On July 29, the Environmental Protection Agency (EPA) formally proposed to revoke its 2009 “Endangerment Finding,” in which the EPA declared that greenhouse gases contribute to air pollution and endanger public health. This determination has served as the legal prerequisite for the EPA’s regulation of greenhouse gas emissions from cars, power plants and other industrial sources pursuant to the Clean Air Act (CAA). If upheld in court, this revocation could lead to significant rollbacks of regulations aimed at implementing climate change policy.
This memo will provide an overview of the 2009 Endangerment Finding and how it came to be. It will also evaluate the Trump administration’s proposal, outlining the EPA’s justification for reconsidering the Endangerment Finding and assessing its alternative conclusions. The memo will then evaluate the proposal’s legal implications.
Legal Background
In 1999, a group of private organizations filed a rulemaking petition to request that the EPA regulate greenhouse gases from new motor vehicles pursuant to the CAA. In 2003, the EPA denied the rulemaking petition, arguing that despite opinions put forth by two former general counsels that the EPA had the power to regulate carbon dioxide and other greenhouse gases, the CAA did not provide such authority because greenhouse gases do not satisfy the CAA definition of “air pollutants,” and are not, therefore, included in the statutory directive to prescribe standards for the emission of “any air pollutant” from motor vehicles. The EPA also contended that even if the CAA did authorize regulations to address greenhouse gas emissions from motor vehicles, doing so was “not appropriate” at the time.
In 2005, Massachusetts Attorney General Martha Coakley led a challenge in the U.S. Court of Appeals for the D.C. Circuit (“D.C. Circuit”) against the EPA for denying this rulemaking petition, seeking to have the EPA regulate carbon dioxide, methane, nitrous oxide and hydrofluorocarbons under the CAA. Environmental groups, three cities, an American territory and the state attorneys general from California, Connecticut, Illinois, Maine, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont and Washington joined the multistate coalition (collectively, the petitioners).
The D.C. Circuit rejected the legal challenge, upholding the EPA’s decision to deny the petition for rulemaking. In its ruling, the D.C. Circuit noted that CAA Section 202(a)(1) authorizes the EPA Administrator to prescribe standards applicable to emissions from new motor vehicles or engines that “in his judgment” cause, or contribute to, air pollution and could be anticipated to “endanger public health or welfare.” The D.C. Circuit ruled that this language gave the EPA Administrator significant discretion over whether to regulate, adding that Congress does not require the EPA Administrator to exercise this discretion “solely on the basis of his assessment of scientific evidence.”
The petitioners sought review of this rejection in the Supreme Court, presenting the following two questions:
- Whether the EPA Administrator has authority to regulate carbon dioxide and other air pollutants associated with climate change under Section 202(a)(1); and
- Whether the EPA Administrator may decline to issue emission standards for motor vehicles based on policy considerations not enumerated in Section 202(a)(1).
The petitioners’ opening brief argued in the affirmative and in the negative on the first and second questions, respectively. First, the petitioners argued that the EPA has the authority to regulate greenhouse gases under Section 202(a)(1) because the chemicals at issue—carbon dioxide, methane, nitrous oxide and hydrofluorocarbons—were indeed the “air pollutants” referred to in the CAA. The petitioners also contended that the EPA erred in finding that previous legislative proposals expressed a congressional intent to forbid the EPA from regulating air pollutants associated with climate change under Section 202(a)(1).
Second, the petitioners argued that the EPA could not decline to regulate emissions standards for motor vehicles based on other policy considerations not mentioned in the CAA because the cited policy considerations were irrelevant under the statutory language or failed to take account of the statutory endangerment standard.
In its denial of the original rulemaking petition and on appeal to the Supreme Court, the EPA argued that it exercised reasonable discretion in determining that, even if it possessed statutory authority in this sphere, it could decline to exercise that authority at the present time, highlighting, for example, its alternative role in advancing fuel cell vehicles and hydrogen fuel technologies. It also argued that it was already taking a number of other actions to address climate change and suggested it could not do so via the transportation sector without “raising unusually significant economic and political issues” that “Congress has specifically addressed … in other statutes,” citing FDA v. Brown & Williamson Tobacco Corp., 529 U.S. 120 (2000) as support. In Brown & Williamson, the Supreme Court held that Congress had not given the Food and Drug Administration (FDA) authority to regulate tobacco products as customarily marketed. Relying on the principle of Chevron deference, the Supreme Court reasoned, inter alia, that the history of tobacco-specific legislation demonstrated that Congress had spoken directly to the FDA’s authority to regulate tobacco products, creating a specific regulatory scheme for addressing the problem of tobacco and health. As to the rulemaking petition, the EPA therefore analogized that because Congress had specifically addressed the subject of global climate change in legislation enacted outside the CAA framework, the EPA was precluded from regulating vehicle carbon dioxide and other greenhouse gas emissions under Section 202.
