EO12866_GHG Emissions from Aircraft _2060-AS31 NPRM_ANPRM_FRN_ 201527.docx
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 87 and 1068
[EPA-HQ-OAR-2014-0828; FRL_XXXX-X]
RIN 2060-AS31
Proposed Finding that Greenhouse Gas Emissions from Aircraft Cause or Contribute to Air Pollution that May Reasonably Be Anticipated to Endanger Public Health and Welfare and Advance Notice of Proposed Rulemaking
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed Rule and Advance Notice of Proposed Rulemaking.
SUMMARY:  In this action, the Administrator is proposing to determine that greenhouse gas concentrations in the atmosphere endanger the public health and welfare of current and future generations within the meaning of section 231(a) of the Clean Air Act.  She proposes to make this finding specifically with respect to the same six well-mixed greenhouse gases that together were defined as the air pollution in the 2009 Endangerment Finding under section 202(a) of the Clean Air Act and that together constitute the primary cause of the climate change problem.  The Administrator is also proposing to find that greenhouse gas emissions from certain classes of engines used in aircraft are contributing to 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 endangers public health and welfare under section 231(a) of the Clean Air Act.  Concurrent with these proposed findings, the EPA is issuing an Advance Notice of Proposed Rulemaking to provide an overview of and seek input on the EPA's efforts at the International Civil Aviation Organization (ICAO) to reduce greenhouse gas emissions from aircraft, ICAO's progress in establishing global aircraft standards that achieve meaningful CO2 reductions, and the potential use of section 231 of the Clean Air Act to implement corresponding aircraft engine standards domestically, ensuring transparency and the opportunity for public comment.
 DATES:  Comments. Comments must be received on or before [Insert date 60 days after publication in the Federal Register].
 	Public Hearing.  If anyone contacts the EPA requesting a public hearing by [insert date 10 days after publication in the Federal Register], we 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 such as audio description, 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.  For further information on the public hearing or to register to speak at the hearing, please see section I.B below or go to [ADD WEBSITE 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<EMAIL_ADDRESS>Attention Docket ID No. EPA-HQ-OAR-2014-0828.
   * Fax:<PHONE_NUMBER>, Attention Docket ID No. EPA-HQ-OAR-2014-0828.
   * Mail:  U.S. Postal Service, send comments to Air and Radiation Docket and Information Center, Environmental Protection Agency, Mail Code: 28221T, 1200 Pennsylvania Ave., NW, Washington, DC 20460. Attention Docket ID No. EPA-HQ-OAR-2014-0828.
   * Hand Delivery:  U.S. Environmental Protection Agency, EPA West, EPA Docket Center, EPA West Building, Room 3334, 1301 Constitution Ave., NW., Washington, DC 20004.  Attention Docket ID No. EPA-HQ-OAR-2014-0828. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for deliveries of boxed information.
 Instructions:  Direct your comments to Docket ID No. EPA-HQ-OAR-2014-0828.  See section I.B on "Public Participation" for more information about submitting written comments. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at http://www.regulations.gov, including any personal information provided, unless the comment includes information claimed to be confidential business information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through http://www.regulations.gov or e-mail.  The http://www.regulations.gov website is an "anonymous access" system, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment.  If you send an 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.  If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment.  Electronic files should avoid the use of special characters, or any form of encryption, and be free of any defects or viruses. For additional information about the EPA's public docket visit the EPA Docket Center homepage at: http://www.epa.gov/dockets. For additional instructions on submitting comments, go to section I.B of this document.
  Docket. The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2014-0828.  All documents in the docket are listed in the www.regulations.gov index.  Although listed in the index, some information is not publicly available, e.g., CBI or other information whose disclosure is restricted by statute.  Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy in the EPA's docket.  Publicly available docket materials are available either electronically in www.regulations.gov or in hard copy at the Air and Radiation Docket and Information Center, EPA/DC, EPA WJC West, Room 3334, 1301 Constitution Ave., NW, Washington, DC.  The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays.  The telephone number for the Public Reading Room is<PHONE_NUMBER>, and the telephone number for the Air Docket is<PHONE_NUMBER>.
 FOR FURTHER INFORMATION CONTACT:  JoNell Iffland, Office of Transportation and Air Quality, Assessment and Standards Division (ASD), Environmental Protection Agency, 2000 Traverwood Drive, Ann Arbor MI 48105; Telephone number:<PHONE_NUMBER>; Fax number:<PHONE_NUMBER>; E-mail address<EMAIL_ADDRESS> Please use this contact information for general questions about this rulemaking, to request a hearing, to determine if a hearing will be held, and to register to speak at the hearing, if one is held.
 SUPPLEMENTARY INFORMATION:
 Acronyms and Abbreviations.  We use multiple acronyms and terms in the preamble.  While this list may not be exhaustive, to ease the reading of the preamble and for reference purposes, the EPA defines the following terms and acronyms here:
 [INSERT]
TABLE OF CONTENTS
I. GENERAL INFORMATION
   A. Does this Action Apply to Me?
   B. Public Participation
            1. What Should I Consider as I Prepare My Comments for the EPA?
            2. Public Hearing
   C. Did the EPA Conduct a Peer Review before Issuing this Notice?
   D. Children's Environmental Health
   E. Environmental Justice

II. INTRODUCTION:  OVERVIEW AND CONTEXT FOR THIS PROPOSAL
      A. Summary
      B. Background Information Helpful to Understanding This Proposal
            1. Greenhouse Gases and Their Effects
            2. Statutory Basis for This Proposal
      C. The EPA's Responsibilities under the Clean Air Act
            1. The EPA's Regulation of Greenhouse Gases
            2. Background on the Aircraft Petition, 2008 ANPR, and 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
            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 Language
            2. How the Origin of the Current Statutory Language Informs the EPA's Interpretation of Section 231(a)(2)(A)
            3. Additional Considerations for the Cause or Contribute Analysis
      B. Air Pollutant, Public Health and Welfare

IV. GREENHOUSE GASES ENDANGER PUBLIC 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 Atmospheric Concentrations of the Six Greenhouse Gases Are the Root Cause of Observed Climate Change
            2. More Recent Evidence that Greenhouse Gases Endanger Public Health
            3. More Recent Evidence that Greenhouse Gases Endanger Public Welfare
            4. Consideration of Other Climate Forcers
      C. Summary of the Administrator's Proposed Endangerment Finding under CAA Section 231

V. THE PROPOSED CAUSE OR CONTRIBUTE FINDING FOR THE SIX LONG-LIVED, WELL-MIXED GREENHOUSE GASES
      A. The Air Pollutant
            1. Proposed Definition of Air Pollutant
            2. How the Definition of Air Pollutant in the Endangerment Determination Affects Section 231 Standards
      B. Proposed Cause or Contribute Finding
            1. The Administrator's Approach in Making this Proposed Finding.
            2. Overview of Greenhouse Gas Emissions
            3. Proposed Contribution Finding for the Single Air Pollutant Comprised of the of Six Well-Mixed Greenhouse Gases
            4. Additional Considerations

VI. ADVANCE NOTICE OF PROPOSED RULEMAKING:  DISCUSSION OF ONGOING INTERNATIONAL PROCEEDINGS TO DEVELOP AIRCRAFT CO2 EMISSIONS STANDARD AND REQUEST FOR COMMENT
      A. Purpose of the International Standard
      B. Applicability of the International 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 System, Applicability, and Certification Requirement
            1. CO2 Metric System
            2. Applicability
            3. Certification requirement
            4. Regulating the Entire Aircraft Instead of the Engine
      E. Stringency Options
      F. Costs, Technology Responses for Stringency Options, and Cost-Effectiveness Analysis
            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 REVIEWS
   A.          Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review
   B.          Paperwork Reduction Act (PRA)
   C.          Regulatory Flexibility Act (RFA)
   D.          Unfunded Mandates Reform Act (UMRA)
   E.          Executive Order 13132: Federalism
   F.          Executive Order 13175: Consultation and Coordination with Indian Tribal Governments
   G.          Executive Order 13045: Protection of Children from Environmental Health Risks and Safety Risks
   H.          Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution or Use
   I.          National Technology Transfer and Advancement Act (NTTAA)
   J.          Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations
   K.          Determination Under Section 307(d)

VIII. STATUTORY PROVISIONS AND LEGAL AUTHORITY

General Information
 Does this Action Apply to Me?
These proposed findings, if finalized, would trigger new duties that would apply to the EPA, but would not themselves apply new requirements to other entities outside the federal government.  Specifically, if the EPA issues final findings that greenhouse gas emissions from certain classes of engines -- those used in certain aircraft -- cause or contribute to air pollution which endangers public health or welfare, then the EPA would have a duty under section 231 of the Clean Air Act to promulgate aircraft engine emission standards applicable to emissions of that air pollutant from those classes of engines.    Only those standards would apply to and have an effect on other entities outside the federal government.  Entities potentially interested in this proposed action are those that manufacture and sell aircraft engines and aircraft in the United States.  Potentially future-regulated categories include:
Category
                                 NAICS[a] Code
                                  SIC[b] Code
Examples of Potentially Affected Entities
Industry
3364412
3724
Manufacturers of new aircraft engines.
Industry
336411
3721
Manufacturers of new aircraft.
 a North American Industry Classification System (NAICS).
 b Standard Industrial Classification (SIC) code.
	This table is not intended to be exhaustive, but rather provides a guide for readers regarding entities likely to be interested in today's proposed action.  This table lists the types of entities that the EPA is now aware could potentially have an interest in this proposed action.  If the EPA issues final affirmative findings under section 231(a) regarding greenhouse gases, the EPA would then be required to undertake a separate notice and comment rulemaking to issue emission standards applicable to greenhouse gas emissions from the classes of aircraft engines that the EPA finds cause or contribute in such a finding, and the FAA would be required to enforce these emissions standards in such aircraft per section 232 of the Clean Air Act.   Other types of entities not listed in the table could also be interested and potentially affected by subsequent actions at some future time.  If you have any questions regarding the scope of this proposed action, consult the person listed in the preceding FOR FURTHER INFORMATION CONTACT section.
	Public Participation
The EPA requests comment on all aspects of the proposed aircraft endangerment and cause or contribute findings and Advance Notice of Proposed Rulemaking (ANPR).  This section describes how you can participate in this process.
If you submitted comments on the issues raised by this proposal in dockets for other, earlier Agency efforts (e.g., the 2009 Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202 of the Clean Air Act or the Advance Notice of Proposed Rulemaking on Regulating Greenhouse Gases under the Clean Air Act), you must still submit your comments to the docket for this action (EPA-HQ-OAR-2014-0828) by the deadline if you want them to be considered.
         1.   What Should I Consider as I Prepare My Comments for the EPA?
We are opening a formal comment period by publishing this document.  We will accept comments during the period indicated in the DATES section.  If you have an interest in the proposed aircraft endangerment and cause or contribute findings and/or the ANPR described in this document, we encourage you to comment on any aspect of this rulemaking.
