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Life can be much hotter for Americans in or near big cities, new analysis shows

MARY LOUISE KELLY, HOST:

Tens of millions of Americans continue to deal with scorching temperatures. July is on pace to be the hottest month the world has seen since we started keeping records. A new analysis shows that for the vast majority of Americans who live in urban areas, the heat is even worse. To explain that, we're joined by a member of NPR's Climate Desk, Nathan Rott. Hey there.

NATHAN ROTT, BYLINE: Hey, Mary Louise.

KELLY: OK. So I think most of us kind of know that cities are hotter - feel hotter than rural areas. Why? What's contributing to that?

ROTT: Yeah. I mean, so it's because of something called the urban heat island effect, which, you know, as you said, I think a lot of people intuitively know. And it is not a new discovery. You know, researchers have shown for decades, if not longer, that temperatures are generally hotter in urban centers than they are in rural areas. And the reason for that is the built environment. You know, fewer trees mean less shade. Buildings can block cooling winds. You know, concrete absorbs heat during the day and emits it at night. If you've ever felt the hood of your car after driving it a bit or, you know, walked behind a window air conditioning unit, you know that those things generate heat.

KELLY: Oh, yes. OK, so it's all those factors together combining that are making our cities hotter. What did we learn from this new analysis?

ROTT: Yeah. So this new analysis we're talking about, which was conducted by the nonprofit research group Climate Central, aims to see how much hotter different census tracts are in 44 of the country's biggest cities. And they did that by creating an index that essentially shows how much hotter a developed area is compared to what it would be if it was just a field or a forest. So they're not measuring actual temperatures, which is something that researchers I've talked to prefer. Jen Brady, the lead data analyst at Climate Central, co-led this project.

JEN BRADY: I was surprised at how far out the urban heat island effect was. I was thinking, once you kind of got out of the city core, it was just going to drop off the cliff, and it would go from, you know, eight degrees more to two degrees more. But really, in a lot of these cities, you're maintaining four or five degrees further and further outside even the city core.

ROTT: And Mary Louise, it's important to remember - when we're talking about these kinds of record heat events that so many places are dealing with right now, five degrees more is actually a really big deal.

KELLY: Yeah.

ROTT: Because we know that even a small increase in temperature can lead to much greater health risks for people and higher cooling costs.

KELLY: OK, next question - are these hotter temperatures felt evenly across a city?

ROTT: No, definitely not. This analysis by Climate Central did not layer on socioeconomic or race data, but there is a lot of other research that shows there are huge discrepancies in who experiences even hotter temperatures in just a single city. So Angel Hsu, an assistant professor at the University of North Carolina - she published a study on this just a couple of years ago.

ANGEL HSU: So we find that Americans in major U.S. cities living two times below the poverty line are exposed to almost a full degree higher Celsius of this urban heat island effect compared to their wealthier counterparts. And the same thing goes with people of color.

ROTT: And she says that's generally because of a lack of tree cover in these neighborhoods, greater density of people and more pollution and industry.

KELLY: OK, so what options do we have to protect people from all this heat?

ROTT: So, I mean, the biggest thing people can do is stop warming the planet. Research published earlier this week found that heat waves in America and Europe - the ones that they're dealing with right now - would be virtually impossible without human-caused climate change. On a smaller scale, though, there's a lot communities can do. They can plant more trees. They can install shade structures. Los Angeles, Charlotte, N.C., and other cities are painting streets brighter colors to help reflect sunlight. So there's a lot that can be done from an urban planning standpoint to try to make these temperatures a little more bearable.

KELLY: NPR's Nathan Rott. Thanks for your reporting.

ROTT: Yeah, thank you. Transcript provided by NPR, Copyright NPR.

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Nathan Rott
Nathan Rott is a correspondent on NPR's National Desk, where he focuses on environment issues and the American West.