“The EPA's 2009 endangerment finding "had no basis in fact — none whatsoever. And it had no basis in law."”

White House news conference announcing EPA's final rescission of the 2009 endangerment finding

The U.S. Supreme Court itself established the legal basis for EPA climate regulation. In Massachusetts v. EPA (2007), the Court held that greenhouse gases are air pollutants under the Clean Air Act and that EPA must regulate them if they endanger public health. The 2009 endangerment finding directly implemented that ruling, and the D.C. Circuit upheld it in 2012, with the Supreme Court declining to disturb it. Regulations commanded by the Supreme Court are the opposite of 'illegal.' No court has ever ruled EPA's climate regulations 'illegal' as a category. Even West Virginia v. EPA (2022), which narrowed one specific power-plant rule, did not overrule Massachusetts v. EPA and inherently acknowledged EPA's authority to regulate greenhouse gases. Seventeen years of litigation left the endangerment finding standing every time. It is the rescission, not the original finding, that is on shaky legal and scientific ground. EPA's repeal, proposed in 2025 and finalized in February 2026, leaned on a Department of Energy report by five hand-picked contrarian scientists that independent reviewers found riddled with errors, while the National Academy of Sciences and hundreds of thousands of public comments affirmed the 2009 finding is scientifically sound and stronger than ever. State attorneys general and environmental groups are challenging the rescission in federal court.

"Greenhouse gases fit well within the Clean Air Act's capacious definition of 'air pollutant.'" — U.S. Supreme Court majority opinion, Massachusetts v. EPA (2007)