Media Briefings

Wildfires: Climate connections & community impacts

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Climate change is contributing to the increasing size and intensity of, and damage from, Western U.S. wildfires. SciLine’s media briefing covered how climate, vegetation, and other locality-specific factors play a role in wildfire activity; how forest managers can assess vulnerability, and increase resilience, to wildfires; and what scientists know about the health effects of proximity to wildfires, including exposure to wildfire smoke. Three scientific experts briefed reporters and then took questions on the record.

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RICK WEISS: Thank you, Josh. And hello, everyone. And welcome to SciLine’s media briefing on wildfires. For those of you who are not already familiar with SciLine, we are a philanthropically funded, editorially independent free service for journalists and scientists based at the nonprofit American Association for the Advancement of Science. Our mission is simple. It’s just to help reporters like you get more scientifically validated evidence into your news stories. And I’ll note here in particular that, in addition to these briefings and our other services, we offer a free matching service through which we connect you one-on-one to scientists who are both deeply knowledgeable and excellent communicators, on deadline or as needed. Just go to and click on I Need An Expert.

Now, today’s briefing features three experts to help get us all up to speed on the escalating problem of wildfires in the United States. And because the connections between wildfires and climate are complicated and also because there’s been a lot of misinformation generated on this topic over the past several years, many of you covering these fires may be hesitant to say much about the role of climate change or of forest management for fear of getting the science wrong. So we’re going to clear that up for you today so you don’t need to skip over these important contextual connections when you cover these events. You’ll also get some important context about the implications of these fires for people and communities and ecosystems.

Now, I’m not going to take the time to give full introductions for today’s experts. We’d like to get started. Their bios are on the website. I will just tell you that we will hear first from Dr. Phil Higuera, a professor – a – sorry – a professor of fire ecology at the University of Montana, who’s going to describe how wildfires and wildfire seasons have been changing in recent years and decades and ways in which climate change and other factors are driving those changes. Second, you’re going to hear from Dr. Colleen Reid, an assistant professor in geography at the University of Colorado Boulder, who specializes in environmental health issues and is going to speak about these huge plumes of smoke that wildfires create, what’s in them and what are the health effects from breathing those pollutants. And third, you’ll hear from Dr. Crystal Kolden, assistant professor at the University of California, Merced, who will speak about the role of forest management in getting wildfire activity back in balance and will describe some of the individual- and community-level inequities that exist when it comes to the burden of risk from wildfires. Just a quick reminder, you can submit questions for me to collate any time during these short presentations using the Q&A icon at the bottom of your screen. And with that, let’s get started. Over to you, Phil.


PHILIP HIGUERA: All right. Thank you. Sharing the screen – give a thumbs-up, maybe.


RICK WEISS: Looks good.


Recent changes in wildfires and wildfire seasons


PHILIP HIGUERA: OK. Thank you. Thank you very much, Rick. Thank you, everybody. And I appreciate the opportunity to speak with everybody. Thanks for tuning in. I’m going to dive right in here to make the most of this time. What I’d like to do in these few minutes is to help us set – I’m going to provide two points of context that help us think about making sense of increasing fire activity in the West. And then I’m going to go over three overarching drivers or reasons why we’re seeing increasing fire activity in the West.

So the first point of context that I want to start with here is just to remind ourselves that fire, this one word that we use, it’s a really diverse process. So while we think of fire in terms of maybe area burned, as I’m showing in this graph here, showing the increase in area burned across the Western U.S. over the last several decades, the reasons we have any individual fire, the impacts of a fire within one fire or among many fires vary widely across the West. And one thing that that means is that the path forward, in terms of being able to more sustainably or safely live with wildfire, is likewise going to vary across the West. So I want to put that out there as the first point of context.

Second point of context that I want to start with here is that fire is – fire itself can’t really be considered the problem that we’re trying to deal with, right? We live on an inherently flammable planet. We’ve had fire on our planet for over 420 million years – basically as long as we’ve had vegetation that could burn. So fire is a long-standing natural phenomenon. And what that means is it’s been present over the evolution of many species – plants, animals and including humans. So when a fire burns, it’s not inherently an ecological disaster. Many organisms have traits that allow them to survive fire or reproduce after fire. And many cultures, human cultures have worldviews and traditions that allow them likewise to exist with fire. So these are things that allow organisms to exist in fiery environments.

So really, what we’re focused on and, I suspect, why we’re here is because we’re interested in minimizing and understanding why fires and wildfires are increasingly becoming human disasters. So that’s one aspect of fire on our planet. So of the three overarching drivers of fire that I’m going to highlight here, I’m going to start with climate and a changing climate. So abundant evidence from the scientific literature highlights this link between warm, dry seasonal conditions – so over a summer, over a fire season and even over many years to decades – so across multiple timescales, we know there’s a strong link between climate conditions and the amount of fire activity. So this could be the size of an individual wildfire, the total area burned in an individual fire season, which is what is shown on this graph on the right. Each dot there is the total area burned in an individual fire season, and that’s on the y-axis or the vertical axis. And on the horizontal axis, there is a measure of how dry fuels are, fuel aridity. And so you can see, the drier the fuels, the further to the right, the more area burned we have in Western U.S. forests. You can also see that trend that I started with reflected in this graph by those red dots piled up in the upper right. So there is a strong link between climate conditions, ultimately, that impact how dry and flammable fuels are, and total area burned across the West. Changing climate is making conditions more conducive to burning, so easier to start fires. And once fires start, it’s easier for those fires to spread.

And very importantly, we know now through attribution science that human-caused climate change is part of this story. So this increase in fire activity and, in particular, the climate conditions that are making fuels drier is directly linked to human-caused climate change. And kind of the best estimate from the paper I’m citing there is that about half of that increase in area burned in Western U.S. forests over the last several decades is attributable to human-caused climate change. So importantly, that doesn’t mean that every fire we see is because of climate change, right? Again, fire is a long-standing natural process. We expect fires in the absence of climate change. But climate change is making them occur more frequently, making them larger and kind of exacerbating a lot of the other drivers of fire activity.

