AILSA CHANG, HOST:

Now, these deadly flash floods on the border of Nepal and Chinese-administered Tibet are not a surprise to many climate scientists. NPR's Julia Simon joins us now to explain why. Hi, Julia.

JULIA SIMON, BYLINE: Hello, Ailsa.

CHANG: So the way I understand it, this flooding - it came from a glacier - right? - that collapsed. Is that correct?

SIMON: Yeah. So the reports are still preliminary, but many scientists think this was a glacier collapsing - this giant chunk of ice that snapped off triggering the floods. This mass of ice and rock and mud and water - it started ripping down this Himalayan river valley, down through these villages, destroying communities. If you've seen the videos, you can see it's this avalanche of deadly debris.

CHANG: Yeah. And I mean, these glaciers, they've been around for thousands of years, right? So...

SIMON: Right.

CHANG: ...To have a chunk of glacier just snap off now seems like a huge deal.

SIMON: It does. But sadly, many scientists are not so surprised that this could happen, Ailsa, and that's because of human-caused climate change. These glaciers that were once stable, they're disappearing. NPR has been reporting on Nepal's glaciers for years. A team from NPR traveled to Nepal in 2022. They were climbing up a moraine. That's a massive pile of boulders created by a glacier. But when NPR's Rebecca Hersher got to the top, there was no glacier in sight.

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REBECCA HERSHER: Oh, wow.

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SIMON: That's the sound of water. There was only water - this huge lake - where a glacier should have been, Ailsa. The glacier had melted, and glacial lake floods are a growing threat. In recent years, multiple glacial lake floods have displaced and killed people. Scientists warn that an estimated 15 million people around the world are at risk from such floods.

CHANG: Wow. So just how unstable are these melting glaciers?

SIMON: Yeah. So NPR spoke with Alton Byers about this. He's at the Institute of Arctic and Alpine Research at the University of Colorado at Boulder. He says he's surprised how fast the permafrost - that's the continuously frozen ice, soil and rock that's held the mountains together for millennia - it's now changing.

ALTON BYERS: The analogy I and my colleagues use is take a stick of butter out of the refrigerator and put it on the counter. It's going to get softer, and it's going to lose its structural integrity.

SIMON: Yeah. So these melting glaciers - they pose deadly risks to the communities in their path.

CHANG: I mean, we're seeing it right now. So what are...

SIMON: Yeah.

CHANG: ...Some solutions here to prevent the kind of disaster that we are seeing in Nepal, for example - a disaster that is caused by melting glaciers?

SIMON: Well, the first thing is better alert systems. It seems right now, like Nepal's flood warning system wasn't equipped to handle this, despite quite a bit of investment in those warning systems over the last decade or so. And it's important to mention this area has seen flash floods before. But we also know the primary driver of global warming is the burning of fossil fuels, like oil, gas and coal. The solutions to transition away from fossil fuels are out there, Ailsa. They are scalable. They're affordable. They're reliable. They include solar energy, wind energy and batteries.

CHANG: That is NPR climate and energy correspondent, Julia Simon. Thank you, Julia.

SIMON: Thank you, Ailsa. Transcript provided by NPR, Copyright NPR.

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