Short Wave - The Deadly Toll Heat Can Take On Humans

Episode Date: September 4, 2023

This year, the hottest July ever was recorded — and parts of the country were hit with heat waves that lasted for weeks. Heat is becoming increasingly lethal as climate change causes more extreme heat. So in today's encore episode, we're exploring heat. NPR climate correspondent Lauren Sommer talks with Short Wave host Regina G. Barber about how the human body copes with extended extreme heat and how today's heat warning systems could better protect the public. If you can, stay cool out there this Labor Day, dear Short Wavers.What science story do you want to hear next on Short Wave? Email us at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, short wavers, Regina Barber here with Lauren Summer, one of NPR's climate correspondence. Hey, Lauren. Hey, Gina. So today, we're starting with an experiment that's designed to make you sweat. Well, I am an already sweaty person, and actually thinking about climate change doesn't help, but you know what I'm going to do it? I'm ready. Okay. Well, then this is going to be like the perfect Venn diagram of that. It's at Penn State University inside this climate-controlled room.

And if you're in the study, you go in and you either sit there or walk slowly on a treadmill. Okay, that doesn't sound so bad. I could do that. Yeah, well, here's what Professor of Physiology, Larry Kenny, does next. We start to increase the humidity every five minutes in a stepwise fashion. Okay, that sounds awful. As a Westcoaster, I am very bad with humidity. Yeah, I am too. And in that room, it's getting really mungy. And then the test subjects, they've also swallowed this tiny electronic device that's shaped like a pill and it records their core temperature. Cool.

And what Kenny is looking for is what he calls the critical environmental limit. The combination of temperature and humidity beyond which either they can't sweat enough or they can't evaporate enough sweat to maintain their body temperature. I feel like I'm actually very familiar with that moment. You know, you feel really sticky and uncomfortable. Yeah, yeah. like the sweat is kind of pooling on your skin. Only sweat that evaporates has any ability to cool the body. Sweat that just drips off the skin is essentially a senseless loss of body fluids.

Right. Humid air is full of moisture already. So it's harder for your sweat to evaporate and then it's not doing much to cool you off. Yeah, exactly. And that's where it gets dangerous. When your sweat doesn't really evaporate at all, that's when people die. You know, even just sitting in the shade if they don't do something else to cool off. And that's why humidity is kind of sinister.

People need to understand that heat is the most deadly of all weather-related fatalities, much more so than tornadoes, hurricanes. Wow, that's surprising. Although actually this summer, there has been so many heat waves. And I've personally gotten really sick from the heat and humidity in D.C. before. So I totally believe it. Yeah, it sneaks up on you. And that's why when you look at the weather forecast, the high temperature of the day, you know, isn't really telling you the whole story. The National Weather Service has an alert system.

It's called the heat index. And it tries to fix that by showing you the full danger of heat. But new research is showing that it underestimates the threat. So today on the show, we revisit Lauren's reporting on heat. Why it's an invisible killer that only gets worse as the climate gets hotter. and what today's heat warning systems could be doing better to protect the public. I'm Regina Barber, and you're listening to Shortwave, the science podcast from NPR. Okay, Lauren, so we've heard about how humidity can be really dangerous.

It's really common in much of the U.S. and the world, but I feel like it's hard to know where that line is. Like, when does a heat wave go from uncomfortable to deadly? Yeah, yeah, it's hard to know that, and that makes it also harder to communicate to the public. One example of that actually happened in Chicago in 1995. It was July, and a heat wave was coming, and people heard on the weather report that it was going to be over 100, so pretty hot. But not unheard of for a Chicago summer. But the air was really humid, and that made it extremely dangerous. The heat wave across the Midwest and up and down the East Coast continues to kill people.

That's NPR News in 1995. In some cases, people lose a huge amount of fluids through sweating and don't replace. punish them. More than a thousand people died in the broader region. So it's a mess. That's all I can say. It's a mess. It's worse than a plane crash. Many were people of color and older people who died in their homes trying to ride out the heat. They bring some more bodies in. I can say like every 10 minutes, I guess. That's horrifying, actually. Yeah, I mean, it was almost 30 years ago, but, you know, just a couple years ago, there was a major heat wave in the Pacific Northwest where more than 700 people died.

