net warming from long
- lived greenhouse gases produced b y human activities dominates the recent climate record.” 111 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 over the period 1951
- 2012. This short term variability do es 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 Earth’s surface than all the previous

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

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Page **87** of **193** decades in the instrumental record, and the first decade of the 21st century has been the warmest .” 112 , 113 The NRC Climate Stabilization Targets assessment c oncludes that CO 2 emissions are altering the atmosphere's composition and therefore the climate for thousands of y ears . 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 .” 114 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 years .

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

reviewed the key

conclusions in the recent assessments regarding human
- induced climate change risks and impacts on public health. The EPA finds that the new assessments are consistent with or strengthen the underl yi ng science considered

112 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. 113 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 temperatur e, and that the ten warmest years, with the exception of 1998, have now occurred since 2000. Available at http://www.giss.nasa.gov/research/news/20150116/ (Last accessed February 5, 2015). 114 NRC, 2011: Understanding Earth's Deep Past: Lessons for Our Climate Future . The National Academies Press, p. 138
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Page **88** of **193** in the 2009 Endangerment Findin g 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 l iterature 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 be larger than the decreases in cold
- related mortality
. The USGCRP NCA3 concludes that, “ While deaths and injuries related to extreme cold events are projected to decline due to climate change, these reductions are not expected to compensate for the increase in heat
- related deaths .” 115 The IPCC AR5 also notes a potential benefit of climate change co uld include “ modest reductions in cold
- related mortality and morbidity

in some areas due to fewer cold extremes (low confidence) ,” 116 but that, “[o] verall, we conclude

115 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Cl imate Assessment. U.S. Global Change Research Program, p. 224
. 116 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **89** of **193** that the increase in heat
- related mortality by mid
- century

will outweigh gains due to fewe r cold periods .” 117 Regarding air qualit y effects, the assessment literature cited in the 2009 Endangerment Finding concluded that c limate change is expected to increase regional ozone pollution, with associated risks in respiratory illnesses and premature d eath, 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. ” 118 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 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

117 Ibid. at p. 721
. 118 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 222.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **90** of **193** via changes in outdoor air quality , as well as to indoor allergens, chemical emissions, and dampness/mold. Regarding extreme weather events (e.g. , storms, heavy precipitation, and, in so me 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 di seases, and stress
- related disorders
. Similarly , the USGCRP NCA3 discusses e levated waterborne disease outbreaks and the potential for mold contamination and degraded indoor air qualit y following heav y precipitation. Other impacts include mortality

assoc iated with flooding and impacts on mental health, such as anxiety and post - traumatic stress disorder. T he IP CC AR5 also discusses death and injury in coastal zones and regions vulnerable to inland flooding
. T he USGCRP NCA3 and the IP CC AR5 both find that climate change may increase exposure to and health risks associated with drought conditions, which includ es impacts from wildfires, dust storms, extreme heat events, flash flood ing, degraded water qualit y, reduced water quantit y , and water
- r elated 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
. Th e 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 expan sion of*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **91** of **193** 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 ” 119 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 modification of the landscape, the diver sity of animal hosts, and human behavior that affects vector - human contact, among other factors.” 120 Regarding a eroallergens , the assessment literature cited in the 2009 Endangerment Finding found potential for climate change to affect the prevalence and s everity 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

119 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Re port 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, an d L.L. White (eds.)]. Cambridge University Press, p. 726
. 120 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **92** of **193** 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 lengthened the allergenic pol len 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). ” 121 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 climate
- related health effects
. The 2009 Endangerment Finding also described climate change impacts facing indigenous peoples in the United States, particularly Alaska Natives. The new assessment literature strengthens these conclusions by providing more detailed findings regarding these populations’ vulnerabilities and 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.

121 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. Dokk en, 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **93** of **193** T he USGCRP NCA3 finds that, “ Climate change will, absent other changes, amplify some of the existing health threats the nation now faces. Certain people and communities are especiall y vulnerable, including children, the elderly , the sick, the poor, and some communities of color. ” 122 According to the USGCRP NCA3, cert ain 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 affecting i ndigenous p eoples ’ health in the United States through 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 Arctic and resultant ch anges 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, predominantly
- i ndigenous communities are especially vulnerable given their “ strong dependence on the environment for food, culture, and way of life; their political and

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

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Page **94** of **193** economic marginalization; existing social, health, and poverty disparities; as well as their frequent close proximity to exposed locations along ocean, lake, or river shorelines .” 123 In addition, increasing temperatures and loss of Arctic sea ice increases the risk of drowning for those engaged in traditional hunting and fishing. The USGCRP NCA3 concludes that 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 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 conclude 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

123 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnera bility. Part B: Regional Aspects
. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O . Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, p. 1581.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **95** of **193** 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 Public Welfare The EPA has carefully

reviewed the recent scientific conclusions in the assessments regarding human
- induced climate change impacts on public welfare. 124 The EPA finds that they are largel y consistent with or strengthen the underlying science supporting the 2009 Endang erment 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

124 The CAA stat es that ‘‘[a]ll language referring to effects on welfare includes, but is not l imited 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 co mfort and well
- being, whether caused by transformation, conversion, or combination with other air pollutants.’’ CAA section 302(h). This language is quite broad. Importantly, it is not an exclusive list due to the use of the term ‘‘includes, but is not lim ited to, * * *.’’ Effects other than those listed here may also be considered effects on welfare.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **96** of **193** risk of net adverse impacts on U.S. food production and agriculture over time, with the potential for significant disruptions and crop fai lure 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 ypes of agricultural pr oduction will be relativel y resilient to climate change over the next 25 y ears or so, others will increasingly suffer from stresses due to extreme heat, drought, disease, and heavy downpours. From mid
- century on, climate change is projected to have more n egative impacts on crops and livestock across the country
. ” 125 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 consider adaptation (v ery high confidence). ” 126 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 addit ion, the IPCC SREX assessment specifically

notes that projected changes in extreme weather events will increase disaster risk in the agriculture sector.

125 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. 126 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 Chan ge [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, C am bridge, p. 1462.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **97** of **193** 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 of destructive pests and disease that pre sent 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 disru ption, reorganization, movement or loss. The NRC Arctic assessment states that climate change is likely to hav e a large negative impact on forested ecos ystems in the high northern latitudes due to the effects of permafrost thaw and greater wildfire freque ncy , 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **98** of **193** Similarly , the new assessments further support projections of water resource impacts associated with increased floods and short
- term drought in most U.S. r egions. 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. ” 127 The IPCC AR5 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 .” 128 The IPCC AR5 also projects that climate change will degrade surface water 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 increas ed 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, erosion, wetland submergence, and habitat loss
. The most recent assessments provide further evidence in line with the science supporting the 2009 Endangerment Finding. The USGCRP

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, p. 70. 128 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. Bi lir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, p. 1456
- 1457.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **99** of **193** NCA3 finds that, “S ea level rise, combined with coastal storms, has increased the risk of erosion, storm surge damage, and floodi ng for coastal communities, especially along the Gulf Coast, the Atlantic seaboard, and in Alaska. ” 129
T he IPCC AR5, the USGCRP NCA3 , and three of the new NRC assessments provide estimates of projected global sea level rise. These estimates, while not alwa ys 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 IPCC AR4 assessment , which was referred to in the 200 9 Endangerment Finding. 130 The NRC Sea Level Rise assessment projects a global sea level rise of 0.5 to 1.4 meters by 2100, which is sufficient to lead to a relative rise in sea level even around the northern coasts of Washington State , where the land is st ill rebounding from the disappearance of the great ice sheets
. The NRC National Security Implications assessment suggests that “the Department of the Nav y should expect roughl y 0.4 to 2 meters global average sea
- level rise by 2100. ” 131 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

129 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W . Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 9. 130 The 2007 IPCC AR4 assessment cited in 2009 Endangerment Finding estimated a projected sea level rise of betwe en 0.18 and 0.59 meters by the end of the century, relative to 1990. It should be noted that in 2007, the IPCC stated that including poorly understood ice sheet processes could lead to an increase in the projections. 131 NRC, 2011: National Security Implications of Climate Change for U.S. Naval Forces
. Th e National Academies Press, p. 28.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **100** of **193** assessments continue to recognize and characterize 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 clim ate impacts on energy , infrastructure, and settlements , the 2009 Endangerment Finding cited the assessment literature’s findings that temperature increases will change heating and cooling demand ; that declining water quantit y ma y adversel y impact the avail ability

of cooling water and h ydropower in the energy sector; and that changes in extreme weather events will threaten energy , transportation, water, and other key societal infrastructure, particularly on the coast. The most recent assessments provide further evidence in line with the science supporting the 2009 Endangerment Finding. For example, the USGCRP NCA3 finds that, “ Coastal infrastructure, including roads, rail lines, energy infrastructure, airports, port facilities, and military bases, are incre asingly at risk from sea level rise and damaging storm surges. ” 132 The 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 an d the increasing frequency and severit y of storms .

