# Rescission of the Greenhouse Gas Findings for Fossil Fuel-Fired Power Plants and Repeal of Regulations for Power Plant Greenhouse Gas Emissions Under Clean Air Act Section 111 > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2026-19072 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** September 17, 2026 - **Citation:** 91 FR 59002 ## Text ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 60 [EPA-HQ-OAR-2025-0124; FRL-12674.1-01-OAR] RIN 2060-AX00 Rescission of the Greenhouse Gas Findings for Fossil Fuel-Fired Power Plants and Repeal of Regulations for Power Plant Greenhouse Gas Emissions Under Clean Air Act Section 111 AGENCY: Environmental Protection Agency (EPA). ACTION: Supplemental notice of proposed rulemaking. SUMMARY: In this action, the U.S. Environmental Protection Agency (EPA) is supplementing its proposal to repeal all greenhouse gas (GHG) emission standards for fossil fuel-fired electric generating units (EGUs) to effectuate the best reading of Clean Air Act (CAA) section 111. We propose that CAA section 111 does not authorize the EPA to regulate emissions from power plants in response to global climate change concerns. For the multiple and independent reasons described herein, this additional rationale would also require rescinding the Administrator's contrary findings and determinations in 2015 and repealing all associated 2015 and 2024 GHG standards for the fossil fuel-fired EGU source category. In a separate action published concurrently with this supplemental notice, the EPA is finalizing the repeal of certain 2024 GHG standards for the fossil fuel-fired EGU source category on distinct legal and technical grounds. We are not reopening that final rule. Nor are we soliciting further comment on those issues through this supplemental notice, except to the extent that commenters believe the final rule bears on the distinct questions of statutory authority addressed herein. DATES: Comments must be received on or before November 2, 2026. Comments on the information collection provisions submitted to the Office of Management and Budget (OMB) under the Paperwork Reduction Act (PRA) are best assured of consideration by OMB if OMB receives a copy of your comments on or before October 19, 2026. Please refer to the PRA section under “Statutory and E.O. Reviews” in this preamble for specific instructions. Public Hearing. The EPA will hold a virtual public hearing on October 1, 2026. Please refer to the SUPPLEMENTARY INFORMATION section for information on registering for the public hearing. ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-OAR-2025-0124, by any of the following methods: • Federal eRulemaking Portal: https://www.regulations.gov (our preferred method) website. Follow the online instructions for submitting comments. • Email: a-and-r-docket@epa.gov. Include Docket ID No. EPA-HQ-OAR-2025-0124 in the subject line of the message. • Mail: U.S. Environmental Protection Agency, EPA Docket Center, Docket ID No. EPA-HQ-OAR-2025-0124, Mail Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460. • Hand/Courier Delivery: EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. The Docket Center's hours of operation are 8:30 a.m. to 4:30 p.m. Eastern Time (ET), Monday through Friday (except Federal holidays). Instructions: All submissions received must include the Docket ID No. for this rulemaking. Comments received may be posted without change to https://www.regulations.gov, including any personal information provided. For detailed instructions on sending comments and additional information on the rulemaking process, see the SUPPLEMENTARY INFORMATION section of this document. FOR FURTHER INFORMATION CONTACT: For information about this proposed rule, contact Ms. Lisa Thompson, Industrial Processing and Power Division (D243-02), Office of Clean Air Programs, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-5158 and email address: thompson.lisa@epa.gov. SUPPLEMENTARY INFORMATION: Participation in virtual public hearing. The hearing will be held via virtual platform on October 1, 2026. The EPA will announce further details at https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power. The EPA will begin pre-registering speakers for the hearing no later than 1 business day after a request has been received. To register to speak at the virtual hearing, please use the online registration form available at https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power or contact the public hearing team at (888) 372-8699 or by email at IPPDpublichearing@epa.gov. The last day to pre-register to speak at the hearing will be September 29, 2026. Prior to the hearing, the EPA will post a general agenda that will list pre-registered speakers at: https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power. 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 hearings to run either ahead of schedule or behind schedule. The EPA may close a session 15 minutes after the last pre-registered speaker has testified if there are no additional speakers. Each commenter will have 4 minutes to provide oral testimony. The EPA encourages commenters to submit a copy of their oral testimony as written comments electronically to the rulemaking docket. 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 testimony and supporting information presented at the public hearing. Please note that any updates made to any aspect of the hearing will be posted online at https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power. While the EPA expects the hearing to go forward as set forth above, please monitor our website or contact the public hearing team at (888) 372-8699 or by email at IPPDpublichearing@epa.gov to determine if there are any updates. The EPA does not intend to publish a document in the Federal Register announcing updates. If you require special accommodations such as audio description, please pre-register for the hearing with the public hearing team and describe your needs by September 24, 2026. The EPA may not be able to arrange accommodations without advanced notice. Docket. The EPA established a docket for this action under Docket ID No. EPA-HQ-OAR-2025-0124. The docket lists all documents at https://www.regulations.gov. Although listed, some information is not publicly available, e.g., Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. The EPA does not place certain other material, such as copyrighted material, on the internet; this material is publicly available only as portable document format (PDF) versions accessible only on EPA computers in the docket office reading room. The public cannot download certain databases and physical items from the docket but may request these items by contacting the docket office at (202) 566-1744. The docket office has 10 business days to respond to such requests. With the exception of such material, publicly available docket materials are available electronically at https://www.regulations.gov or on EPA computers in the docket office reading room at the EPA Docket Center, WJC West Building, Room Number 3334, 1301 Constitution Ave. NW, Washington, DC. The Public Reading Room hours of operation are 8:30 a.m. to 4:30 p.m. ET, Monday through Friday (except for Federal holidays). The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the EPA Docket Center is (202) 566-1742. Written Comments. Direct your comments to Docket ID No. EPA-HQ-OAR-2025-0124. Under the EPA's policy, the Agency includes all comments in the public docket without change and makes them available online at https://www.regulations.gov, including any personal information provided, unless a submission contains information claimed as CBI or other information for which a statute restricts disclosure. Do not submit electronically to https://www.regulations.gov any information that you consider to be CBI or other information for which a statute restricts disclosure. Submit such information as described in the Submitting CBI section of this preamble. The EPA may publish any comment it receives to the public docket. A written comment must accompany any multimedia submission ( e.g., audio or video). The EPA considers the written comment the official comment and expects it to address all points the commenter wishes to make. The EPA will generally not consider comments or supporting materials that appear outside the primary submission ( i.e., on websites, cloud storage, or other file-sharing systems). For additional submission methods, the EPA's full public comment policy, information about CBI or multimedia submissions, and guidance on making effective comments, visit https://www.epa.gov/dockets/commenting-epa-dockets. The https://www.regulations.gov website allows commenters to submit comments anonymously, which means the EPA will not know the commenter's identity or contact information unless the commenter provides it in the body of the comment. If a commenter emails a comment directly to the EPA rather than using https://www.regulations.gov, the EPA's system automatically captures the sender's email address, and the Agency includes that address in the public docket and makes it available online. If a commenter submits an electronic comment, the EPA recommends including the commenter's name and other contact information in the body of the comment and with any digital storage media submitted. If the EPA cannot read a comment due to technical difficulties and cannot contact the commenter for clarification, the Agency may be unable to consider the comment. Submit electronic files without special characters, encryption, defects, or viruses. For additional information about the EPA's public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets. The EPA solicits comment on numerous aspects of this proposed rule. The EPA indexes each comment solicitation with an identifier ( e.g., “C-1, C-2, . . .”) to provide a consistent framework for effective, efficient commenting. Accordingly, the EPA asks commenters to include the corresponding identifier when submitting comments relevant to that solicitation. Include the identifier in a heading or within the text of each comment ( e.g., “In response to C-1, . . .”) to make clear which solicitation the commenter is addressing. The EPA emphasizes that the Agency is not limiting comment to these identified areas and encourages commenters to provide any other comments relevant to this supplemental proposal. Submitting CBI. Do not submit information containing CBI to the EPA through https://www.regulations.gov. Clearly mark the part or all the information that you claim to be CBI. For CBI information on any digital storage media that you mail to the EPA, note the docket ID, mark the outside of the digital storage media as CBI, and identify electronically within the digital storage media the specific information that is claimed as CBI. In addition to one complete version of the comments that includes information claimed as CBI, you must submit a copy of the comments that does not contain the information claimed as CBI directly to the public docket through the procedures outlined in the Written Comments section of this preamble. If you submit any digital storage media that does not contain CBI, mark the outside of the digital storage media clearly that it does not contain CBI and note the docket ID. Information not marked as CBI will be included in the public docket and the EPA's electronic public docket without prior notice. Information marked as CBI will not be disclosed except in accordance with procedures set forth in 40 Code of Federal Regulations (CFR) part 2. Our preferred method to receive CBI is for it to be transmitted electronically using email attachments, File Transfer Protocol (FTP), or other online file sharing services ( e.g., Dropbox, OneDrive, Google Drive). Electronic submissions must be transmitted directly to the Office of Clean Air Programs (OCAP) at the email address: ocapcbi@epa.gov and, as described earlier in this preamble, should include clear CBI markings and note the docket ID. If assistance is needed with submitting large electronic files that exceed the file size limit for email attachments, and if you do not have your own file sharing service, please contact the person listed in the FOR FURTHER INFORMATION CONTACT section of this preamble to receive instructions. Preamble acronyms and abbreviations. Throughout this document the use of “we,” “us,” or “our” is intended to refer to the EPA. We use multiple acronyms and terms in this preamble. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here: ACE Affordable Clean Energy [rule] BSER best system of emission reduction CAA Clean Air Act CCS carbon capture and sequestration/storage CO 2 carbon dioxide CPP Clean Power Plan CPS Carbon Pollution Standards rule EGU electric generating unit EIA economic impact analysis E.O. Executive Order EPA Environmental Protection Agency FR Federal Register GHG greenhouse gas GMST global mean surface temperature GSLR global sea level rise HAP hazardous air pollutant HFC hydrofluorocarbons IGCC integrated gasification combined cycle IRA Inflation Reduction Act NAAQS National Ambient Air Quality Standards NPRM Notice of Proposed Rulemaking NSPS new source performance standards OMB Office of Management and Budget Table of Contents I. General Information A. Does this action apply to me? B. Where can I get a copy of this document and other related information? II. Executive Summary A. Introduction B. Need for Regulatory Action III. Background A. Statutory Authority Under CAA Section 111 B. Legislative and Regulatory History of CAA Section 111 C. Regulation of Greenhouse Gases Under CAA Section 111 D. Legislation Concerning CAA Section 111 IV. Legal Framework for Action V. Rescission of the 2015 Findings A. Best Reading of CAA Section 111(b)(1)(A) B. Lack of Clear Congressional Authorization C. Eliminating GHG Emissions From Fossil Fuel-Fired Power Plants Would Be Futile VI. Repeal of GHG Standards of Performance for Fossil Fuel-Fired EGUs Under CAA Section 111 A. Scope of Repeal of GHG Standards of Performance B. Impacts of Repeal of GHG Standards of Performance VII. Requests for Comment VIII. Statutory and E.O. Reviews A. E.O. 12866: Regulatory Planning and Review B. E.O. 14192: Unleashing Prosperity Through Deregulation C. Paperwork Reduction Act (PRA) D. Regulatory Flexibility Act (RFA) E. Unfunded Mandates Reform Act (UMRA) F. E.O. 13132: Federalism G. E.O. 13175: Consultation and Coordination With Indian Tribal Governments H. E.O. 13045: Protection of Children From Environmental Health Risks and Safety Risks I. E.O. 