The Trump administration on Thursday revoked the 2009 endangerment finding, the scientific basis for regulating greenhouse gas emissions under the Clean Air Act. EPA Administrator Lee Zeldin called the Obama-era declaration “the Holy Grail of federal regulatory overreach” while President Trump claimed fossil fuels have “saved millions of lives.”

The 2009 finding determined that carbon dioxide and other greenhouse gases threaten public health and welfare, serving as the legal foundation for emissions standards on vehicles, power plants, and industrial sources. Environmental groups called the move the single biggest attack on federal climate authority in U.S. history, noting evidence supporting the finding has only grown stronger since its adoption.

Legal challenges are expected to follow, with experts predicting the action could invalidate current emissions limits and prevent future climate regulations. The EPA also announced plans to delay Biden-era vehicle emission rules and eliminate tax credits for automatic start-stop ignition systems. Former EPA Administrator Gina McCarthy called the decision reckless, saying the agency would rather “spend its time in court working for the fossil fuel industry than protecting us from pollution.”