So in addition to climate change across the West, vegetation has changed significantly over the last century plus. And importantly, from the perspective of fire, it’s actually a lack of fire in many ecosystems over the past century that has created this fire deficit. So systems that burn frequently in the past – low elevation forests, grasslands – they’re systems that burn once every few years to decades. A century of fire suppression policies and really with Euro-American colonization, a reduction in indigenous fire stewardship, this lack of fire has changed vegetation. And what that means is that when fires do eventually occur in these areas, they burn differently. So they’ll spread faster. They’ll burn more intensely. And one result is, you know, trees that would have typically survived a fire could no longer survive the fire. Importantly, from the perspective of humans, this also makes it more challenging for firefighters to control when, where and how fires burn.

And then finally, the last overarching point here is that humans have – we have our hands all over fire activity in the West. So we expand when and where wildfires occur, pushing fires into the non-summer months, adding ignitions into coastal areas where lightning is otherwise rare. And you see this in the graph on the right, particularly in the wildland urban interface, which is where humans are living in and among vegetation that’s not really manicured. It’s wildland vegetation. We add – we dominate the sources of ignition in these areas. And there you can see that peak is the Fourth of July, so a very distinct pattern. That differs from more remote areas where fires are still dominated by lightning ignitions and most area burned from lightning-started fires.

But really importantly, it’s the fires that humans start that end up threatening our homes and our lives most often. So there’s this statistic there that speaks to that. So just to wrap up and summarize those three key points, you know, one of the reasons that fire is increasing and fire disasters are increasing is because climate is becoming increasingly conducive to widespread fire activity, in part due to human-caused climate change. The vegetation in which fires are burning through is significantly different than it has been in the past. And humans are increasingly living in and among flammable landscapes and adding ignitions to our landscapes. So I’ll stop there. I want to point out that I have some links here that will be available if you’re interested. And we can transition.


RICK WEISS: Fantastic. What a great, information-rich introduction. Thank you, Phil. And over to you, Colleen.

The health effects of wildfires and wildfire smoke


COLLEEN REID: Great. Thank you. OK, so I’m going to transition to talking about the health impacts of wildfires. But to talk about that, I first have to explain what’s happening, what’s in the smoke. And so when we have a wildfire, there’s many air pollutants emitted from wildfires. But the air pollutant that is most focused on in the health literature is fine particulate matter, also known as PM2.5. And when you see the dark smoke cloud, what you’re seeing are solid and liquid particles that are too small that they stay suspended in the air, and that’s what PM2.5 is. PM2.5 means all particles that are 2.5 microns in aerodynamic diameter or smaller. And this image from the EPA shows how small 2.5 microns is. For reference, you could fit at least 20 particles that are exactly 2.5 microns in diameter across the width of a human hair. And it’s important to note that many particles created during wildfires are much smaller than PM2.5. And when we breathe this in, we’re concerned about these small particles because the smaller they are, the deeper they get into the lungs.

And so epidemiological analyses of the health effects of wildfire smoke do demonstrate a clear linkage between wildfire smoke exposure and respiratory health in general. Wildfire smoke exposure can cause symptoms such as respiratory – respiratory symptoms such as cough, shortness of breath, also itchy, watery eyes, headaches and more. When we look at more severe disease, such as through investigations into increases in hospitalizations or emergency departments visits, the clearest impact is on people with asthma. Nearly every study that has investigated wildfire smoke within people who have asthma has shown significant increases in asthma hospitalizations and emergency departments, as well as increased use of medication to control their asthma during wildfire events.

There’s also good evidence that wildfire smoke exposure increases hospitalizations and emergency department visits for chronic obstructive pulmonary disease, which includes emphysema and other chronic lung diseases. And there’s some evidence that there is a link between wildfire smoke exposure and respiratory infections, such as pneumonia, bronchitis and influenza. The evidence to date on cardiovascular disease and wildfire smoke is mixed. However, with more evidence supporting an association in the past few years, this aligns with previous understanding of the biological mechanisms by which PM2.5 can affect the cardiovascular system, which I can go into in the question-and-answer period in more detail. I should note, however, that although some recent studies have found significant associations between wildfire smoke and cardiovascular disease, such as heart attacks and stroke, not all recent studies have. And it’s not quite clear at this point why there are differences between the studies, whether it has to do with how we assess exposure to the smoke, the duration or intensity of the smoke, the chemical composition of what’s being burned, the underlying health of a population or the statistical analyses that are used.

Some epidemiological studies also demonstrate a link between wildfire smoke exposure and increased deaths; birth outcomes, including increased risk of preterm birth and babies born at lower birth weights; exacerbations of diabetes, such as deaths of people who are using hemodialysis as well as ambulance dispatches for diabetic problems; as well as mental health impacts. It’s important to note that each of these outcomes listed here has not been sufficiently studied, meaning that there are only a few papers that have investigated the outcome related to wildfire smoke or that not all the papers on the topic agree that there is a relationship between smoke exposure and that health outcome.

I think it’s also incredibly important to determine if there are subpopulations that are more impacted than others from wildfire smoke. Based on what I’ve already said, it is obvious that people who already have respiratory disease, such as asthma or emphysema, are more susceptible to wildfire smoke. But additionally, some studies have tried to look at whether wildfire smoke affects certain population subgroups differently. And a meta-analysis done by Kondo et al. that came out in 2019 looked across the studies that have investigated that to see if we see consistent evidence. And the only thing that they found that was consistent was within age groups, that wildfire smoke exposure did not seem to affect respiratory health in children as much as in adults. But there was not clear evidence for differential susceptibility by sex or socioeconomic status, possibly due to mixed findings across studies or also the case that there’s just not enough research looking into differential impacts of wildfire smoke on health.

