The United States has rescinded a scientific finding that has long been a core basis for its regulation of greenhouse gas emissions and action to combat climate change.

Thursday’s decision is the president’s most radical move yet Donald Trump Since the start of his second term, he has rolled back environmental regulations.

Under his leadership, the U.S. Environmental Protection Agency (EPA) finalized a rule that repealed a 2009 “hazard finding” statement issued by the government.

It is the legal basis for nearly all climate regulations in the Clean Air Act targeting motor vehicles, power plants and other sources of pollution that heat the planet.

The survey, established during the presidency of Democrat Barack Obama, found that carbon dioxide and other greenhouse gases threaten public health and welfare.

But President Trump, a Republican, called Climate change is a “hoax” and a “hoax.” He called the discovery of harm “one of the biggest hoaxes in history,” adding that it had “no basis in fact” or law.

“On the contrary, over generations, fossil fuels have saved millions of lives and lifted billions of people out of poverty around the world,” Trump said during a White House ceremony on Thursday.

He hailed the repeal of the dangerous findings as “by far the largest single deregulatory effort in American history.”

EPA Administrator Lee Zeldin, who also attended the ceremony, described the hazard finding as “the Holy Grail of federal regulatory overreach.”

Reversing the hazard finding would repeal all greenhouse gas emissions standards for cars and trucks. Experts say it could also lead to a broader relaxation of climate regulations for stationary energy sources such as power plants and oil and gas facilities.

But Thursday’s new rules are likely to face resistance in the U.S. court system.

Environmental law professor Ann Carlson told The Associated Press that overturning the finding would be “much more damaging” than other actions Trump has taken to overturn environmental rules.

Environmental groups called the move the largest single attack in U.S. history on the federal government’s ability to address the problem. climate change. They say the evidence supporting the dangerous finding has grown stronger in the 17 years since it was approved.

As part of Thursday’s decision, the EPA also announced it would end tax credits for automakers that install automatic start-stop ignition systems in vehicles. The device is designed to reduce emissions, but Zeldin said “everyone hates” it.

Zeldin, a former Republican congressman appointed by Trump to head the Environmental Protection Agency last year, criticized his Democratic predecessors, saying they were “willing to bankrupt the country” in the name of fighting climate change.

this Hazard discovery “Trillions of dollars of regulation have resulted in strangling entire sectors of the U.S. economy, including the U.S. auto industry,” Zeldin said, specifically criticizing the leadership of Obama and former President Joe Biden.

“The Obama and Biden administrations have used it to squeeze out a left-wing wish list that includes costly climate policies, electric vehicle mandates and other requirements that impact consumer choice and affordability.”

Hazard findings allow for the development of a range of regulations aimed at preventing climate change and related threats.

These include deadly floods, extreme heat waveCatastrophic wildfires and other natural disasters in the United States and around the world.

Former EPA Administrator Gina McCarthy, who served as White House climate adviser in the Biden administration, called the Trump administration’s actions reckless.

“EPA would rather spend its time in court working for the fossil fuel industry than protecting us from the escalating impacts of pollution and climate change,” she said.

McCarthy explained that the EPA has clear scientific and legal obligations to regulate greenhouse gases, adding that the health and environmental hazards of climate change “have become impossible to ignore.”

The EPA’s action on Thursday came after Trump issued an executive order directing the agency to submit a report on the “legality and continued applicability” of the hazard findings.

Conservatives have long sought to curb emissions of greenhouse gases that contribute to global warming by repealing rules they say are overly restrictive and economically damaging.

Democratic Senator Ed Markey Said keeping dangerous findings should be “a matter of course”.

“Trump and Zeldin are putting our lives and our future at risk,” he said in a video statement.

“They keep removing protections in a race to the bottom. Zeldin is not saying ‘let them eat the cake,’ but ‘let them breathe the soot.'”