(WASHINGTON) — The Environmental Protection Agency is walking back a landmark environmental decision to regulate greenhouse gas emissions and fight climate change.
For more than 16 years, the EPA’s endangerment finding served as the scientific and legal foundation for federal regulations on carbon dioxide and five other heat-trapping greenhouse gases. The 2009 decision found that certain greenhouse gases endanger public health and welfare. The regulations that resulted cover everything from vehicle tailpipe emissions to the release of greenhouse gases from power plants and other significant emission sources.
President Donald Trump, joined by EPA Administrator Lee Zeldin, is expected to announce the decision on Thursday.
In a statement to ABC News, the EPA said it’s “actively working to deliver a historic action for the American people. Sixteen years ago, the Obama Administration made one of the most damaging decisions in modern history – the 2009 Endangerment Finding. In the intervening years, hardworking families and small businesses have paid the price as a result.”
Some climate scientists and policy experts say the agency’s decision to repeal the finding, even just for cars and trucks, could significantly affect U.S. efforts to address human-amplified climate change. The EPA calculates that the transportation sector is the largest contributor of direct greenhouse gas emissions in the country, with cars and trucks accounting for more 75% of those emissions.
“This is taking away the principal federal authority to regulate greenhouse gases. All of the federal regulations under the Clean Air Act to regulate greenhouse gases depend on the endangerment finding. If it’s wiped out, none of those regulations exist,” said Michael Gerrard, a professor at Columbia Law School and the faculty director of the Sabin Center for Climate Change Law.
Gerrard said the immediate impact of the EPA’s decision will be somewhat muted by the fact that the Trump administration has already revoked most regulations on greenhouse gas emissions. These include greenhouse gas emission limits on passenger vehicles, emission controls on fossil fuel-powered power plants, and controls on methane leakage from oil and gas wells.
“But this action attempts to be the nail in the coffin of all those regulations, at least for the balance of the Trump administration,” Gerrard added.
Saying the decision “amounts to the largest act of deregulation in the history of the United States,” the Trump administration estimates the move will save Americans $1.3 trillion, primarily by reducing the cost of cars and trucks. The EPA said consumers will save more than $2,400 on the purchase of a new vehicle.
But Lou Leonard, dean of Clark University’s School of Climate, Environment, and Society, says the repeal could also result in companies facing more financial and legal challenges.
“It’s going to expose, particularly businesses that are very fossil fuel intensive, to legal claims that they might not have otherwise been exposed to,” said Leonard.
“When the EPA vacates the space legally and says we’re not going to regulate, we’re out of this game, then that not only creates room for other state and local governments to do their regulation, but it also creates room for legal claims against companies for not acting on climate, because they can’t say, well, we’re just following the regulations that the federal government has created,” he added.
“The EPA’s 2009 endangerment finding triggered a trillion-dollar regulatory cascade that Congress never authorized,” the conservative nonprofit Pacific Legal Foundation said in a statement to ABC News. “What began as authority to address regional smog and acid rain has been stretched to vehicle emissions, power plants, oil and gas operations, and federal lands – reshaping America’s entire energy economy and ability to harness natural resources through administrative fiat.”
The EPA’s expected repeal of the 2009 finding “restores the principle that decisions of this magnitude require clear congressional authorization, not bureaucratic improvisation,” the statement continued.
A widely anticipated decision
The announcement from the administration was widely anticipated; the Trump administration has made the endangerment finding’s review a priority since the first day of Trump’s second term.
On Jan. 20, 2025, Trump signed an executive order titled “Unleashing American Energy” that required the head of the EPA to work with other agencies to “submit joint recommendations to the Director of OMB on the legality and continuing applicability of the Administrator’s findings” regarding the endangerment finding. The order gave them 30 days to respond.
Then, in March, the EPA announced more than two dozen policy recommendations aimed at rolling back environmental protections and eliminating a series of climate change regulations, including plans to “formally reconsider the endangerment finding.”
In a statement at the time, EPA Administrator Lee Zeldin wrote, “The Trump Administration will not sacrifice national prosperity, energy security, and the freedom of our people for an agenda that throttles our industries, our mobility, and our consumer choice while benefiting adversaries overseas. We will follow the science, the law, and common sense wherever it leads, and we will do so while advancing our commitment towards helping to deliver cleaner, healthier, and safer air, land, and water.”
As part of the March announcement, the agency released a fact sheet about the endangerment finding, describing it as “the first step in the Obama-Biden Administration’s (and later the Biden-Harris Administration’s) overreaching climate agenda” and stating that it has cost the country trillions of dollars.
The EPA announced its proposal to rescind the endangerment finding in late July 2025, citing recent Supreme Court decisions that limited the regulatory power of executive agencies and arguing that the Obama administration misinterpreted Congress’s intent when it passed the Clean Air Act.
The Supreme Court case that led to the endangerment finding
The endangerment finding stems from the 2007 Supreme Court decision Massachusetts v. EPA, which held that the EPA could regulate greenhouse gases from motor vehicles under the 1970 Clean Air Act because those gases are air pollutants.
That ruling became the legal foundation for many of the federal government’s greenhouse gas emissions regulations for vehicles, fossil-fuel power plants, and other sources of pollution responsible for climate change.
Writing for the court at the time, Justice John Paul Stevens said, “If EPA makes a finding of endangerment, the Clean Air Act requires the agency to regulate emissions of the deleterious pollutant from new motor vehicles.”
