The Environmental Protection Agency is holding public hearings this week on its effort to undo the legal foundation for its regulation of greenhouse gases, the heat-trapping gases that cause climate change. In a major policy shift announced in late July, the Trump administration EPA said it would rescind the so-called “endangerment finding,” which allows the agency to regulate such emissions, arguing that legal and scientific developments justify a reconsideration. At the same time, the EPA has proposed to undo limits on greenhouse gas emissions from vehicles.
The endangerment finding, which the EPA issued in 2009 under President Barack Obama, affirmed a well-established scientific finding: that current and future amounts of greenhouse gases such as carbon dioxide and methane in the atmosphere “threaten the public health and welfare of current and future generations.” In a related finding, the Obama EPA asserted that greenhouse gas emissions from new motor vehicles contribute to these harms.
The findings required the EPA to put limits on vehicle greenhouse gas emissions under the Clean Air Act, which tasks the agency with regulating emissions that “cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.”
The endangerment finding also underlies subsequent greenhouse gas regulations, including those on power plants and oil and gas facilities. In its proposed rule on vehicle emissions, the EPA stated that it is separately reconsidering other greenhouse gas emissions standards.
There’s no question in the climate science community that human-caused climate change threatens public health. The scientific basis of the endangerment finding was “extensive” in 2009 and “has been reinforced even further with research not only about the climate system, but also about the impacts of climate change,” Noah Diffenbaugh, who studies the impacts of climate change at Stanford’s Doerr School of Sustainability, said during a July 31 call with reporters.
While the EPA’s proposed rule challenges the scientific basis of the endangerment finding, claiming “substantial uncertainties,” the agency’s primary arguments for rescinding the finding and related vehicle emissions standards are legal.
Below, we answer questions about the EPA’s proposal and what legal and climate experts say about it.
Under the federal rule-making process, the EPA is seeking public comment on its proposed rule through Sept. 22, and public hearings began Aug. 19. The agency must consider and respond to significant public comments before issuing a final rule. Legal experts say litigation challenging the rule is sure to follow, with the court battle potentially lasting several years.
What is the practical impact of the EPA’s decision?
The EPA’s proposed rule takes aim specifically at greenhouse gas emissions from new vehicles. But rescinding the endangerment finding has implications for the agency’s ability to regulate greenhouse gas emissions in general.
The EPA has regulated greenhouse gas emissions from vehicles beginning with model year 2012. The latest rules, made under the Biden administration, were set to begin to take effect in 2027.
The proposed rule would not affect other tailpipe emissions standards for pollutants besides greenhouse gases, nor fuel economy standards. However, the One Big Beautiful Bill Act, signed into law July 4, ended penalties for not meeting fuel economy standards, called Corporate Average Fuel Economy standards. Meanwhile, Trump in June signed congressional resolutions rescinding California’s waivers to set its own emissions standards. States have challenged this move in court.
The new rule would not directly undo the EPA’s regulations on sources of greenhouse gas emissions beyond vehicles. But if the EPA prevails in its argument that it lacks the authority to regulate greenhouse gases, it would provide a basis for the EPA to end regulation of these emissions from other sources.
The EPA under the Obama and Biden administrations had previously attempted to regulate greenhouse gas emissions from power plants. The Trump EPA is separately attempting to undo these regulations, which never went into effect. The endangerment finding also underpins regulations limiting methane emissions from oil and gas facilities, whose compliance deadlines the EPA recently delayed.
In the short term, the administration “won’t enforce” greenhouse gas regulations, Pat Parenteau, an emeritus professor at Vermont Law School’s Environmental Law Center, told us.
Jody Freeman, director of the Environmental and Energy Law Program at Harvard Law School and an adviser in the Obama White House, also told Heatmap News that “basically, for the rest of President Trump’s term, you really shouldn’t expect to see enforcement or action on federal climate rules.”
