Emily Schwing: This is 60 Second Science, I’m Emily Schwing.

“A will-less and speechless human ... [believed] to have died and been supernaturally reanimated.”

“A person markedly strange in appearance or behavior.” 

“A mixed drink made of several kinds of rum, liqueur, and fruit juice.” 

According to Merriam Webster, these are all ways to describe a zombie. But maybe the definition should also include mention of wildfires—the kind that smolder and creep along underground in the boreal forests of the Far North and sub-Arctic.

Jandt: We think they’re out and, you know, snow, and it’s cold all winter. And then in the spring, when they start smoking up again, it’s like they’re back from the dead.

Schwing: This past spring, Randi Jandt and her colleagues published a paper in Nature about wildfires that overwinter in the boreal forest. Jandt is a former wildland firefighter. She’s also a fire ecologist at the University of Alaska Fairbanks’s Alaska Fire Science Consortium. [Rebecca C. Scholten et al., Overwintering fires in boreal forests]

Jandt: If you would have asked me about that in the 1990s or in the 1980s, when I started working in Alaska and in the fire community, I would have said, “Gosh, that is just a really rare thing.”

Schwing: Jandt can recall one memorable zombie fire, which reignited after overwintering in May, 1996. It stands out not only because of how much work it took to put out but also because in 1996 this kind of fire—one that overwinters—was very rare. But according to that study in Nature, zombie fires are becoming a more frequent phenomenon.  

Randi: These can be stubborn, deep-burning fires that require pumps and hoses—and, you know, a lot of effort to put out. One of our colleagues who had a full career smoke jumping in Alaska—46 years as a wildland firefighter—saw that article in Nature and related that it was an overwinter fire near Eagle, Alaska, called the Damien Fire. That was the most work per acre of any fire he was ever on. And that 46 years, I thought that was pretty remarkable.

Dow: Well, I'm Rod Dow, and I smoke jumped for a long time. I fought fire for 45 or 46 or 47 years, depending on what you count. And all of that was on the fire line.

Schwing: Rod Dow is now retired but he has hours of stories to share from his lengthy career as a wildland firefighter and smoke jumper. He says he has vivid memories of that 1996 fire out on the Alaska-Canada border. 

I find it really remarkable that I can call you and say, “Hey Rod, tell me about the Damien Fire,” and you remember all these details.

Dow: Yeah, that one, you know—it was—it was the work.

Schwing: The work?

Dow: There was no—there was nothing enjoyable about any of it. It was just constant 14 days of 14 hours a day. And I’ve never seen a fire that was that, that amount of labor per acre. It was just really amazing.

Schwing: The Damien Fire was estimated at 6.66 acres. It was deemed the Damien Fire, so named for the 1978 thriller The Omen, about a man who replaces his stillborn son with a living one, only to find he may have adopted a relentlessly murderous Antichrist.

[CLIP: Trailer for The Omen]

The fire smoldered underground in the winter of 1995, burning into 1996 under stands of trees that toppled over on one another like pick-up sticks. Firefighters call this “dog hair,” and they have to cut through it all with chainsaws to attack the blaze. 

Dow: If you could picture four football fields continuously strewn with logs at chest-deep level. You know, a gap, in between, the logs would be about big enough to stand in, maybe. So there was—it was nearly continuous logs crisscrossed on top of each other, and then underneath all of that was this foot-deep boiling ash.

Schwing: Much like Damien in The Omen, overwintering fires just don’t seem to give up.

Dow: I mean, that is an enormous amount of chainsawing, and that doesn't even count the, you know, putting the heat out.

Schwing: For two weeks, Dow and a team of firefighters went after the smoldering forest floor. He says eight chainsaws were running at once, alongside a high-pressure fire hose connected to a pump.

Dow: That water is turning to steam at an enormous rate because there’s hundreds of gallons of water coming out the end of the hose, and it’s all turning to steam at once. And so it’s blasting these giant steam clouds. And because it’s exploding out of there, out of the ground, it’s carrying all this ash up into the air around you.

Schwing: Since 2005 scientists have noted at least 40 overwintering wildfires in the Alaskan and Canadian Far North. The Arctic is warming at least three times faster than other parts of the world. That means the snowpack in places like Alaska is melting earlier in the year. According to the Alaska Fire Science Consortium, more than two and half times as much acreage burned in the northernmost state between 2001 and 2020 in comparison to the 1990s. 

These zombie fires are still rare, accounting for just under 1 percent of all land burned annually in Alaska and Canada. But there have been single years where the area burned by these underground infernos has been described as “exceptional”—totaling up to about 38 percent—in the region.

Jandt: Well, really, the reason that they are starting to overwinter somewhat more frequently goes along with these warmer summers and the opportunity for us to get deeper drying into those deep organic moss layers that underlie the forest and the tundra. And that’s the key. So if the fire can get deeply embedded into those organic, peaty, kind of duff layers, they can just hide out.

Schwing: The boreal forest, also known as taiga, is the largest terrestrial biome on the planet. And thanks to climate warming, this ecosystem is becoming increasingly vulnerable to wildfire. That’s significant, because estimates show at least one third of the world’s terrestrial carbon is stored in these forests—in the trees, in the soil, in the understory plants—and when it burns, this carbon is released to the atmosphere as carbon dioxide, a potent greenhouse gas.

Jandt says the increasing prevalence of zombie fires could challenge fire and land managers who are already struggling to find ways to bolster thin budgets.

Jandt: So the time of year they might begin to pop up in early spring is often really early, where fire crews are still being hired, trained, and there’s not many aircraft on contract yet. And, you know, firefighters are aware that a fire, if it’s been smoldering all winter, it may have burned very deep into the ground, and it could be hard to take it out and, you know, extinguish it.

Schwing: In the last two fire seasons, other parts of the world dominated by boreal forest have also seen overwintering fires, and Jandt says that may be where some of her research goes next.

Jandt: So when we start looking at Siberia and Eurasia, that’s going to be really interesting because ... overwintering fires seem to have been [a] really important contributor to that really awesome fire season—awesome in a bad way—that Siberia had in 2020, you know? Did you hear about that? They burned 35 million acres. Yeah, I mean, can you wrap your head around that? Oregon thought they had a bad season in 2020—it was less than a million acres burned. So, I mean, 35 million is amazing.

Schwing: Fires that overwintered started popping up again last spring, contributing to another intense fire season in Siberia this past year. Jandt says there’s no doubt much of this change in the fire environment is due to a changing climate. From a science perspective, she says it’s an exciting time to be a fire ecologist....

Jandt: Just because it’s so astounding to be able to measure it over your career—one person’s career.

Schwing: She says the way these fires are burning has a transformative effect on everything from the topography to the plants that return once the fire is finally out. But what if that fire is never entirely extinguished? Could zombie fires turn more vampiric—like Dracula, draining the life from forests to sustain the flames forever?  It’s unlikely if firefighters like Rod Dow keep their chainsaws sharpened, their certifications current, and there’s enough in the budget to go around.

For Scientific American’s 60 Second Science, I’m Emily Schwing.

[The above text is a transcript of this podcast.]