Short Wave - Nature Quest: Are Summers Getting Hotter?

Episode Date: July 29, 2025

Much of the country is deep in the middle of a heat wave right now. And every summer, Duane Stilwell's town in Arizona seems to get hotter. It has him worried — and he's not the only one. Since 1980, the average number of heat waves in the U.S has doubled and the average length of a heat wave season has increased from 40 days to 70. Future summers, experts say, will be even hotter. But why exactly is that happening, and what can people do to protect themselves from the heat?This episode is part of Nature Quest, a monthly segment that answers listeners' questions about their local environment. If you have a question, send a voice memo to [e-mail] that includes it, your name and where you live. We might make it into our next Nature Quest episode!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.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. Hey everyone, Emily Kwong here with producer Hannah Chin, who's bringing us this month's listener question for Nature Quest. My favorite series ever. Okay, Hannah, who's the question coming from? This question comes from Dwayne Stillwell. He's 68, and he lived a lot of different lives in a lot of different places. I lived in Cleveland, in Chicago, New York City.

Dwayne grew up working summers as a delivery boy in the lush green of Mexico City. He taught chemistry in the dry heat of California, and he even worked as a railway switchment tamping down snow and below freezing temperatures in the Midwest. Basically, he is no stranger to extreme weather. And when he retired and moved to the American Southwest five years ago, he kind of thought he was there to stay, that Guadalupe, Arizona, just outside of Phoenix,

was his forever home. I pretty much thought this was going to be the last place I'd have to move, and I'm tired of moving, you know. Yeah, I feel that. He's lived a lot of places he's ready to settle. But now he's not so sure. Because Emily, over the past four years, the summers where Dwayne lives have become longer and hotter and more dangerous.

Last year, Dwayne said there were 113 days in a row above 100 degrees Fahrenheit. His fig trees stopped producing fruit. Some of the cacti in his yard started dying. and his neighbor, who's an older guy who lives across the road with his family, passed from heat stroke. It's forbiddingly hot. In other words, you know that if you stay outside, you can die. Since 1980, the average number of heat waves in the U.S. has doubled, and the length of an average heatwave season has increased from 40 days to 70.

We are facing a future with more summers like this. So this month's nature quest, extreme heat, how it's linking. to climate change, why humidity makes it worse and more deadly, and how you heatproof your life for the future. You're listening to Shortwave from NPR. Okay, shortwavers, we are on a nature quest. This is our monthly segment that brings you a question from a fellow short waver who is paying attention to the environment around them and the ways that it's changing. And this month, Emily Kwong is looking into extreme heat. Yeah, I want to take you back to the summer of 2022 when COVID restrictions started to loosen and that Kate Bush,

song running up that hill was everywhere. I love the 80s pop. Right? I remember listening to that song thinking, this is so good. And also, this 80s synth will not save me. It is just too hot. I have to go inside. Yeah. I mean, it was that same summer that I think heat records were breaking around the world in Europe and in China. I even remember the U.S. Secretary of Commerce at the time, Gina Romando. She said that this summer is likely to be one of the coolest summers of the rest of our

lives. Yeah, hot as it was. So I want to talk about the physics of why this is happening and why the Earth, which does have natural variations in temperature, cannot simply correct for this much warming. As my PhD advisor would say, if you believe in thermometers, you believe in global warming. It is an observation of what is occurring. This is Justin Mankin. He's a climate scientist and professor of geography at Dartmouth. And he reminded me that greenhouse gas is just a term that scientists used to describe any gas in Earth's atmosphere that traps heat. So water vapor is a greenhouse gas. Oh, I didn't know that.

Yeah, but the gases that have been on the rise since the Industrial Revolution because of humans emitting fossil fuels, the gases we're all so worried about are carbon dioxide, methane, and nitrous oxide. You can think of our atmosphere almost like a bathtub. It gets full. And typically, Earth's forests and oceans and soil act like a drain. They sequester carbon in the long term, bring our planet back into equilibrium. The bathtub empties.

But because human activity is emitting more greenhouse gases, the drain is getting clogged. Oh, so the bathtub, like our atmosphere, is filling up. Yeah, just as the water level in a bathtub fills up to push water down a clogged drain, so too does the Earth warm. The planet needs to heat up to ensure that the amount of energy we're receiving from the sun is balanced by the amount of energy Earth is sending out to space. Justin says this is called radiative balance. Radiative what? It's kind of how the earth and sun do what they do. And it's governed by the unchanging laws of physics. So one law says that all matter that has a temperature radiates energy. The sun, which is very hot, radiates energy. The earth absorbs that energy and heats up too. And another law of physics says that hotter objects will emit more energy, essentially shed that energy to achieve radiative balance. Okay. So the earth has to shed its heat? Yes, and that's because of the law of the conservation of energy, right? Energy cannot be created or destroyed. What goes in has to equal, it comes out, so the earth must achieve equilibrium. And we experience that as warming. Hotter temperatures, here on Earth. Right. And longer summer heat waves. And also humidity, which is going up in some places. Right, because when the humidity is worse, our bodies are less efficient at evaporating sweat. Yeah. And then if our

Sweat doesn't evaporate. Our systems literally can't cool down. Yeah. And when our bodies can't cool down, that is when you put yourself in danger of heat exhaustion or heat stroke or even death. And when we talk about heat-proofing our future, the most important thing to think about is that your location, your geographic location, will be the biggest factor in determining how you experience extreme heat. I mean, Emily, you and I have talked about the urban heat island effect where buildings and roads and other infrastructure basically trap. heat and make these urban areas hotter, this disproportionately affects poorer communities and communities of color because those areas already tend to have fewer parks and trees. Right. So a key adaptation to extreme heat is to green the landscape, especially urban landscapes by expanding parks and community gardens and installing green roofs.

