Short Wave - A new investigation shows heat is even deadlier than we thought

Episode Date: September 4, 2026

Hot weather isn’t just an inconvenience. It’s killing thousands more Americans than show up in official records. That’s the finding from a new NPR investigation, in partnership with Boston University. And the way they came up with that new, better estimate of the true toll of heat is, of course, with science. This episode, we’ll bring you all the details – and chat about why getting good estimates could save lives.Interested in more science-based investigations? Email us your question at [e-mail] public media with NPR+ and enjoy perks for over 25 podcasts like this one. This show’s perks include sponsor-free listening. Learn more at plus.npr.org.See 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. Shortwaver's Nate Rod here. And I am thrilled to say that it is almost fall. Because I don't know about you, but for me, this summer has felt unbearably hot, like many before it. This summer has seen deadly heat waves across the U.S. caused by severe drought and record-breaking heat. The heat wave continues to make life miserable. Excessive heat warnings. Extreme heat.

Or extreme heat. My friend and colleague, Alejandra Barunda, lives just up the coast from me here in Southern California. And Alejandra, I know that you've been feeling this heat, too, because we've complained about it together. Yes, we have Nate. And I can say that I have never been more grateful to have a heat pump that cools our house. I'm grateful that you have that. As a climate correspondent at NPR focused on the intersection between human health and our warming planet, extreme heat is squarely in your beat.

Yeah. And as I've been reporting on it for the last couple of years, I noticed this problem. We as a country and as a world aren't keeping accurate track of how many people are getting sick or dying from heat. And that means that it's been really hard to get people to care in a meaningful way and like do anything about it. Yeah, that makes sense. I'm looking at one of your stories right now and you say the official number from the Centers for Disease Control. The CDC is about 1,700. So on average, 1,700 people die each year from heat.

That was over the last eight years. But you had an inclination that that number was low. Yeah, I really did. And I want to be clear, a low estimate is not really the CDC's fault. The way that we count and track causes of death in this country vary from state to state and even county to county. And CDC is kind of compiling all of those numbers. So the problem stems from somewhere deeper. This is just really hard to do. But Alej, being the enterprising reporter that you are, you decided to come up with a better, underestimate. Yes. This was a huge, probably slightly over-ambitious project, and it took a couple of years. And I really could not have done it without partnering with epidemiologist Quinn Adams at Boston University. And together, we found that we as a country are undercounting the number of people that die from heat and heat-related issues by a factor of about five. Whoa, so meaning the real number is actually five times higher? Yeah, our modeling suggests that it's something like 9,000 people that are dying from heat each year.

And even that might still be an underestimate. So today on the show, why the U.S. is vastly undercounting the deadliness of heat, not just in states like Texas and Florida, but places like even the northeast. And how some of those places are trying to do better to save lives. You're listening to Shortwave, the science podcast from NPR. Okay, Alejandra, I want to get into the numbers and all the fancy statistics that you did, but just from the outset, I want to highlight that these are actual people we're going to be talking about, right? Yeah, and a lot of their stories were just absolutely heartbreaking. And they really stuck with me. And one of the reasons why was because a lot of them were so, so avoidable. Like, one thing I heard over and over was about how someone's AC or swamp cooler would break and they couldn't afford to fix it. And then that turned into an actual death sentence. And that's what happened to Sherry Petty. She was a woman who lived in Tucson,

Arizona, and her daughter, Tara Gettner, told me about it. But I woke up, covered his sweat. I went to the kitchen to get a drink and my mom's laying there on the floor in front of the swamp cooler that's blowing hot air and a rotating fan that's blowing hot air. And a rotating fan that's blowing hot the house was boiling hot and Sherry Petty died later that day. Tara is still totally consumed with grief a year later. And I want to be clear here, Sherry's death actually was counted because it was so obviously affected by heat. But there were a lot of other people I talked to who went through something similar and whose loved ones' deaths weren't counted. So most of the 9,000 heat-related deaths in your analysis, they're not cherries.

