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Disaster experts say heat warning systems are falling short

ARI SHAPIRO, HOST:

Record-breaking heat soared in many Western states today - up to 110 degrees in California and Arizona. That can be extremely dangerous, especially for older people and those with medical conditions. Some disaster experts say today's heat warning system isn't doing enough to alert people to the risk. Lauren Sommer is with NPR's climate team. Hey, Lauren.

LAUREN SOMMER, BYLINE: Hey, Ari.

SHAPIRO: Summer heat is common in many parts of the country. So how can health officials let people know when a particular heat wave is going to be dangerous?

SOMMER: Yeah, it's definitely an issue with heat because now as the climate gets hotter, you know, heat waves are getting longer and more intense. And some are unprecedented, just outside the experiences that people have had. But it's really hard to warn people about that difference. Kristie Ebi, a professor for the Center of Health and Global Environment at the University of Washington, says, you know, it's because people think they can handle it.

KRISTIE EBI: People generally know that it was quite hot, but not that many people take the actions because I don't see myself at risk. And this is where we certainly need better understanding of how to communicate to people that, in fact, they do need to take action.

SOMMER: She says hundreds of people die every year in the U.S. due to heat. It's the most deadly weather-related disaster.

SHAPIRO: Well, tell us how the system works now. What kinds of warnings do people get today that a heat wave might be dangerous?

SOMMER: Yeah. So if you check the weather on your phone, you might see something that says excessive heat warning and then, you know, the high temperature of the day. But temperature is only part of the story because humidity is what makes heat waves really deadly. The more humid the air, the harder it is for our bodies to cool off because we need to sweat - right? - to evaporate that to get cool. And in high humidity, it's just not evaporating very well. It's kind of like pooling on your skin.

SHAPIRO: So temperature is only part of the equation. We should really get humidity warnings?

SOMMER: There is a little bit easier thing to use, and that's the heat index, which is put out by the National Weather Service. That's that feels-like temperature you might have seen. It's, like, 90 degrees out, but it feels like 101, for example. You can find it on weather apps or in some weather forecasts, and it takes humidity into account and how the human body responds to heat. But here's the thing. It's describing what the temperature feels like in the shade because it's based on a model that doesn't account for the sun hitting your body or if you move around a bunch. So it's essentially made for only people sitting in the shade.

SHAPIRO: So what about construction workers, landscapers, student athletes, people who spend all day in the sun?

SOMMER: Yeah, exactly. And it's also calibrated to a healthy, youngish person - so not pregnant people, older people, medically vulnerable people who really are at risk of heatstroke. And the new research has found that the model that measures the heat index may be underestimating really high temperatures. David Romps, who is a professor of Earth and planetary science at UC Berkeley, did a study that shows it might be off by as much as 20 degrees at really high heat.

DAVID ROMPS: Using the correct heat index would allow us to identify those handful of times where the heat is so severe that it is pushing our bodies close to the breaking point. We can identify the times where the warnings really need to be made with clarity, and people really need to pay attention.

SHAPIRO: What does the National Weather Service say about the idea that the current heat index is not useful enough?

SOMMER: They told me they're reviewing that study, and they're committed to making the heat warning system better. They're also piloting a new system in the West that's called heat risk. It has a tiered warning system that has more specific information for vulnerable groups. But, you know, it's important to note the key thing is to get that warning to people. It has to reach people. So experts say that, you know, working with neighborhood groups, community groups or church groups is really important to get the word out when heat is dangerous. And so people are checking on people when these really extreme conditions are hitting.

SHAPIRO: That's Lauren Sommer from NPR's climate team. Thank you. Stay cool out there.

SOMMER: Yeah, thanks so much. Transcript provided by NPR, Copyright NPR.

Lauren Sommer covers climate change for NPR's Science Desk, from the scientists on the front lines of documenting the warming climate to the way those changes are reshaping communities and ecosystems around the world.