Zombie Fires & Climate Change in the Arctic

It sounds like something out of an apocalyptic tale, but we assure you zombie fires do exist. I had the pleasure of interviewing Earth Scientist & Associate Professor, Dr. Sander Veraverbeke to learn more about this rare phenomenon and climate change in the Arctic.

What is a Zombie Fire?

Like their not-so-real namesakes, zombie fires are fires that appear to rise from the dead. This is a rare phenomenon that occurs in the Arctic region where fires smolder and stay alive under extreme cold conditions. They then come back to life as temperatures warm – Hence the name zombie fire. Dr. Veraverbeke is studying this phenomenon and discusses what he has found in this fascinating interview.

How Does Climate Change Affect The Arctic? 

Unfortunately, Arctic forests are experiencing an increase in wildfires, much like we’re seeing throughout the world. In fact, the summer months of 2019 saw record-breaking blazes emerge throughout the Arctic, with over 100 widespread, intense wildfires in the region. Most of the trees in the arctic are in the Boreal forest and scientists claim that the frequency of fires there is potentially higher than it has ever been over the past 10,000 years.  

As Dr. Veraverbeke explains, this is also true of tundra forest fires and zombie fires as well. Directly impacted by longer, hotter summers with increased wildfires, the occurrence of zombie fires, although still rare, could be increasing as well, due to climate change in the Arctic. 

The High Price of Arctic Fires

The interview below goes into greater detail, but long story short, Arctic fires are among the fires with the worst impact on climate. Although studies are still being conducted, it appears that they emit more CO2 than other fires and can lead to the continued release of greenhouse gases long after the fire is extinguished. This is due to a thawing of the permafrost soil which contains lots of methane, an even more destructive greenhouse gas than CO2.

Arctic fires in the Boreal forest and climate change

Interview on Arctic Zombie Fires

Dr. Boose: Welcome Sander, you work a lot on Arctic fires and when people think of the Arctic, they maybe think of the North Pole and a lot of land covered by ice, not necessarily a place where a lot of fires burn. So maybe we can start with the basics. What do you mean when we’re talking about Arctic fires, and how do Arctic fires start? 

Dr. Veraverbeke: I think it’s a really good question, when people talk about the Arctic, that can mean different things. And maybe for now we can take a broad definition in which the Arctic combines two biomes on Earth. The first one being the Boreal forest. These are the northern forests that stretch from Alaska to Canada to Scandinavia over to Siberia (often called the taiga). Then farther north of that, where it’s too cold for tree growth, we have the second biome, the Arctic tundra.

 So when people talk about the Arctic, it’s more focused on the tundra. When we are talking about Arctic fires, the majority of these fires, about 90%, happen in the Boreal forest, but some of them also happen farther north than that, as they are also happening more often now into the tundra. 

Boreal forest and fires in the Arctic

And your second question is what do we need to have these fires going? What needs to be available? It’s almost a little bit like starting a barbecue. First, you need dry fuels, and these are abundantly present in these landscapes from the above ground vegetation, such as shrubs and trees. But there’s also a lot of organic soils, like old plant materials, that have accumulated over decades to centuries. So there’s a lot of fuel available and it’s dry more often now because of climate change, and increases in droughts and heatwaves. Second, we need oxygen, and that’s always available in the atmosphere. 

And third, we need an ignition. There are two main types of ignitions in these ecosystems and a third one that is a bit special. The first one is us, people, especially when you go more to the south in the Boreal forests; for example, in Siberia where there is a lot of human activity that can start fires (sometimes on purpose, sometimes as an accident). Second, if you go farther north, these landscapes are quite remote and there’s not that many people living there. So the main ignition source, when you go to the northern forest and into the tundra, is actually lightning – a natural source of ignition. And then I want to add, something that we’ve discovered, is that it’s possible for fires from the year before to keep smoldering throughout the winter, in organic soils underneath the snow cover. That’s quite crazy to think about, when it can be minus 30 to minus 40 degrees in these places. But when spring comes, the snow melts, and more favorable weather for fires arrives – hotter, drier conditions, a bit of wind – these smoldering over winter, zombie fires (as they are called) reemerge and go from a smoldering phase to a flaming phase. They can actually start spreading as a new forest fire one year later, one season later. So, those are the three types of ignition that we can have within one fire season. 