132 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. G lobal Change Research Program , p. 9.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **101** of **193** 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 Stabilization Targets assessment found that coral bleaching will increase due both to warming and ocean acidification. The NRC Understanding Earth's Deep Past assessment notes four of the five major coral reef cri ses of the past 500 million y ears were caused by acidification and warming that followed GHG increases of similar magnitude to the emissions increases expected over the next hundred years . Similarly, the NRC Ocean Acidification assessment finds that “[t]h e chemistry of the ocean is changing at an unprecedented 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.” 133 The assessment notes that the full range of consequences is still unknown, but the risks “thre aten coral reefs, fisheries, protected species, and other natural resources of value to societ y. ” 134 The IP CC AR5 also projects biodiversity losses in marine ecos ys tems, especiall y in the Arctic and tropics
.

133 NRC, 2010: Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean
. The National Academies Press , p. 5. 134 Ibid.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **102** of **193** 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 inundation 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 liv elihoods are threatened b y climate change and, “[i] n parts of Alaska, Louisiana, the Pacific Islands, and other coastal locations, climate change impacts (through erosion and inundation) are so severe that some communities are already relocating from histo rical homelands to which their traditions and cultural identities are tied. ” 135 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
. ” 136

135 Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Cl imate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, p. 17. 136 IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Wo rking Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, p. 796.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **103** of **193** In the 2009 Endangerment Fin ding , 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. Th e 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 com ing decade . . . and for them to become progressivel y more serious and more frequent thereafter. ” 137 The NRC National Security Implications assessment recommends preparing for increased needs for humanitarian aid; responding to the effects of climate change in geopolitical hotspots, including possible mass migrations; and addressing changing security needs in the Arctic as sea ice retreats. In addition, the NRC Abrupt Impacts report examines the potential for tipping points, thresholds beyond which major an d 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

137 NRC, 2013: Climate and Social Stress: Implications for Security Analysis. The National Academies Press , p. 18.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **104** of **193** from hydrates and permafrost
. But, the same report found that the potential for abrupt changes in eco sy stems, 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 extinct ion risk due to the speed of climate change), and cautioned that even abrupt changes such as the AMOC disruption that are not expected in this century can have severe impacts if/when they happen. 4. Consideration of Other Climate Forcers Both in the 2009 Endangerment Finding and in this action, the Administrator recognizes that there are other substances in addition to the six well
- mixed GHGs that are emitted from human activities and affect Earth’s climate (referred to as climate forcers). These can be gr ouped 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 simil ar recently

identified substances ; and (2) short
- lived substances

—tropospheric ozone and its precursor gases, water vapor, and aerosol particles and precursors. Some of these short
- lived substances

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

– have different, and often larger, climate effects when emitted at high altitudes
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Page **105** of **193** 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 anthropogenic climate change. 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 Ad ministrator’s view that the reasons originally stated for not including these substances in the scope of the GHG air pollution still apply at this time. For example, nitrogen triflouride and other recentl y discovered substances are not as well understood as the six well
- mixed GHG s , and tropospheric ozone is short
- lived in the atmosphere and is not directly emitted (it forms from emissi ons of various precursor gases)
. Regarding the short
- lived substances with different climate effects when emitted at high altitudes , the Aircraft Petition (see s ection 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 discussed in terms of radiative forcing: the IPCC AR5, the IPCC 2007 Fourth Assessment*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **106** of **193** Report (AR4), 138 the IPCC Special Report: Aviation and the Global Atmosphere (IPCC 1999), 139 the NRC’s Advancing the Science of Climate Change (NRC 2010), 140 and the NRC’s Atmospheric Effects of Aviation: A Review of NASA's Subsonic Assessment Project (NRC 1999). 141 In addition to high altitude water vapor and NO x , the literature indicates that aerosol particles, including black carbon, e mitted 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 signific ant scientific uncertainties 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 p urposes of the endangerment finding under section 231 of the CAA. The short
- lived nature of these substances means that, unlike the long
- lived GHGs, the climatic impact of the substance is dependent on a number of factors at the location and time of its e mission. The magnitude,

138 IPCC, 2007: Climate Change 2007: The Physi cal Scientific Basis . Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)] Cambridge University Press, 996 pp. 139 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. 140 NRC, 2010: Advancing the Science of Climate Change
. The National Academies Press , 528 pp
. 141 NRC, 1999: Atmospheric Effects of Aviation: A Review of NASA’s Subsonic Assessment Project. The National Academies Press, 54 pp.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **107** of **193** 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
o ther hemisphere, are often cooling due to increased destruction of methane). As the climatic effects of these substances when emitted at high altitudes were not addressed at length in the 2009 Endangerment Finding, the following subsections briefly summarize the findings of the major scientific assessments regarding these substances’ climatic effects at altitude and the various sources of uncertainty sur rounding 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 by both reflecting solar radiation (cooling) and trapping outgoing longwave radiation (warming). Unlike the warming effects associated with the six*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **108** of **193** long
- lived, well
- mixed GHG s , the warming effects associated with changes in cloud cover are more regional and temporal in nature
. The three key components of aviation
- induced cloudiness are persistent contrails, contrail
- induced cirrus, and induced cirrus. 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 above the United S tates by 2 percent between 1950 and 1988, with similar results reported over Europe. 142 As stated above, clouds can have both warmi ng and cooling effects, and persistent contrails were once considered to have significant net warming effects. However, m ore recent estimates suggest a smaller overall climate forcing effect of persistent contrails
. The IPCC AR5 best estimate for the glo bal 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 ). 143 To put this number into context, some examples of other IPCC AR5 best estimates for global mean radiative forcing include: 1.6 8 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

142 NRC, 1999: Atmospheric Effects of Aviation: A Review of NASA’s Subsonic Assessment Project . The National Academies Press, 54 pp. 143 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **109** of **193** W/m2 for nitrous oxide (very high confidence and with an uncertaint y range of .013 to 0.21 W/m2 ). 144 Inaddition, the NRC (2010) assessment suggested that contrails may a ffect regional diurnal temperature differences , but this has been called into question by the recent findings presented in the IPCC AR5 , which suggests that aviation contrails do not have an effect on mean or diurnal range of surface temperatures (medium confidence)
. Persistent contrails also sometimes lose their linear form and develop into cirrus clouds, an eff

ect 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 uncertainty range of 0.02 and 0.15 W/m 2 )
. 145
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 significant

144 IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science B asis. 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 145 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. A llen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University Press, 1535 pp.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **110** of **193** 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. 146 Neither IPCC AR4 nor AR5 is able to provide 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 been able to provide 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

. 147
b. Direct Radiative Forcing Effects of High Altitude Particle Em issions 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

146 IPCC, 2007: Climate Change 2007: The Physical Scientific Basis . Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)] Cambridge University Press, 996 pp. 147 IPCC, 1999: Aviation and the Global Atmosphere, Special Report to the Inte rgovernmental Panel on Climate Change [Penner, J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] Cambridge University Press, 373 pp.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **111** of **193** cooling and warming effects of aerosols 148 (though from all sources, not just aircraft). The Finding noted that the magnitude of aerosol effects can vary immensel y with location and 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. 149 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 sulfat e 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 attempted to quantify this effect from aviation. Goi ng back to the 1999 IPCC assessment, the direct effect of sulfate aerosols from aviation for the year 1992 is estimated at
- 0.003 W/m 2 with an uncertaint y range between
- 0.001 and
- 0.009 W/m 2

. 150 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 attempted to quantify this effect from aviation. The 1999 IPCC assessment estimates the global mean radiative forcing of