            Tips for Preparing Your Comments.
            When submitting comments, remember to:
         * Identify the rulemaking by docket number and other identifying information (subject heading, Federal Register date and page number).
         * Follow directions - The agency may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number.
         * Explain why you agree or disagree, suggest alternatives, and substitute language for your requested changes.
         * Describe any assumptions and provide any technical information and/or data that you used.
         * If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced.
         * Provide specific examples to illustrate your concerns, and suggest alternatives.
         * Explain your views as clearly as possible, avoiding the use of profanity or personal threats.
         * Make sure to submit your comments by the comment period deadline identified.
                   a. Submitting CBI
Do not submit information to the EPA containing CBI through http://www.regulations.gov or e-mail.  Clearly mark the part or all of the information that you claim to be CBI.  For CBI information on a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CD-ROM the specific information that is claimed as CBI.  In addition to one complete version of the comment that includes information claimed as CBI, you must submit a copy of the comment that does not contain the information claimed as CBI for inclusion in the public docket.  Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.
            2. Public Hearing
If a hearing is held, it will provide interested parties the opportunity to present data, views or arguments concerning the proposed action.  The EPA will make every effort to accommodate all speakers who arrive and register.  Because this hearing, if held, will be at a U.S. government facility, individuals planning to attend the hearing should be prepared to show valid picture identification to the security staff in order to gain access to the meeting room.  In addition, you will need to obtain a property pass for any personal belongings you bring with you.  Upon leaving the building, you will be required to return this property pass to the security desk.  No large signs will be allowed in the building, cameras may only be used outside of the building and demonstrations will not be allowed on federal property for security reasons.  The EPA may ask clarifying questions during the oral presentations but will not respond to the presentations at that time.  Written statements and supporting information submitted during the comment period will be considered with the same weight as oral comments and supporting information presented at the public hearings.
Speakers should 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 presentations if we receive special requests at least 3 business days in advance of the public hearing.  Oral testimony will be limited to 5 minutes for each commenter.  The EPA requests that commenters provide the EPA with at least 2 copies of their oral testimony in hard copy form or a copy 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 hearing 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?
As outlined in section IV.A of this action, the EPA's approach to providing the technical and scientific information to inform the Administrator's judgment regarding the question of whether greenhouse gases endanger public health and welfare was to rely primarily upon the recent, major assessments by the U.S. Global Change Research Program (USGCRP), the Intergovernmental Panel on Climate Change (IPCC), and the National Research Council (NRC) of the National Academies.  These assessments draw synthesis conclusions across thousands of individual peer-reviewed studies that appear in scientific journals, and the reports themselves undergo additional peer review.  The EPA has considered the processes and procedures employed by the USGCRP, IPCC, and the NRC, and has determined that these assessments have been adequately peer reviewed in a manner commensurate with the EPA's Peer Review Policy and the guidelines in Office of Management and Budget's (OMB) Final Information Quality Bulletin for Peer Review ("OMB Bulletin") for highly influential scientific assessments.  According to guidelines in the EPA's Peer Review Handbook, if the Agency has determined that information has already been subject to adequate peer review, then it is not necessary to have further peer review of that information.
The EPA also cites data from its annual Inventory of U.S. Greenhouse Gas Emissions and Sinks report, which the Agency has determined to have been adequately reviewed in accordance with the OMB Bulletin and the EPA's Peer Review Handbook.  For the presentation of emissions inventory information to support the cause or contribute finding, the EPA disaggregated the existing data in one area of the GHG Inventory (for the General Aviation Jet Fuel Category) and had the disaggregation methodology and results peer reviewed in accordance with the EPA's Peer Review Handbook.  All relevant peer review documentation is located in the docket for today's action (EPA-HQ-OAR-2014-0828).
Children's Environmental Health
As described in detail in section IV of this preamble, the scientific evidence and conclusions in the USGCRP, IPCC, and the NRC assessment reports cited in the 2009 Endangerment Finding indicate that children are uniquely vulnerable to climate change related health effects given behavioral, developmental, and physiological factors. The new assessment literature published since 2009 strengthens these conclusions by providing more detailed findings regarding children's vulnerabilities and projected impacts they may experience.
These studies conclude that children will be disproportionately affected by heat waves, air 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 diseases, to which children are among those especially susceptible.  Additional health concerns may arise in low income households, especially those with children, if climate change reduces food availability and increases prices, leading to food insecurity within households.
Environmental Justice
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 elderly, the poor, and 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.
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 indigenous peoples' health, wellbeing, and ways of life.
Introduction:  Overview and Context for this Proposal
     A. Summary
Pursuant to section 231(a)(2)(A) of the Clean Air Act (CAA or Act), the Administrator proposes to find that greenhouse gas (GHG) emissions from aircraft engines used in certain types of aircraft (referred to as "covered aircraft" throughout this notice) contribute to air pollution that endangers public health and welfare.  Covered aircraft would be those aircraft to which ICAO has agreed the international CO2 standard would apply: subsonic jet aircraft with a maximum takeoff mass (MTOM) greater than 5,700 kilograms, and subsonic propeller-driven (e.g., turboprop) aircraft with a MTOM greater than 8,618 kilograms.  Examples of covered aircraft would include smaller jet aircraft such as the Cessna Citation 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.  In this proposed action, the EPA relies primarily on the extensive scientific and technical evidence in the record supporting the 2009 Endangerment Finding under CAA section 202, including the major, peer-reviewed scientific assessments regarding the question of whether GHGs in the atmosphere endanger public health and welfare, and on the analytical framework and conclusions upon which the EPA relied upon in making that finding.  The Administrator's view is that the body of scientific evidence amassed in the record for the 2009 Endangerment Finding also compellingly supports an endangerment finding under CAA section 231(a).  Furthermore, this proposed finding under section 231 accounts for the EPA's careful consideration not only of the scientific and technical record for the 2009 Endangerment Finding, but also of science assessments released since 2009, which, as illustrated below, strengthen and provide further support for the scientific evidence that the Administrator relied upon in making her prior judgment under section 202 that GHGs in the atmosphere are reasonably anticipated to endanger public health and welfare.  No more recent information or analyses 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 reopening or revising our prior findings under CAA section 202.
The Administrator is proposing to define the "air pollution" referred to in section 231(a)(2)(A) of the CAA to be the mix of six well-mixed GHGs:  carbon dioxide (CO2), methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.  This is the same definition that was used for the finding for purposes of section 202(a).  It is the Administrator's judgment that the total body of scientific evidence compellingly supports a positive endangerment finding that elevated concentrations of the six well-mixed GHGs constitute air pollution that endangers both the public health and the public welfare of current and future generations within the meaning of section 231(a) of the Clean Air Act.
Under section 231 of the CAA, the Administrator must also determine whether emissions of any air pollutant from a class or classes of aircraft engines cause or contribute to the air pollution that may reasonably be anticipated to endanger public health or welfare. Following the rationale outlined in the 2009 Endangerment Finding, the Administrator in this action is proposing to use the same definition of the air pollutant as was used for purposes of section 202(a) for purposes of making the cause or contribute determination under section 231(a)  -  that is, the aggregate group of the same six well-mixed GHGs.  Based on the data summarized in section V, the Administrator is proposing to find that GHG emissions from aircraft engines used in covered aircraft, contribute to the air pollution that endangers public health and welfare under section 231(a).
The Administrator's proposed findings come in response to 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 duty 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 Diversity, and Earthjustice (Petitioners) requesting that the EPA issue standards under section 231(a)(2)(A) of the Act 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, EPA anticipates that ICAO will adopt a final CO2 emissions standard in February 2016.  This proposal, and any final endangerment and cause or contribute findings for aircraft engine GHG emissions, are also part of preparing for a possible subsequent domestic rulemaking process to adopt standards that are of at least equivalent stringency as the anticipated ICAO CO2 standards.
Background Information Helpful to Understanding This Proposal
         1. Greenhouse Gases and Their Effects
GHGs are gases that effectively trap some of the Earth's heat that would otherwise escape to space.  GHGs are both naturally occurring and anthropogenic.  The primary GHGs of concern directly emitted by human activities include CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. Of these six gases, two (CO2 and nitrous oxide) are emitted by aircraft engines.
 These six gases, once emitted, remain in the atmosphere for decades to centuries. Thus, they become well mixed globally in the atmosphere and their concentrations accumulate when emissions exceed the rate at which natural processes remove them from the atmosphere.  The heating effect caused by the human-induced buildup of GHGs in the atmosphere is extremely likely (>95 percent likelihood) to be the cause of most of the observed global warming since 1950.  A detailed explanation of climate change and its impact on health, society, and the environment is included in the record for the EPA's 2009 Endangerment Finding under CAA section 202, of which the relevant scientific information has been included in the docket for this proposed determination under CAA section 231 (EPA-HQ-OAR-02914-0828).  Section IV of this preamble discusses this information, as well as information from the most recent scientific assessments, in the context of the Administrator's proposed endangerment finding under CAA section 231.
The U.S. transportation sector is a significant contributor to total U.S. and global anthropogenic GHG emissions.  In 2012, aircraft remained the single largest GHG-emitting transportation source not yet subject to any 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. emissions in 2012.   Section V of this preamble provides detailed information on aircraft GHG emissions in the context of the Administrator's proposed cause or contribute finding under CAA section 231.
         2. Statutory Basis for This Proposal
Section 231(a)(2)(A) of the CAA states that "The Administrator shall, from time to time, issue proposed emission standards applicable to the emission of any air pollutant from any class or classes of  aircraft engines which in [her] judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare."
Before the Administrator may issue standards addressing emissions of GHGs under section 231, the Administrator must satisfy a two-step test.  First, the Administrator must decide whether, in her judgment, the air pollution under consideration may reasonably be anticipated to endanger public health or welfare.  Second, the Administrator must decide whether, in her judgment, emissions of an air pollutant from certain classes of aircraft engines cause or contribute to this air pollution.  If the Administrator answers both questions in the affirmative, she must issue standards under section 231. See Massachusetts v. EPA, 549 U.S. 497,533 (2007) (interpreting analogous provision in CAA section 202). Section III of this preamble summarizes the legal framework for this proposed action under CAA section 231.  Typically, past endangerment and cause or contribute findings have been proposed concurrently with proposed standards under various sections of the CAA, including section 231.  Comment has been taken on these proposed findings as part of the notice and comment process for the emission standards. See, e.g., Rulemaking for non-road compression-ignition engines under section 213(a)(4) of the CAA, Proposed Rule 58 FR 28809, 28813 - 14 (May 17, 1993), Final Rule 59 FR 31306, 31318 (June 17, 1994); Rulemaking for highway heavy duty diesel engines and diesel sulfur fuel under sections 202(a) and 211(c) of the CAA, Proposed Rule 65 FR 35430 (June 2, 2000), Final Rule 66 FR 5002 (Jan. 18, 2001).  However, there is no requirement that the Administrator propose the endangerment and cause or contribute findings concurrently 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 analysis 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) apply to "such other actions as the Administrator may determine."   Any standard setting rulemaking under section 231 will also be subject to the notice and comment rulemaking procedures under 307(d), as provided in CAA section 307(d)(1)(F) (applying the provisions of 307(d) to the promulgation or revision of any aircraft emission standard under section 231).  Thus, these proposed findings will be subject to the same rulemaking requirements that would apply if the proposed findings were part of a standard-setting rulemaking.