What people can do to protect themselves during a wildfire event – something I’m often asked – the most important thing is to know what the air quality is where you live. I recommend using to determine the air quality where you live. This is a map that is put out by the EPA. And one of the things I like about it is it doesn’t just include the regulatory monitors, but it’s also now including low-cost sensors like PurpleAir monitors that have been corrected to provide PM2.5 levels that are more in line with what they would say if they were regulatory monitors. And this also includes temporary monitors put out by the Forest Service to be closer to the fires to give better spatial information. People should use or the Smoke Sense app. The Smoke Sense app is also put out by EPA, and it gives you your current air quality in your ZIP code. It can also predict the air quality for the next day

Some of the other apps that are available also provide forecasts throughout the day, and people can use that to try and decide when they’re going to spend time outside or when they’re going to exercise outside to try and find times during the day when the air quality is projected to be better. And they can use the different colors that are shown with the air quality index to determine when it is they should take precautions depending on whether they are a sensitive subpopulation. If they already have respiratory or cardiovascular disease, I would consider them a sensitive group. For people with pre-existing health issues that could be exacerbated by smoke, they should make sure that their medications are refilled and up-to-date before the wildfire season. To decrease one’s exposures inside, there’s a lot of good evidence that using a HEPA filter air cleaner can significantly reduce the air pollution that does get indoors. And if you want to be outside and decrease your exposure to PM2.5, you can wear an N95 mask. That will protect you best from the air around you. Surgical masks are – that we’ve been using for COVID are designed to protect others from what you breathe. And here’s a list of references that I can make available that are referred to in my talk.


RICK WEISS: Great – another fantastic job. We ask our speakers to do so much in so little time to get things started, and I really appreciate how skillfully that is all put together. Crystal, over to you.

The role of forest management in getting wildfire activity back in balance


CRYSTAL KOLDEN: So the question that many of you are probably asking after hearing about how wildfires are changed over time and what the impacts of smoke are is, well, what do we do about this? What do we do to mitigate these negative impacts? And how do we prioritize the types of mitigation actions that we should be focused on? And this is actually in backwards order – did a preview.

So first, it’s important to understand that mitigation activities will be different depending on where you are at and what the primary drivers of changing fire activity and wildfires generally are. And so, as Phil has detailed, there are some really different drivers in different areas and across different timeframes. And it’s important to understand that this is really a global challenge because, as Phil noted, climate change – human-caused climate change specifically has fundamentally altered fire activity not just in the U.S. but globally. And this is a map that’s showing the 40-year trend in very high-fire danger days, which is another indicator of when we’ll get some of these extreme type of events. And the really dark red areas are places where, over the last 40 years, we’ve basically had more than a month increase in peak fire season, those most high-fire danger days.

And similarly, forest management, as Phil noted, is a factor driving many of these changes in fire activity. And what I like to often think about is an analogy for this climate change versus forest management driver issue is that most folks have either had to build a campfire or a fire in their fireplace themselves at some point in their life. And essentially, the climate change angle is what is controlling how dry that firewood is. The forest management angle is controlling how much firewood there is. It’s the difference between a small campfire and a much bigger bonfire. And so trying to link some of these mitigation activities is thinking about, all right, well, what can we control? We can’t control how dry that fuel is, but what we can control is how much of it there is and the arrangement and structure of that fuel on our landscapes.

And so what we look at with mitigation is that the climate is a controller. We cannot control that without first addressing our fossil fuel combustion. Vegetation is something we absolutely can control, and vegetation and fuel are something that we can control at two different scales. So near the home, we often advocate for defensible space, which is a reduction of the fuels – the vegetative fuels right around the house. Immediately on the home, we advocate for changing the structural materials and design of homes so that they are less flammable. And in states like California, we actually have building codes that reflect this now, but they’ve only been in place since 2006. And then, of course, the other factor that always comes into play is the human factor. And that is one that is much tougher to control because when people are asked to evacuate, they often are caught off guard and can panic. So a big part of mitigating wildfire disasters is doing the education and communication, which is where journalism is so important to this, so that we can actually have people better prepared for if they need to evacuate and aren’t trying to do it in a panic.

So there are many different types of mitigation activities across the landscape. As Colleen just detailed, figuring out how to mitigate smoke is a major concern for people in urban areas and large cities, as well as those out in more rural areas that are more directly exposed to smoke. One of the things that I just mentioned is that we are looking at how to better harden homes and demonstrating that increasing the hardening of homes and using fire-resistant materials is actually making communities more resilient and resistant to wildfire. There’s additional evidence that is showing that increasing our understanding of how to evacuate and identifying evacuation routes ahead of time, working with people to understand those is reducing disastrous outcomes. And even things like grazing in some suburban areas and into the more rural, peri-urban areas is showing to reduce the types of fine fuels that carry fires outside of the forests.

And, of course, one of the big contentious topics that people often ask about is, well, prescribed fire – how do we use that? How is it, you know, something that isn’t risky for us? And so prescribed fire is a type of fire that we ignite intentionally, that is specifically designed to meet several different types of objectives, depending on where it’s at. And in the wildland-urban interface, where houses are intermixed with forests and brush lands, a prescribed fire is often done to reduce the amount of fuel that’s available to burn, which, in turn, reduces the amount of energy that is released when a fire is combusted in that area. And one of the key concerns that people have about prescribed fire is the smoke that is produced. And one of the things that work – recent work that Colleen and many of her colleagues have demonstrated is that there is a big difference in terms of the types of smoke that we see from prescribed fires and, really importantly, the volume of that smoke and how well we can control how it impacts the residence areas. So that is really the key, is that prescribed fire is in – particularly in roomy areas, is looking to reduce fuels. And it’s a much lower risk than allowing those fuels to build up and ultimately result in catastrophic wildfire. That’s also the goal of much of what is advocated as active forest management – thinning the very small-diameter trees, reducing a lot of that brush. When used in connection with prescribed fire and oftentimes with grazing, the goal of these activities is to reduce that ground fuel that results in higher levels of energy released during combustion.

