The Trump administration on Thursday reversed the U.S. government’s longstanding scientific assertion that planet-heating pollution seriously threatens Americans, erasing a foundational piece of the country’s efforts to address climate change.

The repeal of the 2009 endangerment finding — a conclusion based on decades of science that carbon dioxide and other greenhouse gases endanger public health and welfare — represents one of the biggest environmental rollbacks in U.S. history, and the latest in a series of actions by President Donald Trump to scrap policies and regulations designed to curb the use of fossil fuels and accelerate the transition to clean energy.

Experts and scientists condemned the action. The Environmental Protection Network — a bipartisan group of more than 700 former staff and appointees at the Environmental Protection Agency — described it as “unprecedented and dangerous.”

“This move is a fundamental betrayal of EPA’s responsibility to protect human health,” said Joseph Goffman, former assistant administrator of the EPA Office of Air and Radiation. “It is legally indefensible, morally bankrupt and completely untethered from the scientific record.”

Independent researchers around the world have long concluded that greenhouse gases released by the burning of gasoline, diesel and other fossil fuels are warming the planet and worsening weather disasters.

That includes in California, which sits on the “front lines of climate impacts and pollution impacts,” said Leah Stokes, an associate professor of political science at the University of California, Santa Barbara.

“The endangerment finding was really about putting the country on a path to dealing with these emissions,” Stokes said. “This is a policy that basically is protecting Americans, and they’ve decided that they don’t care about that, that no matter what — the wildfires or flooding or drought or heat waves that are killing people — that they’re not going to take action.”

The endangerment finding has been the foundation for federal regulation of six greenhouse gases under the Clean Air Act, making clear the government was serious about cutting emissions, said Chris Field, director of Stanford University’s Woods Institute for the Environment.

“There is, from a scientific perspective, no question that the original endangerment finding was appropriate and important for progress in addressing greenhouse gas pollution,” Field said. He noted that in the more than 16 years since the finding was adopted, the evidence to support it has only increased, as have the effects from emissions.

“Any honest evaluation of that evidence would validate strongly keeping the endangerment finding in place, and the arguments for removing it are ideologically driven, willfully ignoring the evidence that’s out there,” Field said.

The administration first announced its intention to repeal the endangerment finding in March, when EPA Administrator Lee Zeldin referred to it as “the holy grail of the climate change religion.” The EPA released its formal proposal in July and it received more than half a million public comments, the bulk of which were opposed to the plan. Among them were comments from environmentalists, scientists, civil rights groups and public health organizations who argued that rescinding the finding is contrary to climate science and public health.

The reversal also drew formal opposition from more than 50 U.S. cities and nearly two dozen states, including California.

Support for the plan came from industry groups and those geared toward free markets and regulatory reform. The U.S. Chamber of Commerce favored the repeal, saying greenhouse gas vehicle standards that rest on the endangerment finding are “enormously costly and ultimately unachievable” and amount to “regulatory overreach.”

However, opposition also crossed party lines — including from three former EPA administrators who served under Republican and Democratic administrations.

“The scientific evidence is ... clear and overwhelming that greenhouse gas emissions harm public health and welfare,” wrote former EPA Administrators William K. Reilly, Christine Todd Whitman and Gina McCarthy, who served under George H.W. Bush, George W. Bush and Barack Obama, respectively.

Much of the EPA’s argument for abandoning the finding hinges on whether greenhouse gases are “air pollutants” under the Clean Air Act, and thus subject to federal regulations. A 2007 Supreme Court case, Massachusetts vs. EPA, determined that they are.

Opponents said the decision will not only lead to worse air quality but also billions in healthcare costs tied to increased asthma attacks, heart disease and other issues related to pollution. The transportation sector is the single largest source of heat-trapping emissions in the United States.

“As a result of this repeal, I’m going to see more sick kids come into the emergency department having asthma attacks and more babies born prematurely,” said Lisa Patel, executive director of the Medical Society Consortium on Climate and Health. “My colleagues will see more heart attacks and cancer in their patients. These health harms are felt by all of us, but they are disproportionately experienced by communities of color, low-income populations, outdoor workers, pregnant people, those with chronic illnesses and children.”

Others said it boils down to more profits for the oil and gas industry, which made substantial contributions to Trump’s presidential campaign in 2024.

The Trump administration is “doing the bidding of the fossil fuel industry, even if it harms everyday Americans,” Stokes, the UC Santa Barbara professor, said, and the latest action “sends a chilling message across the economy that climate action, making progress on pollution, is not a priority.”

Field, of Stanford, said scrapping this key scientific finding will also degrade U.S. standing on the global stage. The ability to regulate emissions under the Clean Air Act has allowed the nation to push innovation in climate technology and finance related to transportation and power generation, developments that will be jeopardized by the withdrawal of the endangerment finding, he said. What’s more, clean energy is increasingly the cheapest, safest and most reliable option for electricity generation and for vehicles.

“The economies of the 21st century are going to have at their core the production of green energy and clean transportation, and if the U.S. sidelines itself, it’s basically saying we don’t want to be a part of the future, we don’t want to be a part of the enterprises that are driving the global economy in the coming decades,” he said. “And I think that’s clearly to our disadvantage.”

Several groups have vowed to fight the repeal in court.

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