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use J. National Technology Transfer and Advancement Act (NTTAA) and 1 CFR Part 51 I. General Information A. Does this action apply to me? Fossil fuel-fired electric utility steam generating units and stationary combustion turbine EGUs that provide electricity to the electric grid (a utility power distribution system) comprise the source category that is subject to this action. The 2022 North American Industry Classification System (NAICS) code for the source category is 221112. The EPA does not intend this identification to be exhaustive but rather to provide a guide for readers regarding the entities that this proposed action is likely to affect. The proposed repeal of 40 CFR part 60, subpart TTTT, once promulgated, would be applicable to stationary combustion turbines that commenced construction or modification after January 8, 2014, or reconstruction after June 18, 2014, and on or before May 23, 2023, and any steam generating unit or integrated gasification combined cycle (IGCC) facility that commenced construction after January 8, 2014, or commenced modification or reconstruction after June 18, 2014. The proposed repeal of 40 CFR part 60, subpart TTTTa, once promulgated, would be applicable to stationary combustion turbines that began construction or reconstruction after May 23, 2023, and any steam generating unit that commenced modification after May 23, 2023. B. Where can I get a copy of this document and other related information? In addition to the docket, an electronic copy of this proposed action will be on the internet. Following signature by the Administrator, the EPA will post a copy of this proposed action at https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power. Following publication in the Federal Register (FR), the EPA will post the FR version at this same website. II. Executive Summary A. Introduction On June 17, 2025, the EPA published a Notice of Proposed Rulemaking (NPRM) in the Federal Register entitled “Repeal of Greenhouse Gas Emissions Standards for Fossil Fuel-Fired Electric Generating Units.” 90 FR 25752 (“June 2025 NPRM”). In that action, we proposed two independent pathways for revisiting the GHG standards of performance for the fossil fuel-fired EGU source category established in the 2015 New Source Performance Standards, 80 FR 64510 (Oct. 23, 2015) (“2015 NSPS”), and 2024 Carbon Pollution Standards, 89 FR 39798 (May 9, 2024) (“2024 CPS”). The primary pathway proposed to repeal all GHG standards of performance for fossil fuel-fired EGUs for lack of authority based on the conclusion that such power plants do not “contribute significantly” to air pollution that endangers public health or welfare. The alternative pathway proposed to repeal many requirements in the 2024 CPS based on a reconsideration of the best system of emission reduction (BSER) determinations supporting the requirements. In a final rule issued concurrently with this supplemental notice, the EPA is finalizing the repeal of the majority of the 2024 CPS requirements based on a reassessment of the BSER for the relevant subcategories. 1 The EPA notes in that final rule that it is seeking additional public comment in a separate action ( i.e., in this supplemental notice) on the underlying question raised in the primary basis of the June 2025 NPRM: Whether the EPA lacks statutory authority to regulate GHG emissions from power plants under CAA section 111. 2 1 See Partial Repeal of the Carbon Pollution Standards for Fossil Fuel-Fired Electric Generating Units, available in Docket ID EPA-HQ-OAR-2025-0124. 2 The EPA is not reopening or soliciting further comment on the distinct issues addressed in the contemporaneous final rule. Commenters are welcome to articulate whether and why they believe the actions and rationales adopted in the final rule are relevant to the distinct question addressed in this supplemental proposal, but the EPA generally will not respond to comments that are limited to the issues resolved in the final rule. Interested parties were invited to comment on those issues in connection with the alternative basis presented in the June 2025 NPRM and may review the EPA's summary of comments and responses thereto in the final rule preamble and associated response to comments (RTC). This supplemental notice proposes additional approaches to that question in light of the Agency's intervening final action entitled “Rescission of the Greenhouse Gas Endangerment Finding and Motor Vehicle Greenhouse Gas Emission Standards Under the Clean Air Act,” 91 FR 7686 (Feb. 18, 2026) (“Endangerment Finding Rescission”). In that final rule, the EPA rescinded the Administrator's 2009 findings of endangerment and contribution, and repealed all GHG emission standards, for new motor vehicles and engines based on the conclusion that the Agency lacks statutory authority under CAA section 202(a)(1) to regulate in response to global climate change concerns. In this supplemental notice, we propose that the EPA lacks authority under CAA section 111 to regulate power plants in response to global climate change concerns for multiple, independent reasons. The approach and rationales proposed in this supplemental notice would require the same regulatory actions contemplated in the primary proposal in the June 2025 NPRM—the repeal of all fossil fuel-fired EGU GHG standards for lack of authority—but for different reasons. Whereas the primary proposal in the June 2025 NPRM sought public comment on, among other things, whether fossil fuel-fired EGUs “contribute significantly” to air pollution, this supplemental notice seeks public comment on the distinct question whether global climate change concerns satisfy the threshold requirement in CAA section 111(b)(1)(A) that the source category emissions contribute significantly to “air pollution which may reasonably be anticipated to endanger public health or welfare.” We will evaluate both proposed approaches and rationales in taking final action, as both issues— contribution and endangerment—were the subject of significant interpretive and policy changes in the 2009 Endangerment Finding and the 2015 NSPS and 2024 CPS that extended the Agency's novel approach to power plant stationary sources. 3 3 The EPA is not soliciting further comment on the primary proposal in the June 2025 NPRM. Commenters are welcome to articulate whether and why they believe the distinct rationales presented in this supplemental proposal are or are not preferable to the rationale presented in the June 2025 NPRM, but the EPA generally will not respond to comments that are limited to the primary proposal in the June 2025 NPRM. Interested parties were invited to comment on those issues in connection with the primary proposal in the June 2025 NPRM, and the Agency will address such comments as appropriate in a forthcoming final rule addressing the rationales presented in both the primary proposal in the June 2025 NPRM and this supplemental proposal. In 2009, the EPA took the unprecedented step of asserting authority to regulate GHG emissions in a standalone action that launched the Agency into a course of regulation that fundamentally reshaped many aspects of the Nation's economic and social life. 74 FR 66496 (Dec. 15, 2009) (“2009 Endangerment Finding”). 4 In the 2009 Endangerment Finding, we interpreted CAA section 202(a)(1) for the first time to authorize regulation of domestic emissions from new motor vehicles and engines based on global climate change concerns rather than air pollution that endangers public health or welfare through local or regional exposure. 74 FR 66526-27. We relied on that interpretation to define both the relevant “air pollution” and the relevant “air pollutant” as the combination of six “well-mixed GHGs”—carbon dioxide (CO 2 ), methane, nitrous oxide (N 2 O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF 6 )—while reserving the right to include additional “climate forcers” in these definitions in the future. 74 FR 66516-17, 66536-37. 4 See also “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act: EPA's Response to Public Comments” (“EF RTC”), available in a Memorandum to Docket entitled “EPA's Response to Public Comments on the 2009 Endangerment and Cause or Contribute Findings for Greenhouse Gases: Volumes 1-11,” Document ID EPA-HQ-OAR-2025-0194-31053. The EPA subsequently relied on the 2009 Endangerment Finding as the foundation for a new regulatory construct that subjected an increasing number of sectors to controls in the name of addressing global climate change concerns. In 2015, we extended the GHG initiative to power plant stationary sources regulated under CAA section 111 by promulgating GHG emissions standards for new, modified, and reconstructed fossil fuel-fired EGUs in the 2015 NSPS, 80 FR 64510, and GHG emission guidelines for existing fossil fuel-fired EGUs, 80 FR 64662 (“Clean Power Plan” or “2015 CPP”). 5 In these related actions, we applied the expansive reading of CAA section 202(a)(1) adopted in the 2009 Endangerment Finding to conclude for the first time that a source category could be subject to additional regulatory controls under CAA section 111 based on global climate change concerns. We also made a finding in the alternative, again relying on the 2009 Endangerment Finding, that global GHG concentrations in the atmosphere constitute air pollution that endangers public health and welfare and that GHG emissions from power plants cause or contribute significantly to that air pollution. After the Supreme Court largely vacated these regulatory efforts in West Virginia v. EPA, 597 U.S. 697 (2022), we responded by promulgating more stringent GHG standards for new sources and reissuing emission guidelines for existing sources in the 2024 CPS. Meanwhile, global GHG concentrations in the upper atmosphere have continued to rise, driven primarily by increased emissions from foreign sources, 6 all without producing the degree of adverse impacts to public health and welfare in the U.S. anticipated in the 2009 Endangerment Finding and 2015 NSPS and 2015 CPP. 5 References to “GHG standards” here and elsewhere include new source performance standards (NSPS) promulgated under CAA section 111(b) and emission guidelines for existing sources promulgated under CAA section 111(d). See 42 U.S.C. 7411(b), (d). 6 Crippa, M. et al. (2023). GHG emissions of all world countries. Publications Office of the European Union: https://doi.org/10.2760/953322. Upon further review, and in light of subsequent developments since 2009 and 2015, the EPA is seeking further public comment on its statutory authority to regulate GHG emissions from fossil fuel-fired EGUs in response to global climate change concerns. The Supreme Court has significantly clarified the limits on the EPA's authority in recent years, including in West Virginia, Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014) (“ UARG” ), and Michigan v. EPA, 576 U.S. 743 (2015), and made clear in Loper Bright Enterprises v. Raimondo, 603 U.S. 369 (2024), that Federal agencies can no longer rely on statutory silence or ambiguity to expand regulatory power. The EPA recently considered these issues in the Endangerment Finding Rescission, in which we concluded that CAA section 202(a)(1) is best read as authorizing regulation of air pollution that threatens health and welfare through local and regional exposure and does not authorize regulation in the name of global climate change concerns. We further concluded that Congress had not provided the requisite clear authorization for our GHG emissions program under CAA section 202(a)(1), which had resulted in an unprecedented expansion of regulatory power with adverse effects on the economy and American households. And we concluded that attempting to address global climate change through regulation under CAA section 202(a)(1) was futile based on modeling showing that new motor vehicle and engine GHG emission standards would have no more than a de minimis impact on key indicators of the health and welfare concerns animating regulation. We thus rescinded the 2009 Endangerment Finding and repealed all associated GHG emission standards to ensure that the EPA exercised “only those powers given to [it] by Congress” 7 and to follow “the best reading of the statute,” which is fixed at the time of enactment. 8 7 91 FR 7686, 7688 (Feb. 18, 2026) (quoting West Virginia, 597 U.S. at 723). 8 Id. (quoting Loper Bright, 603 U.S. at 400-01). Informed by these conclusions, the EPA in this supplemental proposal seeks additional public comment on the Agency's statutory authority to regulate GHG emissions from power plants. We propose that the text, structure, and history of CAA section 111, the applicability and implications of the major questions doctrine, and the futility of power plant GHG standards in relation to the unique and global scale of the underlying problem similarly support the conclusion that the EPA lacks authority to impose additional controls on power plants in response to global climate change concerns under the statutory standard for regulation. The remainder of this section describes the need for regulatory action and the scope of this proposed action. These interests emphasize the need for urgent action to avoid further expenditures in reliance on a potentially unlawful regulatory framework that may not further public health or welfare in any material respect relevant to the global climate change concerns identified and relied upon by the EPA since 2015. Section III of this preamble sets out relevant background, including the EPA's statutory authority under CAA section 111, our historical approach to regulating emissions from new and existing stationary sources, our changes in position with respect to regulating in response to global climate change concerns in 2009 and 2015, as well as relevant litigation, and our recent reconsideration and rescission of the 2009 Endangerment Finding. Section IV of this preamble describes our legal authority for the proposed rescissions and repeals of the 2015 NSPS, 2024 CPS, and any underlying listings, findings, and determinations with respect to GHG emissions from fossil fuel fired-EGUs under CAA section 111. We propose that CAA section 111 authorizes these proposed actions, together with agencies' authority to revise or rescind prior actions by acknowledging the change, providing a reasonable explanation, and considering legitimate reliance interests. In the June 2025 NPRM, we acknowledged that our prior decisions to regulate GHG emissions from fossil fuel-fired EGUs have caused significant expenditure of resources by Federal, State, local, and private-sector entities and solicited comment on any legitimate reliance interests relevant to the proposed rescissions and repeals. In this supplemental proposal, we solicit comment on whether the additional bases set out in this supplemental proposal implicate distinct reliance interests and how the EPA should consider