Clean Air Act: EPA’s Greenhouse Gas Endangerment Finding and Repeal
Congressional research reportJul 7, 2026
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Clean Air Act: EPA’s Greenhouse Gas
Endangerment Finding and Repeal
July 7, 2026
Congressional Research Service
https://crsreports.congress.gov
R49024
SUMMARY
Clean Air Act: EPA’s Greenhouse Gas
Endangerment Finding and Repeal
The Clean Air Act (CAA) requires the U.S. Environmental Protection Agency’s (EPA’s)
Administrator to address pollutants and sources of air pollution “which, in his judgment, cause or
contribute … to air pollution … which may reasonably be anticipated to endanger public health
or welfare.” This judgment is referred to as an endangerment finding (EF) and has two distinct
parts: a finding that an air pollutant may reasonably be anticipated to endanger public health or
welfare, and a finding that emissions cause or contribute to that air pollution. The CAA requires
that EPA regulate a pollutant if an EF is made. Provisions for EFs are in several sections of the
CAA, including Section 202(a), covering motor vehicles.
R49024
July 7, 2026
Jonathan D. Haskett
Analyst in Environmental
Policy
Omar M. Hammad
Analyst in Environmental
Policy
Since the late 1970s, Congress has provided authority and funds for federal agencies to research
and better understand climate science, but Congress did not direct agencies to promulgate regulations to reduce greenhouse
gas (GHG) emissions. EPA’s regulatory actions to limit GHG emissions from new motor vehicles cited the CAA and its
amendments. In 2007, the Supreme Court held that EPA has the statutory authority to regulate GHGs as “air pollutants”
under the CAA. EPA then issued an EF for motor vehicle emissions in 2009 and subsequently issued GHG regulations for
motor vehicles. In 2025, EPA proposed and in 2026 finalized a rulemaking rescinding the 2009 EF and GHG standards for
motor vehicles.
In the 2009 EF, EPA found that GHG air pollution “is reasonably anticipated to endanger public health” through “direct
temperature effects, air quality effects, the potential for changes in vector-borne diseases, and the potential for changes in the
severity and frequency of extreme weather events.” EPA further found that GHG air pollution “may reasonably be
anticipated to endanger public welfare,” including climate impacts on food production, forestry, water resources, sea level
rise, energy infrastructure, and ecosystems. Finally, EPA found that motor vehicles “contribute to” GHG air pollution.
Following the 2009 EF, EPA issued GHG emissions standards for passenger cars and light-duty, medium-duty, and heavyduty trucks. EPA first promulgated GHG emissions standards for passenger vehicles and light-duty trucks in 2010, and for
medium- and heavy-duty trucks in 2011. To reduce GHG air pollution, these regulatory actions established, for the first time,
GHG emissions standards by setting fleet-wide average carbon dioxide (CO2) targets for on-road mobile sources. These
standards were updated in subsequent years.
In January 2025 EPA announced the reconsideration of the 2009 EF, and in February 2026, EPA finalized the rescission of
the 2009 EF and motor vehicle GHG standards. EPA concluded that “Section 202(a) of the CAA does not provide EPA
statutory authority to prescribe motor vehicle emission standards for the purpose of addressing global climate change
concerns.” EPA determined that GHG emissions standards for new motor vehicles and engines “do not impact in any
material way the public health and welfare concerns identified in the Administrator’s prior findings in 2009.” EPA noted that,
following these regulatory amendments, engine and vehicle manufacturers are relieved of all prospective obligations
regarding the measurement, control, and reporting of GHG emissions for any highway engine or vehicle, including those
produced in model years preceding this final rule.
EPA published cost-benefit analyses in regulatory impact analyses (RIAs) for the GHG emissions regulations in 2024 and
their rescission in 2026. The 2024 RIAs found that the regulations would decrease GHG emissions, while the 2026 RIA
found that rescinding the regulations would increase GHG emissions. RIAs for both the regulations and their rescission found
that the regulations would produce net economic benefits, although the RIAs used different analytical approaches and are
difficult to compare directly. Unlike the 2024 RIAs, the 2026 RIA for the rescission rulemaking did not include estimates for
the health impacts of non-GHG air pollutants. The RIAs for the 2024 rulemakings and three of the four modeled scenarios in
the RIA for the 2026 rescission rulemaking estimated that the associated rulemakings would result in net economic benefits.
Some Members of Congress have supported the 2009 EF, while others have opposed it. Joint resolutions were introduced in
the House and the Senate to overturn the 2009 EF, although they did not become law. If Congress is dissatisfied with the
status quo, Congress could consider a range of legislative options to provide EPA with specific statutory instructions about
how or whether to regulate GHGs under the CAA, such as specifying that GHGs either are or are not air pollutants under the
CAA. Congress could also consider oversight options to obtain information on the effects of the GHG regulations on public
health and public welfare, and on the regulations’ costs and benefits to industry and consumers.
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Clean Air Act: EPA’s Greenhouse Gas Endangerment Finding and Repeal
Contents
Introduction ..................................................................................................................................... 1
EPA’s 2009 Endangerment Finding ................................................................................................. 2
Process of Rulemaking .............................................................................................................. 4
2009 Finding That GHGs Endanger Public Health and Welfare ............................................... 5
2009 Finding That Motor Vehicle Emissions Cause and Contribute to GHG Air
Pollution ................................................................................................................................. 7
EPA’s Motor Vehicle GHG Regulations .......................................................................................... 8
EPA’s Rescission of the 2009 Endangerment Finding ................................................................... 10
EPA’s Regulatory Impact Analyses for GHG Regulations .............................................................11
Considerations for Congress.......................................................................................................... 15
Tables
Table 1. EPA On-Road Motor Vehicle Greenhouse Gas (GHG) Regulations ................................. 9
Table 2. Estimated Regulatory Impact of Motor Vehicle Greenhouse Gas (GHG)
Regulations ................................................................................................................................. 12
Contacts
Author Information........................................................................................................................ 17
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Clean Air Act: EPA’s Greenhouse Gas Endangerment Finding and Repeal
Introduction
The United States has demonstrated varying approaches and intents with regard to reducing
greenhouse gas (GHG) emissions and mitigating climate change.1 Congress has passed legislation
containing provisions addressing climate change, such as P.L. 117-169, a budget reconciliation
measure commonly referred to as the “Inflation Reduction Act of 2022” (IRA).2 The IRA contains
provisions that directly and indirectly address climate change, including the reduction of U.S.
GHG emissions.3 The 119th Congress has passed legislation—P.L. 119-21, a budget reconciliation
measure often referred to as the “One Big Beautiful Bill Act” (OBBBA)—rescinding or repealing
some of the IRA provisions addressing climate change.4 The executive branch has also taken
varying approaches. Presidents Obama and Biden issued executive orders specifying climate
action to reduce emissions across multiple federal agencies and programs.5 President Trump has
issued executive orders revoking some U.S. climate actions both domestically and
internationally.6
One particular policy question is whether or not to regulate GHG emissions from motor vehicles.
In 2022, the transportation sector was the U.S. economic sector with the largest GHG emissions.7
Motor vehicles accounted for approximately 70% of transportation-sector GHG emissions in that
year.8 The U.S. Environmental Protection Agency (EPA) took regulatory action to limit GHG
emissions from new motor vehicles, citing the authority Congress granted the agency under the
Clean Air Act (CAA) and its amendments.9 EPA regulated GHG emissions from motor vehicles
under Section 202(a) of the CAA.10 These regulations were based on a predicate finding by EPA,
known as an endangerment finding (EF), that emissions of GHG air pollution by motor vehicles
endangered public health and welfare and that motor vehicles caused and contributed to this air
pollution.11 EPA promulgated the EF under Section 202(a) of the CAA on December 7, 2009, and
thereafter promulgated GHG regulations for motor vehicles. In 2025, the Trump Administration
1 Brian Murray and Jonas Monast, “Carrots, Sticks, and the Evolution of U.S. Climate Policy,” Texas A&M Law
Review, vol. 11, no. 2 (2024), p. 431, https://doi.org/10.37419/LR.V11.I2.5.
2 CRS Report R47262, Inflation Reduction Act of 2022 (IRA): Provisions Related to Climate Change, coordinated by
Jonathan L. Ramseur.
3 CRS Report R47262, Inflation Reduction Act of 2022 (IRA): Provisions Related to Climate Change.
4 Provisions of P.L. 117-169 related to climate change that were rescinded or repealed by P.L. 119-21 include, among
others, Section 60103—GHG Reduction Fund, Section 60114—Climate Pollution Reduction Grants, and Section
60503—Use of Low-Carbon Materials.