148 74 FR 66517 149 74 FR 66520 150 IPCC, 1999: Aviation and the Global Atmosphere, Special Report to the Intergove rnmental Panel on Climate Change [Penner, J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] Cambridge University Press, 373 pp.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **112** of **193** black carbon emissions to be 0.003 W/m 2 with uncertaint y spanning 0.001 to 0.009 W/m2

. 151 The IPCC 1999 assessment suggests its estimates of radiative forcing are high because the stratospheric black carbon effect remai ns too uncertain to quantify
.
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
. This leads to decreases in the formation of methane , which has a cooling effect i n the long
- term . This eventually contributes to decreases in ozone, which 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 highl y localized atmospheric 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

151 Ibid.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **113** of **193** 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 t ime of NO x in the upper troposphere, or roughly the cruise altitude for jet aircraft, is on the order of several day s. The IP CC AR5 presents the impact of aviation NO x emissions using a different metric, global warming potential ( GWP ), which is a measure o f 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 . 152 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
. Going back to the IPCC 1999 assessment, the globall y averaged radiati ve forcing estimates for aircraft emissions of NO x in 1992 were 0.023 W/m2 for O 3 - induced changes (uncertaint y range of 0. 0 11 to 0. 0 46 W/m 2 ), and
- 0. 0 14 W/m2 for methane

- induced changes (uncertaint y range of
- 0.005 to
- 0. 0 42 W/m2 )
. 153

152 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. 153 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **114** of **193** 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 upon any conclusions regarding 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
. 154 The continuing significant uncertaint ies 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 wel fare due to their contribution to ozone concentrations that exceed the NAAQS. d. Summary Overall, the state of the science as represented in the assessment literature highlights significant scientific uncertainties regarding the total net forcing effect of water vapor , NO 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 the se short
- lived substances is much lower than for the six long
- lived, well
- mixed GHG s . Given these uncertainties, the Agency is not

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

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Page **115** of **193** including these constituents in the proposed definition of air pollution for purposes of the endangerment finding under sect ion 231 of the CAA
. **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 future generations
. In this proposed action under CAA section 231(a)(2)(A), the EPA rel ies primarily on the extensive scientific and technical eviden ce in the record supporting the 2009 Endangerment F inding , including the major , peer - reviewed scientific assessments regarding the question of whether GHGs in the atmosphere endanger public health and welfare , and on the anal yt ical framework and conclusion s 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 a ssessments issued since closing the administrative record for the 2009 Endangerment Finding. N o more recent information or anal ys es suggest that it would be reasonable for the EPA to now reach a different or contrary conclusion for purposes of CAA section 231(a)(2)(A) than the Agency reached for purposes of section 202(a) in 2009. 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 recent judicial decisi ons*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **116** of **193** upholding those findings, the EPA believes the 2009 Endangerment Finding is firml y established and well settled. 155 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 Endan germent 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.

155 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).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **117** of **193** Section V. A of this proposal describes the Administrator’s reasoning for using the same definition and scope of the GHG air pollutant that was used in the 2009 Endangerment Finding. Section V. B puts forth the Administrator’s proposed finding that emissions of well
mixed GHGs from classes of aircraft engines used in covered aircraft contribute to the air pollution which endanger s public health and welfare. **The Air Pollutant** A. 1. Proposed Definition of Air Pollutant Under section 231, the Administrator is to determine whether emissions of any air pollutant from any

class or classes of aircraft engines cause or contribute to air polluti on 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 Administra tor 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 concentration ( e.g., stock) of the well
- mix ed 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 discussion 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **118** of **193** 2009 Endangerment Finding , name ly , the aggregate group of the same six GHGs : 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 p roposing 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 test 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. 156 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

156 As detailed in the 2009 Endangerment Finding proposal (74 FR 18904 (April 24, 2009) and continuing today, the UNFCCC, the U.S. and other Parties report their annual emissions of the six GHGs in 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 potential of multiple GHGs. Emissions of different GHGs are compared using GWPs , which as descr ibed 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 comm on and collective treatment of the six GHGs.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **119** of **193** of defining the air pollutant for the proposed cause or contribute finding under CAA section 231. The Administrator recognizes that in this case, the aircraft engines covered by this notice emit two of the six gases , but not the other four gases. Nonetheless, it is entirely appropriate, and in keeping with the 2009 Endangerment Finding and past EPA practice, for the Administrator to define the air pollutant in a manner that recognizes the shared relevant properties of all these six gases, even though they are not all emitted from the classes of
source s before her. 157 For example, a source 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 substances within the definition of GHG s share common, rele vant 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.

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

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Page **120** of **193**

2. How the Definition of Air Pollutant in the Endangerment Determination Affects Section 231 Standards. Under section 231(a), the Administrator is required to set “emission standards applicable to the emission of 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 det ermination 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 anticipated to endanger public health and welfare , then she is called on to set standards applicable to the emissions of this air pollutant. The term “standards applicable to the emissions of any air pollutant” is not defined, and the Administrator has the discretion to interpret it in a reasonable manner to effectuate the purposes of secti on 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 class. 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 pollutant. The Administrator would consider a variet y of factors in determining what approach to take in setting the*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **121** of **193** standard or standards; for example , she would consider the characteristics of the aircraft emissions, such as rate and variability, the kind and availability of control technology , and other matters relevant to setting standards under section 231. 158 **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 emissions are responsible for the ch ange in the stock of 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 prox y for annual incremental changes in atmospheric conce ntrations.

158 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 standards w ere 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 throu gh reduced refrigerant leakage (hydrofluorocarbons) and indirect CO 2 emissions related to the increased load on the engine. 75 FR 25324 (May 7, 2010).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **122** of **193** 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 used e xclusively 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 the a ir pollutant from the section 231 category to the total U.S. and total global emissions of the six GHGs. The Administrator recognizes that there are other valid comparisons that can be considered in evaluating whether emissions of the air pollutant cause or contribute to the combined concentration of the six GHGs . To inform the Administrator’s assessment, section V.B.2 presents the following t ypes of simple and straightforward comparisons of U.S. aircraft GHG emissions :

 As a share of current total U.S. GH G 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
.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **123** of **193**

2. Overview of Greenhouse Gas Emissions Atm ospheric concentrations of CO 2 and other GHGs are now at essentiall y unprecedented levels compared to the distant and recent past. 159 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 160 of CO 2 equivalent (Tg CO 2 eq)
. 161 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)
.

159 IPCC, 2013: Summary for Policymakers. In: Climate Change 2013 : The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.
- K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, p. 11. 160 One teragram (Tg) = 1 million metric tons = 1 megatonne (Mt). 1 metric ton = 1,000 kg = 1.102 short tons = 2,205 lbs. 161 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. M inx (eds.)]. Cambridge University Press, 1435 pp.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **124** of **193** The Inventory of U.S. Greenhouse Gas Emissions and Sinks Report 162 (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 redu ced 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 heating requirements
. The U.S. Inventory also shows that while overall U.S. G HG 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 no t yet subject to any GHG regulations. Because 2010 is the most recent ye ar for which IPCC em issions data are available, we provide 2011 estimates from another widel y used and recognized global dataset, the World Resources Institute ’s (WRI ) Climate Analy sis Indicators Tool (CAIT) , 163 for comparison. According to WRI/CAIT, the t otal global GHG emissions in 2011 were 43 , 816 Tg of CO 2 eq ,

162 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)
. 163 World Resources Institute (WRI) Climate Analysis Indicators Tool (CAIT) Data Explorer (Version 2.0). Available at http://cait.wri.org (Last accessed February 5, 2015 ).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **125** of **193** represent ing an increase in global GHG emissions of about 42 percent since 1990 and 30 percent since 2000 (excluding l and 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, c urrent U.S. GHG emissions rank only behind Chin a ’s , which was responsible for 24 percent of total global GHG emissions
. 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. GH G 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **126** of **193** electricity generation), contributing 1,948 Tg CO 2 eq or about 30 percent of total U.S. GHG 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 States, behind light
- duty v ehicles and medium
- and heav y - duty trucks ( 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 .E traditionally the EPA (and FAA) participates at ICAO in the development of international standards, and then where appropriate, the EPA establis hes domestic aircraft engine emission standards under CAA section 231 of at least*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **127** of **193** equivalent stringency to ICAO’s standards
. An international CO 2 emissions standard is anticipated in February

2016, and provided that the EPA makes a positive endangerment f inding 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 proceed 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 k ilograms; and for subsonic propeller driven (e.g., turboprop ) aircraft , a MTOM greater than 8 , 618 k ilograms. 164 Applying these gross weight thresholds, our proposed cause or contribute finding applies to GHG emissions from classes of engines used in covered aircraft
. Examples of covered aircraft would include small er jet aircraft such as the Cessna Citation II and the Embraer E170 , up to the largest 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 ap plicability 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

164 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)
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Page **128** of **193** aircraft that fall below the international applicab ility thresholds : smaller turboprop aircraft, such as the Beechcraft King Air, and smaller jet aircraft, such as the Cessna Citation I
. In addition, I CAO (with U.S. participation) has agreed to exclude “ piston
- engine aircraft, ”

“ helicopters, ” and “ military aircraft ” 165 from the ty

pes of aircraft that would be covered b y the anticipated ICAO standards. 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 would 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 global 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.