such interests consistent with applicable legal principles and limits on our statutory authority. Section V.A of this preamble discusses the EPA's additional statutory interpretation rationale for the proposed rescissions and repeals. First, we propose that EPA lacks authority to retain these standards under CAA section 111(b)(1)(A), which subjects a source category's emissions to regulation when the Administrator determines that the source category causes or contributes significantly to “air pollution which may reasonably be anticipated to endanger public health or welfare.” Specifically, we propose that “air pollution” is best read as that which itself threatens health or welfare through local or regional exposure, consistent with the ordinary meaning of the term at the time of enactment, the surrounding language of the provision, the statute's structure and amendment history, and the EPA's longstanding practice prior to 2015. For these reasons, we propose that the 2015 NSPS and 2024 CPS erred in listing and regulating fossil fuel-fired EGUs based on global climate change concerns that fall outside the scope of “air pollution” within the meaning of the CAA section 111. Second, we propose that additional flaws in the Agency's findings and determinations in the 2015 NSPS, as endorsed by the 2024 CPS, render them independently unlawful and reinforce the proposed conclusions previously discussed. These flaws include the effective listing of a new source category without undertaking a new listing under CAA section 111(b)(1)(A) and reliance on the flawed 2009 Endangerment Finding. Section V.B discusses the EPA's major questions doctrine rationale for the proposed rescissions and repeals. We propose that, consistent with the Supreme Court's decision in West Virginia, the major questions doctrine applies to the Agency's economically and politically significant assertion of authority to regulate power plant emissions based on global climate change concerns. We further propose that Congress did not clearly authorize the EPA to regulate power plants in response to global climate change concerns when it enacted the standard for regulation in CAA section 111(b)(1)(A) and authorized the Administrator to determine whether emissions satisfy that standard. That is, Congress did not clearly provide that global climate change concerns may trigger regulation under CAA section 111(b)(1)(A) and therefore did not clearly authorize the Administrator to invoke that standard to subject power plant emissions to additional regulatory controls commensurate with the unique and global nature of the problem. Rather, we propose that the appropriate policy response to global climate change concerns is a decision vested in Congress, and that Congress did not decide that the Nation's policy response to these concerns would include regulating power plants when it enacted CAA section 111. Section V.C discusses the EPA's proposed futility rationale for the proposed rescissions and repeals. In developing this supplemental proposal, the Agency used generally accepted models to estimate the impacts on global mean surface temperature (GMST) and global sea level rise (GSLR) of eliminating all GHG emissions from the U.S. power sector as an overly conservative proxy for the potential impacts of GHG emission restrictions under CAA section 111. The EPA proposes that the results of this modeling demonstrate that even the complete elimination of GHG emissions from the U.S. power sector, and at minimum, any plausible reduction in GHG emissions from the U.S. power sector that could result from application of CAA section 111, would have no more than de minimis impacts on the key indicators of adverse impacts attributed to global climate change. On this basis, the EPA proposes that the futility of regulation supports the conclusion that global climate change concerns cannot satisfy the prerequisite for imposing regulatory controls under CAA section 111. The EPA further propose that the inability of GHG standards to address global climate change supports the conclusion that GHG emissions from fossil fuel-fired EGUs do not “contribute significantly” to air pollution. Finally, the EPA proposes that retaining futile GHG standards for fossil fuel-fired EGUs under CAA section 111 would be unreasonable given the significant costs they impose on regulated parties, consumers, and the economy. Section VI of this preamble discusses the proposed repeals of all GHG regulations for fossil fuel-fired EGUs under CAA section 111, including the relationship of these repeals to distinct regulatory programs and Federal preemption. We propose that absent emissions satisfying the statutory prerequisite for regulation under CAA section 111(b)(1)(A), the EPA must fully repeal the 2015 NSPS and 2024 CPS, which listed (and retained) a combined source category of fossil fuel-fired EGUs for the purpose of regulating GHG emissions. We explain that these repeals would not disturb criteria-pollutant standards or other requirements applicable to power plants currently listed in the fossil fuel-fired EGU source category. Nor would returning to the pre-2015 status quo alter the CAA's displacement of Federal common law or the CAA's preemptive force with respect to State law. Section VII of this preamble specifically requests comment on key aspects of this supplemental notice and indexes comment solicitation to promote public participation and facilitate our review of public comments. The EPA is not limiting public participation to the issues raised in this section and will respond to all significant comments within the scope of this supplemental proposal. Rather, we are highlighting aspects of this supplemental proposal for which public input would be particularly helpful in determining whether to finalize the additional rationales proposed in this supplemental notice. B. Need for Regulatory Action Immediately upon taking office in 2025, President Trump established as the policy of the United States new Executive Branch priorities for energy, transportation, and consumer choice and committed agencies to ensuring regulations remain within constitutional and statutory bounds. On January 20, 2025, President Trump issued Executive Order (E.O.) 14154, “Unleashing American Energy.” 9 In that E.O., the President established that it is “the policy of the United States to ensure that all regulatory requirements related to energy are grounded in clearly applicable law,” 10 and directed Federal agencies, including the EPA, to review existing regulations “to identify those agency actions that impose an undue burden on the identification, development, or use of domestic energy resources—with particular attention to oil, natural gas, coal, hydropower, biofuels, critical mineral, and nuclear energy resources.” 11 The President also directed the Administrator to submit recommendations to the Director of the Office of Management and Budget (OMB) on the legality and continuing applicability of the 2009 Endangerment Finding. 12 9 90 FR 8353 (Jan. 29, 2025). 10 Id. section 2. 11 Id. section 3(a). 12 Id. section 6(f). On February 19, 2025, President Trump issued E.O. 14219, “Ensuring Lawful Governance and Implementing the President's `Department of Government Efficiency' Deregulatory Initiative.” 13 This E.O. established a national policy requiring agencies, including the EPA, to “focus the executive branch's limited enforcement resources on regulations squarely authorized by constitutional Federal statutes” and to “initiate a process to review all regulations subject to their sole or joint jurisdiction for consistency with law and Administration policy.” 14 Among other things, the E.O. instructed agencies to identify regulations that are based on anything other than the best reading of the underlying statutory authority or prohibition and regulations that implicate matters of social, political, or economic significance that are not authorized by clear statutory authority. In the course of this review, the EPA identified GHG standards for power plants as regulations that may be based on interpretations that are inconsistent with the best reading of CAA section 111 and address a significant issue without clear statutory authorization. 13 90 FR 10583 (Feb. 25, 2025). 14 Id. sections 1, 2. On April 8, 2025, President Trump issued E.O. 14261, “Reinvigorating America's Beautiful Clean Coal Industry and Amending Executive Order 14241.” 15 This E.O. states that “coal is essential to our national and economic security” and establishes “a national priority to support the domestic coal industry by removing Federal regulatory barriers that undermine coal production.” 16 The E.O. finds that “coal resources will be critical to meeting the rise in electricity demand due to the resurgence of domestic manufacturing and the construction of artificial intelligence data processing centers” and to increasing “energy supply,” lowering “electricity costs,” stabilizing the power grid, creating “high paying jobs,” supporting “burgeoning industries,” and assisting allies abroad. 17 Accordingly, the E.O. directs the EPA, among other Federal agencies, to identify regulatory actions that seek to transition the Nation away from coal production and electricity generation and consider revising or rescinding such actions consistent with applicable law. 18 15 90 FR 15517 (Apr. 14, 2025). 16 Id. section 2. 17 Id. section 1. 18 Id. section 6(a)-(b). Upon confirmation by the Senate, Administrator Lee Zeldin committed the EPA to prioritizing its core statutory missions and ensuring that all regulatory actions are clearly grounded in statutory authority and the best reading of the law. As part of these efforts, and consistent with E.O. 14154, E.O. 14219, and E.O. 14261, the Administrator initiated a review of the 2009 Endangerment Finding and related regulations bearing on the energy sector, including power plant GHG emission standards. On February 19, 2025, the Administrator submitted a memorandum to the OMB Director recommending that the EPA reconsider the 2009 Endangerment Finding to address legal and scientific developments that appeared to undermine the bases for that action and subsequent regulations. The Administrator noted that recent Supreme Court decisions, including Loper Bright, West Virginia, UARG, and Michigan, provided further instruction as to how we should interpret and apply the statutes Congress entrusted us to administer. The Administrator further noted that the 2009 Endangerment Finding recognized significant uncertainties in its conclusions and assumptions that should be evaluated in light of more recent empirical data and scientific evidence. Accordingly, the Administrator announced on March 12, 2025, that the EPA would reconsider the 2009 Endangerment Finding and subsequent regulations under CAA section 202(a)(1) to determine whether our GHG regulations have an adequate statutory basis and to seek public input on developments since 2009. 19 That same day, the Administrator announced that the EPA would initiate a rulemaking to reconsider our GHG emission standards for power plants under CAA section 111. 20 19 Memorandum from Lee Zeldin, Administrator, U.S. Environmental Protection Agency, to Russell Vought, Director, Office of Management and Budget (Feb. 19, 2025) (Feb. 19, 2025 Memo), Docket ID No, EPA-HQ-OAR-2025-0194-0059. 20 Trump EPA Announces Reconsideration of Biden-Harris Rule, “Clean Power Plan 2.0,” That Prioritized Shutting Down Power Plants While Raising Costs on American Families (Mar. 12, 2025), available at https://www.epa.gov/newsreleases/trump-epa-announces-reconsideration-biden-harris-rule-clean-power-plan-20-prioritized. In June 2025, the EPA completed its initial review of GHG emission standards for power plants under CAA section 111. Based on a reassessment of the legal and technical conclusions in the 2015 NSPS and 2024 CPS, we sought public comment in the June 2025 NPRM on a primary proposal and an alternative proposal. 21 The primary proposal involved repealing all GHG emissions standards for new and existing sources in the fossil fuel-fired EGU source category. Specifically, we proposed to determine that CAA section 111 requires the Agency to make a finding that GHG emissions from fossil fuel-fired power plants “cause[ ], or contribute significantly” to “air pollution which may reasonably be anticipated to endanger public health or welfare” (which we shorthanded as “dangerous air pollution”) as a predicate to regulating GHG emissions from those power plants. We further proposed to find that GHG emissions from fossil fuel-fired power plants do not contribute significantly to dangerous air pollution. The alternative proposal was based on the EPA's reexamination of the BSER determinations and associated requirements for fossil fuel-fired power plants in the 2024 CPS. Specifically, we proposed to repeal requirements in the 2024 CPS predicated on the Agency's prior determinations that 90 percent carbon capture and storage (CCS) and/or 40 percent natural gas co-firing were BSER for the relevant subcategories. 