This past week, the EPA said it is reconsidering the scientific finding that greenhouse gases are a danger to public health.

That finding has been at the center of this country's fight against climate change.

This comes as research shows average global temperatures in 2024 likely rose above a 1.5 degrees Celsius threshold that for years has been an environmental red line.

Ali Rogan spoke with Michael Mann, the director of the Center for Science, Sustainability, and the media at the University of Pennsylvania.

Michael, thank you so much for being here. Simply put, how big a deal is it for the planet to exceed this 1.5 degree

threshold? Well, it's a big deal, but it should be put in context. What happened this year was that

we had an El Niño event. It's a natural warming event that adds to the global temperature. So it

boosted it temporarily above that 1.5 Celsius mark.

What we're really concerned about is when the trend line itself crosses 1.5 Celsius, roughly

3 degrees Fahrenheit.

And that'll probably happen in little more than a decade if we continue on this current course.

And so I sort of liken it to, you know, here in Philadelphia where I live, if you get a, you know, 50 degree or 60 degree day in late February, it doesn't mean winter's over, but it's an indication that the end of winter is probably coming.

This is an indication that we're getting perilously

close to this very dangerous threshold. And what happens if we do continue to exceed this number?

That'll be a sign that things are continuing to move in that direction in a more permanent way, right?

Yeah, and so, you know, it's not like a cliff that we go off at that level of warming.

It's more like a dangerous highway that we're going down.

Every bit of additional warming makes things worse.

But conversely, every bit of warming that we can prevent makes things better.

And so it's important for us to, you know, get off the burning of fossil fuels as

quickly as we can, limit warming as much as we can. And this is just an indication that we are,

you know, headed towards ever more dangerous levels of climate change. And what is it about that

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