Ultimately, the petitioners urged the court to reject the EPA’s reliance on Brown & Williamson and argued the policy judgments the EPA relied upon were irrelevant to the CAA. Instead, the petitioners emphasized that the trigger for regulatory action under the CAA is whether the sources “may reasonably be anticipated to endanger public health or welfare.”
Massachusetts v. EPA
On April 2, 2007, by a 5-4 vote, the Supreme Court ruled in favor of the petitioners. The Supreme Court held that Massachusetts had standing to challenge the EPA’s denial of the rulemaking petition because the EPA’s refusal to regulate greenhouse gas emissions from motor vehicles under the CAA presented a risk of harm to Massachusetts from a rise in sea levels associated with global warming that was both actual and imminent, and there was a substantial likelihood that the EPA could reduce that risk by undertaking the requested rulemaking.
The Supreme Court also ruled that greenhouse gases fit the CAA’s definition of “air pollutant,” thereby imposing a duty upon the EPA to regulate emissions of such gases. The Supreme Court also noted that the EPA did not identify any evidence that Congress meant to curtail the EPA’s authority to treat greenhouse gases as air pollutants, rejecting the EPA’s claim of congressional intent to narrow the EPA’s regulatory power under the CAA.
Lastly, the Supreme Court disagreed with the EPA’s argument that it would be unwise to regulate greenhouse gas emissions under the CAA even if the EPA had authority to do so. The EPA suggested regulation of motor vehicle greenhouse gas emissions could weaken efforts to persuade developing countries to reduce emissions, interfere with the president’s ongoing policy efforts to address climate change, and result in an “inefficient, piecemeal approach.” To this, the Supreme Court clarified that the CAA does authorize the EPA Administrator to forgo prescribing regulations if there is a reasonable explanation as to why greenhouse gas emissions do not contribute to air pollution, but the policy judgments and considerations cited by the EPA were unrelated to the statute and “rest[ed] on reasoning divorced from the statutory text.”
Accordingly, the Supreme Court ordered the EPA to either make an endangerment finding regarding greenhouse gas emissions from motor vehicles or provide a reasoned explanation for not doing so.
Endangerment Finding
Thereafter, the EPA, under President Barack Obama, issued its 2009 Endangerment Finding. In this final rule, the EPA made two key findings:
- A mix of six greenhouse gases, including carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride, constitute “air pollution” pursuant to Section 202(a) of the CAA and are a danger to public health and welfare; and
- The combination of these greenhouse gases from new motor vehicles and new motor vehicle engines contribute to greenhouse gas pollution and threaten public health and welfare.
In the final rule, the EPA made several interpretations of CAA Section 202(a), including that it requires the EPA Administrator to “‘anticipate’ ‘danger’ to public health or welfare” created by air pollutants. Thus, the EPA Administrator is required to consider both current and future risks and be ready to take regulatory action to prevent endangerment to public health and welfare before it occurs. The EPA also interpreted Section 202(a) to require the EPA Administrator to exercise judgment by weighing risks and making reasonable projections of future climate trends that balance the likelihood and severity of effects.
Further, the Endangerment Finding provides that the CAA’s use of the term “contribute” means the EPA Administrator is not required to find that a certain source is the main, sole or even significant cause of air pollution, but instead that it simply contributes to it. The EPA also stated that the EPA Administrator has (1) ample discretion to determine a source’s contribution to air pollution and (2) the regulatory controls to address it, “even if the air pollution problem results from a wide variety of sources.”
In the 16 years since its Endangerment Finding, the EPA has promulgated a series of greenhouse gas-related rules. First, the EPA and the Department of Transportation National Highway Traffic Safety Administration finalized a joint rule establishing tailpipe emissions standards for model years 2012 through 2016 light-duty vehicles. This was the first national greenhouse gas emissions standard issued pursuant to the CAA. Since then, the EPA has continued to update emissions standards for light-duty vehicles and has finalized similar standards for medium- and heavy-duty vehicles, as well as trucks. The EPA has also used the Endangerment Finding as the legal basis to finalize emissions standards for coal and natural gas powerplants and other industrial sources of greenhouse gases.
Proposal to Revoke the Endangerment Finding
The EPA has denied more than a dozen petitions to reconsider the Endangerment Finding since it went into effect; this summer’s proposal marks the first time the 2009 Endangerment Finding will be formally revisited.
The primary justification for reconsidering the Endangerment Finding lies in the assertion that the EPA’s foray into regulating greenhouse gas emissions from new motor vehicles and engines is “inconsistent with the best reading of CAA [S]ection 202(a).” In support, the EPA cites the recent decision of Loper Bright Enterprises v. Raimondo, 603 U.S. 369(2024) (Loper Bright), wherein the Supreme Court overturned Chevron deference, a principle that directed courts to defer to an agency’s reasonable interpretation of ambiguous statutory language, and on which the Supreme Court in Massachusetts v. EPA relied. The EPA argues that significant portions of the Endangerment Finding rely on Chevron deference to “depart from the best reading of the statute,” and therefore exceed the EPA’s authorities in light of Loper Bright.