“Could a future administration restore all of this?” Parenteau said, referring to regulation of greenhouse gases by the EPA. “The answer there is yeah, depending on what the Supreme Court does.”
If the EPA does win its main argument that it doesn’t have the authority to regulate greenhouse gas emissions, “that is going to impact future administrations,” Parenteau said, possibly requiring them to go through Congress to establish future limits.
“The legal risks of finalizing this proposal are considerable,” a trio of attorneys from Harvard Law School’s Environmental & Energy Law Program wrote in an Aug. 12 legal analysis. “However, if EPA proceeds with its primary proposal to rescind the Endangerment Finding based on its new interpretation of the Clean Air Act and courts uphold it, it will bind future administrations and prevent federal regulation of greenhouse gas emissions from the major US sources.”
A full win for the EPA could open up new avenues for states to regulate greenhouse gas emissions, since states could argue there were no longer federal standards preempting others.
Further, companies being sued by organizations and states for the harms of emissions from fossil fuels have argued that the EPA’s regulatory authority preempts these suits. A full repeal of the endangerment finding could open up companies to liability, Parenteau and other legal experts said.
What is EPA’s main legal argument for rescinding this finding?
When we reached out to the EPA about the proposed rule, a spokesperson told us via email: “The Endangerment Finding is the legal prerequisite used by the Obama and Biden Administrations to regulate emissions from new motor vehicles and new motor vehicle engines. Absent this finding, EPA would lack statutory authority under Section 202(a) of the Clean Air Act (CAA) to prescribe standards for greenhouse gas emissions.”
In the proposal, the agency contends that the Clean Air Act only applies to local and regional pollutants, not greenhouse gas emissions; that the agency previously should have considered the contribution of individual classes of vehicles and greenhouse gases to global climate change; and that the agency previously did not properly consider the cost or effectiveness of regulations on vehicles.
“It’s a mashup,” Parenteau told us. “They’re trying to give the courts, and particularly the Supreme Court, a smorgasbord of arguments hoping that something will stick.”
The EPA led with the argument that greenhouse gases do not legally qualify as pollutants that threaten well-being, as defined by the Clean Air Act. The EPA said that the relevant section of the Clean Air Act “does not authorize the EPA to prescribe emission standards to address global climate change concerns.”
Instead, the EPA argued, air pollution “is best read in context as referring to local or regional exposure to dangerous air pollution, consistent with our longstanding practice before 2009.” The agency went on to say that air pollutants governed by the Clean Air Act “are those that cause or contribute to air pollution for which the air pollution itself, through local or regional exposure to humans and the environment, endangers public health or welfare.” This could include a substance, such as carbon monoxide, which is directly harmful to humans, the agency said, or a substance that interacts with sunlight or other chemicals to create air pollution, such as in the case of the chemicals that interact to cause acid rain. In contrast, the agency said, the argument that greenhouse gases endanger public health and welfare relies on too many steps to arrive at these harms, and the harms vary in severity by region.
The EPA also argued that, in issuing a general endangerment finding considering a mixture of greenhouse gases, the Obama EPA improperly “severed” the endangerment finding from the specific set of vehicles and gases the agency was trying to regulate. It is not enough to broadly conclude that greenhouse gases endanger public health, the EPA argued, saying the Obama administration needed to prove endangerment for each greenhouse gas and each source of the emissions.
What does the EPA cite for its scientific argument?
As a secondary argument, the EPA took aim at the scientific basis for the endangerment finding, in many cases citing a new report from the Department of Energy that made a series of false and misleading claims to minimize the harms of climate change. The DOE is also soliciting public comments on its climate change report with Sept. 2 as the deadline.
DOE Secretary Chris Wright hand-picked the authors — four scientists and one economist with a history of disputing the consensus on climate science — to form a “Climate Working Group.”
More than a dozen researchers whose findings were cited in the report have said their work was misused, taken out of context or cherry-picked. Scientists are now working on a more detailed response to the 151-page report.
