The legal reasoning behind the endangerment rescission
On February 12, 2026, the Environmental Protection Agency (EPA) rescinded its greenhouse gas standards for motor vehicles and its 2009 Endangerment Finding—the determination that greenhouse gas emissions endanger public health and welfare and the legal basis for regulating them under the Clean Air Act. This action, largely unwanted by industry and contradicted by science and law, is central to the Trump administration’s effort to eliminate the federal government’s role in addressing climate change. Despite the Clean Air Act’s success in driving emission reductions from vehicles, power plants, and oil and natural gas facilities over the past 16 years, EPA intends to prohibit future administrations from using it.
Climate science – what changed from the proposal?
Although the rescission states that the EPA Administrator “continues to harbor concerns regarding the scientific analysis” in the 2009 Endangerment Finding, EPA does not rely on or evaluate the science to justify its repeal of the 2009 science-based finding.
EPA’s August 2025 proposal relied on a report prepared for the Department of Energy (DOE) by five scientists with fringe views. Based on that report, EPA asserted that many underlying assumptions in 2009 were “unduly pessimistic,” that the 2009 analysis failed to account for the positive impacts of climate change, and that there are significant uncertainties in predicted warming rates and their effects.
Climate scientists, including the National Academy of Sciences, strongly disputed those conclusions in robust comments. These experts affirmed that the 2009 Endangerment Finding remained scientifically sound and was bolstered by even stronger evidence accumulated over the past 17 years. Additionally, a federal court determined that the Trump administration violated federal law when it formed the group of scientists that prepared the report.
Given the strong scientific opposition and the court’s decision discrediting the DOE process, EPA likely determined that any reliance on its proposed assertions regarding climate science would be legally vulnerable.
Without the science, how does EPA justify this action in the final rule?
Rather than a frontal assault on the science, EPA relies on legal reasoning in the final rule. It argues that under its new interpretation of Clean Air Act section 202(a), EPA lacks the statutory authority to regulate greenhouse gas emissions from new motor vehicles because such emissions do not contribute to “air pollution.” In arguing that Congress has not authorized EPA to regulate these emissions because any regulation would not materially affect global climate change, EPA blurs distinct analytical steps of the Clean Air Act.
EPA bases this constrained interpretation of its statutory authority on three interrelated arguments. First, it argues that “air pollution” applies only to pollution with local or regional effects. Second, EPA contends that greenhouse gas emissions from new motor vehicles do not “in any material way” affect public health and welfare. Third, EPA asserts that regulation is “costly and futile” and would not meaningfully address the underlying harm.
In 2007, the Supreme Court in Massachusetts v. EPA rejected similar arguments advanced by the Bush administration to assert it could not regulate greenhouse gases. Although that case addressed a different core legal question, the Court was clear that greenhouse gases are unambiguously air pollutants under the Clean Air Act, and EPA must use its “scientific judgment” in making a finding about endangerment without considering policy or cost. In its 2009 Endangerment Finding, EPA explained how that scientific judgment led it to conclude that greenhouse gas emissions contribute to pollution that endangers public health and welfare consistent with the Clean Air Act.
Until now, that conclusion remained intact.
Congress has had ample opportunity to address the 2009 Endangerment Finding and has declined to limit EPA’s authority. Additionally, since Massachusetts v EPA, the Supreme Court has never suggested that EPA lacked the authority to regulate greenhouse gases under the Clean Air Act. Rather, the Court has only focused on how EPA set regulations predicated on the finding.
What happens next?
Although EPA’s rescission is final, legal challenges will soon follow. Challengers are likely to advance multiple arguments regarding EPA’s legal reasoning and process. That litigation is expected to proceed through the D.C. Circuit, and likely to the Supreme Court, over the coming years.
EPA’s final rule reshapes the legal landscape of climate regulation in the U.S. It is far from certain that courts will agree with EPA. However, if the Supreme Court were to fully accept EPA’s arguments, it would preclude future administrations from regulating greenhouse gas emissions from the transportation sector—the largest source of greenhouse gas emissions in the U.S.—under section 202 of the Clean Air Act and likely from other sources for which their regulations are similarly predicated on an endangerment finding.
The final rule leaves open many questions. Will states address this environmental and public health risk through their own policies? How will the private sector respond—particularly industries that cautioned against EPA’s broad rescission? And, how will other countries continue to drive investments to address climate change as the U.S. government retreats?
All perspectives expressed in the Harvard Climate Brief are those of the authors and not of Harvard University or the Salata Institute for Climate and Sustainability. Any errors are the authors’ own. The Harvard Climate Brief is edited by an interdisciplinary team of Harvard faculty.