In asserting that the EPA previously misinterpreted the CAA in its Endangerment Finding, the proposed revocation argues that the CAA was originally meant to focus on local air pollution, as opposed to global pollution and climate change. It contends that the two major conclusions of the Endangerment Finding did not properly tie together, opening up an impermissible level of discretion within which the EPA Administrator can “construe the scope” of the EPA’s authority. Citing Loper Bright, the proposal argues that CAA Section 202(a) does not authorize the EPA to prescribe emissions standards based on “global climate change concerns in a standalone endangerment finding.” It also asserts that the CAA’s text, structure and history should be read to require the targeting of air pollution that threatens public health and welfare “through local or regional exposure.” With this interpretation, the proposal claims that the EPA’s current interpretation of “air pollution” as six well-mixed greenhouse gases raising global climate change concerns that adversely impact a subset of regions globally “cannot satisfy this standard.”
Further, the proposal asserts that the CAA is best interpreted as distinguishing air pollution that may endanger public health and welfare through local or regional exposure from the six well-mixed greenhouse gases the EPA now claims only “indirectly” impact public health. It proposes construing the terms “air pollutant” and “air pollution” in accordance with the specific pollutants identified in CAA Section 202 as adversely impacting public health or welfare through human exposure, including hydrocarbons, carbon monoxide, nitrogen oxides and particulate matter, which impair human health through inhalation or contact with the skin, as well as lead, ground-level ozone, nitrogen dioxide and sulfur dioxide. The proposal contends that the CAA’s omission of substances that are potentially “indirectly” harmful to public health based on concentrations in the upper atmosphere, including several of the pollutants identified in the Endangerment Finding, signifies that the CAA does not intend to subject them to regulation. These arguments signal an attempt to return the EPA to its pre-2009 authority when the EPA focused its regulations on regionalized air pollution such as smog and soot.
The scope of the EPA’s authority to regulate greenhouse gas emissions from these sources triggers the major questions doctrine, a legal doctrine requiring clear congressional authorization before agencies may implement policies of major national significance. The proposal claims that the EPA lacks the clear congressional authorization to “decide the Nation’s response to global climate change concerns” by prescribing standards for new motor vehicles and engines, and so the EPA should therefore be precluded from doing so. Two cases are relied on for this claim, Utility Air Regulatory Group v. EPA, 573 U.S. 302(2014) and West Virginia v. EPA, 597 U.S. 697 (2022), where the Supreme Court rejected the EPA’s interpretation of the CAA as authorizing the EPA to regulate certain stationary sources, ruling that Congress had not provided explicit authorization to do so.
The proposal states that if the Endangerment Finding is revoked, the EPA will lack authority to prescribe any greenhouse gas emissions standards and enforce current standards. Consequently, the proposal also recommends removing related greenhouse gas emissions standards for light-, medium- and heavy-duty on-highway vehicles.
It should be noted that while the primary arguments offered by the EPA to support revocation are legal in nature, the Trump administration is also working to challenge the adequacy of the climate science relied on in the Endangerment Finding. In particular, the administration wants to reshape the consensus on the impact of greenhouse gases while simultaneously narrowing the EPA’s authority to regulate them. This effort is evidenced by a Department of Energy (DOE) report released the same day as the proposal to revoke the Endangerment Finding, which argues that carbon dioxide-induced warming is less economically damaging than previously thought, U.S. policy is expected to have only small impacts on global climate change and such effects will occur only after “long delays.”
Legal Implications
This action from the EPA under the Trump administration is all but certain to draw legal challenges from environmental groups and attorneys general in blue states—likely the same states that coalesced in 2007. While the Endangerment Finding has previously faced litigation, the courts have consistently upheld it, including favorable rulings from the D.C. Circuit in 2012 and 2023, and later denials of petitions for certiorari in the Supreme Court. However, following last year’s overturning of Chevron deference, the Trump administration likely anticipates that this Supreme Court will be more receptive to arguments that the Endangerment Finding is a result of the EPA’s overreliance on now-defunct precedent.
Further, the Supreme Court twice limited the EPA’s discretion pursuant to the CAA to regulate greenhouse gas emissions under the major questions doctrine. The present six-three conservative majority could this time rely on the major questions doctrine to uphold the EPA’s proposal to revoke the Endangerment Finding.
If the revocation is upheld in court, it is expected that the Trump administration will move quickly to rescind the EPA’s remaining emissions standards for automobiles, powerplants (stationary) and other industrial sources. In fact, such efforts were underway even before a formal proposal to reconsider the Endangerment Finding was released. For example, in June, the EPA proposed a rule to repeal all greenhouse gas emissions standards for fossil fuel-fired power plants, accompanied by a finding that greenhouse gas emissions from these power plants “do not contribute significantly to dangerous air pollution.”
The public has until Sept. 15 to submit public comments on the proposal to revoke the Endangerment Finding.