5 For example, President Obama issued Executive Order 13693, “Planning for Federal Sustainability in the Next
Decade,” 80 Federal Register 15871, March 25, 2015; and President Biden issued Executive Order 14008, “Tackling
the Climate Crisis at Home and Abroad,” 86 Federal Register 7619, February 1, 2021.
6 Executive Order 14154, “Unleashing American Energy,” 90 Federal Register 8353, January 29, 2025. See also
Executive Order 14162, “Putting America First in International Environmental Agreements,” 90 Federal Register
8455, January 30, 2025.
7 U.S. Environmental Protection Agency (EPA), “Fast Facts on Transportation Greenhouse Gas Emissions,”
https://www.epa.gov/greenvehicles/fast-facts-transportation-greenhouse-gas-emissions.
8 EPA, “Fast Facts on Transportation Greenhouse Gas Emissions.” EPA estimated that light-duty vehicles accounted
for 57% of 2022 transportation-sector greenhouse gas (GHG) emissions, while medium- and heavy-duty trucks
accounted for 23% of these emissions.
9 42 U.S.C. §§7401 et seq.
10 42 U.S.C. §7521.
11 EPA, “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air
Act,” 74 Federal Register 66496, December 15, 2009, https://www.federalregister.gov/documents/2009/12/15/E929537/endangerment-and-cause-or-contribute-findings-for-greenhouse-gases-under-section-202a-of-the-clean
(hereinafter EPA, 2009 GHG Endangerment Finding).
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announced policy initiatives on existing regulation of GHGs by EPA.12 In 2026, EPA finalized a
rulemaking rescinding the 2009 EF and GHG standards for motor vehicles.13
This report describes EPA’s 2009 EF with respect to GHG emissions from motor vehicles and its
basis within the CAA. It then describes EPA’s motor vehicle GHG regulations that relied upon the
2009 EF, EPA’s subsequent actions to rescind the 2009 EF (and the associated regulations), and
the estimated change in GHG emissions. The report also discusses the net benefits associated
with both the regulations and their subsequent rescission. It concludes with legislative and
oversight considerations for Congress.
Congressional Action on Climate Change Research
Since the late 1970s, Congress has provided authority and funds for federal agencies to research and better
understand climate science but has not directed agencies to promulgate regulations to reduce GHG emissions. In
1978, Congress passed the National Climate Program Act (NCPA), which created the National Climate Program
Office in the Department of Commerce.14 The NCPA required the office to assess climate change effects, improve
understanding of climate change science, and collect global and domestic climate data.15 Congress also passed the
Global Climate Protection Act of 1987 (Title XI of P.L. 100-204), which stated that U.S. climate policy should,
among other things, increase understanding of the greenhouse effect, foster international cooperation on climate
research, identify climate mitigation technologies, and “work toward multilateral agreements.” Congress
subsequently passed additional legislation authorizing federal climate change research, interagency collaboration,
collection of GHG emissions data, and the establishment of a voluntary program for reporting GHG emissions.
This legislation included the Global Change Research Act of 1990 (P.L. 101-606, Title I, United States Global
Change Research Program), “aimed at understanding and responding to global change, including the cumulative
effects of human activities and natural processes on the environment”;16 the Global Climate Change Prevention
Act of 1990 (P.L. 101-624, Title XXIV, Global Climate Change) directing the Department of Agriculture to study
the effects of climate change on forestry and agriculture;17 and the Energy and Policy Act of 1992 (P.L. 102-486,
§1605, National Inventory and Voluntary Reporting of Greenhouse Gases) requiring the Secretary of Energy to
prepare an annual inventory of GHG emissions and establishing a voluntary reporting program and database.18
These statutes authorized federal agencies to investigate climate change and its potential impacts but did not
direct agencies to promulgate regulations to reduce GHG emissions.
EPA’s 2009 Endangerment Finding
Legal and administrative developments preceded EPA’s 2009 EF. On October 20, 1999, a group
of 19 organizations petitioned EPA to regulate GHG emissions from new motor vehicles under
CAA Section 202.19 The petitioners cited the CAA and a 1998 memorandum from EPA’s general
12 Executive Order 14154, “Unleashing American Energy,” 90 Federal Register 8353, January 29, 2025.
13 EPA, “Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards,” 90 Federal
Register 36288, August 1, 2025; and EPA, “Rescission of the Greenhouse Gas Endangerment Finding and Motor
Vehicle Greenhouse Gas Emission Standards Under the Clean Air Act,” 91 Federal Register 7686, February 18, 2026
(hereinafter EPA, 2026 GHG EF and Motor Vehicle Standards Rescission).
14 National Climate Program Act of 1978, P.L. 95-367, 92 Stat. 601 (1978) (as amended at 15 U.S.C. §§2901-2908); 15
U.S.C. §2904(c).
15 15 U.S.C. §2904(d). For more information on the Climate Program Office, see the National Oceanic and
Atmospheric Administration, “Climate Program Office,” https://cpo.noaa.gov/about-cpo/.
16 Global Change Research Act of 1990, 15 U.S.C. §§2921-2938.
17 7 U.S.C. §6702, Study of Global Climate Change, Agriculture, and Forestry.
18 42 U.S.C. §13385, National Inventory and Voluntary Reporting of Greenhouse Gases.
19 The lead petitioner was the International Center for Technology Assessment (ICTA). The petition may be found at
https://www.ciel.org/Publications/greenhouse_petition_EPA.pdf.
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counsel that argued the agency had CAA authority to regulate certain emissions from power
plants, noting that “CO2, as an air pollutant, is within EPA’s scope of authority to regulate.”20
On August 28, 2003, EPA denied the petition based on a new EPA general counsel memorandum
that concluded that the CAA did not grant EPA authority to regulate carbon dioxide (CO2) and
other GHG emissions based on their climate change impacts.21 Massachusetts, 11 other states, and
a number of petitioners challenged EPA’s denial of the petition in a case that ultimately reached
the Supreme Court.22 In 2007, the Supreme Court held in a 5-4 decision in Massachusetts v. EPA
that EPA has statutory authority to regulate GHGs as “air pollutants” under the CAA.23 After this
decision EPA issued an EF for motor vehicle emissions in 2009.
Endangerment Findings in the Clean Air Act
EPA promulgates EFs as part of the regular process of rulemaking under the CAA, with the EF on lead emissions
from aircraft engines being a recent example.24 The 2009 GHG EF was one of two GHG EFs promulgated by EPA
and was specific to emissions from motor vehicles.25 The other GHG EF is specific to emissions from aircraft and
was promulgated by EPA in 2016.26 Only EPA regulation of GHG emissions from motor vehicles was directly
dependent on the 2009 EF. GHG regulation of other sectors such as aircraft, electric generating units (EGUs), and
oil and gas facilities (O&G) are not dependent on the 2009 EF; however, rulemaking regarding GHG emissions
from all three sectors cite the 2009 EF as providing scientific support for their GHG regulation.27 EPA’s regulatory
authority for setting standards on emissions from the EGU and O&G source categories is based on EFs for these
source categories as stationary sources that emit pollutants under Section 111 of the CAA, rather than EFs
specific to GHGs.28
20 Memorandum from Jonathan Z. Cannon, EPA General Counsel, to Carol M. Browner, Administrator, titled “EPA’s
Authority to Regulate Pollutants Emitted by Electric Power Generation Sources,” issued on April 10, 1998 (President
Clinton’s Administration). EPA later withdrew the Cannon memorandum (President George W. Bush’s
Administration). See EPA’s notice of petition denial for further information: EPA, “Control of Emissions from New
Highway Vehicles and Engines,” 68 Federal Register 52922, September 8, 2003.
21 In an August 28, 2003, memorandum from Robert E. Fabricant, EPA General Counsel, to Marianne L. Horinko,
Acting EPA Administrator, on “EPA’s Authority to Impose Mandatory Controls to Address Global Climate Change
Under the Clean Air Act,” the General Counsel withdrew the 1998 Cannon memorandum. The General Counsel
concluded that the Clean Air Act (CAA) “does not authorize EPA to regulate for global climate change purposes, and
accordingly that CO2 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.” See EPA’s notice of petition denial for further
information: EPA, “Control of Emissions From New Highway Vehicles and Engines,” 68 Federal Register 52922,
September 8, 2003.