165 ICAO regulations only apply to civil aviation (aircraft and aircraft engines), and consequently, ICAO regulations do not apply to military aircraft.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **129** of **193** aircraft GHG emissions 166 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
. 167 The U.S. covered aircraft also represent 3 percent of total U.S. GHG emissions , which is approximately equal to the contribution from total U.S. aircraft of 3.2 percent (Table V.1)
. 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
- zero emissions for total aircraft and covered aircraft. 168 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

166 [INSERT REFERENCE f or ERG analysis of covered aircraft (or the general aviation jet fuel breakout) after it is completed.] 167 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. 168 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)
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Page **130** of **193** do not emit methane, 169 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. TRANSPORTATI ON 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 Share of total U.S. Inventory 228 14% 3.7% 26 2

12% 3.7% 254

12% 3.5% 216

11% 3.1% 215

11% 3.2% 212

11% 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 %

169 Emissions of methane from jet fuels are no longer considered to be emitted across the time s eries from aircraft gas turbine engines burning jet fuel A at higher power settings (EPA, Recommended Best Practice for Quantifying Speciated Organic Gas Emissions from Aircraft Equipped with Turbofan, Turbojet and Turboprop Engines , EPA
- 420
- R
- 09
- 901, May 27, 2009 (see http://www.epa.gov/otaq/regs/nonroad/aviation/420r09901.pdf ). Based on this data, methane emissions factors for jet aircraft were reported as zero to reflect the late st 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 Inventories Programme, The Intergovernmental Panel on Climate Change, H.S. Eggleston, L. Buendia, K. Miwa, T Ngara, and K. Tanabe (eds.). Hayama, Kanagawa, Japan.) The EPA uses an emissions factor of zero to maintain consistency with the IPCC reporting guidelines, while continuing to stay abreast of the evolving research in this area. For example, one r ecent study has indicate d that modern aircraft jet engines oper ating at higher power modes consume rather than emit methane (Santoni et al. , 2011: Aircraft Emissions of Methane and Nitrous Oxide during the Alternative Aviation Fuel Experiment, Environ. Sci. Technol., 45, pp. 7075
- 7082).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **131** of **193** Transportation Sector emissions (Tg CO 2 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. 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **132** of **193** 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”). 170 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 emissi ons , 171 10 percent of global transport GHG emissions, and 1.5 percent of total global GHG emissions in 2010
. Comparing data from the U.S. Inventory to IPCC AR5, we find that total U.S. aircraft GHG emissions represented about 29 percent of global aircraft GHG emissions, about 3.1 percent of global transport GHG emissions , and about 0.5 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 compari sons using 2011 estimates from WRI/CAIT and the International Energy Agency (IEA) 172 and found that they yi eld very similar results. 173

170 ICAO CAEP , 2013 : ICAO Enviro nmental Report 2013, Aviation and Climate Change , 224 pp . Available at http://cfapp.icao.int/Environmental
- Report
- 2013/ (Last accessed February 5, 2015)
. 171 Worldwide GHG emissions from ICAO c overed aircraft include emissions from both international and dom estic aircraft operations around the world. 172 International Energy Agency, Data Services. Available at http://data.iea.org (Last accessed February 5, 2015 ). 173 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **133** of **193 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 o nly China, United States, I

ndia, Russian Federation, Japan, Brazil, Germany, and Indonesia , and ahead of about 175 other countries. Total U.S. aircraft GHG emissions have historically been and continue to be by far the largest contributor to global aircra ft GHG emissions. Total U.S. aircraft GHG emissions are about 7 times higher than aircraft GHG emissions from China, which globally is the second ranked country for aircraft GHG emissions, and about 5 times higher than aircraft GHG emissions

emissions, 3. 3 percent of global transport GHG emissions, and 0.5 percent of total global GHG emissions in 2011
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Page **134** of **193** from all of A sia. 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 emission s 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 f rom U.S. covered aircraft increased b y about 12 percent from 1990 to 2010 , the portion attributable to U.S. international aviation bunker fuels 174 increased b y about 1 00 percent. 175 During this same time period, g lobal aircraft GHG emissions grew b y about 4 0 percent, and the portion attributable to global international aviation bunker fuels increased b y 80 percent
. 176 , 177 Notwithstanding the substantial growth

174 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). 175 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). 176 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
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Page **135** of **193** in GHG emissions from U.S. international aviation bunker fuels, U.S. covered aircraft emissions hav e 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 suffere d several major shocks that reduced demand for air travel. 178 , 179 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 . 180 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 markets) have been growing rapidl y, and the global market is expected to continue to grow significantl y over the next 20 to 30 y ears. 181

177 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 acce ssed February 5, 2015). 178 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). 179 These shocks include the September 11 terror attacks , significant increases in fuel prices , debt restructuring in Europe and U.S. , and a global recession. 180 According to the FAA Aerospace Forecast , in 2013 U.S. air carriers w ere profitable for the fourth consecutive year. 181 According to the FAA Aerospace F orecast , the International Air Transport Association (IATA) reports that world air carriers (including U.S. airlines) are expected to register an operating profit for 2013. Based on financial data compiled by ICAO and IATA, between 2004 and 2013 world airl ines produced cumulative operating profits (with nine years out of ten posting gains) and net profits (with six years out of ten posting gains).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **136** of **193** 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 y ears in the ir abs olute 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 improvements). 182 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. 183 These aircraft groups ( U.S. air carriers and general aviation aircraft operating on jet fuel) are of similar scope to the U.S. covered aircraft whose engine GHG emissions are the subject of this proposed finding . Using fuel burn growth rates provided above as a scaling factor for growth in GHG emissions ( globall y and nationally) , it is estimated that GHG emissions from IC AO covered aircraft and U.S. covered aircraft would increase at a simi lar rate as the fuel burn by

2030, 2034, and 2040
.

182 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)
. 183 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_A erospace_Forecast.pdf (Last accessed February 5, 2015)
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Page **137** of **193**

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 th an 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 contribution 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 fi nding, 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. 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **138** of **193** cause or contribute finding would result in the vast majority ( 9 0 percent) o f 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. GH G 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 com e. 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 positi ve 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 v iewed 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 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 part even if their contributions to the global problem, measured in terms of percentage, are smaller than typicall y encountered when*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **139** of **193** tackling solel y regional or local environmental issues .” 184 The Administrator continues to believe that these unique, global aspects of the climate change problem

—including that f

rom a percentage perspective there are no dominating sources emitting GHGs an d few sources that would even be considered to be close to dominating

—tend to support consideration of contribution to the air pollution at lower percentage levels than EPA t ypically encounters when anal yz ing contribution towards a more localized air pol lution 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 significant weight on the fact that engines used in U.S. covered aircraft contribute 3 percent of total U. S. GHG emissions for the proposed contribution finding and comprise the single largest transportation source in the United S tates that has not y et been regulated for GHG emissions.

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

184 74 FR 66543 (December 15, 2009).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **140** of **193** aircraft and U.S. covered aircraft engines ar e likely to increase by

almost 50 percent. 185 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 i ncrease 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 that have not yet been promulgated). In addition, by 2034 the rail sector is proje cted to experience a 6 percent reduction in GHG emissions from 2010 baseline
. 186 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
.