Like, they're not people that were counted, right? Right, exactly. Okay. So were you surprised that that number came back as 9,000? Yeah, it's a really good question. And it's been interesting to wrap my head around because it's sort of a small number and a big number at the same time. Like, compared to the death toll of something like cardiovascular disease, which is the leading cause of death in the country, it's not huge. But it's a big number because, well, like we said before, it's way more than we knew, five times higher.

And it's way, way more than is a problem. officially reported for other kinds of natural disasters like hurricanes or wildfire. Though I will say that there's also a lot of new research showing that those are also likely way undercounted. So what I'm hearing here is that we have an undercounting problem in this country? Yeah. When we were talking about heat, though, like, why is that? Yeah.

I mean, I think it's because it's genuinely hard to count well. It's really easy to miss and hard to count heat deaths. And that's mostly because heat isn't usually the only thing that kills someone. A lot of times heat is a part of the story, not all of it. It's the trigger for something like a heart attack or a kidney failure. But if you're not looking for it, it's really easy to miss. This one doctor in Arizona, Brian Drummond, kind of explained it to me like this. He's super aware of the problem.

And he's still like, it is hard for me to determine for sure that heat played a role in someone's death. And he'd need to be absolutely sure he played a role in order to put it on a death record. And that means that he has to do the kind of like investigative interviews before someone dies. And that's not always possible. So if I never ask a patient, were you exposed to extreme heat or do you have the ability to cool where you live? If I'm not asking those questions, I would never diagnose them with heat-related illness unless their temperature came in at 105. Oh, that is so tricky. And the other part is that, you know, there's a lot of different.

people in this country who end up certifying deaths. Doctors do some of them. Medical examiners do some, coroners do others. But all of those people are trained really differently. And for example, some coroners are elected and don't actually need any experience or credentials. And there's also not really a standard way to do a heat investigation. And all that means that I honestly, I don't think we're ever going to have a perfectly accurate number. And that to me is why these sorts of statistical estimates like the ones that we did here are so important. They help us see kind of a truth that is not simply the fact written down or not on a death certificate. Okay, so let's get into this actual analysis. What was the process you used to figure out a number that's closer

to reality? Great question, Nate. So basically what we did was some fancy modeling to calculate something called excess mortality. And you might remember that term because it was similar to what public health officials were doing to estimate COVID deaths back in the middle of the pandemic. And how that works is basically you figure out an estimate of how many people are expected to die in a place in any given week. And then you see how many people actually died. And then our modeling figured out how much of that difference was attributable to heat. Here's Quinn Adams. She's our lead partner at this and she's explaining the process a bit more. This is maybe a little bit jargony, but we essentially did this like county specific model in which we basically come up

with an exposure response function where we can say like at these temperatures, this is your risk of death at each temperature. So basically we took into account things like where the deaths were because heat hits differently for someone in like Massachusetts than it does for a Texan based on what their bodies are used to. Yeah, that makes sense. Yeah. And, people do acclimate to the heat in the place they live, like up to a point at least. But I also really want to point out that, like, I think a lot of times we think that it has to be, like, extremely hot to hurt people, like 100, 110. And that's not true. There's a lot of cases in which, you know, it can be 85 out and someone is going to have the same impacts. For example,

there's a lot of common medications that make you more sensitive to heat or not able to sweat effectively and all kinds of stuff that makes your thresholds a lot lower. Well, I had no idea about that. I mean, and I get it. Like, I've complained about our temperatures here on the coast all summer, but the humidity and heated index that we have been having is like a normal summer day in a place like New Orleans or something. Yeah, and different places have different relationships with heat because of that. And also preparedness is different. Yeah. We also looked at something called a lag. Say you have a heart condition and it gets really hot and your body can handle that for a few days, but it's getting more and more stressed

over time. It might not be until a few days later that something happens and lands you in the emergency department or even worse, dead. Or the morgue, yeah. Right, exactly. But it was still the heat that led to something happening. And so our model takes that lag between the heat and kind of the incident into account. Do you feel good about this number? Like, is it possible that this is also an undercounting of the true scale of what's happening? This is definitely a solid first step, but Quinn and I agree. This is the best possible estimate that we have given the most up-to-date methods and the best publicly available data, but it's still an expected underestimate.