And one of the things that we know is that there’s no way we can do all of this at once and that we have to prioritize different types of mitigation activities because they are expensive, because they take a long time to implement, because they need to go through environmental review. And so one of the key new and emerging areas of scientific research is understanding how there are priorities to protect people who are the most marginalized groups, the most vulnerable communities, because wildfire is ultimately an environmental and social justice issue, like many other natural disasters. And so some of the more recent work is asking, where are these most vulnerable communities? And then they ask, well, why do people live in these fire-prone areas? This is a question I am asked constantly. And I like to remind folks that while today, much of the national media and in California, media is focused on the fact that South Lake Tahoe, Calif., is threatened and there are a lot of million-dollar homes in that area, the vast majority of the U.S. is actually fire prone. About 99% of the US is fire prone under the right conditions. And the vast majority of people who live in some of these most fire-prone areas, at the highest risk – they are living there because they can’t afford to live in cities, particularly in places like California, or they are people who are tied to that landscape, like the many Indigenous tribes that still live on their homelands all over the country. And so that is where asking questions about, well, why can’t people just move, really becomes a social justice issue. And these people often have their – excuse me, very, very few resources. So this is an example of where we look at some of these tradeoffs of risk and smoke for things like prescribed fire to support using a mitigation activity which will benefit whole communities who often don’t have the resources to do things like individually harden their homes. And some of these landscape-level mitigation activities protect the whole community and not just focus on a single homeowner. And with that, I’ll turn it back over to you, Rick.


What are some science-backed tips and pitfalls-to-avoid for reporters covering wildfires?


RICK WEISS: Great. Thank you so much, Crystal. Really important points made at the end there, as well as some interesting stuff. I had no idea that we could – different kinds of burns produce different kinds of smoke, with different kinds of health impacts. That’s great to know. There are some solutions in your presentation, which I appreciate.

We’re going to get into the Q&A. Before we do that, I want to remind people, you can click on the Q&A icon below your screen to send in your questions. I also want to point you to for some resources that we have on our website and, in particular, to a very concise fact sheet that we have about wildfires and climate change, specifically, the link to which we will put into the chat mode here as we go.

So while the questions come in, I generally start these media briefings with one question from the moderator for each of our speakers, and it speaks directly to the reporters and how they are doing as they cover this topic. And I’d like to ask each of you, if you would please take a minute, to tell the attendees something that you appreciate or like or want to support in the way coverage of wildfires has been going in this country and/or something that disappoints you or you wish were done more skillfully, that – and you can offer some advice to the reporters on board here so they can do a better job. And I’ll go back and start with you, Phil.


PHILIP HIGUERA: All right, thanks. Yeah, this is a great question, and I guess I want to start with – big picture, I’ve been really impressed at how coverage of wildfire has matured over the last five or so years. And for better or for worse, it’s because there are more wildfires to cover. So I guess I’d like to give kudos to the journalists who I see are reaching out to a variety of sources – scientists, managers and otherwise. And I just – I feel like there are many examples of reaching out to a diversity of folks. The right folks, from my perspective, are people who are well-informed. And what that adds to the coverage of wildfires is that it’s getting increasingly nuanced. I mean, that is the challenge I see for new journalists covering this, is that, you know, it’s not a simple story. There are multiple things contributing, multiple impacts, and I just – I see more nuance added to stories over the past several years, and I really appreciate that.

My one – this will just be – this will be a pet peeve, so a piece of – I don’t know – this isn’t advice. This is a pet peeve, right? One of the things that I still see out there, you know, is when we – when reporting on wildfires just focus on area. The area burned statistic is easy to go to, and is often reported as area consumed or, you know, X acres destroyed, X acres consumed by wildfire. And it’s really impactful to go out and visit a recent fire, and what you will see – right? – is that the land is still there, right? It’s not – it doesn’t disappear. But more to the point is that, you know, fires burn with such a great diversity. There’s a lot of variability in effects. And a lot of media coverage rightfully focuses on houses that are destroyed and things, but it’s important to remember that there’s thousands of acres that are burning every summer where fire is operating much like it has for thousands of years. And really, those types of fires are doing work that’s really useful to managers and society, you know, at large. So I’ll stop there.


RICK WEISS: Great. So being careful with the verbs – not destroyed necessarily, not consumed – radically changed, but in some ways for the better. Colleen.


COLLEEN REID: Well, here’s the problem of going second, is that I think Phil kind of took what I was planning to say – was just I also have found that the journalism has gotten more nuanced and really diving into the – into, I think, the more – the complexity of it, rather than – what used to be a pet peeve, and I still see it occasionally, but not as much anymore, and I think it was addressed by Phil in his talk was just that, you know, it’s not about – especially when journalists ask me about health impacts, it’s not about, OK, because there’s this health impact, we therefore need to suppress all fires. And not that, but just the complexity of – at least for me, I want to think about it more as fires are part of the world we live in. They’re going – they are becoming more frequent and, like, the air quality is getting worse. But how can we address that in a variety of different ways? There’s a lot of different possible ways that we can deal with that, and I tend to come at it from a public health perspective. And so I think that I’m seeing a lot more of that – like, ways that we can protect health of the most vulnerable populations while not trying to just do what we’ve done for 100 years and increase the problems of fire suppressions.


RICK WEISS: OK. And, Crystal, anything to add?