The EPA's Responsibilities under the Clean Air Act
The CAA provides broad authority to combat air pollution to protect public health and welfare. Cars, trucks, construction equipment, airplanes, and ships, as well as a broad range of electric generation, industrial, commercial and other facilities, are subject to various CAA programs.  Implementation of the Act over the past four decades has resulted in significant reductions in air pollution while the nation's economy has continued to grow.
         1. The EPA's Regulation of Greenhouse Gases
In Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court found that GHGs are air pollutants that can be regulated under the CAA. The Court held that the Administrator must determine whether or not emissions of GHGs from new motor vehicles cause or contribute to air pollution which may reasonably be anticipated to endanger public health and/or welfare, or whether the science is too uncertain to make a reasoned decision. In making these decisions, the Administrator was bound by the provisions of section 202(a) of the CAA.
The Supreme Court decision resulted from a petition for rulemaking under section 202(a) filed by more than a dozen environmental, renewable energy, and other organizations.   On April 17, 2009, the Administrator 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 the air pollution ("cause or contribute" finding). On December 7, 2009, the Administrator signed a notice that finalized two distinct findings regarding GHGs under section 202(a) of the CAA:
       * Endangerment Finding: The Administrator found that the current and projected concentrations of the six key well-mixed GHGs  --  CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride  --  in the atmosphere threaten the public health and welfare of current and future generations.
       * Cause or Contribute Finding: The Administrator found that the combined emissions of these well-mixed GHGs from new motor vehicles and new motor vehicle engines contribute to the GHG pollution which threatens public health and welfare.
These findings (collectively referred to as the 2009 Endangerment Finding in today's action) did not themselves impose any requirements on industry or other entities. However, these findings compelled the EPA to promulgate GHG emission standards for new motor vehicles under section 202(a). Subsequently, in May of 2010 the EPA, in collaboration with the National Highway Traffic Safety Administration (NHTSA), finalized Phase 1 GHG emission standards for light-duty vehicles (2012-2016 model years). This was followed in August 2011 by adoption of the first-ever GHG emission standards for heavy-duty engines and vehicles (2014-2018 model years).  On August 29, 2012, the second phase of the GHG emission standards for light-duty vehicles (2017-2025 model years) was finalized further reducing GHG emissions from light-duty vehicles. In 2014, the President directed the EPA and the Department of Transportation to set standards that further increased fuel efficiency and reduced GHG emissions from medium- and heavy-duty vehicles by March 2016.
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 reductions in GHG emissions, and over the lifetime of these vehicles GHG emissions will be reduced by more than 6.2 billion metric tons.,
On June 25, 2013, President Obama announced 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.  As part of the Climate Action Plan, the President issued a Presidential Memorandum directing the EPA to work expeditiously to complete carbon pollution standards for the power sector.  In response, in January 2014, the EPA proposed carbon pollution standards for new electric utility generating units.  This was followed in June 2014, by proposed standards to address carbon pollution from modified and reconstructed power plants and from existing power plants.
 In the Climate Action Plan, the President also indicated that the U.S. was working internationally to make progress in a variety of areas and specifically noted the progress being made by ICAO to develop global CO2 emission standards for aircraft.  The proposed endangerment and cause or contribute findings for aircraft GHG emissions under section 231(a)(2)(A) of the CAA are a preliminary but necessary first step to begin to address GHG emissions from the aviation sector, the highest-emitting category of transportation sources that the EPA has not yet addressed.  As presented in more detail in Section V of this preamble, total U.S. aircraft GHG emissions in 2012 represented 11 percent of GHG emissions from the U.S. transportation sector, and in 2010, the latest year with complete global emissions data, U.S. aircraft GHG emissions represented 29 percent of global aircraft GHG emissions.,    This makes the U.S. the biggest GHG emitter from aircraft by far, and U.S. aircraft GHG emissions are projected to increase by almost 50 percent over the next two decades.  See section V of this preamble for more information about the data sources that comprise the aircraft GHG emissions inventory.
         2. Background on the Aircraft Petition, 2008 ANPR, and D.C. District Court Decision
Section 231(a)(2)(A) of the CAA directs the Administrator of the EPA to, from time to time, propose aircraft engine emissions standards applicable to the emission of any air pollutant from any classes of aircraft engines which in her judgment causes or contributes to air pollution which may reasonably be anticipated to endanger public health or welfare.
 On December 5, 2007, Friends of the Earth, Oceana, the Center for Biological Diversity, Earthjustice, and others (Petitioners) sent a letter to the EPA petitioning the Agency to undertake rulemaking regarding GHG emissions from aircraft.  Specifically, Petitioners requested that the EPA make a finding that GHG emissions from aircraft engines "may reasonably be anticipated to endanger public health and welfare" and that the EPA promulgate standards for GHG emissions from aircraft.
Following the Supreme Court's decision in Massachusetts v. EPA, 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 decision to regulate GHGs under the CAA.  This ANPR described and solicited comment on numerous petitions the Agency had received to regulate GHG emissions from both stationary and mobile sources, including aircraft. 73 Fed. Reg. 44354, 44468-44473 (July 30, 2008).  With regard to aircraft, the Agency sought comment on the impact of aircraft operations on GHG emissions and the potential for reductions in GHG emissions from these operations.
In response to the ANPR, the EPA received comments from a wide range of aviation sector stakeholders including industry trade groups, individual manufacturers, states and local governments, and nongovernmental organizations (NGOs). Industry groups and individual manufacturers stressed that fuel costs (and market forces) created an economic incentive to reduce fuel consumption and thus GHG emissions.  One industry association indicated its commitment to achieve an additional 30 percent fuel efficiency improvement by 2025. Another commenter identified engine technologies that were improving fuel consumption by more than 15 percent.  With regard to CO2 engine emissions standards, these commenters felt that international CO2 standards for aircraft engines were not necessary and that if pursued 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.  Finally industry commenters noted that any program developed by the EPA should incentivize market forces and provide for flexibility.
State/local governments and NGO commenters felt strongly that the EPA had clear authority to find endangerment under section 231 and that there were multiple options to reduce aircraft emissions, so that the Agency must set a GHG emissions standard for aircraft engines as states were pre-empted from doing so under CAA section 233.  These commenters also argued that GHG standards for aircraft engines could provide aircraft manufacturers the incentive to renew or redesign aircraft and to adopt advanced engines brought to market.  In addition these commenters suggested that an engine GHG standard could be set as a function of thrust similar to ICAO's standard for oxides of nitrogen (NOx) and should also include provisions for averaging, banking, and trading (ABT).  Some commenters also stated their support for fleet-wide (in-use fleet) emission reductions through a cap and trade system.  Finally, these stakeholders stated that, absent the EPA rulemaking, quick international actions were unlikely and that the EPA should engage internationally to push for action on reducing CO2 emissions from aircraft.
On July 31, 2008, Earthjustice, on behalf of Petitioners, notified the EPA of its intent to file suit under CAA section 304(a) against the EPA for the Agency's alleged unreasonable delay in responding to its aircraft petition and in making an endangerment finding under section 231.  On June 11, 2010, Petitioners filed a complaint against the EPA in the U.S.  District Court for the District of Columbia claiming that, among other things, the EPA had unreasonably delayed because it had failed to answer the 2007 Petition and to determine whether or not GHG emissions from aircraft cause or contribute to air pollution which may reasonably be anticipated to endanger public health and/or welfare, or whether the science is too uncertain to make a reasoned decision.
The District Court found that while CAA section 231 generally confers broad discretion to the EPA in determining what standards to promulgate, section 231(a)(2)(A) imposed a nondiscretionary duty on the EPA to make a finding with respect to endangerment from aircraft GHG emissions. Center for Biological Diversity, et al. v. EPA, 794 F. Supp. 2d 151 (D.D.C., 2011).  This ruling was issued in response to EPA's motion to dismiss the case on jurisdictional grounds and did not address the merits of the Plaintiffs' claims regarding the Agency's alleged unreasonable delay.  Therefore, it did not include an order for the EPA to make such a finding by a certain date.  In a subsequent ruling on the merits, the Court found that the Plaintiffs had not shown that EPA had unreasonably delayed in making an endangerment determination regarding GHG emissions from aircraft. Center for Biological Diversity, et al. v. EPA, No. 1:10-985 (D.D.C., March, 20, 2012).  Thus, the Court did not find the EPA to be liable based on the Plaintiffs' claims and did not place the Agency under a remedial order to make an endangerment finding or to issue standards.  The Plaintiffs did not appeal this ruling to the U.S. Court of Appeals for the D.C. Circuit.
The EPA issued a Response to the Aircraft Petition 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 minimum 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. Circuit decided pending cases regarding the CAA section 202 Endangerment Finding.  The Court upheld EPA's section 202 findings in a decision of a three-judge panel on June 26, 2012, and issued  a ruling denying petitions for rehearing of that decision on December 20, 2012. Coalition for Responsible Regulation, Inc., v. EPA, 684 F.3d 102 (D.C. Cir. 2012), reh'g denied 2012 U.S. App. LEXIS 26315, 25997 (D.C. Cir 2012).  Given these rulings, we are proceeding with today's proposed findings regarding aircraft engine GHG emissions in furtherance of our prior response to the Petition for Rulemaking.
  The EPA's Regulation of Aircraft Emissions
As required by the CAA, the EPA has been engaged in reducing harmful air pollution from aircraft engines for over 40 years.  In 1973, the EPA began to regulate gaseous exhaust emissions, smoke, and fuel venting from aircraft engines.  We have occasionally revised these regulations.  In a 1997 rulemaking, for example, we made our emission standards and test procedures more consistent with those of ICAO's 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 generally referred to as CAEP/2 standards.  That action included new NOx emission standards for newly 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) and for newly-certified commercial turbofan engines (those engine models that received their initial type certificate after the effective date of the regulations).  It also included a carbon monoxide emission standard for newly-manufactured commercial turbofan engines.  In 2005, we promulgated more stringent NOx emission standards for newly-certified commercial turbofan engines.  That final rule brought the U.S. standards closer to alignment with ICAO CAEP/4 requirements that became effective in 2004.  In 2012, we issued more stringent two-tiered NOx emission standards for newly-certified and in-production commercial and non-commercial turbofan aircraft engines, and these NOx standards align with ICAO's CAEP/6 and CAEP/8 requirements that became effective in 2013 and 2014, respectively.[,]
The EPA's actions to regulate certain pollutants emitted from aircraft engines come directly from its authority in section 231 of the CAA, and we have aligned the U.S. emissions requirements with those promulgated by ICAO.   In addressing CO2 emissions, however, ICAO has moved to regulating a whole aircraft.  Rather than viewing CO2 as a measurable emission from engines, it is addressed as a characteristic applicable to the entirety of the aircraft based on fuel consumption.  In this proposed action, we are giving advance notice that the EPA may potentially propose to adopt domestic CO2 (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.  This ICAO extension beyond pollutant emissions from engines to the whole aircraft was described in a 2013 ICAO circular.  Several factors are considered when addressing whole-aircraft CO2 emissions, as the CO2 emissions are influenced by aerodynamics, weight, and engine-specific fuel consumption.  Since each of these factors may affect aircraft engine fuel consumption, they ultimately affect CO2 emissions.
