The Trump administration's repeal of a key finding on which the Environmental Protection Agency built more than a decade of regulations limiting greenhouse gas emissions to fight climate change is facing a legal challenge.The 2009 declaration, known as the Endangerment Finding, determined that carbon dioxide and other greenhouse gases endanger public health and welfare. It stemmed from a U.S. Supreme Court case involving Massachusetts two years earlier. It became the legal foundation for regulations, including limits on greenhouse gas emissions from vehicles, intended to prevent deadly floods, extreme heat waves, catastrophic wildfires and other natural disasters exacerbated by climate change.President Donald Trump and EPA Administrator Lee Zeldin worked for months to rescind the finding, and the move was finalized in February. Meanwhile, Zeldin and Transportation Secretary Sean Duffy worked to scale back limits on tailpipe emissions that were intended to encourage U.S. automakers to build and sell more electric vehicles. Now, attorneys general of California, Connecticut, Massachusetts and New York are leading a coalition of states, counties and cities in a legal challenge to the EPA's move. "Climate change is real, and it’s already affecting our residents and our economy," Massachusetts Attorney General Andrea Joy Campbell said in a statement. "When the federal government abandons the law and the science, everyday people suffer the consequences."What is the Endangerment Finding? The finding was a direct result of the 2007 U.S. Supreme Court decision in Massachusetts v. EPA, which confirmed that the Clean Air Act authorizes the EPA to regulate greenhouse gas emissions to protect public health and welfare.Since the Obama administration, the Endangerment Finding had become 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.In February, Trump's EPA finalized a change that revoked the Endangerment Finding. Zeldin said the move "will be the largest deregulatory action in the history of America."Environmental groups described the move as the single biggest attack in U.S. history against federal authority to address climate change.Over the years, courts have uniformly rejected legal challenges to the Endangerment Finding, including a 2023 decision by the U.S. Court of Appeals for the District of Columbia Circuit.New legal challengeWhen the EPA first proposed to repeal the Endangerment Finding, it heard testimony from those who opposed the move. A group of 23 state attorneys general, counties and cities also submitted letters arguing the move would violate settled law and precedent set by the Supreme Court.The new legal challenge extends that argument, suggesting that the EPA is ignoring decades of scientific evidence. It also argues that eliminating current and future greenhouse gas emissions standards violates the EPA's mission and legal obligations. The new lawsuit is led by the attorneys general of California, Connecticut, Massachusetts and New York. Other parties joining the lawsuit include attorneys general from 19 other states and Washington, D.C., Pennsylvania Gov. Josh Shapiro and numerous Democratic-led cities, including Boston, Chicago, Cleveland, Denver, Los Angeles, New York, and San Francisco. The Associated Press contributed to this report.