22 The D.C. Circuit, in a split decision, rejected the suit. See Massachusetts v. EPA, 415 F.3d 50, 56, 59-60 (2005)
(Randolph, J., dissenting) (holding that EPA reasonably denied the petition based on scientific uncertainty and policy
considerations).
23 Massachusetts v. EPA, 549 U.S. at 497 (2007). For further information on the Court’s ruling and legal challenges to
the endangerment finding (EF), see CRS Legal Sidebar LSB11320, EPA to Revisit Greenhouse Gas Endangerment
Finding, by Andrew S. Coghlan.
24 EPA, “EPA Determines that Lead Emissions from Aircraft Engines Cause or Contribute to Air Pollution,” press
release, October 18, 2023, https://www.epa.gov/newsreleases/epa-determines-lead-emissions-aircraft-engines-cause-orcontribute-air-pollution.
25 EPA, 2009 GHG Endangerment Finding.
26 EPA, “Finding That Greenhouse Gas Emissions from Aircraft Cause or Contribute to Air Pollution That May
Reasonably Be Anticipated to Endanger Public Health and Welfare,” 81 Federal Register 54422, August 15, 2016
(hereinafter EPA, 2016 Aircraft GHG Endangerment Finding).
27 EPA, 2016 Aircraft GHG Endangerment Finding, p. 48. See also EPA, “NSPS for GHG Emissions from New,
Modified, and Reconstructed Electric Utility Generating Units,” 89 Federal Register 39798, May 9, 2024. See also
EPA, “Oil and Natural Gas Sector: Emission Standards for New, Reconstructed, and Modified Sources,” 81 Federal
Register 35824, June 3, 2016.
28 42 U.S.C. §7411(b).
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Process of Rulemaking
The CAA requires the EPA Administrator to address pollutants, fuel or fuel additives, categories
of sources, or classes of vehicles “which, in his judgment, cause or contribute … to air pollution
… which may reasonably be anticipated to endanger public health or welfare.”29 Under the CAA,
the term air pollutant is defined to include “any physical, chemical, biological, radioactive ...
substance or matter which is emitted into or otherwise enters the ambient air.”30 If the
Administrator finds that an air pollutant or combination of air pollutants may reasonably be
anticipated to endanger public health or welfare, this determination is referred to as an
endangerment finding. Multiple CAA sections include EF clauses, which require EPA to address
air pollutants or specific sources of air pollution if the Administrator determines they cause or
contribute to air pollution that may “endanger public health or welfare.”31
The finding that air pollution endangers public health or welfare is one of two distinct procedural
steps in the CAA and federal regulation of air pollutants. The other finding is a cause or
contribution finding that emissions of a pollutant, fuel or fuel additive, or emissions from a
category of sources or class of vehicles, contribute to the air pollution that endangers public
health or welfare.32 In general usage of the term, endangerment finding often refers to the
regulatory action that includes both of these distinct findings: (1) the endangerment to public
health or welfare by the air pollution finding and (2) the cause or contribution to that air pollution
finding. Both findings are necessary for regulatory action.33 If both findings are made, the CAA
requires the Administrator to regulate and set standards for the pollutant, fuel or fuel additive,
category of sources, or class of vehicles.34 In 2009 EPA completed an EF on GHG emissions from
motor vehicles under the authority of CAA Section 202(a).35
When EPA proposes a CAA rule like an EF, CAA Section 307(d) requires EPA to publish a notice
of proposed rulemaking “accompanied by a statement of its basis and purpose.”36 Specifically, an
EF, when finalized, triggers new duties for EPA to promulgate emissions standards and regulate
the pollutant, fuel or fuel additive, category of sources, or class of vehicles that caused or
contributed to the air pollution that triggered the finding. The statement of basis and purpose shall
include a summary of “(A) the factual data on which the proposed rule is based; (B) the
methodology used in obtaining and in analyzing the data; and (C) the major legal interpretations
and policy considerations underlying the proposed rule.”37 In addition, all data, information, and
documents “on which the proposed rule relies shall be included in the docket on the date of
29 The requirement is found in multiple CAA provisions (42 U.S.C. §§7401 et seq.).
30
42 U.S.C. §7602(g). See also Associate Justice of the U.S. Supreme Court John Paul Stevens, U.S. Reports:
Massachusetts v. EPA, 549 U.S. 497, 2006, https://www.loc.gov/item/usrep549497/.
31 These sections include CAA §108, CAA §111, CAA §115, CAA §122, CAA §202, CAA §211, CAA §213, and
CAA §231.
32 The 2009 endangerment and cause or contribution findings are two distinct findings; however, they are often referred
to as the 2009 endangerment finding. EPA, “Endangerment and Cause or Contribute Findings for Greenhouse Gases
Under Section 202(a) of the Clean Air Act,” https://www.epa.gov/climate-change/endangerment-and-cause-orcontribute-findings-greenhouse-gases-under-section-202a.
33 EPA, “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air
Act.” See also Sarah Vican et al., “Foundations of the Endangerment Finding,” Environmental Law Reporter, vol. 55
(August 2025), p. 10359.
34 The requirements are found in multiple CAA provisions (42 U.S.C. §§7401 et seq.).
35 EPA, “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air
Act.” This text provides the basis and the purpose of this EF.
36 42 U.S.C. §7607(d)(3).
37 42 U.S.C. §7607(d)(3).
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publication of the proposed rule.”38 Pursuant to this requirement, EPA has typically included a
technical support document (TSD) that provides further details regarding the agency’s findings.
The TSD includes an overview of the information, studies, peer-reviewed reports,
recommendations, modeling, and other relevant resources relied upon to make the EF.39
2009 Finding That GHGs Endanger Public Health and Welfare
In the first part of the 2009 EF, EPA reviewed scientific evidence and made findings regarding the
connection between GHG-driven changes in climate and the danger of these changes to public
health and public welfare. The EF determined that “elevated atmospheric concentrations of the
well-mixed greenhouse gases may reasonably be anticipated to endanger the public health and
welfare of current and future generations.”40 The 2009 EF determined that human-caused
emissions of six GHGs—carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O),
hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)—were the
primary drivers of current and projected climate change.41 Of the six gases, CO2, which is largely
produced by combustion of fossil fuels, accounts for about 80% of U.S. annual GHG emissions of
the combined group when measured as CO2 equivalents (CO2e).42 EPA defined the air pollutant
for which the EF was made as these six long-lived directly emitted GHGs.43 It explained that
defining an air pollutant as the aggregate group of substances that share common attributes was
similar to the definition of other air pollutants, such as particulate matter and volatile organic
compounds, that are also groupings of multiple similar substances.44
The 2009 EF determined that emissions of these six GHGs had increased the levels of these gases
in the atmosphere, which, in turn, had increased temperature and caused the climate to change.45
Specifically, EPA stated that it found “the scientific evidence linking human emissions and
resulting elevated atmospheric concentrations of the six well-mixed greenhouse gases to observed
global and regional temperature increases and other climate changes to be sufficiently robust and
38 42 U.S.C. §7607(d)(3).
39 See, for example, EPA, “Technical Support Document for Endangerment and Cause or Contribute Findings for
Greenhouse Gases under Section 202(a) of the Clean Air Act,” 2009, https://www.regulations.gov/document/EPA-HQOAR-2009-0171-11645.
40 EPA, 2009 GHG Endangerment Finding, p. 367.
41 EPA, 2009 GHG Endangerment Finding, p. 302.
42 The term CO equivalent (CO e) is used because GHGs vary by global warming potential (GWP). GWP is an index
2
2
developed by the Intergovernmental Panel on Climate Change (IPCC) that allows comparisons of the heat-trapping
ability of different gases over a period of time, typically 100 years. Consistent with international GHG reporting
requirements, EPA’s most recent GHG inventory (with data from 2022) uses the GWP values presented in the IPCC’s
2013 Fifth Assessment Report. For example, based on these GWP values, a ton of methane is 28 times more potent than
a ton of CO2 when averaged over a 100-year time frame. EPA’s inventory is available at EPA, “Inventory of U.S.
Greenhouse Gas Emissions and Sinks,” https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissionsand-sinks.
43 EPA, 2009 GHG Endangerment Finding, p. 499.
44 EPA, 2009 GHG Endangerment Finding, pp. 499-500. EPA stated in this section that the common attributes used in
grouping the six GHGs into a single air pollutant included the following:
The fact that they are all greenhouse gases that are directly emitted (i.e., they are not formed
through secondary processes in the atmosphere from precursor emissions); they are sufficiently
long-lived in the atmosphere such that, once emitted, concentrations of each gas become well
mixed throughout the entire global atmosphere; and they exert a climate warming effect by trapping
outgoing, infrared heat that would otherwise escape to space.
