The Environmental Protection Agency will issue a final rule rescinding a 2009 government declaration known as the endangerment finding. That Obama-era policy determined that carbon dioxide and other greenhouse gases endanger public health and welfare.

A White House official, speaking on condition of anonymity because they were not authorized to confirm the details ahead of an official announcement, confirmed the plans, which were first reported by the Wall Street Journal.

“This week at the White House, President Trump will be taking the most significant deregulatory actions in history to further unleash American energy dominance and drive down costs,” said White House press secretary Karoline Leavitt in a statement.

The endangerment finding is 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. It is used to justify regulations, such as auto emissions standards, intended to protect against threats made increasingly severe by climate change — deadly floods, extreme heat waves, catastrophic wildfires and other natural disasters in the United States and around the world.

Legal challenges would be certain for any action that effectively would repeal those regulations, with environmental groups describing the shift as the single biggest attack in U.S. history on federal efforts to address climate change.

An EPA spokesperson did not address when the finding would be revoked but reiterated that the agency is finalizing a new rule on it.

Brigit Hirsch said via email that the Obama-era rule was “one of the most damaging decisions in modern history” and said EPA “is actively working to deliver a historic action for the American people.”

President Donald Trump, who has called climate change a “hoax,” previously issued an executive order that directed EPA to submit a report “the legality and continuing applicability” of the endangerment finding. Conservatives and some congressional Republicans have long sought to undo what they consider overly restrictive and economically damaging rules to limit greenhouse gases that cause global warming.

Lee Zeldin, a former Republican congressman who was tapped by President Donald Trump to lead EPA last year, has criticized his predecessors in Democratic administrations, saying they were “willing to bankrupt the country” in an effort to combat climate change.

Democrats “created this endangerment finding and then they are able to put all these regulations on vehicles, on airplanes, on stationary sources, to basically regulate out of existence … segments of our economy,″ Zeldin said in announcing the proposed rule last year. ”And it cost Americans a lot of money.”

Peter Zalzal, a lawyer and associate vice president of the Environmental Defense Fund, countered that the EPA will be encouraging more climate pollution, higher health insurance and fuel costs and thousands of avoidable premature deaths.

Zeldin’s push “is cynical and deeply damaging, given the mountain of scientific evidence supporting the finding, the devastating climate harms Americans are experiencing right now and EPA’s clear obligation to protect Americans’ health and welfare,” he said.

Zalzal and other critics noted that the Supreme Court ruled in a 2007 case that planet-warming greenhouse gases, caused by burning of oil and other fossil fuels, 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 U.S. Court of Appeals for the District of Columbia Circuit.

University of Pennsylvania climate scientist Michael Mann said a rollback would cement the latest form of Republican climate denial.

“They can no longer deny climate change is happening, so instead they’re pretending it’s not a threat, despite the overwhelming scientific evidence that it is, perhaps the greatest threat that we face today,” Mann said.

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Associated Press reporter Bill Barrow in Atlanta contributed to this report.