Right. So if humidity is really crucial to pay attention to, what's the best way for me and for others to keep an eye on that? Yeah, you don't have to try to understand the humidity forecast because there's a shortcut, and that's the heat index. It says what the temperature feels like to a human, you know, as opposed to what the thermometer says. Okay, great. I already kind of look at the heat index on my phone when I scroll down on the weather report, but I don't think I've totally understood it. Right, yeah. And like, you know, one example of it might be like it's 92 degrees out, but if the humidity is at 70%, it feels like 112 degrees. You know, it's kind of meant to be like this cheat sheet for what the real impact of humidity is on the human body. But here's the thing. It only shows what the heat feels like for someone standing in the shade. Okay, that seems like a problem because most people aren't in the shade when they go outside. And there are people who may have to be in the sun, like outdoor. workers. Yeah, exactly. And the sun can add 15 degrees to the temperature. So at that point, you know, you could be talking about heat that's lethal. Yeah. But the heat index, only being in the shade,

leaves out those groups in the sense that they don't have a tool to help them figure out what the danger is. And then the heat index is also designed for a particular person. So it's for a person in the shade who is 5'7 and 147 pounds and healthy. Wow. Okay. So that doesn't show how the heat would feel to somebody more vulnerable to it, like if you have a health condition. Yeah, exactly. So older people are more vulnerable, you know, pregnant people, people with chronic health issues. They're all more susceptible to extreme heat. And the index doesn't really tell them what they need to know. And the last thing is new research has come out that shows the heat index is miscalculating how hot the body feels at high temperatures and humidity. So

it's underestimating of a danger. So why is that? Yeah, so it's done with modeling, which calculates how a body manages heat. And when it was created in 1979, the modeling couldn't really handle high temperatures and humidity. So what the National Weather Service did is it extrapolated and filled in the rest of those missing temperatures by using the lower temperatures as a template. Oh, no. Yeah. So David Rompst, who's a professor of Earth and planetary science at UC Berkeley, he and his colleagues fixed the model to more accurately include humidity and higher temperatures. And when they ran it, they found that the heat index was off by as much as 28 degrees at high temps. So if you look at that Chicago heat wave, I mentioned, it's one example, he says.

The National Weather Service reported the heat index at the time as peaking at 124 degrees Fahrenheit, which is really hot. But if you go back and you look at the values that went into that calculation, the heat index actually hit 141 degrees Fahrenheit. Whoa, that's kind of mind-blowing. So the heat felt so much worse and had a bigger health risk than the heat index had led on. That's what his research is suggesting. You know, it works well at lower temperatures, but at higher temperatures, it's not showing you the full risk. 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. So what does the National Weather Service have to say about that?

So I spoke to Kimberly McMahon, who is a public weather services program manager at the National Weather Service, and she says they're reviewing the study. Generally, heat is seen as a nuisance, and people still want to go about their day. So we are working with the CDC, EPA, and as well as many other of our federal partners to continue to try to find better and more widespread ways. of alerting the general public, our emergency managers, and our decision makers, that heat is dangerous, and these are the things that people need to watch out for. She says they're also piloting a new heat warning system in the West, which is called heat risk. And it has a tiered warning system. So like these different warning levels with information specifically for vulnerable groups.

Oh, wow. Okay. So how do they plan to translate that into like public action? Like there's a heat warning system now, but how will people know about it? And will they do anything after they're alerted? Yeah, right, because even if those warnings are absolutely perfect, right, they still have to persuade people to act to do something, you know? And that can mean don't go outdoors during the hottest part of a day or get to a cooling shelter if you don't have cooling at home, for example. And like if you're pregnant, don't book your doctor's appointment in the middle of the day. It's really hard to change those behaviors. And I spoke to Christy Eby, a professional. professor at the Center for Health and the Global Environment at the University of Washington about that. 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 who are in higher risk groups

but don't see themselves at higher risk, that in fact they do need to take action. She says the research is showing you really need to tap into social networks to reach those vulnerable people. So Those networks and the people around them are reinforcing the message. And those can be, you know, neighborhood groups, senior centers, church groups, or, you know, those who work with the unhoused. And that's where a lot of cities are trying to improve right now because, you know, heat waves are only getting worse. Climate change is making them longer and more intense. So people really need to know when something unprecedented is on the way. Lauren, thanks for sharing this reporting and also making me pay more attention to the heat index.

I'm glad. And yeah, happy to be here. This episode was produced by Rebecca Ramirez, and it was edited and fact-checked by our senior supervising editor, Giselle Grayson. The audio engineer for this episode was Robert Rodriguez, Beth Donovan is our senior director of programming, and Anya Grunman is our senior vice president of programming. I'm Regina Barber. Thanks for listening to Shortwave from NPR. Stay cool out there.