How The Current Heat Dome Can Affect Human Health

This episode explores the risks associated with the current heat dome and its impact on human health, focusing on how extreme heat and humidity can be lethal.

1. Heat domes create conditions where extreme humidity prevents sweat from evaporating, significantly impairing the body's ability to cool itself.
2. Heat is the deadliest weather phenomenon, overshadowing risks from hurricanes and tornadoes.
3. The episode discusses a major shortfall in the National Weather Service's heat index, which often underestimates the real feel of temperature by not accounting for factors like direct sunlight exposure and individual health vulnerabilities.
4. New research indicates that the heat index fails to capture the extreme dangers at high temperatures, potentially underestimating the heat index by up to 28 degrees during severe conditions.
5. Efforts are underway to develop a more effective heat warning system, focused on vulnerable populations, to better communicate the risks and encourage preventive actions.

1: Introduction

Regina Barber introduces the topic of the heat dome and its effects. Regina Barber: "So much of the US has been in a heat wave for the past few days."

2: The Science of Sweating

Discussion on how body temperature is regulated and the critical limits of heat and humidity. Larry Kenney: "Only sweat that evaporates has any ability to cool the body."

3: The Hidden Dangers of Humidity

Exploration of humidity's impact on heat perception and health risks. Lauren Sommer: "When your sweat doesn't really evaporate at all, that's when people die."

4: Flaws in Heat Index

Investigation into the shortcomings of the heat index and its implications for public safety. David Romps: "Using the correct heat index would allow us to identify those handful of times where the heat is so severe."

5: Improving Public Awareness

Discussion on improving heat risk communication and adaptation strategies. Kimberly McMahon: "We are working... to find better and more widespread ways of alerting the general public that heat is dangerous."

1. Monitor the Heat Index: Regularly check the heat index to understand the true impact of humidity on perceived temperature.
2. Stay Hydrated: Increase fluid intake during heat waves to compensate for increased sweat and prevent dehydration.
3. Seek Shade or Air Conditioning: Use available cooling methods, especially during the hottest parts of the day.
4. Plan Outdoor Activities Wisely: Avoid outdoor activities during peak heat times and opt for cooler parts of the day.
5. Educate and Inform: Spread awareness about the risks of heat waves, especially to vulnerable groups.

Right now, there's a "heat dome" lingering over the southwestern U.S. – a high pressure system that pushes hot air down and traps it, raising the temperature. 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. With scientists predicting a very hot summer, if you can, stay cool out there, dear Short Wavers.What science story do you want to hear next on Short Wave? Email us at shortwave@npr.org.

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Larry Kenney, Regina Barber, Lauren Sommer, David Romps, Kimberly McMahon, Christy Ebi

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Regina Barber
You're listening to short wave from NPR.

Hey, short waivers. Regina Barber here. So much of the US has been in a heat wave for the past few days. Right now, there's a heat dome lingering over the southwestern US.

That heat dome is a high pressure system that pushes down hot air and traps it, pushing up the temperature. And scientists are predicting that we're in for a very hot summer. Given all of this, it seemed like today was the time to revisit this episode on Heat that we did with Lauren Sommer, one of NPR's climate correspondents.

Lauren Sommer
So today we're starting with an experiment that's designed to make you sweat.

Regina Barber
Well, I am an already sweaty person, and actually thinking about climate change doesn't help. But, you know, I'm gonna do it. I'm ready.

Lauren Sommer
Okay, well, then this is gonna 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.

Regina Barber
Okay. That doesn't sound so bad. I could do that.

Lauren Sommer
Yeah. Well, here's what professor of physiology Larry Kenney does next.

Larry Kenney
We start to increase the humidity every five minutes in a stepwise fashion.

Regina Barber
Okay, that sounds awful as a west coaster. I am very bad with humidity.

Lauren Sommer
Yeah, I am, too. And in that room, it's getting really muggy. And then the test subjects, they've all 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.

Larry Kenney
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.

Regina Barber
I feel like I'm actually very familiar with that moment. You know, you feel really sticky and uncomfortable.

Lauren Sommer
Yeah, yeah. Like the sweat is kind of pooling on your skin.

Larry Kenney
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.

Regina Barber
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.

Lauren Sommer
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.

Larry Kenney
People need to understand that heat is the most deadly of all weather related fatalities, much more so than tornadoes. Hurricanes.

Regina Barber
Wow, that's, that's surprising. Although, actually, I've personally gotten really sick from the heat and humidity in DC before, so I totally believe it.

Lauren Sommer
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.

Regina Barber
So today on the show, 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 Barbour, and you're listening to short Wave, the science podcast from NPR.

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Regina Barber
Okay, Lauren, so we've heard about how humidity can be really dangerous. It's really common in much of the US 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?

Lauren Sommer
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, you know, 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 replenish them. More than 1000 people died in the broader region.

Unidentified Speaker
So it's a mess. That's all I can say. It's a mess. It's worse than a plane crash.

Lauren Sommer
Many were people of color and older people who died in their homes trying to ride out the heat.

Unidentified Speaker
They're bringing some more bodies in. I can say, like every ten minutes.

Regina Barber
I guess that's horrifying, actually. Yeah.

Lauren Sommer
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.

Regina Barber
Right.

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?

Lauren Sommer
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.

Regina Barber
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.

Lauren Sommer
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.

Regina Barber
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.

Lauren Sommer
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.

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 five foot seven and 147 pounds and healthy.

Regina Barber
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.

Lauren Sommer
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. It's underestimated the danger.

Regina Barber
So why is that?

Lauren Sommer
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 Romps, who's a professor of earth and planetary science at UC Berkeley, he and his colleagues fixed the model to more accurately include humidity in 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.

David Romps
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.

Regina Barber
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 let on.

Lauren Sommer
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.

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.

Regina Barber
So what does the National Weather Service have to say about that?

Lauren Sommer
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.

Kimberly McMahon
Generally, heat is seen as a nuisance, and people still want to go about their day. So we are working with the CDC, EPA, 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.

Lauren Sommer
She says they're also piloting a new heat warning system, which is called heat risk, and it has a tiered warning system. So, like these different warning levels with information specifically for vulnerable groups.

Regina Barber
Oh, wow. How do they plan to translate that into public action?

There's a heat warning system now, but how will people know about it? And will they do anything after they're alerted?

Lauren Sommer
Yeah, right. Cause even if those warnings are absolutely perfect, right, they still have to persuade people to act, to do something. And that can mean don't go outdoors during the hottest part of the 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 eBay, a professor at the center for Health and the Global Environment at the University of Washington, about that.

Christy eBay
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.

Lauren Sommer
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 unwind, unprecedented is on the way.

Regina Barber
Lauren, thanks for sharing this reporting and also making me pay more attention to the heat index.

Lauren Sommer
I'm glad and yeah, happy to be here.

Regina Barber
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. I'm Regina Barber. Thanks for listening to short wave from NPR. Stay cool out there.

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