U.S. Aircraft Regulations and the International Community
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.  Under this approach, international emission standards have first been adopted by ICAO, and subsequently the EPA has initiated rulemakings under CAA section 231 to establish domestic standards equivalent to ICAO's standards where appropriate.  This approach has been affirmed as reasonable by the U.S. Court of Appeals for the D.C. Circuit.  NACAA v. EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007).  After EPA promulgates aircraft engine emissions standards, the FAA under CAA section 232 is required to issue subsequent regulations to insure compliance with these standards when issuing certificates under its United States Code Title 49 authority.  In exercising the EPA's standard-setting and FAA's enforcement authorities, we expect to proceed using a similar approach for the future CAA section 231 aircraft engineCO2 standard (or GHG standard), provided the EPA issues final positive endangerment and cause or contribute findings under CAA section 231.  This approach could be followed provided that ICAO adopts an international aircraft CO2 standard that is consistent with CAA section 231 and is appropriate for domestic needs in the United States.
         1. International Regulations and U.S. Obligations
As noted above, we have worked with the FAA since 1973, and later with ICAO, to develop domestic and international standards and other recommended practices pertaining to aircraft engine emissions.  ICAO is a United Nations (UN) specialized agency,  established in 1944 by the Convention on International Civil Aviation (Chicago Convention_, "in order that international civil aviation may be developed in a safe and orderly manner and that international air transport services may be established on the basis of equality of opportunity and operated soundly and economically."  ICAO sets standards and regulations necessary for aviation safety, security, efficiency, capacity and environmental protection, and serves as the forum for cooperation in all fields of international civil aviation.  ICAO works with the Chicago Convention's member States and global aviation organizations to develop international Standards and Recommended Practices (SARPs) which member States reference when developing their legally-enforceable national civil aviation regulations. .  The U.S. is currently one of 191 participating ICAO member States.[,]
In the interest of global harmonization and international air commerce, the Chicago Convention urges its member States to collaborate in securing to the highest practicable degree of uniformity in regulations, standards, procedures and organization.  The Chicago Convention also recognizes that member States may adopt standards that are more stringent than those agreed upon by ICAO.  Any member State which finds it impracticable to comply in all respects with any international standard or procedure, or which deems it necessary to adopt regulations or practices differing in any particular respect from those established by an international standard, are required to give immediate notification to ICAO of the differences between its own practice and that established by the international standard.
ICAO's work on the environment focuses primarily on those problems that benefit most from a common and coordinated approach on a worldwide basis, namely aircraft noise and engine emissions. Standards and Recommended Practices (SARPs) for the certification of aircraft noise and aircraft engine emissions are covered by Annex 16 of the Chicago Convention. To continue to address aviation environmental issues, in 2004, ICAO established three environmental goals:  (1) limit or reduce the number of people affected by significant aircraft noise; (2) limit or reduce the impact of aviation emissions on local air quality; and (3) limit or reduce the impact of aviation greenhouse gas emissions on the global climate.
The Convention has a number of other features that govern international commerce.  First, member States that wish to use aircraft in international transportation must adopt emissions standards and other recommended practices that are at least as stringent as ICAO's standards.  Member States may ban the use of any aircraft within their airspace that does not meet ICAO standards.  Second, member States are required to recognize the airworthiness certificates of any State whose standards are at least as stringent as ICAO's standards, thereby assuring that aircraft of any member State will be permitted to operate in any other member State.  Third, to ensure that international commerce is not unreasonably constrained, a member State which elects to adopt more stringent domestic emission standards is obligated to notify ICAO of the differences between its standards and ICAO standards.
ICAO's CAEP undertakes ICAO's technical work in the environmental field, which consists of Members and Observers from States, intergovernmental and non-governmental organizations representing aviation industry and environmental interests.  The Committee is responsible for evaluating, researching, and recommending measures to the ICAO Council that address the environmental impacts of international civil aviation.  CAEP's terms of reference indicate that "CAEP's assessments and proposals are pursued taking into account: technical feasibility, environmental benefit; economic reasonableness, interdependencies of measures (for example, among others, measures taken to minimize noise and emissions); developments in other fields; and international and national programs."  CAEP is composed of various task groups, work groups, and other committees whose contributing members include atmospheric, economic, aviation, environmental, and other professionals interested in and knowledgeable about aviation and environmental protection.  The ICAO Council reviews and adopts the recommendations made by CAEP. It then reports to the ICAO Assembly, the highest body of the Organization, where the main policies on aviation environmental protection are adopted and translated into Assembly Resolutions.
At CAEP meetings, the U.S.is represented by the FAA,  and plays an active role at these meetings.  The EPA has historically been a principal participant in various ICAO/CAEP working groups and other international venues, assisting and advising FAA on aviation emissions, technology, and policy matters.  In turn, the FAA assists and advises the EPA on aviation technology and certification matters.  If ICAO adopts a CAEP proposal for a new environmental standard, it then becomes part of ICAO standards and recommended practices (Annex 16 to the Chicago Convention). [,]
The first international standards and recommended practices for aircraft engine emissions were recommended by CAEP's predecessor, the Committee on Aircraft Engine Emissions (CAEE), and adopted by ICAO in 1981.  These standards limited aircraft engine emissions of hydrocarbons, carbon monoxide, and NOx.  In 1994, ICAO adopted a CAEP/2 proposal to tighten the original NOx standard by 20 percent and amend the test procedures.   In 1995, CAEP/3 recommended a further tightening of the NOx standards by 16 percent and additional test procedure amendments, but in 1997 the ICAO Council rejected this stringency proposal and approved only the test procedure amendments.  At the CAEP/4 meeting in 1998, the Committee adopted a similar 16 percent NOx reduction proposal, which ICAO approved in 1998.  The CAEP/4 standards applied only to new engine designs certified 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 recommended a 12 percent NOx reduction, which ICAO approved in 2005.[,]  The CAEP/6 standards applied to new engine designs (newly-certified models) certified after December 31, 2007.  In 2010, CAEP/8 recommended a further tightening of the NOx standards by 15 percent for newly-certified engines.[,]  The Committee also recommended that the CAEP/6 standards be applied to newly-manufactured engines or in-production engines (eliminating the production of CAEP/4 compliant engines with the exception of spare engines).  ICAO approved these recommendations in 2011, then equivalent standards (to CAEP/6 and CAEP/8 standards) were promulgated domestically in 2012 by the EPA in consultation with FAA.
         2. The International Community's Reasons for Currently Addressing Aircraft CO2 Emissions
In October 2010, the 37th Assembly (Resolution A37-19) of ICAO requested the development of an ICAO CO2 emissions standard.  Also, Resolution A37-19 provided a framework towards the achievement of an environmentally sustainable future for international aviation.  With this Resolution, the ICAO Assembly agreed to a global aspirational goal for international aviation of improving annual fuel efficiency by 2 percent and stabilizing CO2 emissions at 2020 levels.  The Resolution included the following statements regarding ICAO policies and practices related to climate change.
" -... ICAO and its member States recognize the importance of providing continuous leadership to international civil aviation in limiting or reducing its emissions that contribute to global climate change;
-Reemphasizing the vital role which international aviation plays in global economic and social development and the need to ensure that international aviation continues to develop in a sustainable manner;
-... the ultimate objective of the United Nations Framework Convention on Climate Change (UNFCCC) is to achieve stabilization of greenhouse gas (GHG) concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system; and
-Acknowledging that international aviation emissions, currently accounting for less than 2 per cent of total global CO2 emissions, are projected to grow as a result of the continued development of the sector."
As the above statements indicate, reducing climate impacts of international aviation is a critical element of ICAO's strategic objective of achieving environmental protection and sustainable development of air transport.  ICAO is currently pursuing a comprehensive set of measures to reduce aviation's climate impact including alternative fuels, CO2 emissions technology-based standards, operational improvements, and market based measures. The development and adoption of a CO2 emissions standard is an important part of ICAO's comprehensive set of measures.
         3. Relationship of the EPA's Proposed Endangerment and Cause or Contribute Finding and International Aircraft Standards
As described earlier, the EPA and the FAA work within the ICAO/CAEP standard setting process to establish international emission standards and related requirements.  Under this approach international emission standards have first been adopted by ICAO (with U.S. participation and agreement), and subsequently the EPA has initiated rulemakings under CAA section 231 to establish domestic aircraft engine emission standards that are of at least equivalent stringency as ICAO's standards.  This approach has been affirmed as reasonable by the U.S. Court of Appeals for the D.C. Circuit. NACAA v. EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007).  In exercising the EPA's standard-setting authority, provided the EPA makes positive endangerment and cause or contribute findings under CAA section 231 and ICAO adopts an international aircraft CO2 standard that is consistent with CAA section 231 and is appropriate for domestic needs in the United States, the EPA expects to proceed along a similar approach for the future CAA section 231 aircraft GHG standard (or aircraft CO2 standard).
We anticipate that ICAO/CAEP will adopt a final aircraft CO2 emissions standard in February 2016.  This proposal, and any final endangerment and cause or contribute finding for aircraft GHG emissions, are part of preparing for the possible subsequent domestic rulemaking process to adopt standards that are of at least equivalent stringency as the anticipated ICAO CO2 standards.  These findings, which are factual and science-based, encompass a determination of whether GHG emissions from aircraft cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare.  If positive findings are made, the EPA 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 cause or contribute finding.  If positive findings are not made, the EPA has not triggered its obligation to set GHG emission standards under CAA section 231.
The EPA has worked diligently over the past four years within the ICAO/CAEP process on a range of technical issues regarding aircraft CO2 emission standards.  The ANPR that accompanies this proposal discusses the issues arising in the ongoing international proceedings and U.S. input at CAEP regarding the international CO2 standard,  which is expected to be finalized in February 2016.  To ensure transparency and to assist the Agency in developing its position with regard to these issues and the aircraft CO2 emission standards that it may potentially adopt under the CAA, the EPA requests public comments on a variety of issues in Section VI.
Legal Framework for This Action
The EPA has previously made an endangerment finding for GHGs under Title II of the CAA, in the 2009 Endangerment Finding for section 202(a) source categories.  In the 2009 Endangerment Finding, the EPA explained its legal framework for making an endangerment finding under section 202(a) of the CAA (79 FR 18886, 18890-94 (Apr. 24, 2009), and 79 FR 66496, 66505-10 (Dec. 15, 2009)).  The text that was the basis for the 2009 Endangerment Finding in section 202(a) addresses "the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in [the Administrator's] judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare."  Similarly, section 231(a)(2)(A) concerns "the emission of any air pollutant from any class or classes of aircraft engines which in [the Administrator's] judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare."  Thus, the text of the CAA section concerning aircraft emissions in section 231(a)(2)(A) mirrors the text of CAA section 202(a) that was the basis for the 2009 Endangerment Finding.
