Trump’s EPA Is Taking Aim at the Legal Backbone of U.S. Climate Policy
The Trump administration is releasing its proposal to undo the “endangerment finding,” the long-standing rationale and legal imperative for regulating greenhouse gases under the Clean Air Act
Environmental Protection Agency (EPA) Administrator Lee Zeldin testifies before the House Committee on Energy and Commerce Subcommittee on Environment in the Rayburn House Office Building on May 20, 2025 in Washington, D.C.
Kevin Dietsch/Getty Images
On Tuesday the U.S. Environmental Protection Agency released its proposal to undo its long-standing rationale and legal mandate to regulate greenhouse gases under the decades-old Clean Air Act—part of the Trump administration’s wide-ranging campaign to dismantle federal efforts to combat climate change.
EPA Administrator Lee Zeldin, Secretary of Energy Chris Wright and other administration officials appeared at an Indianapolis truck dealership, where they announced a new draft rule to undo this “endangerment finding,” which the EPA issued in 2009, along with a proposal to reverse vehicle tailpipe emissions limits enacted under President Joe Biden’s term. The endangerment finding formally stated that carbon dioxide and five other greenhouse gases produced by the burning of fossil fuels “endanger the public health and public welfare of current and future generations” and so could be regulated under the Clean Air Act (alongside other pollutants such as sulfur dioxide and particulate matter). The finding is “the linchpin for everything—all of the carbon regulation under the Clean Air Act,” said Patrick Parenteau, now an emeritus professor of environmental law at Vermont Law School, in an interview with Scientific American in 2017, when the first Trump administration was also attempting to undo climate regulations.
During that first attempt, the EPA’s then administrator Scott Pruitt did not try to jettison the endangerment finding and instead proposed weaker emissions regulations to replace those put in place under President Barack Obama. (The Trump regulations were themselves replaced with more stringent regulations under Biden as part of his pledge to reduce U.S. emissions by up to 66 percent by 2035.) But the second Trump administration is attempting to take a more permanent approach; rescinding the endangerment finding would make it harder for future administrations to regulate carbon dioxide and other greenhouse gases under the Clean Air Act without a specific law or amendment passed by Congress.
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The endangerment finding came about because of a suit against the EPA brought by environmental groups and states during the administration of President George W. Bush. In that 2007 case, Massachusetts v. EPA, the Supreme Court ruled that greenhouse gases qualified as an “air pollutant” under the broad definition in the Clean Air Act: “any air pollution agent or combination of such agents, including any physical, chemical, biological, radioactive … substance or matter, which is emitted into or otherwise enters the ambient air.”
With the finding in place, the EPA cannot legally ignore climate change or completely strike greenhouse gas regulations from the books.
There is no single rationale being offered to undo the endangerment finding; rather “you can see a lot of spaghetti being thrown at the wall,” said Meredith Hankins, senior attorney for climate and energy at the Natural Resources Defense Council, in a Tuesday afternoon press conference. Based on newly released information, as well as comments officials made in March, when the EPA first announced it would reconsider the finding, the agency is citing what it deems a failure to consider the costs imposed by greenhouse gas regulation and the use of well-established scientific methods to combine and quantify the emissions of six different gases based on their heat-trapping potential. The latter measure is called “CO2 equivalent” and is used to express how much a molecule of a given gas can warm the atmosphere compared with a molecule of CO2. For example, methane traps much more heat on a per-molecule basis than CO2 does, though CO2 lingers for much longer in the atmosphere.
The administration is taking a chance by trying all these approaches in the hopes that “maybe something will stick or maybe it will delay things,” said Rachel Cleetus, senior policy director at the Climate and Energy program at the Union of Concerned Scientists, during the press conference.
“I can’t tell if they’re trying to tie it up in litigation and then not actually regulate for four years,”says Camille Pannu, associate clinical professor of law at Columba Law School. Alternatively, the strategy may be to have challenges eventually reach the Supreme Court in the hopes the Court will overturn Massachusetts v. EPA, she says.
Conservatives have long cited the costs imposed by regulations, though climate change itself poses considerable costs to the U.S. economy. Climate-change-fueled disasters alone cost the country $150 billion each year with the warming that has happened to date.
Also, the question of cost is not applicable to the endangerment finding, the purpose of which was to show that greenhouse gases met the Clean Air Act’s statute that, to be regulated, an air pollutant must endanger public health. The regulations that follow the endangerment finding are where costs are considered, Pannu says. And “the Clean Air Act was written to be forward-looking” so that Congress would not have to continually update it as new pollutants emerged. Likewise, the act’s language around what constituted harm to health was purposefully written broadly, Pannu says. Any finding of endangerment “has to be backed by scientific evidence,” she says.
The evidence in the case of climate change is backed up by a robust body of research conducted over many decades. “The science is unequivocal,” said John Balbus, former deputy assistant secretary for climate change and health equity at the Department of Health and Human Services, during the press conference. Not addressing climate change will “risk catastrophic harm to health that would be impossible to reverse,” he added.
And climate scientists are in clear agreement: in order to avoid ever worsening disasters and disruptions to our societies, the world must rapidly reduce greenhouse gas emissions. The U.S. is a major contributor to global emissions—though China is now the highest emitter each year, the U.S. is the biggest emitter historically and still emits more per capita than China does.
READ MORE: See how U.S. emissions compare with those of other countries
And failing to rein in emissions now will disproportionately affect future generations: a child born today will experience many times more heatwaves their parents or grandparents in their lifetimes.
The proposed change will have to go through the usual rule-making process, which includes soliciting public comments. (In its announcement, the EPA said information on submitting public comment would be published in the Federal Register and on the agency’s website.) And the proposed change is expected to be challenged in court. Historically the courts have upheld the endangerment finding, given the robust scientific evidence that climate change causes harm.
“Every major scientific society endorses the scientific consensus on human-caused climate change driven by GHG [greenhouse gas] emissions. The Fifth National Climate Assessment and the IPCC’s Sixth Assessment Report are two major recent authoritative summaries of peer-reviewed climate science, which show that the science on climate change has only become more dire and compelling since 2009,” wrote Cleetus in an April 9 blog post. “The impacts of climate change on human health are also starkly clear and backed by overwhelming evidence.”
Editor’s Note (7/29/25): This article was edited after posting to include updates about the Environmental Protection Agency’s announcement.