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 is set to release 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 are slated to appear at an Indianapolis truck dealership, where they are expected to release a 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.
It is not yet clear exactly what basis the Trump administration will use to undo the endangerment finding. But based on comments officials made in March, when the EPA first announced it would reconsider the finding, the agency may cite what it deems a failure to consider the costs imposed by greenhouse gas regulation or the 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 as 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.
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. Climate scientists are in clear agreement that, in order to avoid ever worsening disasters and disruptions to our societies, the world must rapidly reduce greenhouse gas emissions. And 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.
Whatever way the EPA attempts to remove the endangerment finding, it will have to go through a formal rule-making process, which includes soliciting public comments. And any proposed change will 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 Rachel Cleetus, policy director at the Union of Concerned Scientists, in an April 9 blog post. “The impacts of climate change on human health are also starkly clear and backed by overwhelming evidence.”