The EPA's approach in the 2009 Endangerment Finding was affirmed by the U.S. Court of Appeals for the D.C. Circuit in Coalition for Responsible Regulation, Inc. v. EPA, 684 F.3d 102 (D.C. Cir. 2012), reh'g denied 2012 U.S. App. LEXIS 26313, 26315, 25997 (D.C. Cir 2012) (CRR).  In particular, the D.C. Circuit ruled that the 2009 Endangerment Finding (and the denial of petitions for reconsideration) was not arbitrary or capricious, was consistent with the U.S. Supreme Court's decision in Massachusetts v. EPA and the text and structure of the CAA, and was adequately supported by the administrative record. CRR, 684 F.3d at 116-128.  The D.C. Circuit found that the EPA had based its decision on "substantial scientific evidence" and noted that the EPA's reliance on major scientific assessments was consistent with the methods that decision-makers often use to make a science-based judgment. Id. at 120-121.  Petitions for certiorari were filed in the Supreme Court, and the Supreme Court granted six of those petitions but "agreed to decide only one question: `Whether EPA permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouse gases.'" Utility Air Reg. Group v. EPA, 134 S. Ct. 2427, 2438 (2014); see also Virginia v. EPA, 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA, 134 S. Ct. 418 (2013), and CRR, 134 S. Ct. 468 (2013) (all denying cert.).  Thus, the Supreme Court did not disturb the D.C. Circuit's holding that affirmed the 2009 Endangerment Finding.  Accordingly, the Agency proposes that it is reasonable to use that same approach under section 231(a)(2)(A)'s similar endangerment text, and as explained in the following discussion, is acting consistently with that judicially sanctioned framework for purposes of this proposed section 231 finding.
Two provisions of the CAA govern today's proposal.  Section 231(a)(2)(A) sets forth a two-part predicate for regulatory action under that provision: endangerment and cause or contribute.  Section 302 of the Act contains definitions of the terms "air pollutant" and "welfare" used in section 231(a)(2)(A).  These statutory provisions are discussed below, and the approach taken in this proposed action follows the approach previously used by the Agency in the 2009 Endangerment Finding and upheld in court.
     B. Section 231(a)(2)(A)  -- Endangerment and Cause or Contribute
As noted above, section 231(a)(2)(A) of the CAA (like section 202(a)) calls for the Administrator to exercise her judgment and make two separate determinations: first, whether air pollution 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.
The Administrator interprets the two-part test required under section 231(a)(2)(A) as being the same as that explained in the 2009 Endangerment Finding. (See 74 FR 66505-06.)  As in the section 202(a) context, this analysis entails a scientific judgment by the Administrator about the potential risks posed by GHG emissions to public health or welfare. See CRR, 684 F.3d at 117-118.
First, the Administrator is required to protect public health and welfare.  She is not asked to wait until harm has occurred but instead must be ready to take regulatory action to prevent harm before it occurs.  The Administrator is thus to consider both current and future risks.
Second, the Administrator is to exercise judgment by weighing risks, assessing potential harms, and making reasonable projections of future trends and possibilities.  It follows that when exercising her judgment the Administrator balances the likelihood and severity of effects.  This balance involves a sliding scale; on one end the severity of the effects may be significant, but the likelihood low, while on the other end the severity may be less significant, but the likelihood high.  Under either scenario, the Administrator is permitted to find endangerment.  Accordingly, the Administrator need not set a precise or minimum threshold of risk or harm as part of making an endangerment finding, but rather may base her determination on "`a lesser risk of greater harm . . . or a greater risk of lesser harm' or any combination in between." CRR, 684 F.3d at 123 (quoting Ethyl Corp. v. EPA, 541 F.2d, 1, 18 (D.C. Cir. 1976)).  Because scientific knowledge is constantly evolving, the Administrator may be called upon to make decisions while recognizing the uncertainties and limitations of the data or information available, as risks to public health or welfare may involve the frontiers of scientific or medical knowledge.  At the same time, the Administrator must exercise reasoned decision making, and avoid speculative inquiries.
Third, the Administrator is to consider the cumulative impact of sources of a pollutant in assessing the risks from air pollution, and is not to look only at the risks attributable to a single source or class of sources.
Fourth, the Administrator is to consider the risks to all parts of our population, including those who are at greater risk for reasons such as increased susceptibility to adverse health effects.  If vulnerable subpopulations are especially at risk, the Administrator is entitled to take that point into account in deciding the question of endangerment.  Here too, both likelihood and severity of adverse effects are relevant.  As explained previously in the 2009 Endangerment Finding and as reiterated below for this section 231 finding, vulnerable subpopulations face serious health risks as a result of climate change.
As the Supreme Court recognized in Massachusetts v. EPA, 549 U.S. at 534, the EPA may make an endangerment finding despite the existence of "some residual uncertainty" in the scientific record. See also CRR, 684 F. 2d at 122.  Thus, this framework recognizes that regulatory agencies such as the EPA must be able to deal with the reality that "[m]an's ability to alter his environment has developed far more rapidly than his ability to foresee with certainty the effects of his alterations."  See Ethyl Corp v. EPA, 541 F.2d 1, 6 (D.C. Cir.), cert. denied 426 U.S. 941 (1976).  Both "the Clean Air Act `and common sense * * * demand regulatory action to prevent harm, even if the regulator is less than certain that harm is otherwise inevitable.'"  See Massachusetts v. EPA, 549 U.S. at 506, n.7 (citing Ethyl Corp.); see also CRR, 684 F.3d at 121-122.
In the 2009 Endangerment Finding, the Administrator recognized that the context for an action addressing climate change is unique. 74 FR at 66906.  At that time there was a very large and comprehensive base of scientific information that had been developed over many years through a global consensus process involving numerous scientists from many countries and representing many disciplines, and that informational base has since grown.  She also previously recognized that there are varying degrees of uncertainty across many of these scientific issues, which remains true.  It is in this context that she is exercising her judgment and applying the statutory framework in this proposed section 231 finding.  Further discussion of the language in section 231(a)(2)(A), and parallel language in 202(a), is provided below to explain more fully the basis for this interpretation, which the D.C. Circuit upheld in the 202(a) context.
         1. The Statutory Language
The interpretation described above flows from the statutory language itself.  The phrase "may reasonably be anticipated" and the term "endanger" in section 231(a)(2)(A) (as in section 202(a)) authorize, if not require, the Administrator to act to prevent harm and to act in conditions of uncertainty.  They do not limit her to merely reacting to harm or to acting only when certainty has been achieved; indeed, the references to anticipation and to endangerment imply that to fail to look to the future or to less than certain risks would be to abjure the Administrator's statutory responsibilities.  As the D.C. Circuit explained, the language "may reasonably be anticipated to endanger public health or welfare" in CAA § 202(a) requires a "precautionary, forward-looking scientific judgment about the risks of a particular air pollutant, consistent with the CAA's precautionary and preventive orientation." CRR, 684 F.3d at 122 (internal citations omitted).  The court determined that "[r]equiring that EPA find `certain' endangerment of public health or welfare before regulating greenhouse gases would effectively prevent EPA from doing the job that Congress gave it in § 202(a) -- utilizing emission standards to prevent reasonably anticipated endangerment from maturing into concrete harm." Id.  The same language appears in section 231(a)(2)(A) and the same interpretation applies in that context.  Moreover, by instructing the Administrator to consider whether emissions of an air pollutant cause or contribute to air pollution in the second part of the two-part test, the language is clear that she need not find that emissions from any one sector or class of sources are the sole or even the major part of an air pollution problem.  The use of the term "contribute" clearly indicates that a lower threshold than a finding that such emissions are the sole or major cause is a sufficient basis to make the required finding.  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.  When exercising her judgment the Administrator balances the likelihood and severity of effects.  Notably, the phrase "in [her] judgment" modifies both "may reasonably be anticipated" and "cause or contribute."
         2. How the Origin of the Current Statutory Language Informs the EPA's Interpretation of Section 231(a)(2)(A)
In the proposed and final 2009 Endangerment Finding, the EPA explained that when Congress revised the section 202(a) language that governed that finding, along with other provisions, as part of the 1977 amendments to the CAA, it was responding to decisions issued by the D.C. Circuit in Ethyl Corp. v. EPA regarding the pre-1977 version of section 211(c) of the Act.  74 FR 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 relevant for section 231.  The legislative history of those amendments, particularly the report by the House Committee on Interstate and Foreign Commerce, demonstrates that the EPA's interpretation of the section 231(a)(2)(A) language as set forth here in support of the Agency's section 231 finding which is the same as its interpretation of the parallel language in section 202(a) as explained in the 2009 Endangerment Finding, is fully consistent with Congress' intention in crafting these provisions.  See H.R. Rep. 95-294 (1977), as reprinted in 4 A Legislative History of the Clean Air Act Amendments of 1977 (1978) at 2465 (hereinafter LH).
The legislative history clearly indicates that the House Committee believed the Ethyl Corp. decisions posed several "crucial policy questions" regarding the protection of public health and welfare.  H.R. Rep. 95-294 at 48, 4 LH at 2515.  The following paragraphs summarize the en banc decision in Ethyl Corp. v. EPA and describe how the House Committee revised the endangerment language in the 1977 amendments to the CAA to serve several purposes consistent with that decision.  In particular, the language: (1) emphasizes the preventive or precautionary nature of the CAA; (2) authorizes the Administrator to reasonably project into the future and weigh risks; (3) assures the consideration of the cumulative impact of all sources; (4) instructs that the health of susceptible individuals, as well as healthy adults, should be part of the analysis; and (5) indicates an awareness of the uncertainties and limitations in information available to the Administrator.  H.R. rep. 95-294 at 49-50, 4 LH 2516-17.
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.  After reviewing the relevant facts and law, the full court evaluated the statutory language at issue to see what level of "certainty [was] required by the Clean Air Act before EPA may act."  541 F.2d at 7.
 The petitioners argued that the statutory language "will endanger" required proof of actual harm, and that the actual harm had to come from emissions from the fuels in and of themselves.  Id. at 12, 29.  The en banc court rejected this approach, finding that the term "endanger" allowed the Administrator to act when harm is threatened, and did not require proof of actual harm.  Id. at 13.  "A statute allowing for regulation in the face of danger is, necessarily, a precautionary statute."  Id.  Optimally, the court held, regulatory action would not only precede, but prevent, a perceived threat.  Id.
