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How Climate Change Is Driving Extreme Weather

SARAH MCCAMMON, HOST:

It's been a disastrous summer so far. Heat waves, floods and other forms of extreme weather have killed many people around the world, and the forecast for drought, wildfire and hurricanes are all dire. How is climate change driving this extreme weather? Noel King spoke to Lauren Sommer and Rebecca Hersher from NPR's climate team.

NOEL KING, BYLINE: Lauren, let's start off with you. So the country's experiencing another heat wave this week. And it is July, so we expect heat, but this seems like an unusual summer.

LAUREN SOMMER, BYLINE: It is a bit. I mean, this past June was the hottest June recorded in the U.S. in more than a century. So it was about 4 degrees hotter on average around the country. And then we saw these really extreme heat waves come through like the one in the Pacific Northwest. I mean, more than a hundred people died in that event because heat waves can be extremely deadly, and cities are really realizing their preparations just aren't going far enough.

KING: And do scientists draw a direct link between the extremes in temperature and climate change?

SOMMER: Yes. I mean, scientists are finding that some of these broken records would be extremely unlikely without climate change. There's been about 2 degrees Fahrenheit of warming so far worldwide. And maybe that doesn't sound like a big number, but Radley Horton, a climate scientist at Columbia University, says that can cause big changes.

RADLEY HORTON: Basically, that's enough to profoundly shift the statistics of extreme heat events. It means that these dangerous thresholds of really high temperature and high humidity don't just happen a little more often than they happened in the past. They might happen twice as often.

SOMMER: And importantly, nighttime temperatures are warming even faster than daytime temperatures. And that's important to pay attention to because it means people just aren't getting a break, which can make things even more dangerous.

KING: The western United States is also experiencing an extreme drought right now and a lot of wildfires. Heat has to be making those two things worse.

SOMMER: It definitely is. And at this point, 95% of the West is in drought right now. And there's a clear cycle where the heat just dries out the land and vegetation, and then when the wildfires do come through, they burn hotter, they're more extreme, and they even create their own weather systems where these massive pyrocumulus clouds can generate lightning strikes, and that can cause even more fires.

It's also important to note that wildfires are burning outside the U.S., too. I mean, Siberia is seeing a lot of wildfire activity, and this is the third year in a row. And that's a big concern because the soils there, you know, which are either these peat or permafrost, are really rich in organic matter. And when fires hit them, it releases even more carbon to the atmosphere.

KING: So we have heat and fires on the one hand. And then, Rebecca, on the other hand, we have extreme flooding. What's going on with floods?

REBECCA HERSHER, BYLINE: Yeah. So it has been a wild few weeks. Just a quick rundown - central China got about a year's worth of rain in less than a day, people that were trapped in subway cars underground. Germany and Belgium got a series of rainstorms that turned entire towns into rivers, swept away whole homes. In the U.S., there were dramatic flash floods in Arizona after a heavy rainstorm. And in Mumbai, India, there was so much rain that it triggered landslides, and that buried whole neighborhoods.

So all of these disasters - they have been deadly. Fast-moving water is really dangerous. Hundreds of people have been killed. But at a scientific level, the disasters - they're just not surprising. Like, these are exactly the kinds of weather situations that climate scientists have been warning about for years.

KING: Why is that? What is the link between the Earth getting hotter and more flash floods?

HERSHER: Right. So even though these floods are happening thousands of miles apart all over the world, the cause is basically the same no matter where you are. And that cause is extreme rain, so a lot of rain falling in a short amount of time. And extreme rain, to your question, is getting more common as the Earth heats up, and that's because hot air plus hot water equals tons of moisture in the air. You can think of it as like a sopping-wet sponge. For example, scientists say that the warm air over Europe during the floods earlier this month, it was as saturated as the air during a hurricane. And, you know, Europe is not built to handle hurricane levels of rain.

KING: Are there more connections between the Earth getting hotter and extreme weather?

HERSHER: Well, if you want to get deeper into the science, there is always more. So there's also a potential wind connection. So as the Earth gets hotter, some climate models show that the winds in the upper atmosphere - they slow down in some places. And those winds - they carry our weather systems. That's like boats in a stream. So when the wind slows down, the weather lingers. And if that weather is a rainstorm, that means it rains for longer.

KING: Oh, or like the heat dome getting trapped over certain states...

HERSHER: Exactly.

KING: ...And then just staying for, like, a week, two weeks, OK.

HERSHER: Exactly, yeah. The weather just lingers. And it's important to say these questions - they are the cutting edge of climate science right now. Like, figuring out how climate change is affecting individual weather events, predicting how common disasters like these will get in the next decade - that is what the top scientists are working on.

KING: Rebecca Hersher and Lauren Sommer from NPR's climate team, thank you both for your reporting. We appreciate it.

HERSHER: Thanks.

SOMMER: Thank you. Transcript provided by NPR, Copyright NPR.

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