We were actually in the process of getting access to some finer scale national death data that would help us get an even better estimate. And we think that using that even finer scale data set would probably end up giving us a higher estimate. But we have not yet gotten access to that. We are still trying. Okay. So stay tuned. Yeah.

So Alejandro, I know we're both journalists. Like we don't make policies or decisions for people. You know, we report the news and we give the public information. But I feel like after spending so much time on this, like you have to have some hope that something comes from this. right? Like, what would that be? Oh man, Nate, that's such a good question. I thought about this a lot. And I think the first thing is honestly just awareness, you know?

Like, I truly think oftentimes people think heat is just a nuisance or like an inconvenience. Most people do not see themselves as vulnerable to heat. They're like, oh, that's someone else. It's not me. But then, you know, push comes to shove and it actually is you. And we're learning all kinds of stuff about what heat does to your body. Like it can age you like smoking does. And these kinds of physiological impacts really make it clear that it can hasten deaths in a meaningful way. And that's for people everywhere.

And that leads me to something else that came up when I was talking to this scientist, Patricia Salis, from Arizona State University. She said, we treat heat as a, quote, me problem when really it's a quote we problem i mean yeah that that tracks yeah exactly like we tell people oh man like take care of yourself go inside like make sure your ac is running make sure you cool down but like this is a policy problem right and i hope policymakers hear this and agree that it's a we problem there's so many structural things that we could address that might help keep people safer And it's sort of shocking how many cities or counties or states don't have like real solid action plans to address heat just yet.

Are there places that are doing a better job than others, though? Oh, yeah, definitely. And at the top of that list are places in Arizona, like Maricopa County or Pima County. And that makes sense, right? Because Arizona is like in the epicenter of the heat crisis. Yeah. And so they're putting a ton of effort into better tracking heat deaths. In fact, those counties both counted more heat-related deaths.

than our model predicted. Oh, man. But I will say my reporting also found many people who weren't included in those official counts. So to me, that says both the model and the medical examiners are probably still undercounting. But I will say that Arizona and, like the counties and cities within Arizona, are doing a lot

to experiment with ways to keep people safer. For example, there was this rule that was keeping people from having outward-facing air conditioners sometimes when their landlords didn't want them to because of like aesthetics. And the state was like, no, no, if you need an air conditioner, you can have one, even if it like, you know, affects how. Doesn't look great. Yeah, exactly.

And I will say like places like New York State and City are experimenting, for example, with moratoria where utilities aren't allowed to shot off people's power for nonpayment during heat waves. Same thing that we have in winter to keep people from dying from cold. Yeah, exactly. And so, like, now it's clear that we need to figure something out like that for the summer. as well, but it's still pretty new approach in many parts of the country. Hearing this list of all the places that are trying to address heat, I feel like it's just like an almost overwhelming problem. It's a really hard thing to fix. Yeah. And you can't fix a problem until you know about it. And you don't know if your solutions

are working unless you're keeping track of them. And so I just really hope this work can help with both of those things. Alhandra, I hope so too. Thank you so much for bringing us all of this work and for doing it. Yeah, thanks for talking about it. And just for anyone who wants to look deeper at the model, we made it open source. You can take a look. We'll drop a URL in somewhere. This episode was produced by Burley McCoy. It was edited by Rebecca Ramirez. Tyler Jones checked the facts. The audio engineer was Jimmy Keely. I'm Nate Rot. Thanks for listening to Shortwave from NPR.