21 90 FR 25752 (June 17, 2025). In August 2025, the EPA completed its initial review of GHG emission standards for new motor vehicles and engines under CAA section 202(a)(1). Based on substantial concerns with the legal and scientific underpinnings of these regulations and the associated findings, we proposed to rescind the 2009 Endangerment Finding and repeal associated GHG emission standards on several alternative legal, policy, and scientific bases. In February 2026, the EPA took final action to rescind the 2009 Endangerment Finding and repeal associated GHG emission standards for new motor vehicles and engines under CAA section 202(a)(1). We concluded in the Endangerment Finding Rescission that the EPA lacks statutory authority under CAA section 202(a)(1) to regulate in response to global climate change concerns for the legal reasons discussed at proposal. Specifically, we concluded that global climate change concerns associated with GHG emissions are not “air pollution which may reasonably be anticipated to endanger public health or welfare” within the meaning of CAA section 202(a)(1), that Congress had not clearly authorized such an economically and politically significant assertion of authority, and that the futility of emission standards further supported the rescission and repeals in multiple respects. In today's actions, the EPA is returning to the issues raised in the June 2025 NPRM regarding our statutory authority to regulate GHG emissions from power plants under CAA section 111. Concurrently with this supplemental notice, the EPA is taking final action to repeal most of the provisions of the 2024 CPS based on a record-focused reevaluation of the BSER determinations for the relevant subcategories. That concurrent final rule repeals the associated aspects of the 2024 CPS, consistent with the alternative proposal in the June 2025 NPRM, while taking no action on the primary proposal in the June 2025 NPRM. The EPA responded to comments received on the alternative proposal in the RTC for the final rule. The EPA is not reopening the record for the final rule in this supplemental notice and is not seeking further public comment on the record-based considerations addressed in the final rule. This supplemental proposal seeks public comment on the question whether the EPA lacks authority under CAA section 111 to regulate GHG emissions from power plants in response to global climate change concerns given CAA section 111(b)(1)(A)'s predicate requirement that their emissions contribute significantly to “air pollution which may reasonably be anticipated to endanger public health or welfare.” The rationale proposed in this supplemental notice is distinct from the rationale presented in the primary proposal of the June 2025 NPRM, which sought public comment on whether the EPA has authority to regulate GHG emissions from power plants based on the significance of the fossil fuel-fired EGU source category's contribution. The EPA is not seeking additional comment on the primary proposal in the June 2025 NPRM in this supplemental notice. Rather, we are rather soliciting public comment on distinct statutory authority rationales in light of the Endangerment Finding Rescission: the best reading of CAA section 111 with respect to fossil fuel-fired EGUs; the applicability and implications of the major questions doctrine; the futility of GHG emission standards for power plants in addressing global climate change concerns; and several additional issues, including the ongoing validity of the Agency's endangerment and significant contribution findings in the alternative in the 2015 NSPS, as reaffirmed in the 2024 CPS. In contrast to the record-based issues related to BSER determinations addressed in the concurrent final rule, this supplemental proposal analyzes the text and structure of the CAA to ascertain its best reading, bolstered by statutory and legislative history and the body of regulatory history relevant to the scope of the Agency's legal authority, including all aspects of the 2015 NSPS, the vacated 2015 CPP, and the 2024 CPS, as well as regulatory actions that predated the Agency's 2015 changes in position. This information is relevant to how the statute has been applied and, for major questions doctrine purposes, to the permissibility of the scope of the authority we first asserted in 2015. Should the EPA finalize its proposed conclusion that the Agency lacks statutory authority to regulate GHG emissions from power plants based on global climate change concerns under the statutory standard for regulation in CAA section 111(b)(1)(A), that final action would remove the legal basis for all prior actions taken under CAA section 111 to regulate GHG emissions from these sources in response to global climate change. This conclusion would require the EPA to rescind its findings and determinations in the 2015 NSPS and repeal all GHG regulations and requirements for power plants under CAA section 111, including those in the 2015 NSPS and those in the 2024 CPS that are not being repealed on other grounds in the concurrent final rule. With respect to the aspects of the 2024 CPS being repealed on other grounds in the concurrent final rule, this conclusion would independently reinforce the basis for repeal based on a lack of statutory authority. 22 22 Because the Supreme Court invalidated the 2015 CPP in West Virginia by reversing the D.C. Circuit's vacatur of the EPA's subsequent repeal of the 2015 CPP, any similar findings or determinations in the 2015 CPP are no longer in effect. 597 U.S. 697; see Am. Lung Ass'n v. EPA , No. 19-1140, Order (D.C. Cir. Oct. 27, 2022). Nevertheless, as with the concurrently repealed aspects of the 2024 CPS, finalizing that the EPA lacks statutory authority to regulate GHG emissions from power plants in response to global climate change would necessarily contradict and invalidate any such findings or determinations in the 2015 CPP. III. Background This section discusses the EPA's statutory authority under CAA section 111, relevant statutory, legislative, and regulatory history, and the Agency's prior changes in position with respect to the regulation of GHGs under CAA section 111. A. Statutory Authority Under CAA Section 111 CAA section 111 authorizes the EPA to list and regulate a category of stationary sources if the Administrator, “in his judgment,” finds that it “causes, or contributes significantly to, air pollution which may reasonably be anticipated to endanger public health or welfare.” 23 The listing of a source category triggers the Agency's authority to promulgate “standards of performance” for new sources and, under limited circumstances, to prescribe regulations under which States submit plans that establish standards of performance for existing sources. 24 23 42 U.S.C. 7411(b)(1)(A). 24 42 U.S.C. 7411(b), (d). 1. Regulation of Emissions From New Sources CAA section 111(b)(1)(A) authorizes the Administrator to publish, and from time-to-time revise, a list of categories of stationary sources that the Administrator, “in his judgment,” finds “causes, or contributes significantly to, air pollution which may reasonably be anticipated to endanger public health or welfare.” Once the EPA lists a source category under CAA section 111(b)(1)(A), the EPA must, under CAA section 111(b)(1)(B), establish “standards of performance” for “new sources” in the source category. These standards are referred to as new source performance standards, or NSPS. The NSPS are national requirements that apply directly to new sources within the relevant source category. As discussed later in this section, Congress enacted the NSPS regulatory scheme to work together with the geography-based national ambient air quality standards (NAAQS) program in CAA sections 107-110. Similar to national emission standards for hazardous air pollutants (NESHAPs) that limit emissions of hazardous air pollutants (HAPs) listed and regulated under CAA section 112, NSPS under CAA section 111 apply to a new source regardless whether the area in which the new source is located is attaining the NAAQS (and therefore subject to limited NAAQS-related restrictions) or not attaining the NAAQS (and therefore subject to additional NAAQS-related restrictions). Accordingly, CAA section 111(a)(2) defines a “new source” as “any stationary source, the construction or modification of which is commenced after the publication of regulations (or, if earlier, proposed regulations) prescribing a standard of performance under this section, which will be applicable to such source.” CAA section 111(a)(1) defines “standard of performance” as “a standard for emissions of air pollutants” that must be promulgated or revised in a specified manner. When the EPA establishes or revises a standard of performance, CAA section 111(a)(1) provides that such standard must “reflect[ ] the degree of emission limitation achievable through the application of the best system of emission reduction which (taking into account the cost of achieving such reduction and any nonair quality health and environmental impact and energy requirements) the Administrator determines has been adequately demonstrated.” Thus, the term “standard of performance” as used in CAA section 111 makes clear that the foundation for the regulatory requirements for the source category is the EPA's determination of the “best system of emission reduction” (BSER) that is “adequately demonstrated” for emissions of the relevant air pollutants. 25 The EPA has discretion in determining the BSER, and has historically followed a “technology-based approach” that focuses on “measures that improve the pollution performance of individual sources,” such as “add-on controls.” 26 25 West Virginia, 597 U.S. at 709. 26 See id. at 727 (quoting the 2015 CPP). After determining the BSER, the EPA derives the “degree of emission limitation achievable” through application of the BSER. A standard of performance is “achievable” if a technology can reasonably be projected to be available to an individual source at the time it is constructed so as to allow it to meet the standard. 27 The EPA must then, under CAA section 111(b)(1)(B), promulgate “standard[s] for emissions”—the NSPS—that reflect that level of stringency. The EPA may determine that different sets of sources have different characteristics relevant for determining the BSER for emissions of the relevant air pollutants and may subcategorize sources accordingly. 28 27 Portland Cement Ass'n v. Ruckelshaus , 486 F.2d 375, 391 (D.C. Cir. 1973). 28 42 U.S.C. 7411(b)(2). 2. Regulation of Emissions From Existing Sources The EPA has generally used CAA section 111 to establish NSPS for emissions of specified air pollutants from new sources within a category. In the rare instances in which the new stationary source standards concern air pollutant emissions that are not regulated under the NAAQS program pursuant to CAA sections 108-110, or the NESHAP program pursuant to CAA section 112, the statute provides a separate authority for addressing such emissions from existing sources in the source category. 29 29 42 U.S.C. 7411(d)(1)(A)(i)-(ii); see West Virginia, 597 U.S. at 710 (“Section 111(d) thus `operates as a gap-filler,' empowering EPA to regulate harmful emissions not already controlled under the Agency's other authorities . . . . Reflecting the ancillary nature of Section 111(d), EPA has used it only a handful of times since the enactment of the statute in 1970.”). In contrast to the national regime for new sources under CAA section 111(b), CAA section 111(d) establishes a framework of “cooperative federalism for the regulation of existing sources.” 30 CAA section 111(d)(1) provides that when air pollutants covered by an NSPS for a source category are not already encompassed within the NAAQS program or NESHAP program, the EPA “shall prescribe regulations which shall establish a procedure similar to that provided by” CAA section 110 “under which each State shall submit to the Administrator” a plan for addressing emissions of such air pollutants by existing sources within such source category. 31 Reference to CAA section 110 incorporates the statute's provision for State submission and EPA review of state implementation plans (SIPs) that provide for the implementation, maintenance, and enforcement of the NAAQS for the areas within such State. 32 In a comparable manner, State plans required by the regulations authorized in CAA section 111(d) must “establis[h] standards of performance for any existing source” for the air pollutant emissions at issue and “provid[e] for the implementation and enforcement of such standards of performance.” 30 Am. Lung Ass'n v. EPA , 985 F.3d 914, 931 (D.C. Cir. 2021), rev'd in part sub nom. West Virginia, 597 U.S. 697. 31 42 U.S.C. 7411(d)(1). CAA section 111(a)(6) defines an “existing source” as “any stationary source other than a new source.” 42 U.S.C. 7411(a)(6). 32 42 U.S.C. 7410. In the relatively few instances in which the EPA applies this provision, the Agency generally promulgates regulations, termed “emission guidelines,” that identify the BSER and the degree of emission limitation achievable through the application of the BSER. These regulations then require States to establish standards of performance for emissions of the air pollutant at issue by covered sources that reflect that level of stringency. Once the EPA approves a State's plan, its provisions become federally enforceable in the same manner as the provisions of an approved SIP under the CAA. 33 If a State does not submit a plan or the EPA does not find a State's submission “satisfactory,” the Agency is authorized to issue a Federal plan imposing standards of performance for the State's existing sources. 34 33 42 U.S.C. 7411(d)(2)(B). 34 42 U.S.C. 7411(d)(2)(A). B. Statutory and Regulatory History of CAA Section 111 Congress enacted CAA section 111 in the 1970 CAA Amendments as part of title I of Act, which “establishes three main regulatory programs to control air pollution from stationary sources such as power plants.” 35 In enacting CAA section 111 in 1970 and revising key language in the 1977 CAA Amendments and 1990 CAA Amendments, Congress addressed its requirements as part of a comprehensive scheme including the NAAQS program under CAA sections 107-110 and the NESHAP program under CAA section 112. This subsection discusses the statutory history of CAA section 111, the relation of CAA section 111 to the other provisions of title I, and regulatory history that reflects the EPA's contemporary understanding of the statute as informed by Congress's amendments to key statutory language. 35 West Virginia, 597 U.S. at 707. 1. 1970 CAA Amendments and Subsequent Regulations Congress enacted CAA section 111 in 1970 as one of three related provisions directing the EPA to regulate emissions from stationary sources. The first—CAA sections 107 through 110—addressed what are commonly referred to as criteria pollutants, which are pollutants, “the presence of which in the ambient air results from numerous or diverse mobile or stationary sources” and are determined to have “an adverse effect on public health or welfare.” 36 Under these provisions, the Federal government would develop air quality criteria on the health and welfare impacts of criteria pollutants and promulgate numeric standards—the NAAQS—representing the ambient concentrations of such pollutants in the air of a particular area that are adequately protective. States would have primary responsibility for assuring air quality within their geographic area by developing and submitting SIPs for “implementation, maintenance, and enforcement” of the NAAQS to the Federal government for review and approval. These plans would include “emission limitations, schedules, and timetables for compliance . . . and such other measures as may be necessary to insure attainment and maintenance” of the NAAQS. 37 36 CAA Amendments of 1970, Public Law 91-604, 84 Stat. 1676, 1678. Congress subsequently amended the “adverse effect” criterion in CAA section 108(a)(1)(A) to refer to pollutants “which may reasonably be anticipated to endanger public health or welfare,” 42 U.S.C. 7408(a)(1)(A), and deliberately added identical phrasing to statutory provisions granting the EPA authority to regulate particular sources under certain conditions, see, e.g., 42 U.S.C. 7411(b)(1)(A) (stationary sources), 7521(a)(1) (new motor vehicles and new motor vehicle engines). 