Vegetation siphons water from below the land surface and sends it to the atmosphere through transpiration, which is a form of evaporation, and evaporation cools. And so it's a really effective way of wicking heat away from the surface. And there's another adaptation I want to talk about, Hannah, cooling centers. Cooling centers are air-conditioned, public or private spaces. They're a real tool in the state of Arizona. Nick Stobb is the incident commander for extreme heat response in Maricopa County, where our listener, Dwayne, lives.

And the reason I wanted to talk to him is because, Because by the department's count, heat-related deaths in Maricopa did go down last year. And it is in large part because the county is making an effort to care for those who are most vulnerable. Those who are at highest risk in our community are those who are unsheltered, those who are spending their nights out on the street. Typically at night, you know, the temperature drops and people's bodies have a chance to recover from the heat exposure during the day. But Nick gets worried when he sees a forecast with a string of high overnight. temperatures of nights above 90 degrees Fahrenheit. And people who don't have regular access to shelter aren't the only high-risk groups.

Other groups include children, older adults, people who are pregnant, people who work outdoors, and many more. Kim McMahon, the Public Weather Services Program Manager at the National Weather Service, put it this way. The more susceptible you are, the more exposed you are, the greater your chances of feeling those impacts from heat, starting to get heat rush, starting to get heat exhaustion. before, say, somebody who works in an air-conditioned office building. So in response to these heat-related deaths, the Maricopa County Department of Public Health

decided to expand their heat relief network. A whole bunch of organizations came together to keep cooling centers open longer. Into the evenings, on weekends, holidays, the county also opened up these respite centers, places with blankets where people can lie down and even sleep for a few hours. Right, so that they can rest and they can cool off. And then we put a big effort into advertising the heat relief network as well as getting consistent street signage printed so that we could put them outside of the center so people could see those signs and know it was a cooling center. So did it work? Has it been successful?

It has. At least in 2024, the number of heat-related deaths that they counted went down. But we still had over 600 heat-related deaths in 2024. So while we are encouraged by the reversal of the trajectory, there's still a lot of work to be done. And of course, as with all public health data, undercounts are always a possibility. Summers in Arizona will only get hotter and not everyone may want to stay. Right. I mean, everybody is different. Every community is different. You mentioned that several European countries have these heat early warning systems.

Yeah. And I'm pretty sure we have something similar in the U.S. because I know I have gotten texts about like extreme heat. Yes, let's end on this. Early warning systems. So in the U.S., we have a system of weather emergency alerts, which can be sent directly to your device as a text message or a notification about a flash flood or a thunderstorm or an extreme heat advisory. And one of the main participants in the system is the National Weather Service. Huh, okay. So how does the National Weather Service think about heat? Like, what are they doing to address it? Well, the National Weather Service is responsible for all weather forecasting in the U.S. They do science. And one

of the tools they use is the heat index. The heat index is a measure of how hot it feels to the human body when relative humidity is combined with air temperature. Oh, that's why, like, if I scroll down on the weather app on my phone, like when I look at the daily forecast and then I swipe up, there's this feels like temperature, and it's sometimes a little bit different. Yeah, it's like the heat vibe, you know, and it often feels more accurate because humidity is factored in. So that's the forecasting system, but then you also need a warning system, right? Right. Over the years, each local forecast office of the National Weather Service has developed a unique set of thresholds. For when in that community, the outdoor conditions trigger a heat watch or warning or advisory.

But it's not a full-proof measure, Nick pointed out to me, for assessing your personal risk. We see a significant number of heat-related deaths on days that are not an extreme heat warning, which is why our messaging to the public is you need to plan all summer long. The heat index values are calibrated for shady locations, which means this heat early warning system does not fully account for people being in direct sunlight. And that can be 15 degrees hotter than in the shade. Wow. Okay. So basically don't wait for that text message to change your outdoor plans.

I mean, under these circumstances, I guess I'm wondering what can people realistically do about it? Like, if they know a heat wave is coming and they're worried. Yeah. So assess, you know, where you live, your environment. individual heat tolerance, but if you know it's about to get really hot, you have to take precautions. For Nick in Arizona, it's about treating all Maricopa County summers like a heat watch is constantly in effect. Plan your outdoor activities wisely. Don't be outside during the heat of the day. Install dark curtains. Take cold showers. Check in on friends and family and neighbors to make sure they're doing okay while the heat wave is doing its thing.

It's all good advice, but I was not totally satisfied with some of these answers. Huh. Wait, how come? Because individuals and local governments can only do so much. We cannot cold shower our way out of this. Okay. Justin says, ultimately, it is fossil fuel emissions that are the root of the problem. Mitigating our greenhouse gas emissions is going to be the clearest way to prevent additional warming and extreme heat risks. And we have the tools to do it. We have had policies in place to help. achieve it. And neglecting the problem is not going to make it go away. It's only going to make the world hotter. I'm like Kwong. Thank you so much for bringing us this reporting. You're welcome, Hannah. Thank you, Dwayne, for the great question. Shortwavers, if you have a question about changes in

your environment, email it to us at shortwave at npr.org and we'll consider it for a future nature quest episode. The series comes out the last Tuesday of every month. Special thanks also to the National Weather Service and Alejandra Burunda and Julia Simon on NPR's Climate Desk. This episode was produced by Hannah Chin, that's me, and Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez, Tyler Jones, check the facts. Jimmy Healy was the audio engineer. Beth Donovan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy. I'm Hannah Chin.

And I'm Emily Kwong. Thanks for listening to Shorewave from NPR.