What Is the U.S. Environmental Protection Agency’s Endangerment Finding?
In everyday usage endanger is a loaded word that evokes images of people being exposed to disease, workers at risk of on-the-job injury, children threatened with harm because of negligence or worse, and challenges to long-term plant and animal survival. With the existential threat posed by climate change and its causes—a position held by a consensus of scientists around the world since the early 2000s—the U.S. Environmental Protection Agency (EPA) created an internal rule in 2009 that allowed the agency to view and treat certain greenhouse gases (GHGs) through the lens of public health (see also global warming).
The rule, called the endangerment finding, determined that GHGs posed health risks, and thus the EPA was empowered to regulate them under the Clean Air Act (1970). For the next decade and a half, after overcoming court challenges by industry groups, the endangerment finding guided U.S. policy on climate change, especially rules related to vehicle emissions and their solutions. Despite growing evidence that continues to reinforce the connection between rising GHGs in the atmosphere and the effects of climate change (such as drought, food insecurity, and increases in the frequency and duration of extreme weather), the rule was revoked on February 12, 2026, by federal regulators under the second Trump administration.
- Carbon dioxide (CO2): Formed during the combustion of carbon-containing materials, in fermentation, and through respiration in animals. It is used by plants to photosynthesize carbohydrates.
- Methane (CH4): Produced by bacterial decomposition of vegetable matter under water (where it is sometimes called marsh gas or swamp gas), digestive processes in termites, volcanoes, and hydrothermal vents, and the melting of methane hydrate deposits.
- Nitrous oxide (N2O): Produced by the combustion of ammonium nitrate and used as an anesthetic in short-duration surgeries and as a propellant in food aerosols. It is also injected into an engine’s air intake in automobile racing; the extra oxygen allows the engine to burn more fuel per stroke.
- Hydrofluorocarbons (HFCs): A group of gases manufactured for use in refrigeration and cooling.
- Perfluorocarbons (PFCs): A group of gases manufactured to clean and etch semiconductors and electronic components. These chemical compounds are also used as components in firefighting foams and as surface protectants in consumer products.
- Sulfur hexafluoride (SF6): A manufactured gas used for electrical insulation.
On January 25, 2025—during the first week of his second term—U.S. Pres. Donald Trump ordered a review of this EPA rule. By August 2025 EPA administrator Lee Zeldin released a proposal detailing the EPA’s rationale for retracting the endangerment finding based on two primary reasons. The first reason stemmed from the view that the EPA did not have the power to regulate GHGs from newer cars and trucks because their emissions would not contribute to local and regional air pollution. So, their effects were too small to constitute an endangerment, and thus regulating them would cost too much. Second, Zeldin and his staff argued that climate science was still too uncertain (namely in linking specific causes to specific effects) to associate new vehicles produced in the U.S. with climate-related risks to public health and welfare.
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The response to this was swift. In the same month, experts at the Environmental & Energy Law Program at Harvard Law School noted that the basis of Zeldin’s primary reason for terminating the rule was rooted in the argument that GHGs are not air pollutants, despite the U.S. Supreme Court’s ruling that they were in Massachusetts v. EPA (2007). In addition, Zeldin noted that the EPA did not have the ability to regulate GHGs without the clear approval of the U.S. Congress—a nod to the “major questions doctrine” discussed in West Virginia v. EPA (2022), in which the Supreme Court required that a federal agency receive the explicit authorization of Congress before making a rule involving cases of substantial national significance. However, Massachusetts v. EPA, which dealt specifically with the topic of GHGs from motor vehicles, held that the EPA possessed this power already (see also Major Supreme Court Cases from the 2025–26 Term). Other legal journals and environmental groups have echoed the sentiments put forth by Harvard Law School.
Meanwhile, Trump administration officials claimed that the removal of the endangerment finding was a victory for the American people, saving an estimated $1.3 trillion in regulation costs, thereby freeing the U.S. energy industry and helping American consumers afford new cars and trucks. In practice, however, pulling down the endangerment finding would take away the EPA’s legal authority in regulating automobile and truck emissions—loosening fuel economy standards and reducing financial incentives to purchase electric vehicles. An analysis conducted by the Environmental Defense Fund reported that the decision could release an additional 18 billion metric tons (19.8 billion tons) of climate pollution into the atmosphere by 2055, resulting in $3.9 trillion of negative environmental effects (such as more frequent and more damaging weather-related disasters) and health impacts from reduced air quality (such as asthma and cardiovascular disease). While this change in the EPA’s direction was expected to set up a series of court battles, legal scholars worried that the removal of the endangerment finding could open the door to overturning Massachusetts v. EPA, leaving the EPA (and future presidential administrations) with fewer tools to regulate GHGs.