“Under the clear terms of the Clean Air Act, EPA can avoid taking further action only if it determines that greenhouse gases do not contribute to climate change or if it provides some reasonable explanation as to why it cannot or will not exercise its discretion to determine whether they do,” Stevens added.
In 2009, the head of the EPA made a landmark environmental decision. Lisa P. Jackson, appointed by President Barack Obama to lead the agency, determined that the current and projected concentrations of six greenhouse gases, including carbon dioxide, “endanger both the public health and the public welfare of current and future generations.” Her decision, based on a nearly 200-page EPA analysis of the science, more than 380,000 public comments and two public hearings, became what is now known as the “endangerment finding.”
Critics of decision say the underlying science is even stronger today
Critics of the administration’s plan to rescind the finding argue that the science linking greenhouse gas emissions to climate change is even stronger today than when the endangerment finding was established in 2009. They argue that the repeal lacks both a scientific basis and a legal foundation and will exacerbate the harmful impacts of climate change. Some are already promising to fight the decision in court.
“The Trump administration justifies this assault on science and our health by falsely claiming that U.S. climate-heating pollution doesn’t matter and that it lacks the authority to cut it. That’s a lie, and any 6-year-old knows it’s wrong to lie,” said Dan Becker, director of the Center for Biological Diversity’s Safe Climate Transport Campaign, in a statement to ABC News.
“The United States is the second-largest carbon polluter in the world after China, and the largest historical emitter of greenhouse gases. The U.S. emitted 11% of the world’s greenhouse gases in 2021, and during Trump’s first term his administration admitted that emissions in excess of 3% were ‘significant,’” he added.
“EPA’s own settled science shows that managing greenhouse gases is fundamental to protecting Americans. Rolling back these safeguards is a dangerous breach of responsibility to protect people, the environment, and our economy, benefitting polluters at the expense of all people,” said World Resources Institute (WRI) U.S. Director David Widawsky in a statement.
Overwhelming scientific evidence
In the more than 16 years since the EPA issued its 2009 endangerment finding, the science on how greenhouse gases impact human health has become more robust.
In response to the EPA’s request for public input, the National Academies of Sciences, Engineering, and Medicine conducted a comprehensive independent assessment of the science behind the endangerment finding to help inform the agency’s final decision. They released their report in September, concluding the EPA’s 2009 determination was accurate and is now supported by stronger scientific evidence, with many uncertainties that existed at the time now resolved.
“[T]he evidence for current and future harm to human health and welfare created by human-caused greenhouse gases is beyond scientific dispute,” the report stated.
The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation on such issues. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Abraham Lincoln.
Similarly, the United Nations concluded that “health and the climate are inextricably linked, and today the health of billions is endangered by the climate crisis.” The U.N. cited severe weather events, toxic air pollution, an increased risk of infectious disease outbreaks, and extreme heat as evidence that human-amplified climate change poses a significant danger to people.
In 2021, 200 leading medical journals issued a joint editorial stating that “the science is unequivocal: a global increase of 1.5° C above the pre-industrial average and the continued loss of biodiversity risk catastrophic harm to health that will be impossible to reverse.”
And in 2023, the Fifth National Climate Assessment, a report that the federal government describes as providing “authoritative scientific information about climate change risks, impacts, and responses in the U.S.,” found that “climate changes are making it harder to maintain safe homes and healthy families; reliable public services; a sustainable economy; thriving ecosystems, cultures, and traditions; and strong communities.”
“This is another setback in the fight against climate change. We’re already seeing climate change having very negative impacts. It worsens flooding, heat waves, wildfires and other impacts. We’ve seen catastrophes already in the United States for all of these. We will see more,” Gerrard said.
What happens next?
A coalition of state attorneys general, including those from California, New York, Connecticut, and Massachusetts, along with environmental groups such as the Natural Resources Defense Council, has indicated they will challenge the EPA’s decision. They argue the action is unlawful because it ignores the agency’s obligations under the Clean Air Act to regulate pollutants that endanger public health and welfare.
“This action is unlawful, ignores basic science, and denies reality. We know greenhouse gases cause climate change and endanger our communities and our health – and we will not stop fighting to protect the American people from pollution,” said California Governor Gavin Newsom and Wisconsin Governor Tony Evers, who are also the co-chairs of the U.S. Climate Alliance.
While the courts could overturn the repeal, Gerrard said they could also rule that the EPA needs congressional authorization for significant regulatory actions.
“If the Supreme Court says that, that would tie the hands of another president in reinstating the endangerment finding and in using the Clean Air Act to regulate greenhouse gases. It would not block another president from rejoining the Paris Agreement or doing lots of other things to fight climate change, but it would greatly hurt their ability to use the Clean Air Act,” said Gerrard.
Previous lawsuits challenged the endangerment finding itself, but the courts have consistently rejected those efforts. In 2012, the D.C. Circuit Court of Appeals upheld the endangerment finding after fossil fuel industry groups challenged the EPA’s use of scientific assessments. The court ruled that the EPA’s findings were supported by substantial evidence and that the agency had considered the scientific evidence in “a rational manner.” The following year, the Supreme Court declined to hear petitions specifically contesting the finding.
Leonard warns that it will be a “long road” to learn out how the decision plays out.
“There’s a lot of uncertainty, and we’re gonna have even more starting tomorrow or the next day, and that’s not good. It’s not good for the public health of Americans, it’s not good for the welfare of our communities, and it’s not good for the business climate and the economy in America,” said Leonard.
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