E5: Wildfires—and how we're changing them

DS: In the United States, we had not seen in the modern era, really, since we had modern firefighting and aircraft, a fire that, that, that killed dozens of people and burned thousands of structures all at once, until the Camp fire destroyed the town of Paradise in California back in 2018. So it was, I think, a shock to the system for a lot of folks to see the kinds of extremely destructive fires in populated settings that we've seen recently. You know, just house after house go up in flames.

LHF: If you live in the Mountain West or the Pacific Coast, there’s a good chance a major wildfire has passed near you in the last five or six years—maybe one more intense than anything you’ve ever heard of in your area. If you live on the East Coast like me, you might newly have been exposed to the hazes of smoke that now drift occasionally over the continent, as they did from the Canadian fires of 2023 this past summer. But are wildfires actually getting worse, and, if so, why? Is climate change entirely to blame? And what should we be preparing for next?

I’m Laur Hesse Fisher with the MIT Environmental Solutions Initiative, and this is Today I Learned: Climate. My guest today studies extreme weather events and climate change.

DS: I'm Daniel Swain. I'm a climate scientist with UCLA, the Nature Conservancy and the National Center for Atmospheric Research. So I think a lot about the episodic extreme events, the floods, the droughts, the storms, and things like wildfires, which are changing and affecting society and the environment in a warming world.

LHF: And we brought Dr. Swain on the show to help us understand what’s going on with wildfires.

DS: So there is a wildfire problem, but the problem is often a little bit different than some folks assume it is. The problem is not that we're seeing more fires. The problem is that the fires that we're seeing are more intense and more destructive.

LHF: Why? Well, let’s start by understanding wildfires.

DS: Wildfire is an inherently natural process. This is something that existed long before humans,and is an important part of most ecosystems in which it occurs.

There are a lot of places that are adapted to fires of a particular frequency and intensity.
Some plants require fire to regenerate, to reseed, to germinate.

We also have records  from indigenous peoples around the world who have cultivated fires in different ecosystems for literally thousands of years. Sometimes if you have an area that's overgrown, fire can be a tool to reset the landscape, add nutrients back to the soil through the ash. So these were very purposeful things to improve the landscape.

LHF: In California, native peoples like the Yurok and Mono practiced “controlled burns” to cultivate their forests. This made the forests less dense, more tame — Spanish explorers would compare them to gardens and discover they could easily travel under their canopies for miles.

DS: And all of that abruptly changed about a hundred or 150 years ago, where we started doing two things very differently. One is we removed, in many cases, indigenous peoples off of their ancestral lands and banned these practices of cultural burning. And then at roughly the same time, we started actively suppressing wildfires.

LHF: With the invention of fire engines and other modern equipment, and a growing network of roads deep into the wilderness, it became possible to quash many fires almost as soon as they started. And so a lot of places did. In 1935, the U.S. Forest Service created a “10 am policy,” saying that whenever a fire was reported, it should be out by 10 am the next day.

And that total fire suppression actually changed the landscape we were trying to protect.

DS: Removing that natural fire and those indigenous fires from forested areas resulted in a huge buildup of fuel on the forest floor. You know, when leaves fall down, branches fall down and eventually whole trees fall down. All that becomes dead wood or dead woody debris on the forest floor. Simultaneously, you then have growth of living vegetation that is much denser than it would've been in a natural environment. So you actually get a lot more small, new trees — small to medium size trees.

There's a heck of a lot more stuff to burn. So the fires that come along are going to be a lot more intense. They're going to burn for longer. They're gonna produce more heat and more smoke. And then, enter climate change.

LHF: We asked Dr. Swain to help us unpack how climate change affects wildfires.

DS: So the number one thing that's happening when it comes to climate change and wildfires is that the water vapor holding capacity of the atmosphere increases rapidly with warming. So in other words, a warmer atmosphere holds more water.

LHF: Well, wait—more water in the atmosphere must mean more rain and snow, right? Shouldn’t that help prevent wildfires?

Well, yes and no. On average the world is seeing more rain. Even a wildfire-prone place like California is experiencing bigger rainstorms than it used to. But the thing is, all that water has to come from somewhere.

DS: So essentially as the atmosphere warms, it becomes thirstier. And so this progressively larger atmospheric sponge, if you will, extracts more water out of the landscape, out of the soil, out of plants, leading to drier vegetation. And therefore both more liable to burn and also, and this is critical, more likely to burn at a higher intensity. It's not so much that there are more frequent fires. In fact, there aren't more frequent fires. Fire frequency has been flat or declining in many places over time. It's really  the characteristics of wildfire that are being greatly amplified by a warming climate.

LHF: Fire experts quantify these changing characteristics in a few different ways.

