The Trump administration on Tuesday proposed to repeal a 2009 landmark finding that greenhouse gases pose a threat to the public.

The “endangerment finding” came after the Supreme Court ruled in 2007 that the Environmental Protection Agency (EPA) can regulate greenhouse gases (GHG) if it determines that they harm Americans’ well-being.

But now, the EPA says it no longer believes that gases such as carbon dioxide harm the public.

Here are five things to know:

The finding determined that GHGs caused harm

In 2009, the Obama administration made two key determinations: that greenhouse gases including carbon dioxide and methane endangered public health and welfare, and that auto sector emissions played a part in that danger.

Now, the EPA is proposing to overturn that finding and instead determine “that there is insufficient reliable information to retain the conclusion that GHG emissions from new motor vehicles and engines in the United States cause or contribute to endangerment to public health and welfare in the form of global climate change.”

It underpins automobile regulations

The move to repeal the endangerment finding is not simply symbolic. It was a legal finding that underpins climate regulations, particularly those that pertain to cars and trucks.

The EPA’s proposal on Tuesday also seeks to repeal the nation’s car and truck regulations, meaning the agency is not requiring any set number of electric models on the market and that automakers’ fleets can emit as much as they would like.

It said that the move will have cost savings, but it is also expected to exacerbate climate change and pollutants.

The regulation did not explicitly address climate regulations from other sectors, but the EPA has separately proposed to remove all climate regulations from power plants.

The move stands in contrast with evidence of climate harm

The push to repeal the endangerment finding stands in stark contrast to mounting evidence that climate change is already causing widespread, costly harm.

The EPA itself reports that greenhouse gases including carbon dioxide are heating the planet, leading to “extreme events” that can “harm people, damage property, strain infrastructure, reduce crop yields, and more.” Before the Trump administration pulled it offline, the federal National Climate Assessment showed greenhouse gases causing both an accelerating pace of multibillion-dollar disasters and a more insidious onslaught of sickness caused by heat, smoke and migrating pathogens.

Though plants on land and sea absorb some of the planet-heating carbon dioxide released when fossil fuels are burned, research shows emissions are now outpacing nature’s ability to absorb them. In April, federal scientists reported that atmospheric CO2 rose faster last year than at any point in human history.

Meanwhile, each of the past 10 years has been the hottest ever recorded.

A hotter atmosphere is both thirstier and more volatile, fueling extreme weather — from flash droughts and floods to stronger hurricanes and firestorms.

Repairing damage from natural disasters cost the U.S. economy $1 trillion last year alone. As Federal Reserve Chair Jerome Powell warned in February, rising flood, fire, and wind risks could make parts of the country uninsurable.

That meant, Powell said, that within as little as a decade “there are going to be regions of the country where you can’t get a mortgage.”

Meanwhile, the transportation sector is the largest contributor to U.S. emissions, making up about 28 percent in 2022.

The change is likely to face court challenges

Environmental groups and others are likely to challenge the Trump administration’s move. They say that courts should reject attempts to overturn the endangerment finding because of the overwhelming scientific evidence that climate change poses a threat to the public.

It’s not ultimately clear whether their efforts will be successful. And some experts worry that the move to overturn the endangerment finding and subsequent litigation could constrain a future Democratic administration from regulating altogether.

“I would imagine they will have a real problem with the D.C. circuits, you know, because they really are trying to defy a very clear D.C. circuit precedent,” Joe Goffman, who led the EPA’s Air and Radiation Office under the Biden administration, told The Hill last week.

But he noted that if the case gets to the Supreme Court, it’s not clear how it will rule.

“The Supreme Court has changed considerably since 2007,” Goffman said.

He added that he thinks the Trump administration is “hoping to end up with a reading of the Clean Air Act … that [establishes] certain tests that the agency has to make in order to establish its authority, tests that for all practical intents and purposes, a future agency won’t be able to meet.”

New York Attorney General Letitia James, a frequent challenger of Trump administration actions, released a statement saying, “This is a lawless, shameful gift to Big Oil, and we cannot let it stand.”

The shift is part of broader anticlimate efforts by Trump

The repeal of the endangerment rule is part of a broader second-term Trump effort against climate action — which some senior officials now frame as a greater threat than climate change itself.

In its chapter on the EPA, the far-right Project 2025 plan calls for an “update” to the 2009 finding on “the perceived threat of climate change,” calling it “a favored tool that the Left uses to scare the American public into accepting their … liberty-crushing regulations, diminished private property rights, and exorbitant costs.”

A March EPA press release claimed the overhaul “represents the death of the Green New Scam and drives a dagger straight into the heart of the climate change religion.”

But the campaign goes far beyond the EPA. The administration has pulled billions meant to help cities brace for extreme weather and rebuild stronger after disasters.

It has also repealed billions of dollars in tax credits for low-carbon energy sources and has sought to put up new hurdles for solar and wind power.

And it has launched a broad assault on federal climate research — from Pentagon studies on warming and conflict, to medical research on the spread of tropical diseases, to NASA satellites that help farmers plan crops.

Meanwhile, the administration is ramping up U.S. oil and gas exports — including a deal to pressure Europe into buying nearly 10 times more — while blocking rules to limit the release of the potent greenhouse gas methane from fracking.