AMNA NAWAZ: The Environmental Protection Agency has repealed its own landmark Obama era assessment that greenhouse gases threaten public health and welfare.

Public health and environmental groups warn, today's changes could lead to many more premature deaths and arise in asthma attacks in the coming decades.

Until today's shift, which is expected to be challenged in court, the so-called Endangerment Finding has been the legal foundation for many of the federal government's climate regulations.

William Brangham has more, and it's part of our ongoing series Tipping Point.

WILLIAM BRANGHAM: Amna, the EPA first made that assessment in 2009 after an exhaustive review of the scientific evidence which showed that greenhouse gases were dangerously warming the planet and exacerbating extreme weather events and air pollution.

Under the Clean Air Act, that meant the EPA was then obligated to regulate that pollution.

But, today, President Trump called that finding a scam that had no legal or scientific basis.

His EPA administrator, Lee Zeldin, called it the single largest act of deregulation in American history.

LEE ZELDIN, Environmental Protection Agency Administrator: The 2009 Obama EPA Endangerment Finding is now eliminated.

This action will save American taxpayers over $1.3 trillion.

What that means is lower prices, more choices, and an end of heavy-handed climate policies.

WILLIAM BRANGHAM: Environmental advocates warned that this would worsen public health and deal a major blow to any attempts by the U.S.

to lessen the impacts of climate change.

For more on today's announcement, we are joined now by Maxine Joselow.

She's a climate reporter for The New York Times.

Maxine, thank you so much for being here.

This original finding came out of a Supreme Court ruling, Massachusetts v. the EPA, which said, yes, you can consider carbon pollution a pollutant, but you have to prove that it's detrimental to human health, which the Obama administration did.

Since that time, how has the Endangerment Finding been used by the federal government?

MAXINE JOSELOW, The New York Times: That's exactly right.

And the Endangerment Finding did not in and of itself set any new climate regulations, but it formed the legal and scientific basis for those regulations.

And, in particular, the Obama EPA used it as the justification to set the first limits ever on greenhouse gas emissions from cars, trucks, and eventually from power plants that burn coal or natural gas to make electricity.

And in the intervening years, there's been a back-and-forth between Democratic, Republican administrations, a weakening and a strengthening of those rules.

But they have remained in effect and as that litigation has played out.

WILLIAM BRANGHAM: So, now with that Endangerment Finding gone, what happens now?

MAXINE JOSELOW: So, today, EPA said that not only were they repealing the Endangerment Finding, but they also said they were immediately repealing all greenhouse gas limits on cars and trucks.

So that's already happened.

And then, in the coming months, EPA said it plans to repeal additional limits on greenhouse gases from power plants and other sources as well.

WILLIAM BRANGHAM: The science that undergirded that first finding has not changed.

In fact, the National Academies last year said, not only is the science of that original finding accurate, but it's in subsequent years become more evident.

How does the administration justify this current move?

MAXINE JOSELOW: So, Lee Zeldin, the EPA administrator, said that the Obama administration in 2009, when it issued the Endangerment Finding, used more dire predictions of how much the planet would warm than it actually would.

And, in some ways, that is true.

In 2009, the Obama administration cited some extreme projections of warming that are no longer as likely to happen because the world has taken some climate action, some efforts to reduce emissions and improve the deployment of renewable energy.

That being said, the science was unequivocal in 2009 that greenhouse gases were causing climate change, and that was unleashing more frequent and severe heat waves, floods, other extreme weather events.

And in the past 16 years, the science has only grown more unequivocal, not less.

WILLIAM BRANGHAM: The -- Zeldin also said that this was about saving money.

And we know that the White House is concerned that voters are concerned about energy prices right now.

But he and the president both said that this would really make prices for things cheaper, specifically, like cars getting $3,000 cheaper.

Does your reporting show that there's evidence for that?

Have these regulations cost Americans and will getting rid of them make things cheaper?

MAXINE JOSELOW: Great question.

Affordability is obviously a big concern for voters and a big topic for both political parties right now.

And we saw Karoline Leavitt, the White House press secretary, in the briefing this week also claim that this action would save about $2,400 off the cost of a new car for the average consumer.

And Lee Zeldin and President Trump both repeated that figure today.

The experts that I talk to, though, I had them go back and review the EPA's proposed rule and the math and the calculations that the agency did in that proposal.

And they said that the agency relied on some false and misleading assumptions to reach that $2,400 figure.

So one thing that assumed was that gas prices would be lower in the future, but they didn't explain why they thought that.

And they also didn't account for really rapidly declining costs of batteries used in electric vehicles.

And those are just two examples.

The experts I talked to went on and on.

And they also said that it's not just about the total cost of ownership of a new vehicle.

It's also about the fuel cost.

And more efficient vehicles save you money on gas because you're filling up less often.

WILLIAM BRANGHAM: Right, over the long run.

This move comes as the evidence of a warming planet just grows.

2025 was I think the third hottest year on record, surpassed only by 2024 and 2023.

What do environmental advocates say will be the likely result of this move?

MAXINE JOSELOW: They say this is going to essentially take the U.S.

out of the fight to combat climate change at a time when, as you said, the impacts are only growing more clear, from the wildfires in Los Angeles last year, to the flooding in Texas that claimed dozens of lives.

Those climate disasters are going to continue and accelerate, and the U.S.

government will no longer be playing any role in attempting to contain that.

WILLIAM BRANGHAM: You and your colleague Lisa Friedman had a story recently indicating that the Trump administration wants this to get to the Supreme Court.

Why is that?

MAXINE JOSELOW: The Trump administration is moving very quickly with this repeal of the Endangerment Finding.

They did it in just about a year, which may not feel fast to you and me, but in the world of slow-moving regulations, that's very fast.

And they're doing that because they want to have this litigated in federal court and then at the Supreme Court while Trump is still in office.

And that's important, because then his lawyers at the Justice Department can defend this before the Supreme Court.

If, say, a future Democratic president were to take office when this got to the court, then that Justice Department probably wouldn't defend this rule.

WILLIAM BRANGHAM: I see.

Maxine Joselow with The New York Times, thank you so much for being here.

MAXINE JOSELOW: Thanks so much for having me.