37 CAA Amendments of 1970, 84 Stat. at 1680. The second prong was CAA section 112, which addressed particularly dangerous pollutants—HAPs—through the establishment of NESHAPs at a level that “provides an ample margin of safety to protect the public health.” 38 All new or modified sources of any HAP would be required to meet these emission standards unless, for example, an existing source obtained a waiver or presidential exemption. 38 Id. at 1685. The third prong was CAA section 111, which addressed air pollutant emissions on a source category basis. Under CAA section 111(b), as enacted in 1970, the EPA would list source categories which “contribute significantly to air pollution which causes or contributes to the endangerment of public health or welfare” and then establish “standards of performance” for new sources in the listed category. 39 The relevant Committee Report explained that the provision would apply to “[m]ajor new facilities such as electric generating plants, kraft pulp mills, petroleum refineries, steel mills, primary smelting plants, and various other commercial and industrial operations” along with “any other categories of major stationary sources from which emissions would cause or contribute to endangerment of public health and welfare.” 40 The legislation's Senate sponsor, Senator Edmund Muskie, explained that CAA section 111 was designed to apply across the country to level the playing field among States, thereby avoiding “`shopping around' for open sites” in areas that were subject to fewer local restrictions under the NAAQS program. 41 In this way, the national standards for new sources would reduce an incentive to shift operations from nonattainment areas required to improve air quality to attainment areas that already had acceptable air quality that should be maintained. For existing sources in a listed source category, CAA section 111(d) set out procedures for the establishment of federally enforceable “emission standards” of any pollutant not otherwise controlled under the CAA's NAAQS provisions or CAA section 112. 39 Id. at 1684. 40 S. Rep. No. 91-1196, at 16 (1970). The Committee Report added “New stationary sources which the administration has advised the committee to expect would be subject to the provisions of this section include” 19 industries, ranging from “[c]ement manufacturing” and “[c]oal cleaning operations” to “[m]unicipal incinerators” and “[s]team electric powerplants.” Id. 41 91 Cong. Rec. 32902 (Sept. 21, 1970) (statement of Sen. Muskie, during the Senate debate on S. 4358). These provisions grew out of different bills adopted by the House and Senate and reconciled by a conference committee to create what became CAA sections 107-112. The relevant committees and bill sponsors drafted these provisions to address contemporary air pollution problems causing or threatening harm through exposure at the local and regional level. 42 These included the criteria pollutants addressed by what became CAA sections 107-110; 43 various “hazardous,” 44 “extremely hazardous” 45 or “extra-hazardous” 46 air pollutants, which were subject to what became CAA section 112; and “selected air pollution agents,” which could also be criteria pollutants and were subject to what became CAA section 111. 47 The Senate Report described the air pollutants subject to the language later adopted at conference as CAA section 111 as “agents which are not emitted in such quantities or are not of such a character as to be widely present or readily detectable on a continuous basis with available technology in the ambient air” and specified that “[t]he presence of these agents is generally confined, at least for detection purposes, to the area of the emission source.” 48 The Senate Report further specified that “[t]he information available at this time indicates that the following list of substances are most likely to be considered as the agents to be covered under this section: Arsenic, chlorine gas, hydrogen chloride, copper, manganese, nickel, vanadium, zinc, barium, boron, chromium, selenium, pesticides, [and] radioactive substances.” 49 42 See S. Rep. No. 91-1196, at 18 (1970) (describing the various sets of air pollutants subject to the stationary source provisions of the Senate bill). 43 Prior to 1970, the Secretary of Health, Education, and Welfare issued air quality criteria under an earlier version of the CAA for SO 2 , PM, CO, ozone (photochemical oxidants), and hydrocarbons. See, e.g., 36 FR 1502 (Jan. 30, 1971) (citing 35 FR 4768 and 34 FR 1988). Congress anticipated that these pollutants, along with certain precursors, would be the foundation of the NAAQS program for criteria pollutants under CAA sections 107-110. See, e.g., 91 Cong. Rec. 32902 (Sept. 21, 1970) (Exhibit II to statement of Sen. Boggs during the Senate debate on S. 4358). 44 S. 4358, 91st Cong. section 6 (1970). 45 H.R. 17255, 91st Cong. section 5 (1970). 46 H.R. Rep. No. 1146, at 3 (1970). 47 S. Rep. No. 91-1196, at 93-94 (1970). 48 S. Rep. No. 91-1196, at 18 (1970). 49 Id. In response to the 1970 CAA Amendments, the EPA began listing source categories under CAA section 111(b)(1)(A) and promulgating standards of performance under CAA section 111(b)(1)(B). Between 1970 and 1977, the EPA listed at least 31 source categories in brief notices that did not solicit public comment. 50 In 1975, EPA published regulations that established the process for promulgating standards of performance for new sources and emission guidelines for existing sources 51 and established requirements for modified and reconstructed sources. 52 By 1977, the EPA generally proposed standards of performance for a source category at the same time as the listing and discussed the basis for the listing in the preamble to the proposed standards, including the amount of emissions of relevant air pollutants from the source category. 53 50 See, e.g., 36 FR 5931 (Mar. 31, 1971) (first five source categories, including steam-fired EGUs); 42 FR 22510 (May 3, 1977) (listing lime manufacturing). 51 40 FR 53340 (Nov. 17, 1975). 52 40 FR 58416 (Dec. 16, 1975). 53 See, e.g., 42 FR 22510 (May 3, 1977) (listing lime manufacturing); 42 FR 22506 (May 3, 1977) (proposing standards for lime manufacturing and explaining that “[l]ime manufacturing plants have been shown to be a significant source of particulate matter emissions”). 2. 1977 CAA Amendments and Subsequent Regulations Congress revisited the CAA in 1977 to address growing concerns related to the energy and environmental impacts of the 1973 oil embargo and resolve issues associated with implementing the statutory programs enacted in 1970. 54 The EPA advised relevant committees at the time that increased coal combustion to generate power in response to the oil crisis meant that “vigorous and effective control” of air emissions was “even more urgent.” 55 Congress responded by adding new statutory provisions setting out the prevention of significant deterioration (PSD) program, visibility protections known as the regional haze program, and additional requirements for nonattainment areas under the NAAQS program. As with the 1970 CAA Amendments, the provisions added in the 1977 CAA Amendments required further steps to combat air pollution by reducing emissions of criteria pollutants and other air pollutants that cause or threaten adverse impacts from local or regional exposure. 56 54 CAA Amendments of 1977, Public Law 95-95, 91 Stat. 685. 55 See Senate Hearings on S. 272, S. 273, S. 977, and S. 1469 (1977), reprinted in Library of Congress, 5 A Legislative History of the Clean Air Amendments of 1977 (“1977 CAA Legis. Hist.”) at 3532 (statement of Administrator Costle). 56 For example, Congress recognized that many air pollutants had not been regulated despite “mounting evidence” that these pollutants “are associated with serious health hazards.” H.R. Rep. No. 94-1175, at 22 (1976). Because the EPA “failed to promulgate regulations to institute adequate control measures,” Congress directed the EPA to regulate four specific pollutants that had “been found to be cancer-causing or cancer-promoting.” Id. at 23. This directive, reflected in CAA section 122, specifically added radioactive pollutants, cadmium, arsenic, and polycyclic organic matter “under the various provisions of the Clean Air Act and allows their regulation as criteria pollutants under ambient air quality standards, as hazardous air pollutants, or under new source performance standards, as appropriate.” H.R. Rep. No. 95-564, at 142 (1977); 42 U.S.C. 7422(a). Congress further amended the endangerment and contribution language in CAA section 111, CAA section 202(a)(1), and additional regulatory provisions to provide a comparable standard for invoking each regulatory authority. As amended in 1977, CAA section 111(b)(1)(A) read as it currently does: the Administrator “shall include a category of sources in such list if in his judgment it causes, or contributes significantly, to air pollution which may reasonably be anticipated to endanger public health or welfare.” 57 The House Report for the relevant bill language explained that these related amendments were designed to provide “the same standard of proof for regulation of any air pollutant, whether that pollutant comes from stationary or mobile sources, or both” that allowed for precautionary regulation, consistent with the D.C. Circuit's en banc decision in Ethyl Corp. v. EPA, 541 F.2d 1 (D.C. Cir. 1976). 58 57 CAA Amendments of 1977, section 109(a), 91 Stat. at 791; compare 42 U.S.C. 7411(b)(1)(A), with 42 U.S.C. 7521(a)(1) (the Administrator “shall by regulation prescribe . . . standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines . . . which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare”). 58 H.R. Rep. No. 95-294 at 43 (1977). The House Report further explained that the language eventually enacted set out “a standardized basis for future rulemakings” and the “same basic formula” in CAA sections 108 (defining criteria for NAAQS), 111 (NSPS), 112 (HAP, “although the nature of risk must be more serious”), 202 (new motor vehicle emission standards), 211 (regulation of fuels and fuel additives), and 231 (aircraft emission standards). Id. at 50. Congress also enacted further amendments specific to CAA section 111. First, it amended the definition of “standard of performance” in CAA section 111 to require “all new sources to meet emission standards based on the reductions achievable through the use of the `best technological system of continuous emission reduction.' ” 59 Second, for fossil fuel-fired stationary sources, Congress required a percentage reduction in emissions from the use of fuels. 60 Together, this was designed to “force new sources to burn high-sulfur fuel thus freeing low-sulfur fuel for use in existing sources where it is harder to control emissions and where low-sulfur fuel is needed for compliance.” 61 This change responded to the oil shortage, the resulting energy legislation that restricted power plant use of oil or gas to generate electricity, and the consequent increase in coal combustion by power plants. This increase in coal combustion gave rise to the need to limit low-sulfur coal to existing power plants. 62 63 Third, Congress added CAA section 111(f), which required the EPA to list categories of major stationary sources not already listed and imposed a schedule for establishing standards of performance for those source categories. Finally, Congress added CAA section 111(f)(4), which specifically allowed States to petition the Administrator for new or revised (and more stringent) standards. 64 59 Id. at 192. Congress separately defined “technological system of continuous emission reduction” as “(A) a technological process for production or operation by any source which is inherently low-polluting or nonpolluting, or (B) technological system for continuous reduction of the pollution generated by a source before such pollution is emitted into the ambient air, including precombustion cleaning or treatment of fuels.” CAA Amendments of 1977, 91 Stat. at 700; see 42 U.S.C. 7411(a)(7). 60 CAA Amendments of 1977, 91 Stat. at 700. 61 44 FR 33580, 33581-82 (June 11, 1979) (promulgating NSPS for electric utility steam generating units). 62 H.R. Rep. No. 95-294, at 185-86, 188-89, 190-93. 63 Congress also amended CAA section 111(b)(1)(B) to require the Administrator to periodically review and, if appropriate, revise new source standards of performance; further amended the definition of a standard of performance in section 111(a)(1) to require the consideration of “nonair quality health and environmental impact and energy requirements,” along with cost; amended CAA section 111(d) to require States to promulgate “standards of performance,” as defined under 111(a)(1), in lieu of “emission standards” and to clarify that States could consider “the remaining useful life” of a source when applying a standard of performance to a particular existing source; and added CAA section 111(h), which authorized alternative standards in limited circumstances. CAA Amendments of 1977, 91 Stat. at 699-700. 64 Id. at 697. The EPA responded to the 1977 CAA Amendments by increasing the pace of stationary source regulation. Consistent with CAA section 111(f), the Agency promulgated a list of 59 source categories in 1979 with each assigned a priority for action. 65 The EPA based the list on the source categories' emissions of nine air pollutants: volatile organic compounds (VOC), nitrogen oxides (NO X ), particulate matter (PM), sulfur dioxide (SO 2 ), carbon monoxide (CO), lead, fluorides, acid mist, and hydrogen sulfide. 66 The EPA proceeded to promulgate standards of performance for these air pollutants applicable to new sources in the listed categories. 67 65 44 FR 49225-26 (Aug. 21, 1979). 66 44 FR 49222 (Aug. 21, 1979). 67 See, e.g., 50 FR 26122 (June 24, 1985) (promulgating NSPS for SO 2 emissions from natural gas processing plants). 3. 1990 CAA Amendments and Subsequent Regulations In the 1990 CAA Amendments, Congress overhauled the CAA by strengthening the NAAQS program, thoroughly revising CAA section 112, and adding several new titles to the Act to address emerging problems not adequately encompassed within the design of title I for regulating stationary sources. 68 The newly enacted title IV addressed acid rain, which forms when SO 2 and NO X emissions transform in the atmosphere and return to the earth as precipitation, by requiring the EPA to impose strict limits on SO 2 emissions from existing power plants and other sources. The newly enacted title V established a consolidated permitting program for certain stationary sources intended to improve efficiency, compliance, and enforceability of existing permitting and emission requirements. And the newly enacted title VI provided the EPA with new regulatory authorities and obligations to phase out certain ozone depleting substances in response to rising concerns that anthropogenic emissions were contributing to a global weakening of the stratospheric ozone layer's capacity to deflect radiation from the sun associated with skin cancer and other adverse health and environmental impacts worldwide. 