In its proposed rule, the EPA argued that the Obama administration had been “unduly pessimistic” about warming and the health impacts of extreme heat. The EPA also questioned the reliability of prior conclusions on topics such as extreme weather and sea level rise, while arguing that the EPA should have considered benefits of increased carbon dioxide. As we have said, climate scientists concluded that the overall basis for the finding that greenhouse gas emissions endanger human well-being has in fact strengthened since the original endangerment finding.
In April, the Trump administration dismissed hundreds of experts who had been working to compile the sixth National Climate Assessment, a document mandated by Congress, and subsequently deactivated the website that had hosted the prior reports. Wright most recently said the administration was updating these already-published reports. The National Academies of Sciences, Engineering, and Medicine announced on Aug. 7 that it would conduct its own review focused on evidence since 2009 “on whether greenhouse gas emissions are reasonably anticipated to endanger public health and welfare in the U.S.,” with a planned release in September.
We asked the EPA about its response to scientific concerns related to the DOE report and whether it would consider the NASEM report as it revised its proposed rule. “EPA’s proposal is legal in nature,” the spokesperson told us, before elaborating on the legal argument. “The agency considered a variety of sources and information in assessing whether the predictions made, and assumptions used, in the 2009 Endangerment Finding are accurate and consistent with the limits on EPA’s authority” under the Clean Air Act, the spokesperson said.
“The Climate Working Group and the Energy Department look forward to engaging with substantive comments following the conclusion of the 30-day comment period,” a DOE spokesperson told us via email, in response to a question about criticisms from people whose work was cited in the DOE report.
What do legal experts say?
The current EPA’s legal argument is at odds with a 2007 Supreme Court ruling in a case called Massachusetts v. EPA, a variety of climate lawyers have said. In that case, the justices ruled that greenhouse gas emissions qualified as air pollution that could be regulated under the Clean Air Act and that the EPA needed to evaluate whether the emissions contributed to climate change. The ruling led the EPA to issue the endangerment finding and regulate greenhouse gas emissions, beginning with the vehicle emissions rules.
The current EPA has argued that previously, the EPA misconstrued the findings of the Supreme Court and that the ruling “did not require the Agency to find that [greenhouse gases] are subject to regulation” under the relevant section of the Clean Air Act.
“This local and regional language [in the proposed rule] is not something you find in the Clean Air Act and conflicts with the Act’s purpose of protecting the public’s health and welfare,” Greg Dotson, who leads the Energy Law and Policy Project at the University of Oregon School of Law, told Yale Climate Connections. “Additionally, it runs counter to numerous Supreme Court cases over the last 20 years.”
The EPA is “counting on the Supreme Court not applying precedent or just overruling it,” Parenteau said. “That’s a big leap. That’s a big ask.”
The Harvard Environmental & Energy Law Program analysis pointed out that the Obama EPA did in fact look at impacts of climate change in the U.S. — and that to the degree it looked at global effects of climate change, it was to understand how they would affect the well-being of Americans. “EPA misrepresents the 2009 Endangerment Finding when it asserts that it failed to show local endangerment,” the lawyers wrote.
The Harvard analysis also contended that, contrary to the EPA’s legal claim, the Clean Air Act supports “looking at sources and emissions in combination” when issuing an endangerment finding. Moreover, the analysis said, the EPA did calculate the contribution of each vehicle type and greenhouse gas to emissions in a supporting document for the endangerment finding.
“EPA’s intent with this reasoning appears to be to split US emissions into small pieces, fracturing domestic emissions so they appear to be a less significant share of global emissions,” the analysis said. “This approach would effectively prohibit EPA from regulating [greenhouse gas] emissions from the highest-emitting sources in the US.”
The transportation sector contributes 28% of the nation’s greenhouse gas emissions, according to the EPA. The U.S. as a country is the second-highest emitter of greenhouse gases overall in the world, according to the European Commission.
