Two dozen states, along with more than a dozen cities and counties, sued the Environmental Protection Agency on Thursday, challenging the Trump administration's repeal of a scientific finding that had been the central basis for U.S. action to regulate greenhouse gas emissions and fight climate change.
A rule finalized by the EPA last month revoked the 2009 endangerment finding that determined carbon dioxide and other greenhouse gases threaten public health and welfare. The Obama-era finding had been the legal underpinning of nearly all climate regulations under the Clean Air Act for motor vehicles, power plants and other pollution sources that are heating the planet.
The implications are substantial. The repeal eliminates all greenhouse gas emissions standards for cars and trucks and could unleash a broader undoing of climate regulations on stationary sources such as power plants and oil and gas facilities. The EPA describes this as the single largest deregulatory action in U.S. history.
New York Attorney General Letitia James, who led the suit along with attorneys general of Massachusetts, California and Connecticut, stated: "Instead of helping Americans face our new reality, the Trump administration has chosen denial, repealing critical protections that are foundational to the federal government's response to climate change." In all, 24 states, 10 cities and five counties joined the lawsuit.
The EPA's legal argument rests on a narrower interpretation of congressional authority. The EPA's primary rationale for rescinding the Endangerment Finding is that EPA lacks the statutory authority under Clean Air Act Section 202(a) to regulate greenhouse gas emission standards based on global climate change concerns. The EPA also relied on the Supreme Court's 2024 ruling in Loper Light Enterprises v. Raimondo, which overturned Chevron deference and requires courts to independently interpret ambiguous statutory language rather than defer to agency interpretations.
The case faces significant hurdles for the EPA. The U.S. Supreme Court, in a landmark 2007 case, ruled that carbon dioxide and other greenhouse gases are "air pollutants" under the Clean Air Act. Since the high court's decision, in a case known as Massachusetts v. EPA, courts have uniformly rejected legal challenges to the endangerment finding, including a 2023 decision by the D.C. appeals court.
The lawsuit, filed in the U.S. Court of Appeals for the District of Columbia Circuit, is the second major challenge to the endangerment repeal, following a suit filed last month by public health and environmental groups. The dispute is likely to end up back before the Supreme Court, which is now far more conservative than it was in 2007.
The scientific foundation of the 2009 finding remains contested. The original 2009 determination was based on a nearly 200-page EPA analysis of the science, more than 380,000 public comments and two public hearings. Critics of the administration's plan to rescind the finding argue that the science linking greenhouse gas emissions to climate change is even stronger today than when the endangerment finding was established in 2009.
The outcome remains uncertain. Congress could restore the EPA's role in fighting climate change by passing a new law; the legal route is just faster, and potentially riskier. For now, the states' legal challenge represents the most direct path to challenging a decision that fundamentally reshapes federal climate authority.