zombie fires in the Arctic and Boreal forest

Dr. Boose: Very interesting, and zombie fires sound very spooky. I want to hear more about that, but maybe before we get to that, can you give us a bit of perspective. What are these Arctic fires and what role do they play on climate?

Dr. Veraverbeke: Right, that’s a very good question. The most important way they interact with the climate system is with the greenhouse gasses that are emitted during a fire. There’s a lot of carbon available in these ecosystems, and not just because of the above ground vegetation. When people think about a forest fire, they think mostly about the trees burning, and that’s part of it, but in the soil we also have an accumulation of old organic matter, old carbon, that can be several decimeters thick. And that’s actually a very important carbon pool. When fires burn down into these soils, the majority of the carbon emissions come from the soil, between 70 to 90%. So the above ground component is then 10 to 30%. So the carbon emissions are quite high, actually some of the highest emissions, if you look at it per square meter, from fires on Earth. Tropical peaty plants also have very high emissions. So those two would be the more dangerous fires for climate change. 

Arctic fire carbon emissions are some of the highest emissions from fires on Earth

Another aspect that is important, is that these fires occur in a permafrost landscape. Permafrost is basically permanently frozen soil. And in summer you have the active layer that thaws because of seasonal heating. So what these fires do, is they take 10, 20, 30 centimeters of organic soil away. They remove the insulating buffer, so you get more solar radiation into the permafrost soils. It’s also charcoaled and black, allowing the permafrost to thaw deeper in the summer season. You have to think of the permafrost as an enormous freezer, storing a lot of old carbon. And when that freezer goes above zero, that old organic matter can start rotting, and release additional greenhouse gasses. So on top of the emissions that stem from the fire when it’s burning, these emissions can last for several years to decades later. We are working on this as a scientific community, and we still have work to do to better quantify these longer term emissions after a fire from permafrost. 

Climate change and Arctic fires

Dr. Boose: So, basically, stinking and thawing permafrost, super interesting. You mentioned zombie fires, can you tell us a bit more about those? 

Dr. Veraverbeke: It’s a discovery that we made about a year ago now. I was looking at some satellite data from large fire seasons in Alaska and Canada, and the relationship with lightning. And then, surprisingly to me, when I was looking at the year after one of these big fire years, I saw new flare ups in spring, very close to the edges of the fires from one year before. So we were like, what is going on here? I independently checked with fire managers in these regions of Alaska and Canada, to see whether it was possible for a fire to smolder underground for an entire winter to then flare up again. And they confirmed that it’s possible. So we set up, with one of my PhD students, an algorithm to detect them with satellite data. Basically to know how often this happens, and it’s a relatively rare phenomenon. If you look at the total burned area in the Boreal forest, it accounts for 1 to 3% of the burned area, so that’s not that much. The lightning ignitions represent more of the burned area, and the human ignitions as well. But zombie fires do really happen, especially after these big fire years that are facilitated by hot and dry summers. 

Zombie fires may be happening more often because of climate change

So there is a link between these big fire years and more frequent extreme weather – that’s climate change – and that facilitates overwintering. So indirectly, overwintering fires (zombie fires) may be happening more often because of climate change. These were our first studies, and also in Siberia we have detected them and some colleagues of ours as well. And that was all based on satellite data. Quite excitingly, this summer, some colleagues from the US and Canada, we actually went onsite to places where these overwintering fires have happened. So that was very cool as well. 

Dr. Boose: That sounds fantastic to work in these different countries with various scientists. I also love the approach between satellite data and talking to forest managers on the ground as well. My last question would be, why do zombie fires happen at a specific location? You’ve mentioned Canada and Siberia, is there something that gives you an indication of why here and not there? 

