Air Date: Week of November 28, 2025

The Silver King wildfire in Utah burns near Beaver Canyon, Utah in July 2024. A new study in Nature finds that there have been about 40,000 excess deaths from wildfire smoke every year in the US over the last decade. (Photo: Derrellwilliams, Wikimedia Commons, CC0)

Wildfire smoke is fouling air quality across the US with increasing regularity, and it carries a heavy toll. A September 2025 study published in the journal Nature found that every year around 40,000 Americans are dying from wildfire smoke, with more on the way as the planet warms. Senior author Dr. Marshall Burke, a professor in the Doerr School of Sustainability at Stanford University, joins Host Jenni Doering to discuss how air filters, face masks and low-intensity prescribed burning can help protect the public from this growing threat.

Transcript

DOERING: From PRX and the Jennifer and Ted Stanley studios at the University of Massachusetts Boston, this is Living on Earth. I’m Jenni Doering.

O’NEILL: And I’m Aynsley O’Neill.

Our show today focuses on fire, including the growing threats our society faces from extreme wildfire as the planet warms. But fire is a creative as well as destructive force, so we’ll spend time later in the show discussing the roles of fire in ecology and culture, as well as how we can help each other heal and recover from the collective trauma of living through these megafires.

DOERING: Yeah, and it really is a collective trauma for many here in the U.S. I mean, whether or not you’ve found yourself in the direct path of a wildfire, chances are you have been in the widening path of wildfire smoke and experienced the scratchy throat, coughing, and burning eyes that exposure can bring.

O’NEILL: Yeah, you know Jenni, I certainly remember a lot of extra throat clearing when we’ve recorded this show during some of those really smoky days!

DOERING: Yes, me too. Wildfire smoke has become extremely noticeable anecdotally but also in the scientific data. And a September 2025 study published in Nature quantifies just how deadly that smoke can be in a warming world. The researchers found that around 40,000 Americans are dying from wildfire smoke every year, with more on the way as the planet warms. Here to talk to us about the study is senior author Dr. Marshall Burke, a professor in the Doerr School of Sustainability at Stanford University. Hi Marshall, and welcome to the show!

BURKE: Hi, thanks so much for having me.

DOERING: So we're talking to you about your recent research regarding the link between wildfire smoke and mortality. Talk to me about what kinds of questions you were asking and what you found about how smoke is killing us.

BURKE: People have a sense that breathing in smoke is bad for them. We set out to understand, okay, how bad is it actually? And we looked at really, one of the most severe outcomes, so thinking about excess mortality, and wanted to understand how exposure to wildfire smoke in the days or weeks or even years past an exposure, how that affected excess mortality, the likelihood that you would die. And unfortunately, we see pretty large effects. We see that in the year of smoke exposure, mortality goes up substantially, and those effects last for multiple years. So the largest impacts, in terms of people affected and overall impacts, they're larger in the US West, because exposures tend to be higher. But again, in the last few years, we've just seen a lot more exposure elsewhere in the country, and so people on the East Coast and the Midwest, increasingly in the US South are exposed to wildfire smoke. And so when you count up total mortality across the US, we get a number of about 40,000 excess deaths per year from wildfire smoke over the last decade. Forty thousand, that's roughly on par with the number of people who die in car accidents in the US every year.

DOERING: And then you also projected out these numbers into the future because, you know, we know that these wildfire risks are probably not going to decrease in the coming decades. They may, in fact, be getting worse as climate change intensifies. So what did you find there?