45 EPA, 2009 GHG Endangerment Finding, pp. 308, 310.
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compelling.”46 Further, the Administrator found that these climate changes could potentially
affect “every aspect of human health, society and the natural environment.”47
EPA’s 2009 EF was based on scientific and technical assessments of climate change from the U.S.
Global Change Research Program (USGCRP), the Intergovernmental Panel on Climate Change
(IPCC), and the National Research Council (NRC).48 The 2009 EF stated that it used these three
scientific assessments because they were comprehensive, they were subject to rigorous review,
and they addressed the different stages of the “emissions-to-potential-harm chain necessary for
the endangerment analysis.”49 In making the final endangerment decision, EPA also used its own
emissions data; observational data, such as global temperature datasets from the National
Aeronautics and Space Administration (NASA) and from the National Oceanic and Atmospheric
Administration (NOAA); and information obtained from public comments on the proposal.50
In the 2009 EF, EPA made a finding that “well-mixed greenhouse gas air pollution is reasonably
anticipated to endanger public health, for both current and future generations.”51 The 2009 EF
stated that the Administrator considered how GHG air pollution could endanger public health
through “direct temperature effects, air quality effects, the potential for changes in vector-borne
diseases, and the potential for changes in the severity and frequency of extreme weather
events.”52 Specifically, the 2009 EF concluded the following:
•
•
•
•
Hot temperatures and heat waves are associated with increased mortality, and
global warming is projected to result in increased mortality.53
Climate change is expected to affect U.S. air quality through increases in regional
ozone pollution due to increasing temperatures and weaker circulation.54
Some food- and water-borne diseases are likely to spread under climate change
conditions.55
There are dangers of increased deaths, injuries, infectious diseases, and stressrelated disorders from increases in extreme weather events.56
46 EPA, 2009 GHG Endangerment Finding, p. 369.
47 EPA, 2009 GHG Endangerment Finding, p. 369.
48 EPA, 2009 GHG Endangerment Finding, p. 244. A recent national climate assessment from the U.S. Global Change
Research Program (USGCRP) is the Fifth National Climate Assessment: USGCRP, Fifth National Climate Assessment,
A. R. Crimmins et al., eds., Washington, DC, 2023. A recent climate assessment from the IPCC is the Sixth Climate
Assessment: IPCC, Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth
Assessment Report of the Intergovernmental Panel on Climate Change, H. Lee and J. Romero, eds., Geneva,
Switzerland, 2023, pp. 35-115. The National Research Council is the operating arm of the National Academies of
Sciences, Engineering, and Medicine (NASEM), which published a recent consensus study report on climate change
and its effects: NASEM, Effects of Human-Caused Greenhouse Gas Emissions on U.S. Climate, Health, and Welfare
(The National Academies Press, 2025).
49 EPA, 2009 GHG Endangerment Finding, p. 247.
50 EPA, 2009 GHG Endangerment Finding, pp. 240, 313.
51 EPA, 2009 GHG Endangerment Finding, p. 378 (italics added).
52 EPA, 2009 GHG Endangerment Finding, p. 380.
53 EPA, 2009 GHG Endangerment Finding, p. 381.
54 EPA, 2009 GHG Endangerment Finding, p. 383.
55 EPA, 2009 GHG Endangerment Finding, p. 390. EPA stated, “There will likely be an increase in the spread of
several food and water-borne pathogens among susceptible populations depending on the pathogens’ survival,
persistence, habitat range and transmission under changing climate and environmental conditions.”
56 EPA, 2009 GHG Endangerment Finding, p. 387. EPA stated the following: “The Administrator notes that the
vulnerability to weather disasters depends on the attributes of the people at risk (including where they live, age,
(continued...)
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In addition to its finding about endangerment of public health, in the 2009 EF EPA also made a
finding that “well-mixed greenhouse gas air pollution may reasonably be anticipated to endanger
public welfare, both for current and future generations.”57 The finding included the impacts on
public welfare in six climate-sensitive sectors: food production and agriculture, forestry, water
resources, sea level rise and coastal areas, energy infrastructure and settlements, and ecosystems
and wildlife. Specifically, the EF concluded the following:
•
•
•
•
There may be near-term benefits for agriculture from climate change, but these
effects are uncertain, and long-term climate change effects are likely to be
adverse to agriculture and food production.58
Observed and longer-term risks of the adverse effects of climate change—which
include changes in precipitation patterns; increases in insect, pest, and disease
outbreaks; and the possibility of more frequent extreme weather events—more
than offset near-term beneficial climate impacts for U.S. forestry, which include
the CO2 fertilization effect and elevated temperatures.59
The scientific literature supports the finding that GHG air pollution endangers
water resources now and in the future, putting large areas of national water
supply at risk.60
Sea level is rising and will continue to rise at an increasing rate in the future.61
Further, U.S. coastal cities are at risk from sea level rise and “could have
difficulty coping with the sea level rise projected by the end of the century under
a higher emissions scenario.”62
2009 Finding That Motor Vehicle Emissions Cause and Contribute
to GHG Air Pollution
As noted above, in the first part of the 2009 EF, the Administrator found that GHG air pollution
endangered public health and public welfare. In the second part of the 2009 EF, the cause or
contribution finding, the Administrator found that motor vehicle sources covered under Section
202(a) of the CAA caused or contributed to GHG air pollution.63 The Administrator defined the
GHG air pollution entering the atmosphere through emissions from sources covered by Section
202(a) as consisting of the combination of the same set of six long-lived, well-mixed GHGs
identified as endangering public health and public welfare in the 2009 EF, as described above.64
income, education, and disability) and on broader social and environmental factors (level of disaster preparedness,
health sector responses, and environmental degradation).”
57 EPA, 2009 GHG Endangerment Finding, p. 440 (italics added).
58 EPA, 2009 GHG Endangerment Finding, pp. 449, 451.
59 EPA, 2009 GHG Endangerment Finding, p. 457.
60 EPA, 2009 GHG Endangerment Finding, p. 465. EPA stated, “The Administrator finds that the total scientific
literature provides compelling support for finding that greenhouse gas air pollution endangers the water resources
important for public welfare in the United States, both for current and future generations. The adequacy of water
supplies across large areas of the country is at serious risk from climate change.”
61 EPA, 2009 GHG Endangerment Finding, p. 467.
62 EPA, 2009 GHG Endangerment Finding, p. 467.
63 EPA, 2009 GHG Endangerment Finding, pp. 497, 510.
64 EPA, 2009 GHG Endangerment Finding, p. 116. EPA stated, “The Administrator is defining the ‘air pollution’
referred to in CAA section 202(a) to be the mix of six long-lived and directly-emitted greenhouse gases: carbon dioxide
(CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur
hexafluoride (SF6).”
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The GHGs emitted by motor vehicles—CO2, CH4, N2O, and HFCs—are among the six longlived, well-mixed GHGs.
This cause or contribution finding was based in part on a review of GHG emissions data.65 The
data specific to Section 202(a) sources used for the Administrator’s determination were historical
data for GHG emissions from motor vehicles in the United States for 1990-2007.66 EPA stated
that the relative contribution of Section 202(a)-covered motor vehicles to emissions, as well as
the magnitude of these emissions, were the basis of the cause and contribution determination.