CRYSTAL KOLDEN: Yeah, I mean, I’ll echo Phil and Colleen in saying that I have been so impressed with the questions that are being asked and the evolution of how journalists are covering these. And particularly, one of the things that I’ve really appreciated is that there’s much more attention to the history of fire management and land management and tenure in this country that has contributed to where we’re at today. I’ve really seen an uptick in the acknowledgement of how Indigenous people stewarded this landscape with fire and that they have such knowledge that has been passed down through the millennia that we can’t even hope to match with Western science any time soon. And that’s really important to cover. I’ve just seen a fantastic job of it in a really nuanced and respectful way.

And in terms of, you know, a piece of advice, I think the one thing that I find myself constantly saying to journalists that I talk to is reminding them that fire is still a natural disaster because of, as Phil noted – right? – that – because of the human factor. It’s a natural process, and we humans have made it into a human disaster. And yet, because of this long legacy of the Forest Service and other fire agencies, sort of, having their budgets built on being able to control it, we tend to ask questions around wildfire disasters that we would never ask for other disasters. You know, no one is sitting there asking the poor people that are sitting in the way of Hurricane Ida, you know what? Why don’t you just get out? I know you don’t have a car. I know you don’t have, you know, any money to get out. So why don’t you just get out of here anyway? And that just really – it’s an absurd question, of course, right? And we don’t ask a lot of those questions for other types of disasters. And so, you know, one of the things that I constantly advise is, if you’re starting to ask a question about fire, ask yourself, would I ask the same question if I was covering a different type of disaster – right? – or is it just a fire thing? And so that is something that I think is slowly coming to the fore as we begin to see that we cannot – we simply cannot suppress all fires. And so we are starting to recognize that this is really, truly a disaster situation that we have to look at and more proactively, like we do with other disasters.

What is in store, wildfire-wise, for the Eastern U.S., especially the South?


RICK WEISS: That’s a very interesting perspective. Thank you. All right. We will get into the questions from reporters, and I’m going to start right here and give priority to an editor, actually – Steve Wilent at Natural Resources Management Today, who actually is a former wildland firefighter himself. And he asks, what is in store, wildfire-wise, for the Eastern U.S., especially the South? Phil, are you up on that?


PHILIP HIGUERA: Maybe I can tee it up, but I think Crystal has some good answers to this. I’ll just say that – and dovetailing off of the last question, you know, one of the great things – think Nate Rott at NPR, you know, wrote a great piece recently highlighting fire disasters not in the West, you know? So I think it’s a really good question. And I’ll just say that, like, the overarching impact of climate change, globally – and Crystal highlighted this – right? – what – it’s becoming – with increasingly warm, dry conditions, it’s becoming – the fact that anywhere where there is vegetation, there is the potential for a fire disaster. So I would expect to see our experiences in the West translate to the East. And I’m kind of thinking more Northeast, but I don’t know. There are also important parts of the Southeast that change that answer. And maybe, Crystal, you want to take it from there?


CRYSTAL KOLDEN: Yeah. You know, I think it’s important to acknowledge, A, that we have had some really large wildfires in the Southeast. And it happens, I’m thinking, in 2006. There were some really – you know, almost half a million acres in Georgia and Florida. The Okefenokee Swamp burned at some point. And there was a lot of – you know, a lot of really large fire activity there. And what’s important to note is that when there are large fires in the Southeast, they are often in areas that are managed more naturally and that – they don’t have as much of an impact on the wildland-urban interface in the more urban areas, in part because the Southeast has one of the most proactive mitigation programs in the country for fire. The – I think it’s eight or nine Southeastern states in the – what’s considered the Southeast region for fire – you know, they burn over 5 million acres a year in prescribed fire. And that has really limited the ability of wildfires to sort of grow large and out of control, particularly near a lot of that wildland-urban interface in the Southeast. So it is still a very fire-prone region. You know, they have a solid five-month dry period between January and May. So it’s out of sync with, sort of, the Western wildfire season, but it does get very, very dry. And in the years when that is a more prolonged or a stronger drought signal, particularly aligned with El Nino and La Nina, they get some pretty substantial wildfire activity. But they’ve been very successful in mitigating a lot of those negative impacts because of their very forward-thinking programs and a completely different, sort of, policy approach and cultural acceptance of fire in the Southeast.

Which scientific links between wildfire smoke and health outcomes are robust enough to report on? Which are too new to comment on?


RICK WEISS: Great. Thank you both for that. The question here for Colleen from Nicholas Gerbis at KJZZ Public Radio in Phoenix – you mentioned that some of the literature on health effects of wildfire smoke is still mixed. Which links are robust enough to report as valid, and which are too soon to say?


COLLEEN REID: That’s a really good question. For sure, we know that – respiratory health impacts, right? We breathe in the smoke. Anyone who’s lived near wildfire smoke knows that you’ll – I think everybody feels some sort of impacts. And then people who have asthma or chronic lung disease, I think, feel it a lot more. That’s very clear. The evidence on respiratory infections and cardiovascular disease is very robust in the literature on PM2.5 not from wildfires. And wildfire studies are getting going on those, and I think we’ll see more and more clear findings in that regard as – well, particularly as smoke exposures get longer, some of the reasons that, possibly, we haven’t seen impacts is that the fires we’ve studied in the past have been shorter in duration, so you might – more people might be able to sort of recover. They might feel some symptoms, but then they recover before they feel so bad that they show up at the emergency room.

And I think this – unfortunately, these fires that are happening lately – the exposures are lasting for such a long period of time that I do think we’re going to see more of these impacts that are – that’ll show up in our studies. And then also, because – possibly because fire is becoming so much more common, it’s also – there’s more research funding going into looking at fires and their health impacts, and so I think we will see a lot more studies coming out. And indeed, just the past couple of years has seen so many more. And so I think we’ll be able to say a lot more probably in the next five years or so.

How much agreement is there in the scientific community about the value of thinning and prescribed burns as mitigation tools?