BURKE: That's right. We wanted to understand whether this was the new normal and how it might change in the future. And here, we really built on decades of work showing why we were seeing an increase in wildfire activity and smoke overall. And really there, there are two main causes. One is a century of fire suppression, where we've put out fires instead of let them burn in our forests. Many forests had evolved with fire. We sort of interrupted that about a century ago, and what that led to was a loading of fuels in these forests. So I go hiking in the Sierra Nevada a lot. You go into many of these forests, and there's just an incredible amount of dead wood and fuel on the ground in these forests. You add on top of that a warming climate. These fuels dry out. They become more flammable. And so, when you do get a spark, the fires grow much more quickly. They're much more extreme, and they emit a lot more smoke. So we know from climate models that the climate will continue to warm in the future. And so we were able to model out, okay, what's going to happen over the next 20, 30, years in terms of expected wildfire activity and expected smoke output. And sure enough, as the climate continues to warm, under a business-as-usual scenario where we sort of behave as we have over the last few decades, in the future, we find a pretty substantial increase in smoke exposure and resulting health burden. So we estimate that, you know, again, we're at 40,000 deaths annually now. This could rise to 70,000 deaths by 2050, so like a 70% increase in the health burden just over the next two to three decades.

DOERING: Wow. I imagine that's not just from population increases either.

BURKE: No, it's not just from population increases, although that does play a role. Another important role is the aging of the population. So we certainly find that elderly groups are more susceptible and more vulnerable to wildfire smoke, and so as our population ages, that certainly makes us as a society, more vulnerable. So that's part of the story. The main part of the story, though, is just the overall warming climate, the resulting increase in fire activity and smoke exposure that we get. So what we can do is we can take those total deaths that we spoke of, so 70,000 deaths by 2050, we can do what economists are happy doing, what other people understandably view as sort of insane. But we can convert these deaths to dollars using the official US government number of how much a statistical life is worth, which is about $10 million. And if you do that multiplication, you get many hundreds of billions of dollars of damage every year from wildfire smoke alone. Our estimate is that that is the largest single impact of climate change in the US.

DOERING: Wow. All right, I was already blown away by your research. And how about if we get our act together on climate and really reduce our emissions?

BURKE: So unfortunately, by mid-century, we find that even pretty aggressive climate mitigation, so if we really get our act together and reduce emissions, that will have a benefit. But the benefits, at least by 2050, in the next few decades, are pretty small. And the reason for that is just that climate change is a very slow ship to turn. And so if we reduce our emissions today, that can have massive benefits, but most of those benefits are later on in the century. So by 2050, there are certainly benefits, but they're just not as large as what you get by 2070 or 2080 or end of the century. We find sort of a small difference, so maybe 60,000 or low 60,000 deaths under a very aggressive mitigation scenario, versus about 70,000 under a business as usual. So certainly a benefit, but it doesn't eliminate the problem.

DOERING: Wow. So I guess we all better be a little more prepared for what's coming and what's already here, to be honest. So as wildfire smoke poses this increasing public health threat what are individuals doing to protect themselves?

BURKE: I think there's two questions: What are individuals doing to protect themselves, and what should they be doing to protect themselves? So this is something our group has looked at, is to try to understand what are people doing now to protect themselves? One way we've studied this is to use really nice citizen science data, basically data that are available to us based on individual citizens, just out in the population, collecting data, either on purpose or inadvertently. So specifically, we use these purple air monitors that many people have put in their homes that serve data publicly that we can then as scientists analyze. What we can do is look at people's indoor air concentrations on wildfire smoke days, so on days in which the smoke outside is really bad, to understand, is it sufficient to stay inside and close your windows and doors on a really bad wildfire smoke day? This tends to be the main public guidance. The air is bad outside, stay inside, close your windows and doors. So we can look at people's monitors and say, "Okay, how well are they doing?" These are indoor monitors. What are the pollution concentrations? And these are people with monitors, right? So these are people who should have very good information on what their exposure is. Basically we see two groups. We see one group that seems to be doing something well, their indoor air quality looks quite good on a smoky day. We see it basically the other half of the group where the opposite is true. Their indoor air quality can be almost as bad as the outdoor air quality on a really bad smoke day. And these are in pretty wealthy Bay Area neighborhoods, like these are my neighbors down the street. And so the question is, what's going on? And almost surely, what's happening is they have windows and doors that are open, and so wildfire smoke is infiltrating into these environments. And these are people with monitors. They're the ones who should be best informed about this exposure, right? So that tells us, at least right now, we are not super well-prepared for this.