185 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 i ncrease at a similar rate as the fuel burn by 2030, 2034, and 2040. 186 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
- 2025, and for heavy duty trucks GHG standards for years 2014
- 2018, plus improvements in vehicles and engines for all subsectors due to availability of fuel
- saving technologies and fuel price effects. EIA counts biofuels as zero tailpipe GHG emissions. Because the 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 January 13, 2015).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **141** of **193** 

## VI. **A dvance**  **N otice of**  **P ro**  **posed R** **ulemaking : Discussion of**  **Ongoing International Pr oceedings 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 emissions 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 2016, when ICAO/CAEP is expected to fina lize 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 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 on a variet y of issues related to setting an international CO 2 standard for aircraft , including whether such standards should appl y to in
- production aircraft instead of new*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **142** of **193** a ircraft 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 meeting (CAEP/9) in 2013 in reaching an agreement on the appropriate metric to be used in ass essing fuel efficiency (or CO 2 emissions) 187 of an engine/ aircraft combination
. They also reached agreement on a mature certification requirement 188 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. 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. E , the EPA and the FAA

187 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 Jul y 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.” 188 ICAO defines a certification requirement as a com bination of metric, procedures, instrumentation and measurement methodology, and compliance requirements
.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **143** of **193** 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 b y the U.S. Court of Appeals for the D.C. Circuit. Provided the EPA makes a positive endangerment finding 189 under CAA section 231 and ICAO 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
. **Purpose of the Internati onal 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 crite ria of technical feasibility, environmental benefit, cost effectiveness, and impacts

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

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Page **144** of **193** of interdependencies .” 190 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 standard 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 requests comment on how to achieve the purpose of the standard
. **Applicability of the International CO 2**  **Emissions Standard**  B. 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 type designs.
In
- production aircraft and new aircraft types are defined as follows:

190 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
..*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **145** of **193** - In
- production aircraft : those aircraft ty pes which have alread y 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
. 191 , 192 , 193

- New aircraft ty

pes : aircraft ty

pes that have applied for a Ty pe C ertificate 194 after the effective date of a standard and that have never been manufactured prior to the effective date of a standard. In addition, for context, o ut of production aircraft are those aircraft t ypes which have alread y received a T yp e Certificate, but for which manufacturers either have no existing undelivered sales orders or would n ot be willing and able to accept new sales orders. These aircraft are aircraft ty

pes that are no longer in active production
. 195

191 ICAO, 2013: CAEP/9 Agreed Certification Requireme nt for the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, AN/192 , Available at www.icao.int (Last accessed February 5, 2015). 192 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 types for purposes of the CO 2 standard. 193 According to ICAO Cir 337, a Type Certificate is “[a] document issued by a Contracting State to define the design of an aircraft type and to certify that this design meets the appropriate airworthiness requirements of that State”. 194 A Type Certificate is a design approval process whereby the FAA ensures the manufacturer’s designs meet the minimum requirements for aircraft safety and environmental regulations. This is typically issued only once for each aircraft, and modified as needed as an aircraft is modified over the course of its production life. This Ty pe Certificate (for new aircraft types) would be the initial or new T ype Certificate for this aircraft. 195 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **146** of **193** As described earlier in section II.E , CAEP ’s Steering Group meeting in 2010 agreed that the scope of applicability for the international aircraft 196 CO 2 standard should 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 should appl y to new aircraft types, 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. It is important to further des cribe 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

aircraft engine standards have applied to in
- use aircraft only in very limited situations, such as the prohibition ag ainst 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 21 3(a), section 231 of the CAA does not restrict the EPA’s authority to set standards for only ne w aircraft. 196 ICAO/CAEP utilizes the term “aeroplane” which is the British spelling of “airplane”. According to 40 CFR 87.3, “airplane” means a fixed
- wing air cr aft that is heavier than air. For the purposes of this action, we will instead use the term “aircraft,” which we have previously defined in 40 CFR 87.1 as follows: “A ircraft has the meaning given in 14 CFR 1.1, which defines aircraft to mean a device used or intended to be used for flight in the air. Note that under §87.3, the requirements of this part generally apply only to propulsion engines used on certain airplanes for which U.S. airworthiness certificates are required. ”*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **147** of **193** improvements. 197 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 be 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 packages that may be added to an aircraft or engine at some poi nt 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 , 198 , 199 , 200 indicate that it is un likely a new t ype de sign will seek certification in the next 10 to 15 years . 201 S ignificant partial redesigns do not occur often, but are slightly

more frequent than new ty pe designs. For example, after the current

197 New aircraft types fall und er 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. 198 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)
. 199 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). 200 ICF, CO 2 Analysis of CO 2 -Reducing Technologies for Aircraft , Final Report, EPA Contract Number EP
- C
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. 201 Ibid.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **148** of **193** significant par

tial redesign wave 202 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
o f significant partial redesigns included the Boeing 777
- 200LR in 2004, 777
- 300ER in 2006, 737NG in 1998, Airbus 319 in 1996, and Airbus 330
- 200 in 1998). 203 Incremental improvements will likely be frequent and occur in the near term. O ne approach for CAEP would be to limit the applicability of any international CO 2 standard to new type designs (or new aircraft t ypes). Under this approach s ignificant partial redesigned aircraft and incremental improvements would be characterized as changes made to in
- production aircraft; thus, these categories of aircraft (or these changes) would need to meet the international CO 2 standard onl y if it applied to in
- production aircraft
. Another approach for applicability of the international CO 2 standard that CAEP could adopt would be an approach based on criteria addressing significant changes to aircraft designs , which could be considered an applicability requirement different than that for new aircraft ty pes onl y and in
- produ ction aircraft. This alternative approach could redefine a new aircraft ty pe 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

202 In general, design waves are prompted by the combination of market demand for new aircraft performance needs (e.g., more seats for longer range) and the age of existing aircraft, and design waves are typically enabled by advances i n propulsion technology. 203 Ibid.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **149** of **193** 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 standard204 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 type design that may adversel y affect 205 its CO 2 emissions. This possible definition cou ld 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 conside red to be a new ty pe 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 by CAEP). The EP A requests comment on this change
- based criteria approach , including how to identify

those changes that would result in treating in
- production aircraft as new t ypes subject to the standard
. If CAEP were to limit the scope of applicability to new aircraf t t ypes onl y ( and without the significant change criteria approach described above), the international CO 2 standard would not appl y to later series aircraft with redesigned wings, aircraft that are

204 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)
. See Chapter 1. 205 Due to substantial market forces to alleviate any adverse effects on aircraft fuel burn or CO 2 emissions, adverse changes are rare.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **150** of **193** available with different engines , or aircraft that undergo incremental improvements. Following are several examples that illustrate this situation. The re
- engined Boeing 737 Max is an example of a significant partial redesigned aircraft that is expected to enter into service in 2017. 206 This aircraft would fall under the original Boeing 737 Ty pe Certificate that was 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 a s defined by CAEP. The current 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 t ype aircraft when they

were introduced in 1998 . Another example of an aircraft that 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 engines, 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 Generation 737 performance improvement package which was implemented between 2011 and 2013 and the Boeing 767
- 300 winglets that entered into service in 2008, both of which improve aircraft fuel efficiency
. There are man y other examples that exist for different manufacturers and aircraft around the world as well, but for conciseness, we are

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

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Page **151** of **193** limiting our discussion to these above examples. These examples illustrate the ty pical certification for significant partial redesigns and incremental improvements by various aircraf

t 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 , 207 and there are no currentl y announced new t ype designs that are expected to be introduced after the implementation dates being anal yz ed b y CAEP

– 2020 and 2023. Furthermore, based on provisions to which CAEP has alread y agreed , 208 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. 209 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 from business
- as - usual ( in comparison to CO 2 emissions reductions that would be

207 ICF, CO 2 Analysis of CO 2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
12
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. 208 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) . Sectio n 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 specifies 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. 209 The se dates assum e 5 y ears from application for the aircraft Type Certificate to entry into service, which is how long an application is valid for a Type Certificate
.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **152** of **193** achieved in the absence of a standard) before 2025
. Therefore, an international standard developed for only

new aircraft ty

pes 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 aircraft t ypes will 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 l onger - term of 20 ye ars plus
. 210 , 211 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 )? 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 ?

