The Environmental Protection Agency has repealed its own landmark Obama-era assessment that greenhouse gases threaten public health and welfare.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. Omna, 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. 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. 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 Josalow.

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 versus the EPA, which said,

yes, you can consider carbon pollution a pollutant, but you have to prove that it's detrimental to

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