Specifically, it determined the following:
The relative importance of the CAA section 202(a) source categories is central to making
the contribution determination. Both the magnitude of these emissions and the comparison
of these emissions to other sources provide the basis to determine whether the CAA section
202(a) source categories may reasonably be judged as contributing to the air pollution
problem.67
Specifically, EPA noted that the Administrator used two criteria to assess whether motor vehicles
covered under Section 202(a) caused or contributed to GHG air pollution: the contribution of U.S.
motor vehicle emissions (1) as a share of global aggregate GHG emissions and (2) as a share of
U.S. aggregate GHG emissions.68 Regarding the first criterion, EPA found that in 2005 emissions
from U.S. motor vehicles covered under Section 202(a) were responsible for about 4% of total
global well-mixed GHG emissions. Furthermore, EPA found that in 2005 these emissions were
greater than those of whole countries, ranking behind China, the United States (as a whole),
Russia, and India.69 Regarding the second criterion, EPA found that 2005 emissions from U.S.
motor vehicles covered under Section 202(a) were responsible for about 23% of total U.S. wellmixed GHG emissions. Furthermore, EPA found that these emissions were the second-largest
source of emissions in the United States behind electricity generation.70 Based on this analysis,
EPA stated that levels of GHG emissions supported a finding that these sources caused or
contributed to air pollution “that may be reasonably anticipated to endanger public health and
welfare.”71
EPA’s Motor Vehicle GHG Regulations
Because EPA’s 2009 EF referenced cars and light-duty, medium-duty, and heavy-duty trucks as
among the sources that contributed to the GHG emissions that endangered public health and
welfare,72 it served as the mandatory legal trigger that required EPA to regulate GHG emissions
from these sources.73 By formally concluding that these air pollutants endangered public health
65 EPA, 2009 GHG Endangerment Finding, p. 512.
66 EPA, 2009 GHG Endangerment Finding, p. 515.
67 EPA, 2009 GHG Endangerment Finding, p. 517.
68 EPA, 2009 GHG Endangerment Finding, p. 524.
69 EPA, 2009 GHG Endangerment Finding, p. 529.
70 EPA, 2009 GHG Endangerment Finding, p. 533.
71 EPA, 2009 GHG Endangerment Finding, p. 512.
72 According to EPA, “[T]he transportation sources covered under CAA Section 202(a)—the section of the CAA under
which these Findings occur—include passenger cars, light- and heavy-duty trucks, buses, and motorcycles. These
transportation sources emit four key greenhouse gases: carbon dioxide, methane, nitrous oxide, and
hydrofluorocarbons.” EPA, 2009 GHG Endangerment Finding, p. 139.
73 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.”
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and welfare, the agency established the statutory foundation to finalize all subsequent GHG
standards for new motor vehicles and motor vehicle engines covered by CAA Section 202(a).
Following the 2009 EF, EPA issued GHG regulations for passenger vehicles and light-duty,
medium-duty, and heavy-duty trucks.74
EPA promulgated the first GHG emissions standards for passenger vehicles and light-duty trucks
in 2010 and for medium- and heavy-duty trucks in 2011.75 The regulatory actions in 2010 and
2011 established, for the first time, GHG emissions standards for on-road mobile sources. These
regulations, and subsequent GHG emissions standards (as noted in Table 1), set prospective,
fleet-wide average CO2 targets for manufacturers. The 2010 and 2011 regulations covered model
years 2012-2016 and 2013-2018, respectively. EPA later issued regulations in 2012, 2016, 2020,
2021, and 2024 to cover standards for subsequent model years. For passenger cars and light-duty
trucks, the regulation was achieved by setting CO2 target values in grams-per-mile based on the
vehicle’s physical footprint.76 For medium- and heavy-duty trucks, fleet-wide average CO2 targets
were based on work factor and vehicle weight and by averaging the manufacturer’s production to
ensure it would meet the standards for each model year.77 The standards in the regulatory actions
from 2012 through 2024 all followed this standard-setting framework, with increasing stringency
in subsequent iterations. To meet these GHG standards, vehicle manufacturers altered their
engineering, product planning, and compliance strategies. These adjustments focused on a
combination of internal combustion advancements, fleet-wide electrification, and the use of
regulatory flexibilities.78
Table 1 identifies the on-road motor vehicle GHG regulations, provides a brief historical
chronology, and notes the Trump Administration’s action to rescind the 2009 EF, which is
discussed later in this report.
Table 1. EPA On-Road Motor Vehicle Greenhouse Gas (GHG) Regulations
Category of Vehicle
Administrative Findings and GHG Regulation
All
2009 Endangerment and Cause or Contribution Findinga
Passenger Car and Light-Duty
2010 Model Year (MY) 2012-2016 Ruleb
Medium- and Heavy-Duty
2011 Phase I GHG Emissions and Fuel Efficiency Standardsc
Passenger Car and Light-Duty
2012 MY 2017 and Later Ruled
74 EPA mobile source regulations under Title II of the CAA, 42 U.S.C. §§7521 et seq., were largely prospective,
focusing on setting emissions standards for new motor vehicles, engines, and fuels. These regulations established
requirements for manufacturers prior to the production and sale of vehicles. For example, see 42 U.S.C.
§7521(a)(3)(C), Lead Time and Stability.
75 EPA, “Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards;
Final Rule,” 75 Federal Register 25324, May 7, 2010. EPA, “Greenhouse Gas Emissions Standards and Fuel
Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles,” 76 Federal Register 57106, September 15,
2011.
76 86 Federal Register 74440, December 30, 2021.
77 Work factor is defined at 40 C.F.R. §86.1803-01. See also 40 C.F.R. §86.1818-12 for GHG emissions standards for
passenger vehicles and light-duty trucks; 40 C.F.R §86.1818-12(c) explains the methodology for obtaining fleet
average calculations for passenger vehicles and light-duty trucks. See 40 C.F.R. §86.1819-14 for GHG emissions
standards for medium- and heavy-duty trucks; 40 C.F.R. §86.1819-14(a) explains the methodology for obtaining fleet
average calculations for medium- and heavy-duty trucks.
78 These flexibilities included items such as improved air conditioning systems and off-cycle credits (such as engine
start-stop systems, solar reflective paint, and high-efficiency alternators). For more information, see EPA, “EPA and
NHTSA Set Standards to Reduce Greenhouse Gases and Improve Fuel Economy for Model Years 2017-2025 Cars and
Light Trucks,” August 2012, https://nepis.epa.gov/Exe/ZyPDF.cgi/P100EZ7C.PDF?Dockey=P100EZ7C.pdf.
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Category of Vehicle
Administrative Findings and GHG Regulation
Medium- and Heavy-Duty
2016 Phase 2 GHG Emissions and Fuel Efficiency Standardse
Passenger Car and Light-Duty
2020 SAFE Final Rule for MY 2021-2026f
Passenger Car and Light-Duty
2021 Revised MY 2023 and Later Ruleg
Passenger Car, Light- and Medium-Duty
2024 Multi-Pollutant Rule MY 2027 and Laterh
Heavy-Duty
2024 Phase 3 GHG Emissions Standardsi
All
2026 Rescission of the 2009 GHG EF and Motor Vehicle GHG
Emissions Standardsj
Source: Prepared by CRS, based on various U.S. Environmental Protection Agency (EPA) motor vehicle
regulations.
a. EPA, “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the
Clean Air Act,” 74 Federal Register 66496, December 15, 2009.
b. EPA, “Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy
Standards; Final Rule,” 75 Federal Register 25324, May 7, 2010.
c. EPA, “Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty
Engines and Vehicles,” 76 Federal Register 57106, September 15, 2011.
d. EPA, “2017 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average
Fuel Economy Standards,” 77 Federal Register 62624, October 15, 2012.
e. EPA, “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and
Vehicles—Phase 2,” 81 Federal Register 73478, October 25, 2016.
f.
EPA, “The Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule for Model Years 2021–2026 Passenger Cars
and Light Trucks,” 85 Federal Register 24174, April 30, 2020.
g. EPA, “Revised 2023 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions Standards,” 86
Federal Register 74434, December 30, 2021.
h. EPA, “Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty
Vehicles,” 89 Federal Register 27842, April 18, 2024. The 2024 regulation included medium-duty vehicles
along with passenger and light-duty vehicles.
i.
EPA, “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles—Phase 3,” 89 Federal Register 29440,
April 22, 2024. Note the Phase 1 and Phase 2 regulations covered medium- and heavy-duty vehicles,
whereas the Phase 3 regulation covered heavy-duty vehicles with minor changes to medium-duty vehicles.
j.
EPA, “Rescission of the Greenhouse Gas Endangerment Finding and Motor Vehicle Greenhouse Gas
Emission Standards Under the Clean Air Act,” 91 Federal Register 7686, February 18, 2026.
EPA’s Rescission of the 2009 Endangerment Finding
On January 20, 2025, President Trump issued Executive Order (E.O.) 14154, entitled
“Unleashing American Energy.” Paragraph (f) of E.O. 14154 states the following:
Within 30 days of the date of this order, the Administrator of the EPA, in collaboration
with the heads of any other relevant agencies, shall submit joint recommendations to the
Director of OMB on the legality and continuing applicability of the Administrator’s
findings, “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under
Section 202(a) of the Clean Air Act,” Final Rule, 74 FR 66496 (December 15, 2009).79
On August 1, 2025, EPA proposed and on February 16, 2026, EPA finalized the rescission of the
2009 EF and motor vehicle GHG standards under the CAA, as set out in E.O. 14154.80 EPA noted
79 Executive Order 14154, “Unleashing American Energy,” 90 Federal Register 8353, January 20, 2025.
80 EPA, “Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards,” 90 Federal
Register 36288, August 1, 2025; EPA, 2026 GHG EF and Motor Vehicle Standards Rescission.