RICK WEISS: All right. Another question here now is from Amy Matthews Amos, who’s a freelance reporter in Santa Fe, N.M. The issue of prescribed burns and thinning the surrounding national forests is a huge issue. Many people oppose it and fear the smoke, as has been mentioned but also doubt the science that these activities actually make a difference. I’ve even heard arguments among journalists about the science behind this. How much agreement is there in the scientific community about the value of thinning and prescribed burns as mitigation tools?


CRYSTAL KOLDEN: Yeah, that’s a great question. And, of course, this has been quite topical lately. So they – the key here is that the scientific agreement around a very specific type of thinning – right? – which is essentially thinning out the small diameter – when we say small diameter, we’re talking about, you know, less than 10 inches across – right? – so these are pretty small trees. When we’re talking about small-diameter trees, particularly in dry pine forests, which are – one of the early maps that Phil showed the forested parts of the western U.S. There’s also dry pine forests in the east. And when we thin out those really small trees and leave the larger ones and reduce that understory brush and then also follow up with prescribed fire, the evidence is sound, right? And where I look at – the analogy that I would like to use here – and my colleagues could disagree with me if they like – but, you know, I would say that we’re at about 97% of forest and fire ecologists who look at this literature and say, OK, when we’ve got this very specific type of treatment – right? – thinning out small-diameter trees in dry forests and then following up with prescribed fire so that we’re reducing that understory load – you know, there’s very, very high agreement and consensus that that is incredibly effective for reducing fire. And what often becomes the concern is that in the past – right? – there have been a lot of concerns about, well, what they’re actually going to do when they thin is go in and clear cut – right? – or they’re going to take all the big trees. And that is not what the Forest Service is able to do because they have to go under such thorough environmental review.

You know, the other big thing that I see a lot – and there’s been some news on this recently – is suggestions that this type of active forest management, where we’re restoring the health of the forest because these forests, historically, were very well-spaced forests with the low understory and regular fire in them every five to 30 years – you know, we see this question of, well, does this sort of treatment and this sort of fuel reduction still work to modify fire behavior even under climate change? And the answer is yes. The evidence is there to support that it still works. And what we often are seeing is that the places where there has been active forest management but that it wasn’t maintained – right? – that it was done 20 or 30 years ago, and there was not follow-up, either because there wasn’t the budget or they couldn’t get the follow-up elements through environmental review – that those are the places that are not as effective at reducing fire severity. And that’s really what the goal of most of these fuel-reduction treatments is, right? They’re not going to stop a fire. What they do is they modify fire behavior so that instead of a running crown fire that firefighters can’t do anything on – instead, they drop the fire to the forest floor and allow it to essentially burn with incredibly low severity, short flame lengths, which firefighters can work safely to try and stop or suppress when they get to key fire break areas. So the evidence is there to support this.

And there’s a lot of concern about whether this is going to be effective under climate change. And the main areas that the treatments are not continuing to reduce – fire severity under climate change – are areas that were treated a long time ago in which the follow-up has not been done because that vegetation grows back, right? So we have to keep treating in these areas. That’s where they devolved with because before, it was lightning fire and Indigenous fire that was continually retreating these areas. And so now we have to go in and do the same.

How have the federal air quality maps incorporated PurpleAir real-time sensor technology?


RICK WEISS: Got it. Thank you. Great clarification there. I have a question directed here to you, Colleen, from Judy Fahys at Inside Climate News. You mentioned that PurpleAir is now incorporated into the AirNow maps. Can you explain how they’ve been corrected to account for the PurpleAir monitor technology?


COLLEEN REID: So it’s in the, not the So that’s actually just an important distinction. If you go to, it includes the regulatory monitors, as well as the PurpleAir monitors, and it also shows you some smoke plumes derived from satellites. If you just look at AirNow, it’s still just using the regulatory monitors as far as I know. And I checked on it over this – you know, maybe in the past month. In terms of the correction – so we know that the PM 2.5 values you get from PurpleAir monitors just off the shelf tend to be higher than you would get if you were using a regulatory monitor which – they have different technologies for how they calculate the PM 2.5, which I won’t get into right now. But the correction factor – and PurpleAir – the company that makes it knows about it, and they have a correction factor that you can use. But what researchers at the EPA found was that the correction factor differs based on the concentration. And so they came up with a different correction factor for the high concentrations we have during wildfires. And that’s what’s being applied. We – the specifics of that – I could find that paper and, you know, share it with someone who wants to read the technical details of the calibration and correction equations. But that’s the gist of what’s happening.

What are some emerging and future areas of study in fire management and wildlife impacts?


RICK WEISS: Great. OK, another question here, and this one I’m going to throw to you, I think, for starters, Phil. It’s from your brethren, Amanda Eggert at the Montana Free Press. What are some emerging areas of investigation where the research has yet to catch up to lines of inquiry in fire ecology management and impacts to wildlife? Looking ahead, what needs to still be addressed?


PHILIP HIGUERA: There is a ton, especially – I mean, I guess I’d say, you know, as the field of fire science evolves into being more integrative and really recognizing the social and the ecological components, there’s a whole host of questions under there. I’ll just zoom into one kind of along the lines of fire and climate change and what we expect to see in the future. So generally, right now – and this has been predicted for decades like this – the degree to which climate change is increasing fire activity is something that scientists have predicted for decades. So for better or for worse, we’re kind of – we’re seeing these predictions come true. As we play this forward, as temperature and as, basically, fuel aridity is expected to increase – continue to increase, there are a whole host of questions around how our ecosystems will transition to this warmer and drier climate that includes more fire. And there’s some interesting questions in there in terms of feedbacks between how often you burn an area and if, when and how the – you know, the vegetation that comes back after these fires is increasingly different from what was there before in part because the way the fires are burning and in part because the climate now is different than when the trees that were there before it germinated. So we know that fire is going to be catalyzing, literally, accelerating the rate at which our landscapes change. And as those fuels change, that’s going to influence future fire activity. So there’s some possibilities for feedbacks in future vegetation to actually limit the amount of fire that occurs, and that’s a really important area of inquiry because it – you know, getting from here to there, you know, if there’s a future where there’s less flammable vegetation because a lot of it’s burned up, that’s important for us to understand in terms of anticipating future fire activity. And it’s the getting from where we are now to that point where there are a lot of question marks in terms of the timing and where across different landscapes that will happen and just exactly what that will look like. So that’s one area more on the fire ecology side.


