The U.S. Environmental Protection Agency on Tuesday formally proposed rescinding the 2009 “endangerment finding,” the scientific determination that greenhouse-gas emissions threaten public health and thus must be regulated under the Clean Air Act. Administrator Lee Zeldin announced the plan during a podcast interview and said it constitutes “the largest deregulatory action in the history of America.” Eliminating the endangerment finding would strip the agency of its primary legal foundation for curbing carbon dioxide, methane and other heat-trapping gases from vehicles, power plants and industrial sources. The proposal also seeks to repeal federal tailpipe-emission standards, which the EPA says flow directly from the 2009 decision. EPA officials contend the rollback could unwind roughly $1 trillion in climate-related regulations and save industry more than $54 billion a year. Critics, including environmental lawyers and former EPA administrators, warned that the move contradicts years of scientific evidence and could face lengthy legal challenges; the 2009 finding has withstood multiple court tests since the Supreme Court affirmed the agency’s authority to regulate greenhouse gases in 2007. The agency will accept public comments once the proposal is published in the Federal Register. If finalized, it would mark the Trump administration’s most sweeping reversal of federal climate policy to date.