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that, following these regulatory amendments, engine and vehicle manufacturers are relieved of all
prospective obligations regarding the measurement, control, and reporting of GHG emissions for
any highway engine or vehicle, including those produced in model years preceding this final rule.
In its final rule, EPA made several arguments to support its action. Specifically, EPA concluded
that “Section 202(a) of the CAA does not provide EPA statutory authority to prescribe motor
vehicle emission standards for the purpose of addressing global climate change concerns.”81 EPA
argued that in the absence of such authority, the 2009 EF is not valid and EPA cannot retain the
GHG regulations that resulted from it.82 In addition, EPA concluded that Congress never intended
to give EPA authority to impose GHG regulations for cars and trucks.83
Furthermore, EPA determined that GHG emissions standards for new motor vehicles and engines
“do not impact in any material way the public health and welfare concerns identified in the
Administrator’s prior findings in 2009.”84 EPA contended that its regulations of GHGs from
motor vehicles and engines have “not and cannot have any material impact on global climate
change concerns, rendering them futile and providing another basis for” the rescission of the 2009
EF.85 EPA did not include a technical support document (TSD) for its repeal of the 2009
endangerment finding rulemaking in the rulemaking docket.
EPA’s Regulatory Impact Analyses for GHG
Regulations
As part of its rulemakings, EPA produced regulatory impact analyses (RIAs) that estimated the
change in GHG emissions, the compliance costs, and the societal benefits for motor vehicle GHG
regulations and their rescission for the period 2027-2055.86 Cost-benefit analyses are presented in
RIAs, which are generally part of a rulemaking docket.87 The estimates for the GHG regulations
were reported in the 2024 RIA for light-duty and medium-duty motor vehicles and in the 2024
RIA for heavy-duty motor vehicles. The estimates for the rescission of the GHG regulations were
reported in the 2026 RIA for GHG EF and motor vehicle standards rescission. The RIAs up to
and including the 2024 rulemaking typically included monetized estimates for the climate and
health impacts of regulating GHG emissions; however, the RIA for the 2026 rulemaking
rescinding the EF did not include these estimates.
81 EPA, “Fact Sheet: Legal; Final Rule: Rescission of the Greenhouse Gas Endangerment Finding and Motor Vehicle
Greenhouse Gas Emission Standards Under the Clean Air Act,” EPA 420-F-26-003, February 2026,
https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P101HV00.pdf (hereinafter EPA, 2026 EF Rescission Fact Sheet).
82 EPA, 2026 EF Rescission Fact Sheet.
83 EPA, 2026 EF Rescission Fact Sheet.
84 EPA, 2026 GHG EF and Motor Vehicle Standards Rescission, p. 3.
85 EPA, 2026 EF Rescission Fact Sheet.
86 EPA has prepared cost and benefit estimates for all economically significant rules since the Carter Administration.
See the Carter Administration order, Executive Order 12044, “Improving Government Regulations,” March 23, 1978,
http://www.thecre.com/pdf/12044.PDF. The methodologies for the determination of costs and benefits of CAA
regulations by EPA is complex, with varying estimates depending on parameters used in the estimation and modeling
processes. A detailed discussion of regulatory cost estimates under the CAA is beyond the scope of this report. For
further information, see EPA, “Economic and Cost Analysis for Air Pollution Regulations,” updated May 26, 2026,
https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations.
87 Sometimes also referred to as economic impact analyses (EIA). EPA, “Regulatory Impact Analyses for Air Pollution
Regulations,” https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/regulatory-impact-analysesair-pollution.
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The latest EPA projections of the effects of GHG regulations on the motor vehicle sector from
their respective RIAs and rulemakings are presented in Table 2 below. The table includes the
estimated change in cumulative GHG emissions and the net monetized benefits associated with
the motor vehicle GHG regulations and their rescission for the years 2027-2055. As shown in
Table 2, according to EPA, the 2024 rulemakings would have decreased GHG emissions (relative
to a baseline in which these rules were not in place), whereas the 2026 rulemaking would increase
GHG emissions (relative to the baseline in which the 2024 rules were in place). The estimated
cumulative increase in GHG emissions of 8,300 million metric tons (MMT) of CO2e projected to
occur with the rescission approximately reverses the estimated cumulative decrease in GHG
emissions of 8,225 MMT CO2e that was projected to occur if the 2024 motor vehicle rules had
remained in place. Also as shown in Table 2, each of the RIAs found that the agency’s action,
including promulgating the rules in 2024 and rescinding them in 2026, would have net positive
monetized benefits. However, the RIAs used different approaches to calculating benefits, which
makes the estimates difficult to compare, as discussed below.
Table 2. Estimated Regulatory Impact of Motor Vehicle Greenhouse Gas (GHG)
Regulations
Regulatory
Impact Time
Period
Estimated Change in
Cumulative GHG
Emissions Compared to
Baselinea
Net Monetized
Benefitsb
2024 Light-Duty and Medium-Duty Motor
Vehicles Model Year 2027 and Laterc
2027-2055
-7,200 MMT CO2e
$2,000d
2024 Heavy-Duty Motor Vehicles Model
Year 2027 and Latere
2027-2055
-1,025 MMT CO2e
$280f
2026 GHG Endangerment Finding and All
Motor Vehicle Standards Rescissiong
2027-2055
8,300 MMT CO2e
From -$180 to
$920h
EPA Rulemaking
Source: EPA, RIA documents for each respective sector.
Notes: MMT = million metric tons. The combined influence of all six GHGs included in the finding (CO2, CH4,
N2O, SF6, HFCs, and PFCs) may be determined by normalizing the global warming potentials of the GHGs to the
global warming potential of carbon dioxide (CO2). This results in a metric of carbon dioxide equivalent (CO2e)
to compare across various GHGs.
a. A negative number indicates a reduction in emissions, and a positive number indicates an increase in
emissions. Total GHG emissions for the U.S. transportation sector for 2022 were approximately 1,808
MMT CO2e (EPA, “Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2022,” EPA 430-R-24-004,
2024). EPA assumed the baseline to be a no-action scenario (for example, the baseline for the 2024
rulemakings was a scenario where EPA did not finalize its Model Year 2027 and Later regulations, and the
2026 rulemaking baseline was a scenario where the 2024 rulemakings were not rescinded).
b. In billions of dollars over the regulatory impact time period. Based on scenarios with a 3% discount rate per
the Office of Management and Budget’s (OMB's) Circular A-94, “Guidelines and Discount Rates for BenefitCost Analysis of Federal Programs,” https://www.whitehouse.gov/wp-content/uploads/2023/11/CircularA94.pdf. The RIAs also include estimated costs and benefits under scenarios with 2% and 7% discount rates,
which are not shown here.
c. EPA, “Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty
Vehicles,” 89 Federal Register 27842, April 18, 2024; see Table 8-25, p. 8-49, and Table 9-19, p. 9-22.
d. Billions of 2022 dollars. These benefits are due to a calculation summing the climate change mitigation
benefits and health benefits associated with reductions in other air pollutants minus the cost of
implementing the rule.
e. EPA, “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles: Phase 3 Regulatory Impact Analysis,”
Table 4-39, p. 627, and Table 8-8, p. 816, 2024.
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f.
g.
h.
Billions of 2022 dollars. These benefits are due to a calculation summing the climate change mitigation
benefits and health benefits associated with reductions in other air pollutants minus the cost of
implementing the rule.
EPA, “Rescission of the Greenhouse Gas Endangerment Finding and Motor Vehicle Greenhouse Gas
Emission Standards Under the Clean Air Act,” 91 Federal Register 7757, February 18, 2026; see Tables 14
and 18, p. 815.
Billions of 2024 dollars. The range encompasses the highest estimate and the lowest estimate among the
four scenarios EPA modeled, which ranged from a net cost of $180 billion to a net benefit of $920 billion.
All scenarios assumed all GHG regulations were rescinded. Scenario one used fuel prices from U.S. Energy
Information Administration’s (EIA’s) Annual Energy Outlook (AEO) 2025. Scenario two assumed oil costs
dropped to $47 per barrel. Scenarios three and four are similar to one and two, but did not consider fuel
costs after two-and-a-half years. None of the scenarios removed the non-GHG air pollutant standards that
were finalized in the 2024 rulemakings noted in the table.