RICK WEISS: Interesting. Anyone else on the panel want to address the question of what is crying out to be understood better?


CRYSTAL KOLDEN: I think there’s a lot. I believe the question asker asked about wildlife. Was that the…


RICK WEISS: That’s part of it.


CRYSTAL KOLDEN: Yeah, I mean, I think that what Phil’s – you know, Phil’s answer points directly to this question about, how is habitat changing, right? And that has been one of the major areas that is of concern because there’s a substantial amount of time and money invested in conserving habitat corridors and sort of key habitat areas for certain species. And so this is an area where, you know, the expectation is that once we conserve that habitat corridor, that that’ll maintain the species. But what happens when, then, you have substantial fire impacting those habitat corridors and fundamentally changing the vegetation? So that, I think, is an area that is sort of a – not yet well-projected in terms of what that means for conservation groups and trying to understand what some of those long-term impacts will be on conservation efforts.


RICK WEISS: We know that climate change is already affecting some of that, but it’s very interesting to throw in the wild card, as it were, of wildfires.


PHILIP HIGUERA: Yeah. If you allow me, I’ll throw in one more thing. And that is – let’s just add on to wildlife habitat. Carbon – that is a major area. So as carbon and carbon sequestration becomes a bigger part of our economy, of our society, obviously, there’s – there are very strong links between carbon sequestration and emissions and wildfire. And that is one reason why understanding this transition between where we are now and where we’re going to be in upcoming decades, that’s another main motivating factor.

How much preparation for fires, via thinning, prescribed burns, hardening homes, etc., has been done in Tahoe? Considering climate change, is it enough?


RICK WEISS: Great. I’m going to squeeze in one more question here from a reporter and then ask you each to offer our reporters a take-home message that they can leave with. We may run a couple of minutes past the end of the hour here, but I want to get this in. This is from Ezra Romero at KQED in San Francisco, directing it to Dr. Kolden, but can you talk about how much fire preparation – that is, thinning, prescribed burns, hardening homes – has been done in Tahoe compared to other parts of the Sierra Nevada? And with the pace and scale of climate change, is that work enough?


CRYSTAL KOLDEN: Yeah. Hi, Ezra – great question. The reality is that South Lake Tahoe has actually done a lot – right? – in the last – especially the last 15 years after the – I think it was the 2004 Gondola Fire at Heavenly and then, of course, after the 2007 Angora Fire that was just to the west of the Meyers-South Lake Tahoe area that destroyed quite a few homes. There was a real effort to ramp up the amount of work done around South Lake Tahoe in the forest, you know, and to an extent, in the – you know, in the private lands themselves – right? – because when we talk about thinning, there’s this real challenge where the Forest Service only has so much ownership, and then there are private lands. And we obviously can’t force people to do things on private lands, you know, unless it’s under certain jurisdictions. So the challenge in South Lake Tahoe has been to try and work at a community level. They’ve had a very, very active effort in the community. The – I think it’s called the Tahoe Living with Fire program – was very well-funded and was working really hard on education and communication. You know, I think one of the biggest challenges they have is that a lot of those houses are old. And you know – and then you have a large component of second homeowners that are oftentimes less aware of the immediate threat of fire.

So, you know, it’s the type of community that I look at and think, they’ve done a lot. Could they do more? The answer is always yes. Right? The answer is always that they could do more. And there’s sort of always that trade-off where – how much more money would it take to do a lot more, right? But what a lot of these communities are realizing is that there are strategic investments that they can make – things like fuel treatments along the side of community that is most vulnerable given, you know, standard fire and wind directions. And South Lake Tahoe has done a lot of that in partnership with the Lake Tahoe Basin Management Unit of the Forest Service. So, you know, we’re watching to see sort of what happens today and the next couple of days with the Caldor Fire. But I think part of what we’re seeing right now is that it’s paying off. And part of the reason it’s paying off is because the residents, particularly around the edges of South Lake Tahoe, have made their properties defensible for firefighters. We use that term defensible space, and we don’t really often stop to think about what it means. If you’re going to call a space defensible, that means there has to be a human being standing there defending it. And so firefighters, you know, they have taken a lot of risk. They are incredibly hardworking, but they also will only work really hard to, you know, save homes where their lives are not at risk. And what they are able to do and the success that they’re having along the – some of these impacted areas in South Lake Tahoe and Meyers is demonstrating that people are giving them that defensible space that they need to work and turn back the fire. And they’ve certainly been helped by the winds, too, to date. So that – you know, that’s a really long, nuanced answer, and I’m happy to follow up with you, Ezra, if you want to talk more about it.

What is one key take-home message for reporters covering wildfires?


RICK WEISS: No, it’s wonderful and a very dramatic, you know, image at the end of what it takes to really do this – great reminder of what’s involved. So I want to go around the horn here and have each of you, you know, give the reporters who are aboard here a last clear, clean take-home point, that if there’s one thing that they’re going to walk away with, this is something they should remember, something for their stories. So, Phil, let’s start with you.