68 CAA Amendments of 1990, Public Law 101-549, 104 Stat. 2399. Congress also made several further changes to CAA section 111. For the CAA section 111(a)(1) definition of “standard of performance,” Congress repealed the percentage reduction requirement added in the 1977 CAA Amendments, which had come to be understood as unduly restrictive, and returned the definition to how it read after the 1970 CAA Amendments while retaining the 1977 language providing that the EPA must consider nonair quality environmental impacts and energy requirements. 69 In connection with the newly enacted title IV, Congress directed the EPA to revise its NSPS for SO 2 emissions from fossil fuel-fired power plants and required the revised standards to be at least as stringent as earlier regulations. 70 And Congress revised CAA section 111(f) to update the schedule for regulating listed source categories according to a prioritization scheme that reinforced the provision's design: establishing national minimum standards for emitting sources that may shift over time from one area of the country to another. 71 69 Congress designed this repeal to apply only so long as the SO 2 cap in the newly established acid rain program of title IV remained in effect. CAA Amendments of 1990, 104 Stat. at 2631. 70 Id. 71 See id. at 2467. Specifically, Congress instructed the EPA to prioritize regulation based the quantity of a source category's emissions, the extent to which each emitted pollutant may endanger public health or welfare, and “the mobility and competitive nature of each such category of sources and the consequent need for nationally applicable new source standards of performance.” 42 U.S.C. 7411(f)(2). In response to the 1990 CAA Amendments, the EPA began implementing the new programs in title IV, title V, and title VI, continued to promulgate standards of performance for new sources in listed source categories under CAA section 111(b), and, in limited instances, promulgated regulations addressing existing-source emissions under CAA section 111(d). C. Regulation of Greenhouse Gases Under CAA Section 111 1. The EPA's Historical Approach to CAA Section 111 During the first four decades of regulatory activity under CAA section 111 and related provisions, the EPA listed and regulated source categories to address air pollution with adverse impacts from local and regional exposure and never attempted to list or regulate in response to global climate change concerns. In the limited instances in which the Agency addressed emissions of what have since been labeled GHGs, the justifications for and requirements of the regulatory action were based on such local and regional impacts. For example, in 1996, we listed the municipal solid waste (MSW) landfills source category primarily to regulate nonmethane organic compound (NMOC) emissions but also included limited requirements for methane emissions. 72 In the 1991 proposal, we explained that there is a “well-documented danger of fires and explosions, both on- and off-site” from methane emitted from MSW landfills. 73 After surveying multiple additional bases for regulating methane and other emissions form that source category, we also noted that “[a]n ancillary benefit from regulating air emissions from MSW landfills is a reduction in the contribution of MSW landfill emissions to global emissions of methane,” 74 and that methane was “under discussion by the Intergovernmental Negotiating Committee for a Framework Convention on Climate Change, convened by the United Nations.” 75 The 1996 final rule further discussed these issues, 76 again making it clear that our justification for listing the MSW landfill source category and regulating landfill gases was not contingent on global climate change concerns. 77 72 61 FR 9905 (Mar. 12, 1996). 73 56 FR 24468, 24474 (May 30, 1991). 74 Id. 75 Id. at 24473. 76 See, e.g., 61 FR at 9906 (Mar. 12, 1996). 77 See id. (analyzing the health and welfare impacts of local and regional exposure to landfill gas emissions that constitute the basis for listing and regulating the source category, as well as discussing methane's role as a GHG); see also id. at 9914, 9916, 9917 (explaining that the methane-related requirements function in part to response to the EPA's obligations under President Clinton's 1993 “Climate Change Action Plan” and repeating that global climate change benefits are “[a]n ancillary benefit” of the regulation). In 2003, the EPA expressly took the position that CAA section 202(a)(1) did not authorize the Agency to regulate GHG emissions in response to global climate change concerns in denying 1999 petitions for rulemaking on mobile-source emissions of CO 2 , methane, N 2 O, and HFCs. 68 FR 52922 (Sept. 8, 2003) (“2003 Denial”). In the 2003 Denial, the EPA asserted three primary reasons for denying the petitions. First, after “examin[ing] the fundamental issue of whether the CAA authorizes the imposition of control requirements” to “reduce the risk of global climate change,” we concluded that “CO 2 and other GHGs cannot be considered `air pollutants' subject to the CAA's regulatory provisions for any contribution they may make to global climate change.” 68 FR 52925. Citing the Supreme Court's decision in FDA v. Brown & Williamson Tobacco Corp., 529 U.S. 120 (2000), we noted that the CAA does not address GHGs as a regulatory matter, including in then-recent amendments, and that the “EPA has used these provisions to address air pollution problems that occur primarily at ground level or near the surface of the earth.” 68 FR 52926. On this basis, we concluded that GHGs “are not air pollutants under the CAA's regulatory provisions, including sections 108, 109, 111, 112, and 202” because they categorically are not “air pollutant[s]” under the Act-wide definition in CAA section 302(g). 68 FR 52928. Second, we raised several policy reasons for declining to regulate GHG emissions, including that regulating GHG emissions from motor vehicles and engines under the CAA would interfere with the National Highway Traffic Safety Administration's authority to implement fuel economy standards. 68 FR 52929. We also asserted that regulating GHG emissions from motor vehicles and engines under the CAA would undermine then-President Bush's policy approach of addressing global climate change concerns multilaterally. 68 FR 52930-31. That is, we reasoned that establishing GHG emission standards through unilateral action would “result in an inefficient, piecemeal approach to addressing the climate change issue” because “all significant sources and sinks of GHG emissions” should be considered in deciding the best way to achieve emission reductions. 68 FR 52931. In Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court narrowly reversed the D.C. Circuit's decision upholding the EPA's denial of the 1999 petitions for rulemaking. 78 The Court took particular issue with the EPA's reading of the Act-wide definition in CAA section 302(g), ruling that “[t]he Clean Air Act's sweeping definition of `air pollutant' . . . embraces all airborne compounds of whatever stripe” and provided no textual basis for excluding CO 2 or the three other GHGs raised in the petitions for rulemaking. 549 U.S. at 528-29. The Court also addressed the EPA's reliance on Brown & Williamson, which the majority construed as having found no congressional intent to ban the sale of tobacco products outright because such an application of the relevant statute would have been highly unlikely given the Food and Drug Administration (FDA)'s refusal to assert such authority in the past. Id. at 530-31. In contrast, in Massachusetts, the Court found that the CAA did not reflect a congressional intent to categorically exclude GHGs from the “sweeping definition of `air pollutant'” and, citing several EPA memoranda, that we had not similarly foresworn all authority to regulate GHGs as a categorical matter. Id. at 528, 530-31. Notably, the Court expressly declined to decide whether the EPA was required to issue an endangerment finding as to GHG emissions under the standard set out in CAA section 202(a)(1). Id. at 534 (“We need not and do not reach the question whether on remand EPA must make an endangerment finding.”). Nor did the Court address “whether policy concerns can inform EPA's actions in the event that it makes such a finding.” Id. at 534-35. Rather, the Court emphasized that the scope of its review of the denial of a rulemaking petition was “extremely limited,” id. at 527-28 (citation omitted), and held that we must respond to the petitions by deciding whether GHG emissions from new motor vehicles and engines meet the standard for regulation in CAA section 202(a)(1) or whether the science was too uncertain to make any determination, and that, in doing so, we must “ground [our] reasons for action or inaction in the statute,” id. at 535. 79 78 The D.C. Circuit majority had upheld the denial on the merits because “the EPA Administrator properly exercised his discretion under section 202(a)(1) in denying the petition for rulemaking.” Massachusetts v. EPA , 415 F.3d 50, 58 (D.C. Cir. 2005). The dissent argued that CAA section 202(a)'s breadth provided the EPA sufficient authority to regulate GHGs, that more specific authorization was not required, and that the Agency's policy justifications were inadequate reasons to deny the petitions. Id. at 67-82 (Tatel, J., dissenting). 79 Writing for four members of the Court, Chief Justice Roberts would have dismissed the petitions for review for lack of Article III standing. 549 U.S. at 535 (Roberts, C.J., joined by Scalia, Thomas, and Alito, J.J., dissenting). Writing for the same four members of the Court, Justice Scalia would have denied the petitions on the grounds that the Administrator reasonably exercised judgment in declining to regulate and that CAA section 302(g)'s definition of “air pollutant” does not clearly encompass CO 2 and other GHGs that naturally occur in the ambient air. Id. at 549 (Scalia, J., joined by Roberts, C.J., and Thomas and Alito, J.J., dissenting). The EPA responded in 2008 by issuing an advanced notice of proposed rulemaking titled “Regulating Greenhouse Gas Emissions Under the Clean Air Act,” 73 FR 44354 (July 30, 2008) (“2008 ANPRM”), which analyzed the extent to which various CAA provisions could address GHGs. The Agency noted that the CAA was not specifically designed to address GHGs, 73 FR 44397, and that the Agency had traditionally used its air pollution authorities to address local and regional problems, 73 FR 44408. The EPA further noted that CAA section 111 provided significant discretion over which stationary sources should be regulated and in determining the appropriate technologies and costs. 73 FR 44486-93. The EPA subsequently retained this position in implementing CAA section 111. In June 2008, the EPA promulgated revised standards of performance for petroleum refineries, including NO X standards for certain types of facilities. 80 In response to comments asserting that the EPA was required to promulgate standards for CO 2 and methane emissions because they contribute significantly to dangerous air pollution, we stated that “it is reasonable for EPA not to promulgate performance standards for GHG emissions as part of this 8-year review cycle” because “we believe that the nature of GHG emissions renders them readily distinguishable from other air pollutants for which we have previously promulgated new performance standards concurrent with an 8-year review of the existing standards.” 81 We further stated that “[i]ndeed, GHG emissions present issues that we have never had to address in the context of even an initial NSPS rulemaking for a source category,” and that “[t]hese differences warrant proceeding initially through a more deliberate process, i.e., the announced [2008 ANPRM], than in this source category-specific rulemaking.” 82 80 73 FR 35838, 35846 (June 24, 2008). 81 Id. at 35859. 82 Id. 2. Developments Between 2009 and 2015 In 2009, following a change in administration, the EPA adopted a new position on its authority to regulate in response to global climate change concerns under CAA section 202(a)(1). President Obama and the Administrator at the time initially urged Congress to amend the Act to provide additional statutory authority. As discussed later in this section, Congress considered legislation that would have added a new title to the Act specific to GHGs and global climate change, similar to the approach taken in the 1990 CAA Amendments with respect to title IV's acid rain program and title VI's provisions for phasing out ozone-depleting substances. When this legislation stalled, however, the EPA finalized a new interpretation of its existing authority under CAA section 202(a)(1) in the 2009 Endangerment Finding. In the 2009 Endangerment Finding, the Administrator found that “the science [was] sufficiently certain” to compel a determination and interpreted Massachusetts as “allow[ing] for the consideration only of science.” 74 FR 66501. The Administrator interpreted Massachusetts as holding not only that “GHGs fall within the definition of `air pollutant' under the CAA,” but also as standing for the proposition “that EPA may regulate GHGs if required findings were made.” EF RTC 11:5. The EPA based the endangerment determination on the Intergovernmental Panel on Climate Change's (IPCC) Assessment Report 4 projections concerning global mean surface temperature and linked that warming to indirect health risks driven by, among other things, more frequent heat waves, air quality effects and extreme weather events, 74 FR 66525, as well as welfare effects related to global sea level rise, and other downstream impacts, including, among other things, food production and agriculture and water resources, 74 FR 66531-35. 83 Importantly, the Administrator acknowledged that the understanding of public health and welfare in the Endangerment Finding was atypical, particularly with respect to considering indirect effects and because “[n]one of th[e] human health effects are associated with direct exposure to [GHGs],” but asserted the approach was necessary given the “unique” challenge presented by global climate change. 74 FR 66527. The EPA subsequently issued GHG standards for multiple new motor vehicle and engine categories under CAA section 202(a)(1) and attempted to expand its regulatory program to stationary sources by establishing GHG emission thresholds for stationary source permitting under the PSD program and title V. 84 83 The EPA acknowledged that the identified welfare impact pathways involved multiple causal steps, unlike more typical situations analyzed in the past. 74 FR 66531. 