210 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. 211 ICF, CO 2 Analysis of CO 2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
12
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...*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **153** of **193** 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 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 reductions and the likely share of annual aircraft production that would be affected under the alternative approach. As a third approach, it may be more practical and flexible to regulate airline fleet average CO 2 emissions. Under such an approach we would set a slowl y - declining fleet average CO 2 emission standard for each airline, based on the CO 2 emission characteristics of its entire fleet. This would require CO 2 certification emission information for all engine s in the fleet from the aircraft engine manufacturers and information on hours flown and average power (e.g., thrust). Airlines would have CO 2 emission baselines for a given y ear based on the engine emission characteristics of their fleet, and beginning in a subsequent y ear, airlines would be required to reduce their emissions at some annual rate, at some rolling average rate, or perhaps to some prescribed lower level in a future year. This could be done as a fleet average CO 2 emission standard for each airline or through a surrogate measure of CO 2 emissions such as airline total fuel consumption, perhaps adjusted for flight activity in some way . The standards could cover all domestic operations and international departures of domestic airlines. The fleet av erage program could potentially be implemented in the near term since it is not as reliant on lead times for technology change. Although we might develop*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **154** of **193** such a declining fleet average emissions program based on engine emissions, an operational declining f

leet average program could potentially be designed to consider the whole range of engine, aircraft and operational CO 2 control opportunities discussed above. Under this approach compliance with a declining fleet average standard would be based not only on parameters such as engine emission rates and activity , but could also on efficiencies gained b y use of improved operational controls. It is important to note that as part of this approach, a recordkeeping and reporting s ys tem would need to be established f or airlines to measure and track their annual CO 2 emissions. Perhaps this could be accomplished through a surrogate measure of CO 2 emissions such as airline total fuel consumption. Today each airline reports its annual fuel consumption to the Department of Transportation. We request comment on the operational fleet average CO 2 emission standard concept, way s that it could be designed and implemented, an y important program design considerations, and potential metrics for establishing standards and determinin g compliance. 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 production . This includes (as described earlier) in
- production aircraft with incremental improvements (though we reiterate this would not include in
- use aircraft) . As an example of in
- production aircraft, the Gulfstream G650, which is currentl y in production and expected to*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **155** of **193** 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
. **CAEP Discussion on In**  **- Production Aircraft Applicability**  C. 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 optio ns provided to the 2014 Steering Group meeting, CAEP decided that it should continue to investigate potential in
- production aircraft applicability options, and that these should be presented at the July 2015 Steering Group meeting, so that a decision can b e taken at the 10th meeting of CAEP (CAEP/10) in February 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 processes for in
- production aircraft applicability , but the 2014 Steering Group meeting requested that CAEP focus on defining the mandatory

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

to In
- Production Aircraft and Date of I mplementation 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 pr ocess manufacturer certification applications. CAEP did not rule out later dates though and could consider implementation dates for an in
- production aircraft*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **156** of **193** CO 2 standard later than 2023 ( five ye ars following the new aircraft ty pe applicability

date, i.e. dates ranging from 2023 to 2028). The EPA seeks comments on both a 2023 implementation date and on possible later implementation dates for an in
- production domestic CO 2 (or GHG) aircraft engine emissions standard that would be adopted under CAA section 231 , 212 the impact the date of 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 articulated 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. 213 The EPA request s comments regarding whether appl yi ng an international CO 2 standard to in
- production aircraft is consistent with the purpose of the standard as advised by the CAEP Steering Group meeting in 2011 : “ to achieve CO 2 emission reductions from the

212 Traditionally, international emission standards have first been adopted by ICAO, and subsequently the EPA had initiated rulemakings under CAA section 231 to establish domestic standards equivalent to ICAO’s standards where appropriate. Provided ICAO adop ts an international aircraft CO 2 standard that is consistent with CAA section 231 and it is appropriate for domestic needs in the United States, we expect to proceed along a similar approach for the future CAA section 231 aircraft engine CO 2 standard (or a ircraft engine GHG standard), provided the EPA issues final positive endangerment and cause or contribute findings under CAA section 231. 213 CAEP determined in 2012 that all technology responses would have to be based on technology that would be in common u se 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 2 016 or shortly thereafter.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **157** of **193** aviation sector beyond expected ‘ business as usual ’
... anal yz ed using IC AO criteria of technical feasibility , environmental benefit, cost effectiveness, and impacts of interdependencies.” 214 The International Coalition for Sustainable Aviation (ICSA) , 215 which is a CAEP Observer organization, submitted papers to CAEP that analy zed this issue. Also, a member of ICSA 216 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 for 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. 217 , 218 Another study funded by

the EPA corroborates this analy sis. 219 The

214 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
. International Coalition for Sustainable Aviation (ICSA), “ ICAO’S CO2 Standard as Part of a Basket of Measures to Meet Emissi on Reduction Goals ” , ICAO Assembly
- 38th Session, Executive Committee, Agenda Item 17
- Environmental Protection, A38
- WP/297 , EX/99 , September 19, 20 13
. 215 The International Coalition for Sustainable Aviation (ICSA) is a structured network of enviro nm ental non governmental organiz ations (NGOs) who share a common concern with civil aviation’s contribution to air quality issues, climate change and noise, and who are committed to developing and providing technical expertise, common policy positions and strateg ies with a view to reducing emissions an d noise from aviation
. See http://www.icsa
- aviation.org/
. 216 The International Council on Clean Transportation (ICCT) is a member of ICSA, and ICCT is an independent no nprofit organization founded to provide research and technical and scientific analysis to environmental regulators. See http://www.theicct.org/
. 217 ICCT, Efficiency Trends for New Commercial Jet Aircraft 1960 to 20 08, November 2009.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **158** of **193** EPA requests c omments on whether applying the international CO 2 aircraft standard onl y to new aircraft t ypes would be consistent with the stated purpose of the international standard. Lastl y, the EPA requests comment on the appropriateness of following either of th e s e approach es (applicability to only new aircraft t ypes or both new aircraft types and in
production 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 international 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 cos ts 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 internat ional CO 2 standard to in
- production aircraft
.

218 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
. 219 ICF, CO 2 Analysis of CO 2 -Reducing Technologies for Aircraft , Final Report, EPA Contract Number EP
- C
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Page **159** of **193**

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 requirement220 , 221 , 222 for in
- production aircraft CO 2 e missions rates (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 r ates data are gathered quickly prior to an effective date for the final standard (tracking CO 2 emissions rates is

220 Currently, CAEP is developing a publi cly 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, if the international aircraft CO2 standard applies to only new aircraft types, it could be many years before any data exists in this database. 221 For many years, ICAO ha s 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 also have aircraft engine emission standards for these pollutants). It conta ins 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
. 222 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).*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **160** of **193** beneficial for the reasons discussed later in this section and for potentiall y assisting with the assessment of a future CO 2 standard)
. The E PA requests 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
. In 2009 the EPA promulgate d 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 . 223 , 224 The EPA’s experience with reporting programs indicates that the EPA 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
-

223 EPA’s 2009 rule on Mandatory Reporting of Greenhouse Gases included engine manufacturers for the following mobile source sectors: highway h eavy - duty (engine and vehicle) , non - road, aircraft, locomoti ve, marine , snowmobiles, and motorcycles. Manufacturers of aircraft jet engines of rated output (or thrust) greater than 26.7 kilonewtons are required under this program to report annually to the EPA 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 n ot 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. 224 An aircraft manufacturer rep orting requirement 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 aircr aft 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **161** of **193** production international aircraft standard is adopted would enab le 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. When similar methods for monitoring, measurement, and reporting are applied across an industry , it can lead to more consistent, accurate, and timel y data to inform decision
- making for individual manufacturers and the EPA (inc luding a comparison of the CO 2 emissions 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 take 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). 225 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

225 This GHG or CO 2 emissions rate data will help to track tre nds, raise awareness, better understand the technology in the fleet, etc.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **162** of **193** 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
- pr oduction aircraft226 (after we promulgate such a requirement)? Additionally , if we were to pursue such an independent reporting requirement, should we require the annual reporting of the GHG or CO 2 emissions rates from in
- production aircraft ( and an y new t y pe aircraft) 227 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.

226 In this case, manufacturers 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 wh ich 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. 227 By applying a reporting requirement to in
- production aircraft after a certain implementation date, this reporting requirement also includes ne w aircraft types that are produced after this implementation date.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **163** of **193 Metric System, Applicability, and Certificat**  **ion Requirement** D. T he CO 2 metric sy stem and mature certification procedure were agreed upon by CAEP in 2013. 228 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
.