Further, the analysis said, the decision in Massachusetts v. EPA “makes clear that issuing an endangerment finding and developing regulations are two distinct steps,” and it is appropriate to consider costs, as the EPA did under prior administrations, when issuing regulations of greenhouse gas emissions from specific sources.
The current EPA said that legal developments since Massachusetts v. EPA justify revisiting the 2009 endangerment finding.
One of these is the overturning of the Chevron doctrine in 2024. Under this doctrine, courts gave deference to agencies’ interpretations of ambiguous statutes. The EPA argued that the Obama administration had overreached in claiming the authority to regulate greenhouse gas emissions, saying that “we can no longer rely on statutory silence or ambiguity to expand our regulatory power.”
Others argued the overturning of the Chevron doctrine might in fact hurt EPA’s case. Parenteau said the 2024 ruling means the courts do not need to give deference to the agency’s current interpretation of the Clean Air Act.
“They no longer can just say, you ought to defer to us under Chevron” in interpreting the Clean Air Act, Freeman, the climate lawyer from Harvard, told Heatmap News. Rather, the EPA will need to convince the courts that its interpretation of the Clean Air Act is the correct one.
The EPA also cited the 2022 case West Virginia v. EPA, in which the Supreme Court ruled that the Obama administration’s Clean Power Plant Plan was invalid. The court cited the major questions doctrine, or the idea that an agency must get clear authorization from Congress before asserting a novel regulatory authority if the issue at hand has vast economic and political consequences.
The Obama EPA’s decision to regulate greenhouse gases “implicates the ‘major questions doctrine’ because it involves questions of great political and economic significance, and Congress has not clearly given EPA authority to regulate such pollutants under the Clean Air Act,” climate lawyer Jeffrey Holmstead, assistant administrator of the EPA’s Agency for Air and Radiation under former President George W. Bush and associate counsel to former President George H.W. Bush, told E&E News.
But the Harvard legal analysis said that the court in the West Virginia ruling “never questioned EPA’s authority to regulate greenhouse gases,” but rather questioned details of how the agency was regulating them.
Parenteau argued that the major questions doctrine could hurt the EPA’s argument. He said the EPA’s argument that it does not have the authority to regulate greenhouse gas emissions is itself novel and hugely consequential.
What do climate scientists say?
The EPA cited the DOE report to minimize the harms of extreme events and sea level rise, and highlight the positive impacts of carbon dioxide on plant growth. It also downplayed evidence of harms from emissions on agriculture.
As we’ve said, climate scientists have argued that the evidence for the harms of greenhouse gas emissions on public health have strengthened over time.
In a review published in Science in 2018, researchers wrote that “the case for endangerment, which was already overwhelming in 2009, is even more strongly justified.”
This year, another group of scientists again reviewed the evidence. The group in the early 2000s had filed an amicus brief for Massachusetts v. EPA. “Sixteen years later, the scientific evidence supporting the endangerment finding is even stronger, with zero countervailing evidence,” the scientists wrote in a commentary published in June 2025 in AGU Advances. “Our amicus brief’s predictions of future climate trends have all come true, some alarmingly faster than anticipated.”
The scientists wrote that the “most extreme years” on record for global surface temperature, global ocean heat content, arctic sea ice retreat, sea level rise and ocean acidity increase have all happened since the 2009 finding.
Further, they said, heat-related deaths are increasing, and woodland and forest fires are becoming more severe in Mediterranean climates, leading to smoke events. In addition, they said, climate change is aiding the spread of disease and disrupting agriculture.
Andrew Dessler, a climate scientist at Texas A&M University, has been helping to coordinate scientists’ efforts to respond to the DOE climate report. “The report they produced should be thought of as a law brief from attorneys defending their client, carbon dioxide,” he wrote in a statement on social media. “Their goal is not to weigh the evidence fairly but to build the strongest possible case for CO2’s innocence. This is a fundamental departure from the norms of science.”
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