 The court also rejected petitioner's argument that any threatened harm must be "probable" before regulation was authorized.  Specifically, the court recognized that danger "is set not by a fixed probability of harm, but rather is composed of reciprocal elements of risk and harm, or probability and severity."  Id. at 18.  Next, the court held that the EPA's evaluation of risk is necessarily an exercise of judgment, and that the statute did not require a factual finding.  Id. at 24.  Thus, ultimately, the Administrator must "act, in part on `factual issues,' but largely `on choices of policy, on an assessment of risks, [and] on predictions dealing with matters on the frontiers of scientific knowledge * * *."  Id. at 29 (citations omitted).  Finally, the en banc court agreed with the EPA that even without the language in section 202(a) (which is also in section 231(a)(2)(A)) regarding "cause or contribute to," it was appropriate for the EPA to consider the cumulative impact of lead from numerous sources, not just the fuels being regulated under section 211(c).  Id. at 29-31.
The dissent in the original Ethyl Corp. decision and the en banc opinion were of "critical importance" to the House Committee which proposed the revisions to the endangerment language in the 1977 amendments to the CAA.  H.R. Rep. 95-294 at 48, 4 LH at 2515.  The Committee addressed those questions with the language that now appears in section 231(a)(2)(A) and several other CAA provisions -- "emission of any air pollutant * * * which in [the Administrator's] judgment causes, or contributes to, air pollution which may reasonably be anticipated to endanger public health or welfare."
As noted above in section III.A.1, the phrase "in [her] judgment" calls for the Administrator to make a comparative assessment of risks and projections of future possibilities, consider uncertainties, and extrapolate from limited data.  Thus, the Administrator must balance the likelihood of effects with the severity of the effects in reaching her judgment.  The Committee emphasized that the Administrator's exercise of "judgment" may include making projections, assessments and estimates that are reasonable, as opposed to a speculative or "`crystal ball' inquiry."   Moreover, procedural safeguards apply to the exercise of judgment, and final decisions are subject to judicial review.  Also, the phrase "in [her] judgment" modifies both the phrases "cause and contribute" and "may reasonably be anticipated," as discussed above.  H.R. Rep. 95-294 at 50-51, 4 LH at 2517-18.
As the Committee further explained, the phrase "may reasonably be anticipated" points the Administrator in the direction of assessing current and future risks rather than waiting for proof of actual harm.  This phrase is also intended to instruct the Administrator to consider the limitations and difficulties inherent in information on public health and welfare.  H.R. Rep. 95-294 at 51, 4 LH at 2518.
Finally, the phrase "cause or contribute" ensures that all sources of the contaminant which contribute to air pollution are considered in the endangerment analysis (e.g., not a single source or category of sources).  It is also intended to require the Administrator to consider all sources of exposure to a pollutant (for example, food, water, and air) when determining risk.  Id.
         3. Additional Considerations for the Cause or Contribute Analysis
By instructing the Administrator to consider whether emissions of an air pollutant cause or contribute to air pollution, the statute is clear that she need not find that emissions from any one sector or class of sources are the sole or even the major part of an air pollution problem.  The use of the term contribute clearly indicates a lower threshold than the sole or major cause.
Moreover, like the section 202(a) language that governed the 2009 Endangerment Finding, the statutory language in section 231(a)(2)(A) does not contain a modifier on its use of the term "contribute."  Unlike other CAA provisions, it does not require "significant" contribution.  Compare, e.g., CAA sections 111(b); 213(a)(2), (4).  Congress made it clear that the Administrator is to exercise her judgment in determining contribution, and authorized regulatory controls to address air pollution even if the air pollution problem results from a wide variety of sources.  While the endangerment test looks at the entire air pollution problem and the risks it poses, the cause or contribute test is designed to authorize the EPA to identify and then address what may well be many different sectors, classes, or groups of sources that are each part of the problem.
As explained for the 2009 Endangerment Finding, the D.C. Circuit has discussed the concept of contribution in the CAA, and its case law supports the EPA's interpretation that the level of contribution need not be significant.  74 FR at 66542.  In Catawba County v. EPA, 571 F.3d 20 (D.C. Cir. 2009), the court upheld EPA's PM[2.5] attainment and nonattainment designation decisions, analyzing CAA section 107(d), which requires EPA to designate an area as nonattainment if it "contributes to ambient air quality in a nearby area" not attaining the national ambient air quality standards.  Id. at 35.  The court noted that it had previously 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 a significant causal relationship.  Specifically, the D.C .Circuit again noted that the term is ambiguous, leaving it to EPA to interpret in a reasonable manner.  In the context of this discussion, the court noted that "a contribution may simply exacerbate a problem rather than cause it * * *." 571 F.3d at 39.
This is consistent with the D.C. Circuit's discussion of the concept of contribution in the context of CAA section 213 and rules for nonroad vehicles in Bluewater Network v. EPA, 370 F.3d 1 (D.C. Cir. 2004).  In that case, industry argued that section 213(a)(3) requires a finding of a significant contribution before the EPA can regulate, while the EPA's view was that the CAA requires a finding only of contribution. Id. at 13. Section 213(a)(3), like section 231(a)(2)(A), is triggered by a finding that certain sources "cause, or contribute to," air pollution, while an adjacent provision, section 213(a)(2), is triggered by a finding of a "significant" contribution.  The court looked at the "ordinary meaning of `contribute'" when upholding the EPA's reading.  After referencing dictionary definitions of "contribute," the court also noted that "[s]tanding alone, the term has no inherent connotation as to the magnitude or importance of the relevant `share' in the effect; certainly it does not incorporate any `significance' requirement." 370 F.3d at 13.  The court found that the bare "contribute" language invests the Administrator with discretion to exercise judgment regarding what constitutes a sufficient contribution for the purpose of making an endangerment finding. Id. at 14.
Like the statutory language considered in Catawba County and Bluewater Network, as well as the section 202(a) language that governed the Agency's previous findings for GHGs emitted by other types of mobile sources, section 231(a)(2)(A) refers to contribution and does not specify that the contribution must be significant before an affirmative finding can be made.  To be sure, any finding of a "contribution" requires some threshold to be met; a truly trivial or de minimis "contribution" might not count as such.  The Administrator therefore has ample discretion in exercising her reasonable judgment and determining whether, under the circumstances presented, the cause or contribute criterion has been met.  As noted above, in addressing provisions in section 202(a), the D.C. Circuit has explained that the Act did not require the EPA to identify a precise numerical value or "a minimum threshold of risk or harm before determining whether an air pollutant endangers." CRR, 648 F.3d at 122-123.  Accordingly, EPA "may base an endangerment finding on `a lesser risk of greater harm . . . or a greater risk of lesser harm' or any combination in between." Id. (quoting Ethyl Corp., 541 F.2d at 18).  Recognizing the substantial record of empirical data and scientific evidence that the EPA relied upon in the 2009 Endangerment Finding, the court determined that its "failure to distill this ocean of evidence into a specific number at which greenhouse gases cause `dangerous' climate change is a function of the precautionary thrust of the CAA and the multivariate and sometimes uncertain nature of climate science, not a sign of arbitrary or capricious decision-making." Id. at 123.  As the language in section 231(a)(2)(A) is analogous to that in section 202(a), 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 minimis 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 pollutant, the air pollution, the nature of the endangerment, the type or classes of sources at issue, the number of sources in the source sector or class, and the number and type of other source sectors or categories that may emit the air pollutant) when determining 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 totality of the circumstances approach); see also 74 FR at 66542.  Further discussion of this issue can be found in sections 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 GHGs emitted by the subject source classes.  Such an approach would collapse the two prongs of the test by requiring that any climate change impacts upon which an endangerment determination is made result solely from the GHG emissions of aircraft.  See 74 FR 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.  The threshold endangerment and cause or contribute criteria are separate and distinct from the standard setting criteria that apply if the threshold findings are met, and they serve a different purpose.  Indeed, the more serious the endangerment to public health and welfare, the more important it may be that action be taken to address the actual or potential harm even if no one action alone can solve the problem, and a series of actions is called for.
Air Pollutant, Public Health and Welfare
The CAA defines both "air pollutant" and "welfare."  Air pollutant is defined as: "any air pollution agent or combination of such agents, including any physical, chemical, biological, radioactive (including source material, special nuclear material, and byproduct material) substance or matter which is emitted into or otherwise enters the ambient air.  Such term includes any precursors to the formation of any air pollutant, to the extent the Administrator has identified such precursor or precursors for the particular purpose for which the term `air pollutant' is used." CAA section 302(g).  Greenhouse gases fit well within this capacious definition.  See Massachusetts v. EPA, 549 U.S. at 532.  They are "without a doubt" physical chemical substances emitted into the ambient air. Id. at 529.  Section V below contains further discussion of the "air pollutant" for purposes of 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 property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being, whether caused by transformation, conversion, or combination with other air pollutants."  CAA section 302(h).  This definition is quite broad.  Importantly, it is not an exclusive list due to the use of the term "includes, but is not limited to, * * *."  Effects other than those listed here may also be considered effects on welfare.
Moreover, the terms contained within the definition are themselves expansive.  For example, deterioration to property could include damage caused by extreme weather events. Effects on vegetation can include impacts from changes in temperature and precipitation as well as from the spreading of invasive species or insects.  Prior welfare effects evaluated by the EPA in other contexts include impacts on vegetation, as well as reduced visibility, changes in nutrient balance and acidity of the environment, soiling of buildings and statues, and erosion of building materials.  See, e.g., Final Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Sulfur, 77 FR 20218 (2012); Control of Emissions from Nonroad Large Spark Ignition Engines and Recreational Engines (Marine and Land-Based), 67 FR 68242 (2002); Final Heavy-Duty 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 definitions of "public health" or "public welfare" in the Clean Air Act.  The Supreme Court has discussed the concept of "public health" in the context of whether costs can be considered when setting National Ambient Air Quality Standards. Whitman v. American Trucking Ass'n, 531 U.S. 457 (2001).  In Whitman, the Court imbued the term with its most natural meaning: "the health of the public." Id. at 466.  When considering public health, the EPA has looked at morbidity, such as impairment of lung function, aggravation of respiratory and cardiovascular disease, and other acute and chronic health effects, as well as mortality.  See, e.g., Final National Ambient Air Quality Standard for Ozone, 73 FR 16436 (2008).
The Proposed Endangerment Finding under CAA section 231
This section describes the Administrator's proposed endangerment finding under CAA section 231(a)(2) and its basis.  Beginning with the air pollution under consideration, the Administrator is proposing to use the same definition of the "air pollution" under CAA section 231(a)(2) as that used under CAA section 202(a)(1), namely the mix of six well-mixed GHGs: CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.  It is the Administrator's view that the reasons detailed in the 2009 Endangerment Finding for defining the scope and nature of the air pollution as these six well-mixed GHGs remain valid and well-supported by the current science and are therefore reasonable bases for adopting the same definition of "air pollution" in this section 231(a)(2)(A) finding. Information from the new scientific assessments described in section IV.B below provide further support that the six well-mixed GHGs are the primary cause and driver of climate change.  The Administrator considered other climate-forcing agents both in the 2009 Endangerment Finding and in today's action; however, these substances are not included in the air pollution definition proposed today for the reasons discussed below in section IV.B.4.
