The rule finalised by the Environmental Protection Agency rescinds a 2009 government declaration known as the endangerment finding that determined that carbon dioxide and other greenhouse gases threaten public health and welfare.
The Obama-era 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.
The repeal eliminates all greenhouse gas emissions standards for cars and trucks and could unleash a broader undoing of climate regulations on stationary sources such as power plants and oil and gas facilities, experts say.
Legal challenges are near certain.
President Donald Trump called the move "the single largest deregulatory action in American history, by far", while EPA Administrator Lee Zeldin called the endangerment finding "the Holy Grail of federal regulatory overreach".
Trump called the endangerment finding "one of the greatest scams in history", claiming falsely that it "had no basis in fact" or law.
"On the contrary, over the generations, fossil fuels have saved millions of lives and lifted billions of people out of poverty all over the world," Trump said at a White House ceremony on Thursday, although scientists across the globe agree that carbon dioxide and other greenhouse gases are driving catastrophic weather and rising sea levels.
Environmental groups described the move as the single biggest attack in US history against federal authority to address climate change.
"This action will only lead to more climate pollution, and that will lead to higher costs and real harms for American families," said Fred Krupp, president of Environmental Defense Fund, adding the consequences would be felt on Americans' health, property values, water supply and more.
The EPA also said it would propose a two-year delay to a Biden-era rule restricting greenhouse gas emissions by cars and light trucks.
Zeldin, a former Republican congressman who was tapped by Trump to lead EPA in 2025, has criticised his predecessors in Democratic administrations, saying that in the name of tackling climate change, they were "willing to bankrupt the country".
The Supreme Court ruled in a 2007 case that planet-warming greenhouse gases, caused by the burning of oil and other fossil fuels, were air pollutants under the Clean Air Act.
The endangerment finding is widely considered the legal foundation that underpins a series of regulations intended to protect against threats made increasingly severe by climate change.
That includes deadly floods, extreme heatwaves, catastrophic wildfires and other natural disasters in the United States and around the world.
Gina McCarthy, a former EPA administrator who served as White House climate adviser in the Biden administration, called the Trump administration's actions reckless.
Former president Barack Obama said on X that repeal of the endangerment finding would make Americans "less safe, less healthy and less able to fight climate change - all so the fossil fuel industry can make even more money".
The repeal could erase current limits on greenhouse gas pollution from cars, factories, power plants and other sources and could hinder future administrations from imposing rules to address global warming.
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.