84 Reconsideration of Interpretation of Regulations That Determine Pollutants Covered by Clean Air Act Permitting Programs, 75 FR 17004 (Apr. 2, 2010) (“Triggering Rule”); Prevention of Significant Deterioration and Title V Greenhouse Gas Tailoring Rule, 75 FR 31514 (June 3, 2010) (“Tailoring Rule”). The EPA did not immediately apply the new legal interpretation developed in the 2009 Endangerment Finding with respect to CAA section 202(a)(1) to CAA section 111. In October 2009, for example, we promulgated NSPS for SO 2 , NO X , and CO from the coal preparation and processing plants source category for the first time. 85 Commenters again argued that we were required to, or at least should, regulate GHG emissions—CO 2 , N 2 O, and black carbon—from the source category to address global climate change concerns. We declined to regulate such emissions, stating: “At this time EPA is not aware of any emissions or mitigation data for the pollutants noted by the commenter for this source category. Hence, we lack sufficient information on which to base an NSPS for emissions of CO 2 , N 2 O, and black carbon from the source category at this time.” 86 85 74 FR 51950 (Oct. 8, 2009). The EPA had listed the source category in 1974, 39 FR 37807 (Oct. 24, 1974), and regulated PM emissions from the source category in 1976, 39 FR 2232 (Jan. 15, 1976). 86 74 FR 51957-58. Litigation by proponents of regulations seeking other avenues for controlling GHG emissions from power plants continued during this period. In Connecticut v. American Electric Power Co., 582 F.3d 309 (2d Cir. 2009), the Second Circuit held (among other things) that litigants could seek pollution controls under the Federal common law because the EPA had not yet taken regulatory action with respect to GHG emissions from stationary sources. 87 The Supreme Court unanimously reversed this holding in American Electric Power Co. v. Connecticut, 564 U.S. 410 (2011) (“ AEP” ). 88 In AEP, the Court found that CAA section 111, together with the Act's avenues for enforcement, rulemaking petitions, and judicial review, “provides a means to seek limits on emissions of carbon dioxide from domestic powerplants—the same relief the plaintiffs seek by invoking federal common law.” Id. at 425. The Court held that the Act's preclusive effect does not turn on whether the EPA actually exercises its regulatory authority: “The critical point is that Congress delegated to EPA the decision whether and how to regulate carbon-dioxide emissions from powerplants; the delegation is what displaces federal common law.” Id. at 426. Further, “were EPA to decline to regulate carbon-dioxide emissions altogether,” the courts “would have no warrant to employ the federal common law of nuisance to upset the Agency's expert determination.” Id. 87 See 582 F.3d at 379-80 (“In sum, at least until EPA makes the requisite findings, for the purposes of our displacement analysis the CAA does not (1) regulate greenhouse gas emissions or (2) regulate such emissions from stationary sources. . . . We express no opinion at this time as to whether the actual regulation of greenhouse gas emissions under the CAA by EPA, if and when such regulation should come to pass, would displace Plaintiffs' cause of action under the federal common law.”). 88 The Supreme Court affirmed by an equally divided court the Second Circuit's holding that plaintiffs had standing to maintain the lawsuit. See AEP, 564 U.S. at 420. Separate litigation addressed aspects of the EPA's GHG regulatory initiative without definitively resolving important questions regarding the scope of the Agency's statutory authority. In Coalition for Responsible Regulation v. EPA, 684 F.3d 102 (D.C. Cir. 2012), the D.C. Circuit rejected certain challenges to the 2009 Endangerment Finding and the suite of rules promulgated under CAA section 202(a)(1) and the Act's stationary source permitting provisions. Among other things, the court read Massachusetts as precluding us from declining to regulate for policy reasons that “were not part of the calculus” and, citing generally to the entirety of the opinion, as holding that the “EPA indeed wields the authority to regulate greenhouse gases under the CAA.” 684 F.3d at 118. Applying this reading, the court rejected petitioners' arguments that we should have considered the “ 'absurd' ” results for stationary source permitting when issuing the 2009 Endangerment Finding. Id. The court understood the interpretation of the statutory definition of “air pollutant” in Massachusetts to apply anywhere that term is used in the substantive provisions of the CAA. Id. at 134-44. The court acknowledged that “nothing in the CAA requires regulation of a substance simply because it qualifies as an `air pollutant' under this broad definition.” Id. at 135. Applying its broad understanding of Massachusetts, however, the court held that reading “air pollutant” as “any regulated air pollutant” was “compelled by the statute” and rejected petitioners' arguments that the PSD provisions should be read in context as focusing on localized “air pollution” problems. Id. at 134, 138. 89 89 The D.C. Circuit subsequently denied rehearing en banc. See Coal. for Responsible Regulation v. EPA, 2012 U.S. App. LEXIS 25997 (Dec. 20, 2012). Judge Brown dissented, arguing that the CAA was designed to address “the harmful effects of poisoned air on human beings and their local environs,” that such important policy decisions were for Congress to decide, and that the panel had overread “dicta” in Massachusetts. Id. at *29-62. Then-Judge Kavanaugh also dissented, arguing that the EPA exceeded its statutory authority in regulating GHG emissions under the PSD program by failing to read the term “air pollutant” in context and that the issue was “plainly one of exceptional importance” that Congress should decide. Id. at *62-93. In UARG, the Supreme Court granted review of the D.C. Circuit's decision in Coalition and revisited issues related to those it had addressed seven years earlier in Massachusetts and three years earlier in AEP. The Court disagreed with the D.C. Circuit's reasoning and held that the EPA's approach to extending PSD permitting to GHG emissions exceeded the Agency's statutory authority. 573 U.S. at 316. The Court rejected the D.C. Circuit's application of Massachusetts in this context as a “flawed syllogism,” id. at 319 (citation omitted), holding that “while Massachusetts rejected EPA's categorical contention that greenhouse gases could not be `air pollutants' for any purposes of the Act, it did not embrace EPA's current, equally categorical position that greenhouse gases must be air pollutants for all purposes regardless of the statutory context,” id. Rather, “ Massachusetts does not foreclose the Agency's use of statutory context to infer that certain of the Act's provisions use `air pollutant' to denote not every conceivable airborne substance, but only those that may sensibly be encompassed within the particular regulatory program.” Id. The Court rejected the EPA's attempt to require a permit based on GHG emissions as “ ‘incompatible’ with `the substance of Congress' regulatory scheme' ” and contrary to the principle that “Congress . . . speak[s] clearly if it wishes to assign to an agency decisions of vast ‘economic and political significance.' ” Id. at 322-24 (quoting Brown & Williamson, 529 U.S. at 159). 3. The EPA's Regulation of GHGs Under CAA Section 111 Since 2015 In August 2015, the EPA announced “a historic and important first step in reducing carbon pollution from power plants.” 90 This “first step” consisted of two related final rules that, for the first time since 1970, regulated stationary source emissions in response to global climate change concerns. This watershed moment fundamentally changed what and how the EPA regulates under CAA section 111. 90 https://archive.epa.gov/epa/cleanpowerplan/fact-sheet-overview-clean-power-plan.html. a. Regulation of CO 2 Emissions From Fossil Fuel-Fired Power Plants i. 2015 NSPS for CO 2 Emissions From New Power Plants In the 2015 NSPS, the EPA laid out a novel legal basis for regulating GHG emissions under CAA section 111 based on global climate change concerns. The EPA explained that CAA section 111(b)(1)(A) requires the Administrator to list any source category that “causes, or contributes significantly to, air pollution which may reasonably be anticipated to endanger public health or welfare.” The EPA posited that, unlike other CAA provisions, CAA section 111(b)(1)(A) does not require the EPA to make endangerment and significant contribution findings for individual pollutants. Rather, the EPA asserted that once such findings are made for any pollutant emitted by a source category, the Agency has discretion to regulate all pollutants emitted by the source category subject only to rational basis constraints. 80 FR 64529-30. Using this framework, the EPA created a new source category consisting of the type of power plants previously listed in the 1970s under several source categories. The source category encompassed all fossil fuel-fired EGUs and focused on CO 2 emissions on the understanding that subject power plants did not emit substantial quantities of the additional GHGs encompassed within the 2009 Endangerment Finding. 91 The Agency maintained, however, that it was not listing a new source category and therefore was not required to make any endangerment or significant contribution finding for the fossil fuel-fired EGU source category to promulgate NSPS. The EPA determined that it had a rational basis for concluding that emissions of CO 2 from fossil fuel-fired power plants merit regulation under CAA section 111. In reaching that conclusion, the Agency stated that it had determined in the 2009 Endangerment Finding that GHG emissions may reasonably be anticipated to endanger public health or welfare and that more recent information confirmed this determination. The EPA explained that the approach it was taking to endangerment from GHG emissions from the fossil fuel-fired EGU source category was “substantially similar to that reflected in the 2009 Endangerment Finding and the 2010 denial of petitions to reconsider.” 80 FR 64531. 92 The EPA added that “the high level of GHG emissions from fossil fuel-fired EGUs makes clear that it is rational for the EPA to regulate GHG emissions from this sector.” 80 FR 64530. 91 Specifically, referencing the determination in the 2009 Endangerment Finding that GHGs constitute both the relevant “air pollutant” and “air pollution” for purposes of regulating in response to global climate change, the EPA stated in the 2015 NSPS that “[t]he air pollutant regulated in this final action is greenhouse gases. However, the standards in this rule are expressed in the form of limits on only emissions of CO 2 , and not the other constituent gases of the air pollutant GHGs.” 80 FR 64537. 92 See 75 FR 49556 (Aug. 13, 2010) (denying petitions for reconsideration of the 2009 Endangerment Finding). Nevertheless, the EPA purported to make separate endangerment and significant contribution findings in the alternative pursuant to CAA section 111(b)(1)(A). While maintaining that no pollutant-specific contribution findings were required, the EPA asserted that the information and conclusions in the preamble to the 2015 NSPS would suffice for such findings. 80 FR 64530-31. That is, the EPA took the position in the 2015 NSPS that regardless whether the Agency needed only a rational basis to regulate CO 2 emissions from fossil fuel-fired EGUs or whether the Agency was instead required to make new endangerment and contribution findings, it had made the requisite determinations based on the 2009 Endangerment Finding and the additional information presented in the preamble to the 2015 NSPS. The standards of performance in the 2015 NSPS limited CO 2 emissions based on several different BSER determinations. For new coal-fired steam boilers, the EPA based the standards on a BSER of 16 to 23 percent (depending on the type of coal combusted) carbon capture and storage (CCS). 80 FR 64548. For new natural gas-fired combustion turbines, the EPA based the standards on a BSER of efficiency measures. 80 FR 64515. The EPA subsequently denied multiple petitions for reconsideration, 93 and several States and industry groups filed petitions for review in the D.C. Circuit. 94 93 81 FR 27442 (May 6, 2016). The EPA deferred action on one petition with respect to the treatment of biomass. Id. at 27443. 94 North Dakota v. EPA , No. 15-1381 (D.C. Cir.). These petitions have been held in abeyance since 2016 given intervening developments. ii. Emission Guidelines for CO 2 From Existing Power Plants (A) 2015 Clean Power Plan In the 2015 CPP, issued the same day as the 2015 NSPS, the EPA promulgated emissions guidelines under CAA section 111(d) establishing presumptive standards of performance for existing fossil fuel-fired EGUs and requiring States to submit plans for implementation and enforcement. 80 FR 64661. The Agency asserted that its authority under CAA section 111(d) derived from the 2015 NSPS under CAA section 111(b) and noted that GHGs, and CO 2 in particular, are not separately regulated through the NAAQS program under CAA sections 107-110 or the NESHAP program under CAA section 112. The Agency based the emission guidelines for existing coal-fired steam plants on a BSER that consisted of a set of measures, including heat-rate improvements ( i.e., the amount of fuel that must be burned to generate a unit of electricity) and substituting fossil fuel-based power generation with lower-emitting power generation, such as renewable sources. 80 FR 64667. The latter type of measure is known as “generation shifting.” 80 FR 64728-29. The emission guidelines authorized the States to include trading or averaging programs in their State plans. 80 FR 64840. In February 2016, the Supreme Court stayed the 2015 CPP after the D.C. Circuit denied preliminary relief. 95 95 West Virginia v. EPA , 577 U.S. 1126 (2016). The D.C. Circuit held the litigation in abeyance and later dismissed in light of subsequent developments. See Am. Lung Ass'n, 985 F.3d at 937. (B) 2019 ACE Rule and Clean Power Plan Repeal In 2019, following a change in administration, the EPA repealed and replaced the 2015 CPP in the Affordable Clean Energy (ACE) Rule, 84 FR 32529 (July 8, 2019). In the 2019 ACE Rule, the Agency determined that the statutory “text and reasonable inferences from it” indicate that the best “system” of emission reduction as defined in CAA section 111(a)(1) “is limited to measures that can be applied to and at the level of the individual source,” meaning the BSER must be control measures for reducing emissions at individual sources. 