The Administrator is proposing to find, for purposes of CAA section 231(a)(2)(A), that elevated concentrations of the six well-mixed GHGs constitute air pollution that endangers both the public health and the public welfare of current and future generations.  The Administrator's view is that the body of scientific evidence amassed in the record for the 2009 Endangerment Finding compellingly supports an endangerment finding under CAA section 231(a).  Information from the new scientific assessments described in section V.B below provides further support and justification for this proposed finding.
Section IV.A below summarizes the 2009 Endangerment Finding under CAA section 202, explains the approach EPA took in compiling an extensive record to inform the Administrator's judgment on that finding, and describes the recent judicial affirmation of the 2009 Endangerment Finding.  Section IV.B provides a summary of new scientific assessments that strengthen or provide further scientific evidence, in addition to that which the Administrator relied upon in making her prior judgment, for a finding that GHGs endanger public health and welfare.   Finally, section IV.C summarizes the Administrator's conclusion for purposes of section 231, in light of the evidence, analysis, and conclusions that led to the 2009 Endangerment Finding as well as more recent evidence, that emissions of the six well-mixed GHGs in the atmosphere endanger public health and welfare.
     C. Scientific Basis of the 2009 Endangerment Finding under CAA section 202(a)(1)
In the 2009 Endangerment Finding, the Administrator found that elevated concentrations of the well-mixed GHGs in the atmosphere may reasonably be anticipated to endanger public health and welfare of current and future generations. See, e.g., 74 FR 66516.  The Administrator reached this judgment by carefully considering a significant body of scientific evidence and public comments submitted to the Agency.  The sections below summarize the scope and nature of the relevant air pollution for the 2009 Endangerment Finding, as well as the public health and welfare considerations within the finding.
         1. The Definition of Air Pollution in the 2009 Endangerment Finding
The Administrator defined the scope and nature of the relevant air pollution as the aggregate group of six key, well-mixed GHGs: CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.  The Administrator considered five primary reasons for focusing on this aggregate group as the air pollution in the 2009 Endangerment Finding: (1) they share common physical properties that influence their climate effects; (2) they have been determined to be the primary cause of human-induced climate change, are the best-understood driver of climate change, and are expected to remain the key driver of future climate change; (3) they are the common focus of climate change science research and policy analyses and discussions; (4) using the combined mix of these gases as the definition (versus an individual gas-by-gas approach) is consistent with the science, because risks and impacts associated with GHG-induced climate change are not assessed on an individual gas-by-gas basis; and (5) using the combined mix of these gases is consistent with past EPA practice, where separate substances from different sources, but with common properties, may be treated as a class (e.g., oxides of nitrogen, particulate matter, volatile organic compounds).  The common physical properties these six GHGs share that are relevant to the climate change problem include the following: all are long-lived in the atmosphere; all become globally well mixed in the atmosphere, resulting in similar GHG concentrations around the globe and at all measured altitudes regardless of geographic location or altitudeof emissions; all trap outgoing heat that would otherwise escape to space; and all are directly emitted as GHGs rather than becoming a GHG in the atmosphere after emission of a precursor gas.  The Administrator acknowledged that other anthropogenic climate forcers also play a role in climate change but for various scientific and policy reasons, these substances were not included in the air pollution definition.
As explained in more detail in the 2009 Endangerment Finding, the EPA made the judgment that the scientific evidence is compelling that elevated concentrations of heat-trapping GHGs are the root cause of recently observed climate change and that the scientific record showed that most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.  The attribution of observed climate change to anthropogenic activities was based on multiple lines of evidence.  The first line of evidence arises from our basic physical understanding of the effects of changing concentrations of GHGs, natural factors, and other human impacts on the climate system.  The second line of evidence arises from indirect, historical estimates of past climate changes that suggest that the changes in global surface temperature over the last several decades are unusual.  The third line of evidence arises from the use of computer-based climate models to simulate the likely patterns of response of the climate system to different forcing mechanisms (both natural and anthropogenic).
         2. Public Health Impacts Detailed in the 2009 Endangerment Finding
Climate change resulting from anthropogenic GHG emissions threatens multiple aspects of public health.  In determining that the well-mixed GHG air pollution is reasonably anticipated to endanger public health for current and future generations, the Administrator noted her view that climate change can increase the risk of morbidity and mortality.  In making that public health finding, the Administrator considered direct temperature effects, air quality effects, the potential for changes in vector-borne diseases, and the potential for changes in the severity and frequency of extreme weather events.  In addition, the Administrator considered whether and how susceptible populations may be particularly at risk.  As explained in more detail in the 2009 Endangerment Finding, with respect to direct temperature effects, by raising average temperatures, climate change increases the likelihood of heat waves, which are associated with increased deaths and illnesses.  Climate change is also expected to lead to reductions in cold-related mortality.  The 2009 Endangerment Finding, while noting uncertainty about how heat and cold related mortality would change in the future, also pointed to a USGCRP assessment report discussion that increases in heat-related mortality due to global warming in the United States was unlikely to be compensated for by decreases in cold-related mortality.  With regard to air quality effects, climate change is expected to increase ozone pollution over broad areas of the country, including large metropolitan population centers, and thereby increase the risks of respiratory infection, aggravation of asthma, and premature death.  Other public health threats stem from the potential for increased deaths, injuries, infectious and waterborne diseases, stress-related disorders, and other adverse effects associated with increased hurricane intensity and increased frequency of intense storms and heavy precipitation associated with climate change.  In addition, climate change is expected to be associated with an increase in the spread of food-, water-, and vector-borne diseases in susceptible populations.  Climate change also has the potential to change aeroallergen production (for example, through lengthening the growing season for allergen-producing plants), and subsequent human exposures could increase allergenic illnesses.  Children, the elderly, and the poor are among the most vulnerable to climate-related health effects.
         3. Public Welfare Impacts Detailed in the 2009 Endangerment Finding
Climate change resulting from anthropogenic GHG emissions also threatens multiple aspects of public welfare.  In determining that the well-mixed GHG air pollution is reasonably anticipated to endanger public welfare for current and future generations, the Administrator considered the multiple pathways in which GHG air pollution and resultant climate change affect public welfare by evaluating the numerous and far-ranging risks to food production and agriculture; forestry; water resources; sea level rise and coastal areas; energy, infrastructure, and settlements; and ecosystems and wildlife.  The Administrator also considered impacts on the U.S. population from climate change effects occurring outside of the United States.  As explained in more detail in the 2009 Endangerment Finding, the potential serious adverse impacts of extreme events, such as wildfires, flooding, drought, and extreme weather conditions provided strong support for the determination.  Climate change is expected to place large areas of the country at serious risk of reduced water supplies, increased water pollution, and increased occurrence of extreme events such as floods and droughts.  Coastal areas are expected to face increased risks from storm and flooding damage to property, as well as adverse impacts from rising sea level such as land loss due to inundation, erosion, wetland submergence and habitat loss.  Climate change is expected to result in an increase in peak electricity demand, and extreme weather from climate change threatens energy, transportation, and water resource infrastructure.  Climate change may exacerbate existing environmental pressures in certain settlements, particularly in Alaskan indigenous communities.  Climate change is also very likely to fundamentally change U.S. ecosystems over the 21st century and to lead to predominantly negative consequences for biodiversity, ecosystem goods and services, and wildlife.  Though there may be some benefits for agriculture and forestry in the next few decades, the body of evidence points towards increasing risks of net adverse impacts on U.S. food production, agriculture and forest productivity as average temperature continues to rise.  Looking across all sectors discussed above, the risk and the severity of adverse impacts on public welfare are expected to increase over time.  Lastly, these impacts are global and may exacerbate problems outside the United States that raise humanitarian, trade, and national security issues for the United States.
         4. The Science Upon Which the Agency Relied
As outlined in section III.A of the 2009 Endangerment Finding, the EPA's approach to providing the technical and scientific information to inform the Administrator's judgment regarding the question of whether GHGs endanger public health and welfare was to rely primarily upon the recent, major assessments by the USGCRP, the IPCC, and the NRC.  These assessments addressed the scientific issues that the EPA was required to examine, were comprehensive in their coverage of the GHG and climate change issues, and underwent rigorous and exacting peer review by the expert community, as well as rigorous levels of U.S. government review, in which the EPA took part.  Primary reliance on the major scientific assessments provided assurance that the Administrator was basing her judgment on the best available, well-vetted science that reflected the consensus of the climate science research community.  The major findings of the USGCRP, IPCC, and NRC assessments supported the Administrator's determination that elevated concentrations of GHGs in the atmosphere may reasonably be anticipated to endanger the public health and welfare of current and future generations.  The EPA presented this scientific support at length in the comprehensive record for the 2009 Endangerment Finding.  Relevant sections of documents from the 2009 Endangerment Finding record have been placed in the docket for this proposed finding under CAA section 231.
The EPA then reviewed ten administrative petitions for reconsideration of the Endangerment Finding in 2010.  In the Reconsideration Denial, the Administrator denied those petitions on the basis of the Petitioners' failure to provide substantial support for their argument that the EPA should revise the Endangerment Finding and their objections' lack of "central relevance" to the Finding.  The EPA prepared an accompanying three-volume Response to Petitions document to provide additional information, often more technical in nature, in response to the arguments, claims, and assertions by the Petitioners to reconsider the Endangerment Finding.
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. On June 26, 2012, the Court upheld the Endangerment Finding and the Reconsideration Denial, ruling that the Finding (including the Reconsideration Denial) was not arbitrary or capricious, was consistent with the U.S. Supreme Court's decision in Massachusetts v. EPA (which affirmed the EPA's authority to regulate greenhouse gases) and the text and structure of the CAA, and was adequately supported by the administrative record.  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."  The Court found that the EPA had based its decision on "substantial scientific evidence," observing that "EPA's scientific evidence of record included support for the proposition that greenhouse gases trap heat on earth that would otherwise dissipate into space; that this `greenhouse effect' warms the climate; that human activity is contributing to increased atmospheric levels of greenhouse gases; and that the climate system is warming," as well as providing extensive scientific evidence for EPA's determination that anthropogenically induced climate change threatens both public health and welfare.  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.  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 material to use in deciding whether GHG emissions may be reasonably anticipated to endanger public health or welfare. * * * It makes no difference that much of the scientific evidence in large part consisted of "syntheses" of individual studies and research. Even individual studies and research papers often synthesize past work in an area and then build upon it. This is how science works. The EPA is not required to re-prove the existence of the atom every time it approaches a scientific question.
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. The Administrator considered the fact that "some aspects of climate change science and the projected impacts are more certain than others."  The D.C. Circuit subsequently noted that "the existence of some uncertainty does not, without more, warrant invalidation of an endangerment finding."
As noted above the Supreme Court granted some of the petitions for certiorari that were filed, while denying others, but agreed to decide only the question: "Whether EPA permissibly determined that its regulation of greenhouse gas emissions from new motor vehicles triggered permitting requirements under the Clean Air Act for stationary sources that emit greenhouse gases." Thus, the Supreme Court did not disturb the D.C. Circuit's holding that affirmed the 2009 Endangerment Finding.
