Contents

• Introduction
• EPA's 2009 Endangerment Finding
• Process of Rulemaking
• 2009 Finding That GHGs Endanger Public Health and Welfare
• 2009 Finding That Motor Vehicle Emissions Cause and Contribute to GHG Air Pollution
• EPA's Motor Vehicle GHG Regulations
• EPA's Rescission of the 2009 Endangerment Finding
• EPA's Regulatory Impact Analyses for GHG Regulations
• Considerations for Congress

Summary

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.

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 heavy-duty 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.

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 119^th 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 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.

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 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.

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 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 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 stress-related disorders from increases in extreme weather events.⁵⁶

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 The GHGs emitted by motor vehicles—CO₂, CH₄, N₂O, and HFCs—are among the six long-lived, 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. well-mixed 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 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.

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 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.

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.

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 (PM_2.5) 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 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 PM_2.5 and ozone-forming volatile organic compounds (VOCs).⁹⁶ PM_2.5 and ground-level 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 PM_2.5 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 PM_2.5 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

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 111^th Congress, Members introduced resolutions disapproving of the 2009 EF and urging the EPA Administrator to reevaluate the finding.¹⁰⁶ None of the resolutions passed in either the House or the Senate.¹⁰⁷ In the 111^th 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 118^th 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 115^th 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 112^th 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 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 116^th 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.

Footnotes