84 FR 32523-24. The Agency concluded that generation shifting is not such a control measure. 84 FR 32546. In addition, the EPA concluded that the 2015 CPP was a “major rule” subject to the major questions doctrine and therefore must be supported by “a clear statement from Congress.” Because the statutory phrase “best system of emission reduction” does not clearly speak to generation shifting, the Agency reasoned that CAA section 111 should not be read to encompass generation-shifting measures. 84 FR 32529. To replace the 2015 CPP, the EPA promulgated as part of the 2019 ACE Rule a new set of emission guidelines for existing coal-fired steam-generating EGUs. 84 FR 32532. In American Lung Association, a divided panel of the D.C. Circuit vacated the 2019 ACE Rule, including the CPP Repeal. First, the panel majority held that CAA section 111(d) does not limit the EPA, in determining the BSER, to measures applied at and to an individual source. 985 F.3d at 944. Second, the panel majority rejected in the strongest terms the argument that generation-shifting implicated “the so-called `major questions' doctrine” based on its interpretation of the Supreme Court's decisions in Massachusetts and AEP. Id. at 959. The panel majority reasoned that the EPA had “complied” with Massachusetts by issuing the 2009 Endangerment Finding and that in AEP, “the Court [ ] told the EPA directly that it is the Agency's job to regulate power plants' emissions of greenhouse gases under Section [111].” Id. at 959-60. Therefore, the panel majority concluded, all questions as to “what,” “whom,” and “how” the Agency may regulate “have all been resolved and so do not trigger the major questions doctrine.” Id. at 962. 96 Finally, the panel majority rejected certain additional challenges to the findings (or lack thereof) supporting the 2015 NSPS and therefore the 2015 CPP as well as arguments that coal power plants could not be regulated under CAA section 111(d) given the EPA's regulation of mercury emissions from coal plants under CAA section 112. Id. at 971-88. Ultimately the panel majority vacated the 2019 ACE Rule, including the CPP Repeal, thereby placing the 2015 CPP back into effect. 97 96 The panel majority further held that the major questions doctrine “does not apply” to the interpretation of “best system of emission reduction” because, among other reasons, “the regulatory authority and its reach have been affirmed and enforced by the Supreme Court” and generation shifting was an “already-in-use” system. 985 F.3d at 963-68. 97 In a partial dissent, Judge Walker argued that the 2015 CPP (and aspects retained in the 2019 ACE Rule) violated the major questions doctrine because CAA section 111 does not include a clear statement of authority to regulate GHG emissions from power plants. Id. at 995-1003 (pointing to failed legislation in 2009 that would have provided the requisite authority to regulate GHG emissions from power plants). In West Virginia, the Supreme Court reversed the D.C. Circuit's treatment of the major questions doctrine and held that the 2015 CPP exceeded the EPA's authority under CAA section 111(d). First, the Court surveyed its precedents to confirm that an agency must have more than “a colorable textual basis” to assert “ `unheralded' regulatory power over `a significant portion of the American economy.' ” 597 U.S. at 721-23 (quoting UARG, 573 U.S. at 324). In such cases, “both separation of power principles and a practical understanding of legislative intent” require the agency to “point to `clear congressional authorization' for the power it claims.” Id. at 723 (quoting UARG, 573 U.S. at 324). The Court explained that its decision in UARG “addressed another question regarding EPA's authority—namely, whether EPA could construe the term `air pollutant,' in a specific provision of the Clean Air Act, to cover greenhouse gases,” and held that despite the “textual plausibility” of the interpretation supporting the Agency's assertion of authority, the significant consequences involved required more than a “plausib[le]” statutory basis. Id. at 722. Next, the Court held that our reliance on CAA section 111(d) to regulate GHG emissions was “a major questions case” because we had asserted the power “to substantially restructure the American energy market.” Id. at 724. That provision “had rarely been used in the preceding decades,” and we had used it in an “unprecedented” manner “to adopt a regulatory program that Congress had conspicuously and repeatedly declined to enact itself.” Id. at 724-28. The Court specifically rejected the argument that AEP precluded application of the major questions doctrine, stating that the case involved the question “whether Congress wanted district court judges to decide, under unwritten federal nuisance law, `whether and how to regulate carbondioxide emissions from powerplants' ” and “said nothing about the ways in which Congress intended EPA to exercise its power under that provision.” Id. at 730 (quoting AEP, 564 U.S. at 426). Finally, the Court concluded that we lacked statutory authority for the 2015 CPP based on a lack of statutory authorization to require generation shifting. Id. at 732-35. 98 98 In dissent, Justice Kagan argued that the Court had obstructed the EPA's efforts to regulate GHG emissions: “Today, the Court strips the [EPA] of the power Congress gave it to respond to `the most pressing environmental challenge of our time.'” West Virginia, 597 U.S. at 753 (Kagan, J., joined by Breyer and Sotomayor, J.J., dissenting) (quoting Massachusetts, 549 U.S. at 505); see also id. at 755 (“This Court has obstructed EPA's effort from the beginning.”). In October 2022, the D.C. Circuit recalled its mandate for the vacatur of the 2019 ACE Rule, revised its judgment to place the CPP Repeal back into effect, and stayed further proceedings. Am. Lung Ass'n v. EPA, No. 19-1140, Order (Oct. 27, 2022). (C) 2024 Carbon Pollution Standards Rule In May 2024, the EPA responded to the Supreme Court's decision in West Virginia by promulgating more stringent requirements for fossil fuel-fired EGUs than those contained in the 2015 NSPS or vacated 2015 CPP. 89 FR 39798. The 2024 CPS included several related components. First, the EPA repealed the 2019 ACE Rule (aside from its repeal of the 2015 CPP) after determining that the BSER for existing coal-fired power plants was not the suite of heat-rate improvements identified in the 2019 ACE Rule. Second, the EPA promulgated new emission guidelines for GHG emissions from existing fossil fuel-fired power plants subcategorized into coal-fired units, oil-fired units, and gas-fired units. For existing coal-fired units, the EPA based the requirements on a new BSER of either 90 percent CCS or 40 percent gas cofiring. For existing natural gas- and oil-fired steam generating units, the EPA based the requirements on BSERs of either routine methods of operation and maintenance or uniform fuels. Finally, the Agency promulgated NSPS for new and reconstructed combustion turbines, based on efficiency measures, 90 percent CCS, or use of lower-emitting fuels. In addition, the EPA revised the standards of performance for coal-fired steam generating units that undertake a large modification to be based on the BSER of 90 percent CCS. 99 99 In the 2024 CPS, the EPA also withdrew the separate proposed revisions to the New Source Review (NSR) regulations that were included the ACE Rule proposal ( see 83 FR 44746, 44773-83 (Aug. 31, 2018)). Following promulgation of the 2024 CPS, States and industry groups filed petitions for review in the D.C. Circuit, and many subsequently filed motions to stay the rule. The D.C. Circuit denied the stay motions on July 19, 2024, 100 and the Supreme Court denied them on October 16, 2024. 101 These challenges have been held in abeyance since the change in administration. 100 West Virginia v. EPA , No. 2420, Order, 2024 U.S. App. LEXIS 17856 (July 19, 2024). 101 West Virginia v. EPA , 145 S. Ct. 2 (2024). Justice Thomas would have granted a stay, and Justice Kavanaugh, joined by Justice Gorsuch, wrote separately that “the applicants have shown a strong likelihood of success on the merits as to at least some of their challenges to the [EPA's] rule.” Id. D. Recent Developments 1. Rescission of the 2009 Endangerment Finding In February 2025, the Administrator initiated reconsideration of the 2009 findings of endangerment and contribution under CAA section 202(a)(1) that launched the EPA's GHG regulatory initiative across multiple statutory programs. The Administrator explained that the Agency would address legal and scientific developments that presented reason to question the ongoing validity and reliability of the conclusions in the 2009 Endangerment Finding and to seek public comment on these important issues for the first time since 2009. 102 These efforts culminated in a proposed rule issued on July 29, 2025, 103 followed by a public comment period in which we received hundreds of thousands of comments from a variety of perspectives. 102 See Feb. 19, 2025 Memo at 1. 103 See 90 FR 36288 (Aug. 1, 2025). On February 12, 2026, the Administrator signed a final rule rescinding the 2009 Endangerment Finding and repealing all associated GHG emission standards for new motor vehicles and engines under CAA section 202(a)(1). 104 The EPA concluded in the Endangerment Finding Rescission that we lack statutory authority to regulate GHG emissions from new motor vehicles and motor vehicle engines based on global climate change concerns. We further concluded that the appropriate policy response to global climate change concerns is a decision vested in Congress, and that Congress did not give the EPA the authority to decide the Nation's policy response to these concerns when it enacted CAA section 202(a)(1) to address domestic air pollution problems. And we concluded, based on an analysis of commonly accepted climate impact modeling, including models and arguments received from multiple perspectives during the public comment period, that the inability of GHG emission standards for new motor vehicles and engines to have more than a de minimis impact on phenomena attributed to global climate changes rendered the standards futile. 105 104 See 91 FR 7586 (Feb. 18, 2026). 105 This discussion summarizes the bases of the Endangerment Finding Rescission for informational purposes, only, and does not reopen that final rule or seek additional comment on issues addressed in that final rule. For more information, see the final rule preamble, accompanying RTC, and supporting documentation for the Endangerment Finding Rescission. 2. Proposed Repeal of GHG Standards for Fossil Fuel-Fired EGUs On June 17, 2025, the EPA issued a proposed rule to repeal GHG standards for fossil fuel-fired EGUs. The June 2025 NPRM included a primary proposal, which would repeal all such GHG standards, and an alternative proposal, which would repeal most of the GHG standards promulgated in the 2024 CPS. This subsection summarizes the June 2025 NPRM for informational purposes only; as noted above, the EPA is not soliciting additional comment on issues addressed in the concurrently issued final rule based on the alternative proposal in the June 2025 NPRM and will address comments received on the primary proposal in the June 2025 NPRM in a final action addressing that proposal and this supplemental proposal. The primary proposal in the June 2025 NPRM proposed to conclude that CAA section 111 is best read to require, or at least authorize the EPA to require, an Administrator's determination that an air pollutant emitted by a source category causes, or contributes significantly to, air pollution which may reasonably be anticipated to endanger public health or welfare as a predicate to establishing emission standards for that pollutant. As such, we proposed to conclude that the Administrator must make a significant contribution finding before issuing GHG emission standards for a new source category even if covered sources had previously been listed under a distinct category. We further proposed to determine, in a change from the 2015 NSPS and 2024 CPS, that GHG emissions from fossil fuel-fired EGUs do not contribute significantly to air pollution as required for the promulgation of new and existing source standards. We proposed that a determination of significant contribution must consider whether such determination would have an influence or effect on the targeted air pollution and the public health or welfare impacts attributed to such air pollution, and that this inquiry entails considering the policies that would inform the resulting regulation. Based on this understanding, we proposed to find that regulation of GHG emissions from fossil fuel-fired EGUs under CAA section 111 would not have a significant effect on GHG air pollution and the public health or welfare impacts attributed to such air pollution, and that the contribution of this source category is therefore not significant for a host of reasons. The EPA thus proposed to repeal all GHG emissions standards for the power sector under CAA section 111, including the 2015 NSPS, codified in 40 CFR part 60, subpart TTTT, and the 2024 CPS, codified in 40 CFR part 60, subparts TTTTa and UUUUb. The alternative proposal in the June 2025 NPRM proposed to reconsider the BSER determinations in the 2024 CPS through a record-based evaluation and in light of applicable requirements for determining an appropriate BSER. The EPA proposed to rescind the requirements for existing coal-fired units on grounds that 90 percent CCS and 40 percent natural gas co-firing do not qualify as the BSER for existing coal-fired units. The EPA is finalizing that proposal concurrently with this supplemental proposal. The EPA is not taking further action at this time on the primary proposal in the June 2025 NPRM and will consider and respond to comments on that proposal together with comments submitted on this supplemental notice in a forthcoming final action. 3. Relevant Legislative Action Both before and since the 2009 Endangerment Finding, “ `Congress considered and rejected' multiple times” legislation that would have authorized or required the EPA to regulate GHG emissions from stationary sources that were subject to CAA section 111 for their non-GHG emissions, as well as mobile sources. West Virginia, 597 U.S. at 731 (quoting Brown & Williamson, 529 U.S. at 144). This history is particularly relevant because of the established pattern in the 1970, 1977, and 1990 CAA Amendments of Congress ad [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2026-19072. Public record. Not legal advice.