1. CO 2 Metric System The metric s ys tem was developed to cover a wide range of aircraft t ypes, designs, technology , and uses. To do this, the metric system was designed to differentiate between generations of aircraft and to equitably capture improvements in aerospace technology (structural, propu lsion, and aerodynamic) that contribute to a reduction in the airplane CO 2 emissions. I

n 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 aircra ft. 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

228 As described earlier, the c ertification 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 certifica tion requirement.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **164** of **193** performance which measures the distance an aircraft can travel for a unit of fuel. This is similar to the instantaneous “miles per gallon” readings in man y cars today. The SAR data
are gathered at three gross weight points. The three equall y weighted points are used to represent a range of day

to day aircraft operations. 229 The functio nal form of the metric sy stem is provided below.

= 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 * (MTOM0.924) ) 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,

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

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Page **165** of **193** 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 to apply the international CO 2 standard to subsonic jet and propeller
- driven aircraft meeting the following criteria : All subsonic jet aircraft over 12,566 lbs (5,700kg) MTOM. All subsonic propeller driven (e.g. turb oprop) 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **166** of **193**

3. Certification require ment CAEP has developed a mature certification requirement230 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 incudes 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 aircraft conformity , weighing, fuel specifications, test condition stability criteria, required confidence intervals, measurement instrumentation required, and corrections to reference conditions. These CO 2 test procedures are based upon manufacturer’s existing 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 there 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 sep arate equivalent certification

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

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Page **167** of **193** 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 equitabl y reward improvements in aircraft technologies that reduce emissions, including advances in structures (aircraft weight), propulsion (engine specific fuel consumption), and aerodynamics
. T hese three factors are key to the overall aircraft CO 2 emissions. Inaddition, CAEP believes (as do es the EPA) 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 key factors have on the aircraft CO 2 emissions from engines
. The three factors
-- and technology

categories that improve these factors
-- are described as follows : 231
S tructures: reducing basic aircraft weight to increase the commerci al 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

231 ICAO, Environmental Report 2010

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

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Page **168** of **193** Aerod ynamics: advancing the aircraft aerody namics, to reduce drag and its a ssociate impacts on thrust. Specific examples of technologies that affect these three factors help to further illustrate that it is best to consider the aircraft as a whole in addressing CO 2 emi ssions. For structural improvements, aircraft manufacturers have shown significant weight reduction results over time due to the progressive introduction of new technologies such as: advanced alloy s and composite materials, improved and new manufacturing processes and techniques (including integration and global evaluation simulation ), and new s ys tems ( e.g. fly
- by
wire ). 232 For propulsion improvements, technologies include enhanced compressors (e.g., i ntercooled compressors ) and r educed hub
- tip ratio fan s . 233 As another example, manufacturers seek higher operating pressure ratios (OPR) to improve combustion and engine cycle refinements. For aerod ynamics, 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

232 Ibid. 233 ICF, CO 2 Analysis of CO 2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
12
- 011, [INSERT FINAL DATE]
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Page **169** of **193** give an increase in the effective aerod yn amic span of wings, particularl y where wing lengths are li mited 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 mainta in laminar flow via Natural Laminar Flow and Hy brid Laminar Flow Control (HLFC) to reduce turbulent skin friction. 234 The first production example of a HLFC system went into service on the new Boeing 787
- 9 in 2014. **Stringency Options** E. 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 t his includes the wide range of technology that is currentl y in the aircraft fl eet. 235 Generally, the stringency options that are being evaluated fall into three categories as follows: (1) CO 2 stringency levels that would impact only the oldest, least ef fi cient aircraft in
- production around the world, (2) middle range CO 2 stringency levels that would impact many aircraft currentl y in
production and composing much of the current operational fleet, and (3) CO 2 stringency

234 ICAO, Environmental Report 2010

– Aviation and Climate Change , 2010, which is located at http://www.icao.int/environmental
- protection/Pages/EnvReport10.aspx
. 235 The ICAO standard has the follow ing applicability weight threshold s: ma ximum takeoff mass greater than 5,700 kilograms for subsonic jet aircraft and ma ximum takeoff mass greater than 8 , 618 kilograms for turboprops
.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **170** of **193** levels that could impac t 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, 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 considerat ion at CAEP and CO 2 metric value levels of today ’s in
- production and in
development 236 aircraft
. The data shown were generated by the EPA using a commerciall y available aircraft modeling tool called PIANO. 237 This model contains non
- OEM estimates of th e 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 upwards sloping and have a “kink” at 60 ,000 kilograms . The “kink” was included in the stringency options as a technical approach to reflect the different behaviors observed between the larger and smaller aircraft.

236 Aircraft that are currently in
- development but will be in production by the applicability dates. These could be new types or significant partial redesigned aircraft. 237 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 publicly available software suite used across the industry, and academia to model aircraft performance.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **171** of **193** The official stringency

options under consideration at CAEP have not been cleared for release outside of the participating members since deliberations on the standard are still ongoing (proceedings are expected to be completed at CAEP/10 in February 2016). To show the relative efficiency

of the aircraft , Figure 1 and Figure 2 below show the aircraft metric values 238 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 notionally reflect the three ranges of options discussed above. Figure 1 shows the makeup of the current produc tion fleet and the in
- development aircraft. This is what CAEP is using as the starting point for modeling the effect of the CO 2 standard . Figure 2 shows what the EPA expect s the market to look like in 2023, considering the publicly announced plans b y indus try to replace existing aircraft with new products.

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

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Page **172** of **193 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **173** of **193**

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

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Page **174** of **193 Figure**  **2**

**– Lines of constant technology level over the predicted 2023 in**  **- production fleet** 
A standard set near the upper constant technology level would affect a very modest number of aircraft, namely the oldest, least efficient ty pes. Man y of the aircraft that would be affected b y such a stringency level are being produced in very limited numbers and may not be eligible to operate in U.S. air space
. Aircraft around the middle two constant technology levels reflect the performance of many aircraft that are c urrently 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. Constant technology levels at the bottom of the charts 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 b y the effective date of the standard. The replacement single aisle aircraft and new twin aisle aircraft from Boeing and Airbus are at the edge of the most stringent option. Figure 3 and 4 sho w the margin of the lines of constant techn ology to the upper bound or worst performing technology bound under consideration. This is shown to further illustrate the range of technology

present in the in
- production and in development fleet. Figure 3*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **175** of **193** provides the perspective from the current in
- production and in
- development fleet, and Figure 4 shows a viewpoint of the projected 2023 market.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **176** of **193** -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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **177** of **193 Figure**  **3**

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

**production and in development fleet**

**Fig ure**  **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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **178** of **193** 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 woul d 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 1
. There is ongoing discussion on what appropriate levels of stringency may be for new ty pe and in
- production aircraft. An y final EPA decisions will have to wait until the full anal y sis has been conducted at CAEP. As explained in sections B and 1 , n ew 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 t ype aircraft to improve. However, this is challenging to develop 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 level s at CAEP
.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **179** of **193** 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 consideration at CAEP is still based on technology available today . An y new ty pe aircraft that may be developed and certified 10 years or more from now would be expected to use more advanced fuel efficient technology that is not y et developed or tested. The implications for an in
- production standard are more significant in the near term for manufacturers. Aircraft 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 not y et 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 technology 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 e ffect. 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
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Page **180** of **193 Costs, Technology Responses for Stringency Options, and Cost**  **- Effectiveness**  F. **A nalysis**  The EPA has been involved in CAEP’s effort to analyze the CO 2 stringency options and the potential costs and environmental impacts that would result fr om both new ty pe only CO 2 standards and in
- production international CO 2 standards. CAEP is still determining the best way to conduct portions of this analysis. The inputs that have been developed b y the CAEP include non
- recurring costs data and technology responses for the various stringency options under consideration. Th is section describes the development of these inputs. The EPA requests comments on how the modeling should be conducted to differentiate in
production and new type scenarios.

