The Endangerment Finding: A History of Regulation

The endangerment finding, formally instituted in 2009, provided the legal basis for the EPA to regulate emissions under the Clean Air Act. Its origins trace back to 2007, when the Supreme Court, in the landmark case of Massachusetts v. EPA, ruled that greenhouse gases qualified as “air pollutants” under the Act, thereby obligating the EPA to consider their regulation. Justice John Paul Stevens, writing for the majority, emphasized that “Collaboration and research do not conflict with any thoughtful regulatory effort; they complement it.”

The current legal battle stems from the Trump administration’s assertion that the EPA lacks the statutory authority to regulate greenhouse gases, a claim fiercely contested by legal experts and environmental advocates. This position was formalized through an executive order issued on January 20, 2025, calling for a reconsideration of the endangerment finding. The EPA subsequently proposed rolling back the finding in August 2025, culminating in the final rule published on February 18.

A Multi-Front Legal Assault

The response was swift and decisive. On March 19, a coalition of 24 Democratic-led states, the District of Columbia, the U.S. Virgin Islands, and 12 cities and counties filed a lawsuit against the EPA, alleging that the rollback was arbitrary, capricious, and violated the Clean Air Act. New York Attorney General Letitia James, leading the charge, declared, “The American people need their leaders to be honest and pragmatic about the threat of the climate crisis. We will not let the federal government abandon its responsibility to the people.”

Simultaneously, the American Public Health Association, Natural Resources Defense Council, and 15 other organizations filed their own petition challenging the EPA’s decision. The legal arguments hinge on the established precedent set by Massachusetts v. EPA and the EPA’s long-standing authority to regulate pollutants that endanger public health. Kate Sinding Daly, senior vice president for law and policy at Conservation Law Foundation, noted, “The Trump administration has been signaling from pretty close to day one of this term that they were coming after the endangerment findings, so it’s no surprise that it’s come to this.”

Adding another layer to the legal complexity, 25 Republican-majority states filed a motion to intervene in support of the EPA’s rollback, framing the issue as one of federal overreach and economic burden. The case is expected to be consolidated and heard before the D.C. District Court of Appeals, with a likely ultimate destination at the Supreme Court.

The EPA, however, maintains that its actions are consistent with the law. A spokesperson stated, “Unlike our predecessors, the Trump EPA is committed to following the law exactly as it is written and as Congress intended — not as others might wish it to be.” The administration points to recent Supreme Court decisions, including West Virginia v. EPA (2022) and Loper Bright Enterprises v. Raimondo (2024), as justification for its position. These cases, however, addressed different regulatory contexts and have been interpreted by environmental lawyers as not directly impacting the validity of the endangerment finding.

David Pettit, a senior attorney with the Center for Biological Diversity, explained, “Here you’ve got a situation where these rules have been in effect for many years, and the EPA isn’t relying on some new hidden provision. They’re relying on the fundamental basis of the Clean Air Act and pollutants.” Marvin Brown, a senior attorney at Earthjustice, echoed this sentiment, stating, “I feel very confident that EPA has taken the wrong interpretation of the Clean Air Act and is doing so in a way that is abandoning both its authority, but also its mission and obligation to regulate greenhouse gases.”

But what does this mean for the future of climate regulation in the United States? And how will these legal battles impact the global effort to mitigate climate change?

Frequently Asked Questions About the EPA Emissions Rollback

• What is the “endangerment finding” and why is it important? The endangerment finding is a crucial EPA determination made in 2009 that greenhouse gases endanger public health and welfare, providing the legal basis for regulating these emissions under the Clean Air Act.
• What is the Massachusetts v. EPA case and how does it relate to this legal challenge? The 2007 Supreme Court case Massachusetts v. EPA established that greenhouse gases are “air pollutants” under the Clean Air Act, obligating the EPA to consider regulating them, and forming the foundation for the endangerment finding.
• What is the “major questions doctrine” and how is the EPA using it to justify the rollback? The major questions doctrine, as interpreted by the Supreme Court in cases like West Virginia v. EPA, suggests that Congress must explicitly authorize agencies to make decisions of vast economic and political significance. The EPA argues that regulating greenhouse gases falls under this doctrine and requires explicit Congressional authorization.
• What is the Chevron deference and how does the Loper Bright Enterprises v. Raimondo case affect the EPA’s authority? The Chevron deference previously allowed courts to defer to an agency’s interpretation of ambiguous statutes. The Loper Bright Enterprises v. Raimondo case reversed this precedent, potentially giving courts more power to review agency decisions.
• What are the potential consequences of rolling back the endangerment finding? Rolling back the endangerment finding could lead to increased greenhouse gas emissions, exacerbating climate change and its associated health and economic impacts.
• What role are states and cities playing in challenging the EPA’s decision? A coalition of states, cities, and counties have filed lawsuits against the EPA, arguing that the rollback is unlawful and harmful to public health and the environment.