DS: We often measure that in terms of area burned. So it is correct to say in many places that there's more acreage burning. It depends exactly where you're looking, but These are not small increases. They're 200%, 300% increases in the acreage burned. But that's sort of an imperfect metric because, in the natural state of things, a lot more land probably would be burning today than it is because we've suppressed so many of those naturally occurring fires.

There's a couple of tentative studies that are suggesting that the radiative power — this is measured by the temperature of the fires when they're occurring by satellites — has increased. But I think on the impact side, you can look at literally, you know, how many structures burn in these fires, we've gone from having many fire seasons where you wouldn't even see cumulatively more than a hundred structures burn, to now seeing individual fires that are burning 3,000, 5,000, 10,000 structures in one fell swoop.

LHF: We’re even beginning to see types of fire that were once so rare there’s little historical record of them.

DS: When we talk about intense fires, it's not just that they're burning hotter, which they are, or moving more quickly, which they are. But it's that they start to interact with the atmosphere and the environment in increasingly exotic and extreme ways. I know this sounds like something out of a science fiction movie, but arguably the strongest tornado in California history was now a swirling vortex of flame, several thousand feet tall with winds of almost 150 miles an hour that actually killed people and destroyed houses in its own right.  This occurred in the Carr Fire up in 2018 near Redding. So these are the kinds of fires that we're talking about.

LHF: Look, this is really within the far extremes of what wildfire can do. Not every fire in the future is going to become a tornado. But it did happen just in 2018.

And here’s the thing: we are not helpless to respond to these extreme events. Hotter temperatures, and drier dry seasons, are a reality now. But there is still a lot that we can do to avoid supercharged wildfires in the future.

DS: Climate change is a global problem that requires global solutions. And so if you're an at-risk community in the woods somewhere — as a community, there's not a whole lot you can do to alter the long-term trajectory of climate change. That's the global challenge. But there are actually things you can do to alter local fire suppression policies and the local urban development and sprawl. You can design structures to be more fire resilient. You can manage the landscape, either, you know, a couple acres of land surrounding a structure or better, you know, hundreds of thousands of acres of land surrounding communities using a bunch of different tactics specifically to mitigate fire risk.

LHF: In at-risk areas, you can create large gaps between homes and the surrounding trees and brush. And you can choose foliage that are more fire resilient: some plants hold more water in their leaves, and have fewer flammable oils and resins, which can help slow the spread of wildfire. Buildings themselves can also use more fire-resilient materials, like concrete and masonry, or be renovated with brick facing or stucco so they don’t catch as easily. And because things like decks and crawl spaces catch dead vegetation, it’s a good idea to eliminate those in high-risk areas, too, or clear them out frequently.

These kinds of measures can help buildings survive fires. And we could also rethink where we’re building new communities in the first place.

DS: More people live in risk zones than ever before. There are now suburbs and exurbs in places that are extremely high risk for wildfire and this expanding bullseye effect — as other folks have termed it — it's just if you throw wildfires randomly out there on the landscape, it's easier and easier to hit a populated target.

LHF: In much of the U.S., as the population has grown, we’ve tended to build out—expanding farther into the forests and grasslands where wildfire risk is highest. We could instead build in, adding more housing in the urban and suburban areas that are already well removed from the wildlands and the wildfires.

Or here’s a totally different strategy: we may do best of all by actually living with more fire.

DS: We really should be seeing and, and embracing more fire on the landscape to prevent the catastrophic fires.

LHF: Yeah, we can try to make today’s fires look more like the fires that native peoples around the world cultivated for thousands of years: a regular, renewing feature of the landscape.

DS: There really isn't a no fire option. I think the consensus among fire and climate communities these days is there is no way to not see more fire on the landscape in a warming climate. The real question is, do we wanna see more of the catastrophic fires that we've recently been seeing? Or are we willing to embrace seeing more fire on the landscape in the form of prescribed burning, cultural burning, these fires that are — yes, they're still going to produce some smoke, but they're gonna produce less smoke and at more opportune times. That's the kind of choice that we potentially have. And I think that that's actually an optimistic thing because those are two very different options, and we do have some control over which option we choose.

LHF: That’s our episode. To learn more about wildfires, and how we can respond to them, check out our show notes, or our Educator Guide which includes a classroom activity about fire resilience. That’s all at tilclimate.org.

TILclimate is produced by the MIT Environmental Solutions Initiative at the Massachusetts Institute of Technology. David Lishansky is our Editor and Producer. Aaron Krol is our Scriptwriter and Associate Producer — and did our artwork. Ilana Hirschfeld is our Production Assistant. Michelle Harris is our fact-checker. Sylvia Scharf is our Climate Education Specialist. The music is by Blue Dot Sessions. And I’m your Host and Producer, Laur Hesse Fisher.

Thank you to Dr. Daniel Swain for joining us, and thank you for listening.