The Trump administration is moving to dismantle one of the foundational pillars of federal climate policy: the Environmental Protection Agency’s (EPA) 2009 so-called ‘endangerment finding’.

This Obama-era determination concluded that greenhouse gases [GHGs] – including carbon dioxide and methane – pose a significant risk to human health and welfare. It underpins key regulations aimed at curbing emissions from vehicles, power plants, and industrial sources.

Now, under President Trump’s leadership, the EPA, led by Administrator Lee Zeldin, is proposing to rescind it.

Speaking at a truck dealership in Indianapolis, Zeldin announced the agency had sent the proposal to Trump’s Office of Management and Budget.

“Through the endangerment finding, there has been into the trillions worth of regulations, including tailpipe emissions and including electric vehicle mandates,” he said in an interview with the conservative outlet Newsmax.

Zeldin characterized the repeal effort as the most substantial deregulatory action in US history and a necessary step to roll back what he described as burdensome climate rules.

The endangerment finding was a direct result of a 2007 Supreme Court ruling, which required the EPA to determine whether greenhouse gas emissions from vehicles posed a public health threat under the Clean Air Act. The Obama administration’s conclusion in 2009 – that such emissions do indeed endanger the public – provided the legal foundation for climate regulations that followed.

The Biden administration had used that same authority to craft ambitious vehicle emissions standards aimed at pushing the market toward electric vehicles.

Zeldin's proposal, if finalised, would remove the EPA’s ability to regulate greenhouse gases under the Clean Air Act. That could leave the federal government powerless to tackle emissions without new legislation from Congress – a daunting prospect given the political gridlock on climate policy.

This initiative marks a dramatic escalation from the Trump administration’s first term, during which it rolled back climate rules without undoing the endangerment finding itself. Now, the administration is directly targeting the scientific consensus that greenhouse gas emissions drive dangerous climate change.

Critics have called the move a return to outright climate denial. Zealan Hoover, a former senior EPA advisor under President Biden, likened the current moment to the early 2000s. “We are right back to full-throated climate denialism,” he told the New York Times, noting that climate change affects human health by intensifying extreme weather, driving heat-related illnesses, and contributing to sea level rise that worsens dangerous flooding.

The EPA’s justification for this repeal rests on a report commissioned by the Department of Energy. That report came from a group of scientists known for challenging the mainstream scientific understanding of climate change, including Steven E. Koonin and John Christy.

In it, they argue that computer models overstate future warming and that carbon dioxide has beneficial effects on agriculture. They also assert that US vehicle emissions are too small a share of global totals to justify regulation.

Reflecting these claims, the EPA's draft rule suggests that greenhouse gases from US vehicles “would not have a scientifically measurable impact” on the global climate. Instead, the agency contends that climate regulations themselves harm public welfare by raising vehicle costs and reducing consumer choice.

That position contradicts data from the EPA itself, which identifies the transportation sector as the country’s largest source of greenhouse gas emissions. By some estimates, if America’s vehicle fleet were considered a separate country, it would rank as the fourth-largest emitter in the world. “If vehicle emissions don’t pass muster as a contribution to climate change, it’s hard to imagine what would,” said Dena Adler, an attorney at New York University’s Institute for Policy Integrity, told the Times.

Dan Becker of the Center for Biological Diversity criticised the plan as a "cynical one-two punch" that would allow more polluting cars on the road while stripping the EPA of tools to regulate them. He noted, in an interview with the Times, that the standards targeted for rollback would have prevented 7bn tonnes of carbon emissions and saved drivers thousands of dollars in fuel and maintenance over their vehicles' lifetimes.

Still, the move has supporters. Daren Bakst of the right-wing Competitive Enterprise Institute argued that it is “unreasonable to claim that pollutants contribute to endangerment if emissions are de minimis.” Indiana Governor Mike Braun, a Republican, also voiced support, saying Biden-era rules had hurt the state's auto sector. “You can count on Indiana being for common sense and reining in government,” he told the Times.

Automakers, meanwhile, responded more cautiously. John Bozzella, who heads a trade group representing most major car manufacturers, the Alliance for Automotive Innovation, acknowledged that the Biden-era rules were difficult to meet under current market conditions. However, he stopped short of endorsing a full repeal of the endangerment finding.

Even some longtime opponents of environmental regulation expressed reservations about repealing the 2009 finding. Jeffrey Holmstead, an attorney and former EPA official under Presidents George H W and George W Bush, said he was not aware of any industry groups actively pushing for its reversal. Marty Durbin, who runs the US Chamber of Commerce’s energy arm, recently called the finding “settled law.”

Environmental advocates say the proposed repeal faces a tough road legally. David Doniger, a lawyer with the Natural Resources Defence Council, expects it will be struck down in court, pointing out that climate science has only grown more conclusive since 2009.

Former Vice President Al Gore called the EPA’s move “an abandonment of reality” in service of fossil fuel interests. “Today’s EPA announcement ignores the blindingly obvious reality of the climate crisis and sidelines the EPA’s own scientists and lawyers in favour of the interests and profits of the fossil fuel industry,” he told the Times.

The proposal is not yet final. Once it is published in the Federal Register, the agency will accept public comments for 45 days. The EPA would then review the feedback before deciding whether to finalise the rule, a process that could stretch into the next year or longer. Meanwhile, legal battles are expected to ensue.

The stakes are high. If the repeal stands, it could severely limit the federal government’s authority to act on climate, not just under Trump, but for future administrations as well.

Without the endangerment finding, the EPA would lose its clearest legal pathway to regulate greenhouse gases – just as scientists warn that global emissions must be drastically cut to avoid catastrophic warming beyond 1.5 degrees Celsius. The outcome could shape the country’s environmental trajectory for years to come.