Fires in the Arctic and Climate Change

Dr. Veraverbeke:  That was, for us, also a very intriguing question. What makes these fires keep going throughout an entire winter? Somehow there needs to be fuel available, and our hypothesis is that it would be available because of the peaty thick soils. There needs to be enough oxygen, not that much because it’s in a smoldering phase, but there needs to be enough to keep it going. And then of course, we were wondering are there certain landscape positions that favor this overwintering? We had some indications and some hypotheses from looking at the satellite data; but to really know it, you have to go into the field. We were actually there with colleagues from the University of Waterloo this summer.

It was really exciting and we were flying with helicopters to the exact locations where we had mapped from satellite data where [zombie fires] have happened. So flying over these wild northern landscapes was just amazing. We were very curious about what we were gonna see. We could kind of already see from the helicopter when getting close to the area where fermenting fire happens, that all the trees were down. Usually after a fire, the tree bowls keep standing for a longer time. Going onsite, we thought the hypothesis was that they would have been smoldering in these peaty soils because these peaty soils are further consumed, there’s very little left where the tree roots are actually going into the ground and into the soil, so they kind of just all fell down. That explained why a lot of these trees were down now.

Interestingly, what we also found, which was not something we expected, is that some other sites were kind of drier ecosystems that had bigger trees, not really thick organic layers. We think that they just kept smoldering on the tree roots and tree bowls. So that was an interesting observation. 

There’s a lot that we need to do with the data, so I’m just talking about what I saw, and now we really want to analyze the data. We took a lot of soil of course, we made a lot of observations and measurements of the vegetation and so on, permafrost as well. 

Zombie Fires in the Arctic

Dr. Boose: Great, a lot more work left. That sounds very promising. Wow, thank you. It’s now time to discuss our environmental heroes of the week, where we ask our guests to highlight a company, an organization, or an individual person who they believe is making a positive impact on the environment. So Sander, can you share with us your environmental hero nominee for this week and why? 

Dr. Veraverbeke: Yeah, definitely. I was thinking about Rachel Treharne, from the Woodwell Climate Research Center in the US. Rachel is a very active, young researcher that works in a related field as me, looking at climate change effects on ecosystems in the arctic, fires, and permafrost thaw. She does great research, but she does more than that as well. She’s great at explaining the science to a larger public, and the importance of that. And not only just the public, but she also actively engages with policy makers, because obviously it’s quite important that our results are integrated in future plans for policy. So, yeah, that’s why I would like to nominate Rachel. 

Dr. Boose: Great. That’s an excellent nomination. Thank you for that. My nomination is also related, not directly to fire, but to forests, as my nomination is Peter Wohlleben. He is a German forester and is very active in engaging the public, in thrilling them, for the forest. He does so by writing popular books that explain a bit the interaction between trees, trees in a system, and why certain trees grow at a certain location and not somewhere else, which I, as a non-expert on the forest as a whole, found extremely nice. Especially how he manages to put it in very simple words and to connect to people. And I think from how I’ve experienced the reaction to him, he’s very good at engaging people in that. So that’s my nomination. 

Dr. Veraverbeke: I just wanted to add that I’m pretty sure that I’ve read his book about the forest in West Germany. And I highly, highly recommend it. 

Dr. Boose: Great, so he reached to the Netherlands. I think at least one of his books is translated to English, The Hidden Life of Trees. So we’ve reached the end of our interview today. Thank you so much Sander, for joining us and for very interesting insights, from a scientist, on fires in the Arctic and on zombie fires.

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Dr Yvonne Boose
Dr Yvonne Boose

Data and Accuracy Lead Scientist @BreezoMeter. I hold a PhD in Atmospheric Physics and formerly worked as a Postdoc at the German Aerospace Center. I love translating science to real-life improvements at BreezoMeter.