PHILIP HIGUERA: OK. I’m going to stick on my theme of the role of climate in climate change. What I didn’t say in my presentation is a lot of my research is focused on understanding fire and fire history over thousands of years. I emphasize the overarching role that climate change is having in enabling widespread fire activity. It is increasingly clear as global temperatures enter into uncharted territories, areas that we haven’t experienced for millennia. It’s increasingly clear that wildfire is likewise entering into long-uncharted territory – so burning at rates over – you know, individual fires over years, over decades that ecosystems, including humans, haven’t experienced ever. So what that means is we need to be thinking kind of outside of the box, literally, because we are increasingly in uncharted territory in terms of this challenge that we would face anyways, but it’s so amplified with climate change. And of course, we see it, right? Like, we never – I never thought that 20 – the year that we’ve experienced was 2021, I never thought that would come right after 2020. The Caldor Fire jumping into the Lake Tahoe basin seemed extraordinary. Last year, East Troublesome Fire jumping over the continental divide into Rocky Mountain National Park – extraordinary. So, you know, I bounce back and forth between being, like, fire’s a longstanding natural process; a lot of what we see is what we’ve seen for thousands of years. But I think, increasingly, we are seeing systems exceed long-term levels of variability, and we are legitimately entering into uncharted territories in many areas. And it’s following the way that global temperature is and a whole other host of climate metrics are going. So I’ll leave you with that overall point – that wildfire is inherently linked to climate change, and we’re entering uncharted territory. So unfortunately, it’s going to be a topic that we’re going to be covering and thinking about a lot in upcoming years and decades.


COLLEEN REID: All right. That was great. I completely agree. And so I do think that we have to be thinking about the long term as well as thinking about the short term. In the short term, I feel like wildfire smoke events are becoming more common, lasting longer with higher air pollution concentrations, similar to how Phil just mentioned that 2021’s fire year is quite horrible, and we thought 2020 was really bad. I heard someone say – and I want to echo – that it’s possible that these years are, you know, some of the best that we might see in the future. And so I do think that we need not just to implement all the public health approaches that we can to try to protect people’s health, we need to better understand ways to protect people’s health and particularly understanding the most susceptible people. We also need to think through these intersecting health threats of extreme heat and extreme air pollution at the same time because the public health recommendations tell you to do completely opposite things. Open your windows to try not to overheat; close your windows to keep out the air pollution. And we need to have solutions that also don’t contribute to our climate change problem. Right? Like, right now, people are getting air conditioning, but that we know has – until we can electrify everything and put it all in renewable energy, we’ve got problems there. So I think that we just need – we really – it’s uncharted territory, and we need to start thinking about better solutions.


CRYSTAL KOLDEN: Yeah. And I’ll echo that and say that, you know, what Phil and Colleen have both just described is that we are in uncharted territory, and we have to come up with different solutions. And for me, what that means is the solution of trying to suppress wildfires, which we – has been our go-to for 110 years. It is not working. And that is not through any fault of the firefighters. That is not because we don’t have enough airplanes. That is not because we don’t have enough bulldozers or hand crews. It is because these are fundamentally very different, incredibly high-energy and fast-moving, you know, very unstoppable fires. The fact that in the last year we’ve had three fires go over major mountain ranges, which we never saw before in modern history, is really phenomenal. And it speaks to that we have to stop focusing on suppression and we need to be focusing on mitigating. That doesn’t mean we’re not going to let every – you know, we’re not going to let every fire go. What we’re going to do is focus on point protection of homes and communities, that we’re going to change our tactics so that we’re not trying to stop these multi-hundred-thousand-acre fires in the closest possible space, but instead, look at what do we need to do to minimize the negative impacts. Right? We can’t stop it. We would never suggest we would try and stop a hurricane or an earthquake or, you know, any other major natural disaster. And we need to start thinking about wildfires that way, too. We can’t stop them. We need to engineer and mitigate so that we don’t see the negative impacts that we’ve been seeing.


RICK WEISS: Fantastic summaries. And I want to thank our panelists so much for really such information-rich and articulate and clear descriptions of what’s going on with wildfires today – very useful presentation for reporters. I want to thank the reporters for attending, remind you that the video and transcript will be posted to our site soon – video first, transcript a day or two later. And if you do need raw video more immediately for some programming, get in touch with us by email or through chat right now or through Q&A. I do want to remind reporters – as you log off today, you will get a prompt for a short survey. It’s very short. It’s, like, three questions. It’s super helpful to us. Please take that extra half a minute to answer that survey so we can keep making these briefings as practically useful to you as possible. And with that, I just encourage everyone to check out our website at, to follow us on Twitter @RealSciLine. Thanks again to everyone who was here today, and we’ll see you at the next SciLine media briefing.

Dr. Phil Higuera

University of Montana

Dr. Phil Higuera is a professor of fire ecology in the department of ecosystem and conservation sciences at the University of Montana, where he directs the PaleoEcology and Fire Ecology Lab. Research in the PaleoEcology and Fire Ecology Lab focuses on understanding the interactions among climate, vegetation, and wildfire activity over a range of spatial and temporal scales in the past, present, and future. Understanding ecological change over time integrates projects within the lab, revealing patterns and processes unobservable over human life spans, providing context for ongoing environmental change, and helping anticipate the consequences of future environmental change.

Dr. Crystal Kolden

University of California, Merced

Dr. Crystal Kolden is a pyrogeographer in the management of complex systems department at the University of California, Merced, and a former wildland firefighter. She holds a doctorate in geography and served as a research scientist for both the U.S. Forest Service in California and U.S. Geological Survey in Alaska prior to her academic career. She conducts research on reducing vulnerability to wildfire disasters globally through improved understanding of coupled human-environment drivers.

Dr. Colleen Reid

University of Colorado Boulder

Dr. Colleen Reid is an assistant professor in the department of geography at the University of Colorado Boulder. Her work looks at how environmental and social exposures interact to influence health with a particular focus on exposures caused by global climatic changes and society’s responses to those changes. To date her research has focused on the health impacts of exposure to air pollution from wildfires, extreme heat events, and proximity to urban vegetation.

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