EPA estimates costs and benefits in monetary terms using a process known as monetization.88 In
monetization, EPA assigns a dollar value to the costs and the benefits that the regulated industry
and the public would experience as a result of its rulemaking. Costs in the 2024 RIAs included
vehicle technology costs, repair and maintenance costs, and insurance costs, among other
associated costs.89 Benefits in the 2024 RIAs included fuel saving benefits, energy security
benefits, climate change mitigation benefits, and fine particulate matter (PM2.5) reduction health
benefits, among other associated benefits.90 In the 2026 RIA for the rescission, net monetized
costs included fuel costs, repair and maintenance costs, insurance costs, congestion costs, and
energy security and refueling costs.91 Net monetized benefits in the RIA included vehicle
technology benefits, as well as electric vehicle supply equipment and replacements benefits.92
Each of these RIAs estimated net benefits as the total monetized benefits minus the total
monetized costs of the rulemaking.93
Although both the 2024 RIAs for the GHG regulations and the 2026 RIA for their rescission
monetized costs and benefits, their estimates of net benefits are difficult to compare. This is
because they took different approaches toward whether or not to monetize the climate and the
public health effects from changes in emissions. In the 2024 RIAs, EPA monetized the climate
change mitigation benefits and public health benefits of emissions reductions resulting from its
88 EPA, “Chapter 7: Analyzing Benefits,” in Guidelines for Preparing Economic Analyses—Third Edition, EPA-240-R-
24-001, 2024.
89 EPA, “Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty
Vehicles: Regulatory Impact Analysis,” EPA-420-R-24-004, 2024, Table 9-19, p. 9-22 (hereinafter EPA, RIA for LD
and MD MY 2027 and Later); EPA, “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles: Phase 3
Regulatory Impact Analysis,” EPA-420-R-24-006, 2024, Table 8-8, p. 816 (hereinafter EPA, RIA for HD MY 2027
and Later).
90 EPA, RIA for LD and MD MY 2027 and Later, Table 9-19, p. 9-22 and Table 8-8, p. 816. According to EPA, the
climate impacts associated with GHGs included “changes in net agricultural productivity, human health effects,
property damage from increased flood risk and natural disasters, disruption of energy systems, risk of conflict,
environmental migration, and the value of ecosystem,” and the benefits are realized in “avoiding that increase” in
GHGs. EPA also noted that “exposure to pollutants such as PM2.5 … are linked to adverse environmental and human
health impacts, such as premature deaths and non-fatal illnesses. Reducing human exposure to these pollutants results
in significant and measurable health benefits.” EPA, “Multi-Pollutant Emissions Standards for Model Years 2027 and
Later Light- Duty and Medium-Duty Vehicles,” 89 Federal Register 27842, April 18, 2024.
91 EPA, RIA for the Rescission of the EF, Table A-1, p. 28.
92 EPA, RIA for the Rescission of the EF, Table A-1, p. 28. Vehicle technology benefits refer to the advanced
machinery and software requirements of an electric vehicle in comparison to a fossil-fuel-powered vehicle. The supply
equipment refers to the hardware and safety technology needed to connect an electric vehicle to a power source.
93 EPA, RIA for LD and MD MY 2027 and later, Table 9-19, p. 9-22; Table 9-20, p. 9-23; Table 9-21, p. 9-24. Also see
EPA, RIA for HD MY 2027 and Later, Table 8-8, p. 816.
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GHG regulations.94 EPA used estimates of the Social Cost of GHGs (SC-GHG) to estimate the
climate change mitigation benefits of reductions in GHG emissions.95 In addition to GHGs, motor
vehicles emit PM2.5 and ozone-forming volatile organic compounds (VOCs).96 PM2.5 and groundlevel ozone can increase rates of respiratory illness and fatalities, and emissions of these
substances are reduced when motor vehicle emissions are reduced. As a consequence, reductions
in PM2.5 and ozone exposures account for a large portion of the monetized benefits for GHG
regulations. To monetize the public health benefits of reducing these pollutants, EPA used a
benefit-per-ton dollar value.97
In the RIA for the rescission, by contrast, EPA did not monetize the public health effects of
emissions increases associated with the rulemakings. In making this determination, EPA
“acknowledged significant uncertainties related to monetized PM2.5 and ozone impacts” and noted
that it was “considering various techniques for characterizing the uncertainty in such estimates.”98
It further stated that due to the “significant impacts of environmental regulations on the U.S.
economy, it is essential that the Agency have confidence in the estimated benefits of an action
prior to utilizing these estimates in a regulatory context.”99 In addition, the 2026 RIA did not
monetize the public health effects resulting from climate change associated with increased
emissions. It noted in the draft RIA that “the accuracy of previous assumptions about links
between worldwide emissions and future climate bears little relationship to the fact that these are
proper ingredients of benefit-cost analysis.”100
The RIAs for the 2024 GHG regulations and the 2026 RIA for their rescission also differed in
other ways. For example, in the scenarios modeled for the rescission, EPA reflected the changes
to the IRA tax credits, removed California’s Advanced Clean Truck rule, reduced battery electric
vehicle acceptance levels, and updated the costs of particulate filters. The 2024 RIAs, by contrast,
were completed before the IRA tax credits were terminated by OBBBA, and therefore made
different assumptions. In the 2026 RIA EPA also included reduced fuel costs in some of the
modeled scenarios and concluded a net benefit in monetary terms for three of the four scenarios
modeled for the rulemaking, as noted in Table 2.101
94 EPA’s RIAs typically discuss the monetized benefits associated with emissions reductions. For more information and
a list of various RIAs, see EPA, “Regulatory Impact Analyses for Air Pollution Regulations,” https://www.epa.gov/
economic-and-cost-analysis-air-pollution-regulations/regulatory-impact-analyses-air-pollution. See also EPA,
“Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards; Draft Regulatory Impact
Analysis,” Appendix A, p. 33, https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P101HKBB.pdf (hereinafter EPA, DRIA
for the Reconsideration of the EF).
95 EPA, RIA for HD MY 2027 and Later, “6.2 Climate Benefits,” p. 6-6; EPA, RIA for HD MY 2027 and Later, “5.2
Climate Benefits,” p. 660.
96 EPA, “Smog, Soot, and Other Air Pollution from Transportation,” https://www.epa.gov/transportation-air-pollutionand-climate-change/smog-soot-and-other-air-pollution-transportation. See also EPA, “Ground-Level Ozone Basics,”
https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics#:~:text=air%20emission%20sources.,How%20does%20ground%2Dlevel%20ozone%20form?,can%20experience%20high%20ozone%20levels.
97 EPA, “Sector-Based PM and Ozone Benefit Per Ton Estimates,” https://www.epa.gov/benmap/sector-based-pm252.5
and-ozone-benefit-ton-estimates.
98 EPA, “New Source Performance Standards Review for Stationary Combustion Turbines and Stationary Gas
Turbines,” 91 Federal Register 1964, January 15, 2026, p. 34: “The EPA is no longer monetizing benefits from PM2.5
and ozone but will continue to quantify the emissions.”
99 EPA, “New Source Performance Standards Review for Stationary Combustion Turbines and Stationary Gas
Turbines,” 91 Federal Register 1964, January 15, 2026. EPA, “National Emission Standards for Hazardous Air
Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units: Final Repeal,” 91 Federal Register 9112,
February 24, 2026. Also see EPA, 2026 GHG EF and Motor Vehicle Standards Rescission, p. 816.
100 EPA, DRIA for the Reconsideration of the EF, Appendix A, p. 33.
101 EPA, RIA for the Rescission of the EF, Appendix A, pp. 26-32.
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Considerations for Congress
Given the importance of the EPA rules to public health, the U.S. economy, and the environment,
Congress has shown a continuing interest in the EPA EF. If Congress is not satisfied with the
status quo, it has several potential options to make changes. Congress may also choose not to act
on the current situation regarding the EPA EF.
Congress may choose from a range of legislative options with respect to the GHG EF. Broadly
speaking, these options may entail providing EPA with specific statutory instruction on whether
or how to regulate GHGs under the CAA.
One option is for Congress to pass legislation regarding the 2009 EF or its 2026 rescission.