1. Non
- Recurring Costs (engineering development costs) CAEP developed a singl e 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 includin g high level information that has been made available to the public. This was considered to be a top down estimate because it included all aircraft development costs (airworthiness certification, noise, etc.) not just those for CO 2 improvements. The EPA saw the need to supplement this dataset with an estimate of CO 2 - only changes, which was considered to be a bottom up estimate. The EPA contracted with ICF to*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **181** of **193** develop an estimate of the cost to modify in production aircraft to comply with a CO 2 standard. ICF conducted a detailed literature search, conducted a number of interviews with industry leaders, and did its own modeling to estimate the cost of making modifications to in production aircraft. 239 The results from this peer - reviewed stud y were then combined with inputs from the industry

and the rest of the CAEP 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. A top
- do wn approach was used to model large changes to aircraft design, such as what would be seen in significant partial redesigns or new ty pes. For significant partial redesigns that result in new series of an established model, these ty pes of changes may

i nclude : redesigned wings, new engine options, longer fuselages, improv ed aerod ynamics, or reduc ed weight. When making significant changes to an aircraft many other changes and updates get wrapped into the process that do not have an effect on the CO 2 emi ssions of the aircraft , and significant partial redesigns may not have been spurred b y 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 t ype (clean sheet) or significant partial redesign for major changes. Total costs for past projects were used to estimate non
- recurring cost for the CAEP

239 ICF, CO 2 Analysis of CO 2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Num ber EP
- C
12
- 011, page 32 [INSERT FINAL DATE]
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Page **182** of **193** anal ys is. This t ype of aircraft improvement/development program has historically ranged approximately

from 1 to 1 5 billion Dollars (U.S.) depending on the size of the aircraft and scope of the improvements desired. A bottom
- up approach was used 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 man y changes that would not be required for smaller CO 2 reductions. The EPA used the information gathered b y IC F to provide input on the cost for individual technologies which were used to build up non
- recurring costs for these incremental improvements (a bottom
- up approach). The technologies available to make incremental improvements to aircraft is wide ranging an d aircraft specific. Some examples of technologies that could be integrated into an aircraft for incremental improvements include improved fan blade design or reduction in turbine clearances in the engine, reducing the gap between control surfaces, carbon brake pads, or advanced wing tip devices. As an example, I CF estimated that depending on the additive nature of specific technolog ies and the magnitude*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **183** of **193** improvement required, the cost to incrementally improve the Boeing 767 could range from approximatel y 230 million to 1.3 billion US dollars
. 240

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 stan dard. At the outset, CAEP decided the international CO 2 standard would be a technology

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

responses would have to be based on technology that would be in common use by the time the standard was to be decided upon in 2016 or shortly thereafter, This generation of technology was defined within CAEP as a Technology Readiness Level (TRL) 8 241

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

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

240 ICF, CO 2 Analysis of CO 2 -Reducing Technologies for Aircraft, Final Report, EPA Contract Number EP
- C
12
- 011, page 33, [INSERT FINAL DATE]
. 241 TRL8 is a measure of Technology Readiness Level. “ Technology has bee n 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 me ets design specifications .” As defined by the US Department of Defense in: DOD Deskbook 5000.2

-R Appendix 6

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

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Page **184** of **193** and potentially

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

thereafter. EPA is reques ting 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 can be achieved c onsidering 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 of 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 market 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. Because CAEP has modeled all in
- production aircraft as respond ing by the implementation date of th e new - ty pe standard, CAEP has by definition , performed an in
-*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **185** of **193** 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 o nl y standard (b y assuming in
- production aircraft 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 e mission standard. CAEP is still determining the best way to conduct an analysis 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 typ es for the future international CO 2 standard , if it were to apply onl y to new types. The EPA also requests comment on how the modeling should be conducted to differentiate in
- production and new ty pe scenarios. **Request for Comment on Potential for a Different EPA Standard than International**  G. **CO 2**  **Standard** 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 to establish domestic standar ds that are of at least equal stringency as IC AO’s engine*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **186** of **193** standards. However, the Chicago Convention, 242 which established ICAO, recognizes that ICAO member s tates may adopt their own unique standards that are more stringent than ICAO standards
. A participating member state (or nation) that adopt s more stringent standards is obligated to notify I CAO of the differences between its standards and I CAO ’s standards
. S ection 231(b) of the CAA requires that an y emission standards “ take effect after such period as the Administrator finds necessary (after consultation with the Secretary of Transportation) to permit the development and application of the requisite technology , giving appropriate consideration to the cost of compliance during such period. ” 42 U.S.C. 7571(b). 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). As discussed in the 2005 rule (CAEP/4 aircraft engine NO x standard) , 243 the EPA needs to have a technical basis for expecting the standards will be achievable in a specific period of time. While the statutory langu age of section 231 is not identical to other provisions

242 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
. 243 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.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **187** of **193** in title II of the CAA that direct the EPA to establish technology
- based standards for various ty pes of mobile sources , the EPA interprets its authority under section 231 to be similar to those provis ions that grant us significant discretion to identify a reasonable balance of specified emissions reduction, cost, safet 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 stated policy for the purpose of the international CO 2 standard, 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 , 244 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, 1230
- 32 (D.C. Cir. 2007). T he Court also held that section 2 31 of the CAA confers a broad degree of discretion on the EPA to adopt aircraft emission standards that the Agency determines are reasonable. Id
.

244 Ibid
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Page **188** of **193** The EPA requests comment on our traditional approach of establishing domestic standards of at least equiv alent stringency to ICAO’s standards. Should we follow this 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 certification 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 Orde**  **r** A. **13563: Improving Regulation and Regulatory Review** This action is a significant regulatory action because it raises novel policy issues. Accordingl y, it was submitted to the Office of Management and Budget (OMB) for review. This action proposes a find ing 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **189** of **193** reductions and, if the EPA finds that aircraft GHG emissions do cause or contribute to endangerment, the potential use of CAA section 231 to implement these standards 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. **Paperwork Reduction Act (PRA)** B. This action does not impose an information collection burden und er the PRA. The proposed endangerment and cause or contribute f inding s under CAA section 231 do not contain any information collection activities. **Regulatory Flexibility Act (RFA)** C. I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. This action will not impose any requirements on small entities
. The proposed endangerment and cause or contribute 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 determination that GHG emissions from certain classes of aircraft engines

—those used in U.S. covered aircraft

— cause or contribut e to air pollution that may be reasonabl y anticipated to endanger public health and welfare. Accordingly, this action affords no opportunity

for the EPA to fashion for small entities less burdensome compliance or reporting requirements or timetables or ex emptions from all or part of the proposal
.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **190** of **193 Unfunded Mandates Reform Act (UMRA)**  D. 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 impo ses no enforceable duty on an y state, local or tribal governments or the private sector. **Executive Order 13132: Federalism** E. 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
. **Executive Order 13175: Consultation and Coordination with Indian Tribal**  F. **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 section 231 do not in
- and
- of
- themselves impose any 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 pollution that may be reasonably anticipated to endanger public health and welfare. Thus, E xecutive O rder 13175 does not apply to this action.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **191** of **193 Executive Order 13045: Protection of Children from Environmental Health Risks**  G. **and Safety Risks** This action is not subject to Executive Order 13045 because it is not economically significant as defined in Executive Or der 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 i s 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 pl aced in the public docket for this action.*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **192** of **193 Executive Order 13211: Actions Concerning Regulations That Significantly Affect**  H. **Energy Supply, Distribution or Use** This action is not a “significant energy action” because it is not likely to have a significant adverse effect on the supply, distribution or use of energy
. Further, we have concluded that this action is not likely to have any

adverse energy

effects because the proposed endangerment and cause or contribute finding s under section 231 do no t in
- and
- of themselves impose any n ew 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. **National Technology Transfer and Advancement Act (NTTAA)**  I. This action does not involve technical standards. **Executive Order 12898: Federal Actions to Address Environmental Justice in**  J. **Minority Populations and Low -**  **Income Populations** The EPA believes this action will not have potential disproportionately high and adverse human health or environmental effects on minority , low
- income , or indigenous populations becau se 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*** Interagency Working Comments on Draft Language under EO1 2866 and EO 1 3563 Interagency

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Page **193** of **193** 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 o f all documents pertaining to the impacts on these communities from climate change have been placed in the public docket for this action. **Determination Under Section 307(d)** K. Section 3 07(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). 

## VIII. **Statutory Pr ovisions and Legal**  **Authority**

Statutory authority for this action comes from 42 U.S.C. sections 7 571 , 7601 and 7607
.
Dated: _______________________________

_____________________________________ Gina McCarthy, Administrator