Recent Science Further Supports the Administrator's Judgment that the Six Well-Mixed Greenhouse Gases Endanger Public Health and Welfare
Since the closure of the administrative record concerning the 2009 Endangerment Finding (including the denial of petitions for reconsideration), a number of new major, peer-reviewed scientific assessments have been released.  The EPA carefully reviewed the updated scientific conclusions in these assessments, largely to evaluate whether they would lead the EPA in this CAA section 231(a)(2)(A) finding to propose a different interpretation of, or place more or less weight on, the major findings reflected in the previous assessment reports that underpinned the Administrator's judgment that the six well-mixed GHGs endanger public health and welfare.  From its review, the EPA finds that these new assessments are largely consistent with, and in many cases strengthen and add to, the already compelling and comprehensive scientific evidence detailing the role of the six well-mixed GHGs in driving climate change, detailed in the 2009 Endangerment Finding.  Therefore, the new scientific assessments do not provide any reasonable basis on which to propose under CAA section 231(a)(2)(A) a different conclusion than the one the EPA reached in 2009 under CAA section 202(a).  Rather, they provide further support for today's proposed finding under section 231.  In particular, the new assessments discussed in this preamble provide additional detail regarding public health impacts, particularly on groups and lifestages especially vulnerable to climate change including children, the elderly, low-income communities and individuals, indigenous groups, and communities of color.
 	The subsections below present brief summaries of the relevant key findings from the new major peer-reviewed scientific assessments, which include the IPCC's 2013-2014 Fifth Assessment Report (AR5); IPCC's 2012 "Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation" (SREX): the USGCRP's 2014 "Climate Change Impacts in the United States: the Third National Climate Assessment" (NCA3); the NRC's 2010 "Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean" (Ocean Acidification); 2011 "Climate Change, the Indoor Environment, and Health" (Indoor Environment); 2011 "Report on Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia" (Climate Stabilization Targets), 2011 "National Security Implications for U.S. Naval Forces" (National Security Implications), 2011 "Understanding Earth's Deep Past: Lessons for Our Climate Future" (Understanding Earth's Deep Past), 2012 "Sea Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future" (Sea Level Rise), 2013 "Climate and Social Stress: Implications for Security Analysis" (Climate and Social Stress), 2013 "Abrupt Impacts of Climate Change" (Abrupt Impacts), and 2014 "The Arctic in the Anthropocene: Emerging Research Questions" (Arctic) assessments.
         5. 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 underlying science supporting the 2009 Endangerment Finding that the six well-mixed GHGs are the root cause of recently observed climate change.  Key findings are described briefly here.
The IPCC AR5 concludes that the global average net effect of the increase in atmospheric GHG concentrations, plus other human activities (e.g., land use change and aerosol emissions), on the global energy balance since 1750 has been one of warming.  This total net heating effect, referred to as "forcing," is estimated to be 2.3 Watts per square meter (W/m2), which has increased from the previous 2007 IPCC Fourth Assessment Report (AR4) total net estimate of 1.6 Watts per square meter (W/m2) that was referred to in the record for the 2009 Endangerment Finding.  The reasons for this increase include continued increases in GHG concentrations, as well as reductions in the estimated negative forcing due to aerosols.  The IPCC AR5 rates the level of confidence  in their radiative forcing estimates as "high" for methane and "very high" for CO2 and nitrous oxide.
The new assessments also have greater confidence in attributing recent warming to human causes.  The IPCC AR5 stated that it is extremely likely (>95 percent likelihood) that human influences have been the dominant cause of warming since 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 concentrations.  The AR4 conclusion was referred to in the record for the 2009 Endangerment Finding.  In addition, the IPCC AR5 found that concentrations of CO2 and several other of the major GHGs are higher than they have been in at least 800,000 years. This is an increase from what was reported in IPCC AR4, which found higher concentrations than in at least 650,000 years.
The USGCRP NCA3 states that there is very high confidence that the global climate change of the past 50 years is primarily due to human activities.  Human activities are affecting climate through increasing atmospheric levels of heat-trapping gases, through changing levels of various particles that can have either a heating or cooling influence on the atmosphere, and through activities such as land use changes that alter the reflectivity of the Earth's surface and cause climatic warming and cooling effects.  The USGCRP concludes that "considering all known natural and human drivers of climate since 1750, a strong net warming from long-lived greenhouse gases produced by human activities dominates the recent climate record."
These recent and strong conclusions attributing human influence to recent observed global warming have been made despite what some have termed a warming slowdown or "hiatus" over the past 15 years or so.  The IPCC AR5 notes that global mean surface temperature exhibits substantial natural decadal and interannual variability, such that trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.  As an example, the IPCC AR5 notes that the rate of warming over the 15 year period from 1998-2012 was less than that over the period 1951-2012.  This short term variability does not alter the long-term climate trend that the IPCC AR5 finds after its review of independently verified observational records: "Each of the past three decades has been successively warmer at the Earth's surface than all the previous decades in the instrumental record, and the first decade of the 21st century has been the warmest.",
The NRC Climate Stabilization Targets assessment concludes that CO2 emissions are altering the atmosphere's composition and therefore the climate for thousands of years. The NRC Understanding Earth's Deep Past assessment finds that "the magnitude and rate of the present greenhouse gas increase place the climate system in what could be one of the most severe increases in radiative forcing of the global climate system in Earth history."  This assessment finds that CO2 concentrations by the end of the century are projected to increase to levels that Earth has not experienced for more than 30 million years if no emissions reductions are made.
         6. More Recent Evidence that Greenhouse Gases Endanger Public Health
The EPA has carefully reviewed the key conclusions in the recent assessments regarding human-induced climate change risks and impacts on public health.  The EPA finds that the new assessments are consistent with or strengthen the underlying science considered in the 2009 Endangerment Finding regarding public health effects from changes in temperature, air quality, extreme weather, and climate-sensitive diseases and aeroallergens. These key findings are described briefly here.
Regarding temperature effects, the conclusions of the assessment literature cited in the 2009 Endangerment Finding were uncertain with respect to the exact balance of how heat- versus cold-related mortality will change in the future, but noted that the available evidence suggested that the increased risk from heat would exceed the decreased risk from cold in a warming climate.  The most recent assessments now have greater confidence that increases in heat-related mortality will be larger than the decreases in cold-related mortality.  The USGCRP NCA3 concludes that, "While deaths and injuries related to extreme cold events are projected to decline due to climate change, these reductions are not expected to compensate for the increase in heat-related deaths."  The IPCC AR5 also notes a potential benefit of climate change could include "modest reductions in cold-related mortality and morbidity in some areas due to fewer cold extremes (low confidence)," but that, "[o]verall, we conclude that the increase in heat-related mortality by mid-century will outweigh gains due to fewer cold periods."
Regarding air quality effects, the assessment literature cited in the 2009 Endangerment Finding concluded that climate change is expected to increase regional ozone pollution, with associated risks in respiratory illnesses and premature death, but that the directional effect of climate change on ambient particulate matter levels was less certain.  The USGCRP NCA3 similarly concludes that, "Climate change is projected to harm human health by increasing ground-level ozone and/or particulate matter air pollution in some locations. [... .] There is less certainty in the responses of airborne particles to climate change than there is about the response of ozone."  The IPCC AR5 finds that ozone and particulate matter have been associated with adverse health effects in many locations in North America, and that ozone concentrations could increase under future climate change scenarios if emissions of precursors were held constant.  For particulate matter, both the USGCRP NCA3 and IPCC AR5 discuss increasing wildfire risk under climate change, and explain that wildfire smoke exposure can lead to various respiratory and cardiovascular impacts.  The NRC Indoor Environment assessment identifies potential adverse health risks associated with climate-change induced alterations in the indoor environment, including possible exposure to air pollutants like ozone via changes in outdoor air quality, as well as to indoor allergens, chemical emissions, and dampness/mold.
      Regarding extreme weather events (e.g., storms, heavy precipitation, and, in some regions of the United States, floods and droughts), the conclusions of the assessment literature cited in the 2009 Endangerment Finding found potential for increased deaths, injuries, infectious and waterborne diseases, and stress-related disorders.  Similarly, the USGCRP NCA3 discusses elevated waterborne disease outbreaks and the potential for mold contamination and degraded indoor air quality following heavy precipitation.  Other impacts include mortality associated with flooding and impacts on mental health, such as anxiety and post-traumatic stress disorder.  The IPCC AR5 also discusses death and injury in coastal zones and regions vulnerable to inland flooding.  The USGCRP NCA3 and the IPCC AR5 both find that climate change may increase exposure to and health risks associated with drought conditions, which includes impacts from wildfires, dust storms, extreme heat events, flash flooding, degraded water quality, reduced water quantity, and water-related diseases.  The IPCC SREX assessment projects further increases in some extreme weather and climate events during this century, and specifically notes that changes in extreme weather events have implications for disaster risk in the health sector.
The effects of climate change on climate-sensitive diseases were also cited in the 2009 Endangerment Finding, including a likely increase in the spread of several food and water-borne pathogens among susceptible populations, and the potential for range expansion of some zoonotic disease carriers such as the Lyme disease carrying tick.  The new assessment literature similarly focuses on increased exposure risk for some diseases under climate change, finding that increasing temperatures may expand or shift the ranges of some disease vectors like mosquitoes, ticks, and rodents.  The IPCC AR5 notes that climate change may influence the "growth, survival, persistence, transmission, or virulence of pathogens" that cause food and water-borne disease.  The USGCRP NCA3 notes that uncertainty remains regarding future projections of increased human burden of vector-borne disease, given complex interacting factors such as "local, small-scale differences in weather, human modification of the landscape, the diversity of animal hosts, and human behavior that affects vector-human contact, among other factors."
Regarding aeroallergens, the assessment literature cited in the 2009 Endangerment Finding found potential for climate change to affect the prevalence and severity of allergy symptoms, but that definitive data or conclusions were lacking on how climate change might impact aeroallergens in the United States.  The most recent assessments now have greater confidence that climate change will influence production of pollen that affects asthma and other allergic respiratory diseases such as allergic rhinitis, as well as effects on conjunctivitis and dermatitis.  Both the USGCRP NCA3 and the IPCC AR5 found that increasing temperature has lengthened the allergenic pollen season for ragweed, and that increased CO2 by itself can elevate production of plant-based allergens.  The IPCC AR5 concludes that in North America, "warming will lead to further changes in the seasonal timing of pollen release (high confidence)."
The assessment literature cited in the 2009 Endangerment Finding concluded that certain populations, including children, the elderly, and the poor, are most vulnerable to climate-related health effects.  The 2009 Endangerment Finding also described climate change impacts facing indigenous peoples in the United States, particularly Alaska Natives.  The new assessment literature strengthens these conclusions by providing more detailed findings regarding these populations' vulnerabilities and 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.