Members of Congress who support the 2009 EF could seek to overturn its 2026 rescission under
the Congressional Review Act. Some Members of Congress have supported the 2009 EF and
have opposed its reevaluation or repeal, stating, “Disabling that ‘endangerment finding’ would
cripple the Agency’s ability to regulate carbon pollution under the Clean Air Act.”102 In recent
months, some Members of Congress have expressed concern regarding, and opposition to, the
Trump Administration’s decision to rescind the 2009 EF. For example, Members from both the
House and Senate have sent letters to EPA Administrator Lee Zeldin expressing “grave concern”
and opposition to rescinding the 2009 EF.103
Alternatively, Members of Congress who oppose the 2009 EF could seek to pass legislation to
codify its 2026 rescission. When EPA finalized the 2009 EF, some Members of Congress
criticized the process, pace, and data sources used in development of the 2009 EF and raised
“very serious concerns” about the process for developing the EF.104 Other Members have
expressed support for EPA’s repeal of the EF.105 In the 111th Congress, Members introduced
resolutions disapproving of the 2009 EF and urging the EPA Administrator to reevaluate the
102 Sen. Sheldon Whitehouse, “Climate Change,” remarks in the Senate, Congressional Record, vol. 168, no. 61, April
6, 2022, p. S2025.
103 Sustainable Energy and Environment Coalition (SEEC), “SEEC Condemns Trump Administration’s Unlawful
Attack on EPA Endangerment Finding,” press release, February 27, 2025, https://seec.house.gov/media/press-releases/
seec-condemns-trump-administrations-unlawful-attack-epa-endangerment-finding. See also U.S. Senate Committee on
Environment and Public Works (EPW), “Whitehouse Opening Statement at Hearing to Consider Fotouhi, Szabo for
EPA,” https://www.epw.senate.gov/public/index.cfm/2025/3/whitehouse-opening-statement-at-hearing-to-considerfotouhi-szabo-for-epa. For a copy of the letter, see EPW, “Letter to EPA RE: Endangerment,”
https://www.epw.senate.gov/public/_cache/files/7/6/76dff0b6-7f0e-4f8a-95a9-5d364b0a91d6/
DA82892DE0D05AC11896AFD0BB6E8CEF29D2CC4221FF20DFEB34F1879B59EBB6.2.28.2025-letter-to-epa-reendangerment-finding.pdf.
104 Rep. Michael Burgess, “Providing for Consideration of H.R. 806, Ozone Standards Implementation Act of 2017,”
remarks in the House, Congressional Record, vol. 163, no. 121, July 18, 2017, p. H5932. See also Sen. James Inhofe,
“Cap-and-Trade,” remarks in the Senate, Congressional Record, vol. 156, no. 88, June 14, 2010, p. S4874.
105 Committee on Science Space and Technology (SST), “Chairman Babin Applauds White House Decision to Repeal
2009 Endangerment Finding,” press release, February 12, 2026, https://science.house.gov/press-releases?ID=
C2495D60-D3EC-4C52-ABD2-427B14F8E061. See also Rep. Troy A. Carter Sr., “Congressman Carter Statement on
EPA Abolishing the Endangerment Finding, Leaving Americans Vulnerable to Pollution and the Climate Crisis,” press
release, February 12, 2026.
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finding.106 None of the resolutions passed in either the House or the Senate.107 In the 111th
Congress, Members also introduced legislation to repeal the 2009 EF finding so it would have no
legal effect, but none of this legislation became law.108
A second option is for Congress to pass legislation regarding the status of GHGs under the CAA
that would remove the requirement for a GHG EF. Specifically, Members who support the
regulation of GHGs under the CAA could seek to pass legislation declaring that GHGs are air
pollutants under the CAA or that GHGs endanger public health and welfare. Legislation was
introduced in the 118th Congress defining GHGs as “air pollutants” under Section 302(a) of the
CAA (H.R. 9319). This bill did not become law.
Alternatively, Members who oppose the regulation of GHGs under the CAA could seek to pass
legislation stating that GHGs are not air pollutants subject to the CAA or that they do not
endanger public health or welfare. For example, legislation to exclude the GHGs carbon dioxide,
water vapor, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, or sulfur
hexafluoride from the statutory definition of “air pollutant” under Section 302(a) of the CAA was
introduced in the 115th Congress (H.R. 637). Relatedly, legislation to exclude GHGs from the
statutory definition of “air pollutant” under Section 302(a) of the CAA, except for purposes other
than addressing climate change concerns, was introduced in the 112th Congress (S. 482 and H.R.
910, among others). Neither of these bills became law.
Congress also has options with respect to its oversight authority over the process of rulemaking
and the repeal of the 2009 EF. In the oversight process, Congress may seek to determine the
effects of these regulations, or of the rescission of these regulations, on GHG emissions, on health
and welfare, and on the costs and benefits to industry and consumers. For example, EPA has
stated that it is “considering various techniques for characterizing the uncertainty” in estimates of
health effects.109 Congress may request EPA to undertake an RIA of the rescission that includes
monetizing the effects of the rulemaking on public health, public welfare, and the climate.110 In
addition, for the 2026 rescission rulemaking, EPA modeled scenarios with stable or declining oil
prices and modeled oil prices for a period of two-and-a-half years into the future. Congress may
106 On December 15, 2009, Rep. Rodney Alexander introduced H.Res. 974, “Urging the Administrator of the
Environmental Protection Agency to reevaluate the endangerment and cause or contribute findings regarding
greenhouse gases signed on December 7, 2009.” On January 21, 2010, Sen. Lisa Murkowski introduced S.J.Res. 26, “A
joint resolution disapproving a rule submitted by the Environmental Protection Agency relating to the endangerment
finding and the cause or contribute findings for greenhouse gases under Section 202(a) of the Clean Air Act.” Other
Members of Congress also introduced resolutions to reevaluate the EF. CRS was not able to find congressional
resolutions in support of the 2009 EF.
107 See “All Actions” tab, H.Res. 974, 111th Congress (2009-2010), https://www.congress.gov/bill/111th-congress/
house-resolution/974/all-actions?overview=closed#tabs. See also “All Actions” tab, H.J.Res. 66, 111th Congress (20092010), https://www.congress.gov/bill/111th-congress/house-joint-resolution/66/all-actions?overview=closed#tabs. See
also “All Actions” tab, S.J.Res. 26, 111th Congress (2009-2010), https://www.congress.gov/bill/111th-congress/senatejoint-resolution/26/all-actions. See also “All Actions” tab, H.J.Res. 76, 111th Congress (2009-2010),
https://www.congress.gov/bill/111th-congress/house-joint-resolution/76/all-actions?overview=closed#tabs. See also
“All Actions” tab, H.J.Res. 77, 111th Congress (2009-2010), https://www.congress.gov/bill/111th-congress/house-jointresolution/77/all-actions?overview=closed#tabs.
108 For example, H.R. 3409 and S. 1720.
109 EPA, “New Source Performance Standards Review for Stationary Combustion Turbines and Stationary Gas
Turbines,” 91 Federal Register 1964, January 15, 2026. See also EPA, “National Emission Standards for Hazardous
Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units: Final Repeal,” 91 Federal Register 9112,
February 24, 2026; and EPA, 2026 GHG EF and Motor Vehicle Standards Rescission, p. 816.
110 EPA, “New Source Performance Standards Review for Stationary Combustion Turbines and Stationary Gas
Turbines,” 91 Federal Register 1964, January 15, 2026, p. 34: “The EPA is no longer monetizing benefits from PM2.5
and ozone but will continue to quantify the emissions.”
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request EPA model scenarios with changes in oil prices that include potential price increases and
that include oil costs for longer time periods. This discussion of congressional oversight is
illustrative and should not be considered a comprehensive description of the range of potential
congressional oversight actions.
Congress could also address the rescission of the EF through appropriations. Congress could
restrict funding for rescission of the 2009 EF and the repeal of GHG motor vehicle regulations, or
alternatively, could appropriate additional funds to expedite these processes. In the past,
legislation was introduced in the 116th Congress to prohibit funding for the implementation of the
2009 EF (H.Rept. 116-119). This legislation did not become law. The potential options for
legislation and oversight described in this section are examples and are not necessarily a
comprehensive listing.
Author Information
Jonathan D. Haskett
Analyst in Environmental Policy
Omar M. Hammad
Analyst in Environmental Policy
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
shared staff to congressional committees and Members of Congress. It operates solely at the behest of and
under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other
than public understanding of information that has been provided by CRS to Members of Congress in
connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not
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This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.