DOERING: So what really should people be doing? I mean, obviously, closing windows, trying to keep doors closed as much as possible when there's a lot of smoke around. But I mean, is there anything else that we should be doing, especially when we do have to go outside?

BURKE: Yeah, there's a number of things we can do. And the science is still catching up in terms of the overall health benefits of these strategies, but there's some things that look pretty promising. Number one, closing your windows and doors is certainly the place to start, but the key thing is having an ability to filter your air indoors. So these can be portable air filters. They cost, typically, a few hundred dollars. You can build them yourself with fans and a MERV filter for about $50. And these work really well, if they're sized correctly, work really well to keep air quality pretty clean indoors, even if it's bad outdoors. And so that is our main strategy, if you're inside, for improving air. So what we need to make sure, though, is that, number one, people have this technology and know when to use it. And number two, you know, everyone can afford it. Many of us can go out and spend a few hundred dollars on an air filter. Others can't. And so, we need to make sure, using public policy that everyone has access to this technology. That's number one. Number two, many people do have to work outside. Many of us have to go outside in various parts of our lives, and so we need to protect ourselves as best we can when we're outside as well. Wearing a good-fitting N95 mask can help a lot. And so we have those masks. They might be buried in a drawer now, but dig them out on a wildfire day, put them on as best you can. You can't wear them always. If you're doing heavy activity, they're obviously hard to wear. Our goal is probably not to eliminate exposure, it's to reduce exposure as much as we can.

DOERING: So if we do everything in our power to address the climate crisis, the conditions that lead to extreme wildfires will still be with us for a long time. So it makes sense. We need to thin these fuels. Prescribed fire can be one way to do that. That, of course, is creating smoke. But to what extent is there a difference between that smoke and the really intense burning that we're seeing with some of these out-of-control wildfires?

BURKE: Yeah, that's a great question. There's two main components of the difference. One is, is the smoke itself somehow different in terms of its toxicity? So when we think about wildfire smoke, we're really thinking about a really broad and complicated mix of pollutants and chemicals and toxins, potentially. And unfortunately, they are toxic chemicals you get when you get increasing urban incursion of wildfires, right? When wildfires burn into cities and towns, and they burn up our houses, everything that's under our sink or in our garage. They burn up cars or bicycles. And so when you inhale that wildfire smoke, you're inhaling part of a car, right? And what does that do to you? It certainly can't be good. And again, this is a place where science is, I think, trying to catch up in terms of understanding the toxicity. To me, that's not the most important difference. The most important difference is just the overall quantity of the smoke that you get. And the whole goal with prescribed fire is to put low severity fire on the ground that really doesn't generate that much smoke in the hopes of reducing really extreme wildfires that we know generate a lot of smoke. Our estimate suggests that the reduction in smoke you get is three to five times higher than the initial smoke that you emit from prescribed burning. So to us, that looks pretty good from a cost benefit perspective. Again, it's a tradeoff, though you are going to get some smoke initially, and people need to be aware of that. And they need to be, I think, educated about the tradeoffs. This is indeed a tradeoff.

DOERING: Dr. Marshall Burke is senior author on the study and a professor in the Doerr School of Sustainability at Stanford University. Thank you so much, Dr. Burke.

BURKE: Great to talk to you. Thanks so much for having me.

DOERING: Dr. Burke and his team have put together a tool where you can learn more about smoke pollution trends and health impacts, and we’ll post the link at the Living on Earth website, loe.org. We’ll also link to a guide to that DIY $50 air filter.
And if your home has forced air, don’t forget to check those air filters, since they usually need to be replaced every 3 months or more often when it’s smoky out!

 

Links

Read Dr. Burke’s study in the journal Nature

Learn more about the air quality near you with a tool built by Dr. Burke and his team

Learn how to build a DIY air filter