by Aparna Nathan

figures by Sean Wilson

Last summer, satellite cameras captured a strange image: a shroud of smoke hovering over the Arctic. But beneath these still, swirling clouds, towers of flames punctuated the bleak expanses. In short, the Arctic was on fire.

The summer of 2019 saw record-breaking blazes emerge throughout the dry polar desert—known as tundra— and the surrounding forests. Arctic wildfires aren’t new, but they had never before consumed such a large area so far north or raged for so long. In just two months, there were over 100 intense wildfires spanning Alaska, Siberia, Canada, and Greenland. Some were as big as 100,000 soccer fields, and in Siberia, they burned for over 3 months, during which they consumed almost 10 million acres of forest.

As we enter the 2020 wildfire season in the Northern Hemisphere, we need to think beyond fires in arid California. Now, Arctic wildfires are another critical hotspot. These areas are remote, allowing the fires to burn indefinitely without threatening human activity, but they are especially dangerous because the Arctic holds some of the biggest carbon stores anywhere on the planet. Burning this carbon is like running a massive engine on raw coal: it releases tremendous amounts of particles and greenhouse gases into the atmosphere that can affect the whole planet.

Anatomy of an Arctic wildfire

To start a fire, you need two main ingredients (other than oxygen): a fuel to burn, and an ignition source to turn up the heat. The Arctic might not seem like an intuitive place to find either of these, but you have to look beyond (and under) the ice. What we traditionally think of as the Arctic is considered a tundra biome. This is a cold, dry desert environment with few plants on the surface, other than shrubs and mosses. If you look underground, though, there are also hidden treasures in the permafrost (a layer of soil and water mixed and frozen together). One key element is peat, thousands-of-years-old semi-decomposed organic matter rich in carbon, maintained by a unique moss coating. The moss can take up lots of water—26 times its weight—and forms a coating over the peat layer that is crucial for keeping the peat from fully decaying and releasing its carbon.  

Now, take this frigid landscape that usually hovers around 32 degrees Fahrenheit and turn up the temperature by 10 degrees, which is how much some parts of the Arctic have warmed over the last 25 years. Compared to the rest of the planet, the Arctic is warming twice as fast, and as it gets hotter, it also gets drier, causing the soil—especially the peatlands, and their hydrating coat of sphagnum moss—to lose its moisture. The same drying process happens in the boreal forest, or taiga, that encircles the Arctic tundra. These vast, dense forests are filled with hardy trees—like pines and spruces—and even more carbon-rich peatlands. These forests contain 50% of the planet’s soil carbon stores—equal to the amount of carbon in the atmosphere. Beyond natural forces, human industries like lumber and mining are also siphoning the water resources of the northern forests and tundra, intensifying the land’s dehydration. 

With the tundra and forest drying out, there is an abundance of dry vegetation to serve as kindling for a fire. Dried peat is even more dangerous because carbon burns quickly and intensely—think of factories that burn coal, or wood in a fireplace (Figure 1). The only remaining ingredient required is the spark to start the conflagration. And that arrives straight from the sky: lightning. Normally, the North pole is not a common site for storms because the air doesn’t have enough heat or moisture. However, as the Arctic has warmed and the ice that keeps the poles cold has melted, warmer water temperatures have heated the air just enough to form storm clouds and discharge lightning. Between 2012 and 2018, there were only 3 lightning strikes north of the 85th-degree latitude, which cuts through the Arctic Ocean and northern Greenland. But in 2019, just one weekend storm produced 48 lightning strikes at that latitude. With lightning as the flint and dried earth as the fuel, it is the proverbial “perfect storm” for starting fires.

An Arctic furnace warming the planet

Even as Arctic fires become less rare, they remain unique among other blazes because their impact stretches thousands of miles beyond their physical radius. One far-reaching effect of these fires is soot. As the fires reach high into the sky, they throw particles—made of black carbon, one of the main ingredients in soot—in every direction. These particles are like what might fall out of a chimney, but they also float unobserved in polluted air and can be harmful to living creatures like humans and animals, increasing the chances of asthma attacks, strokes, heart attacks, and other potentially fatal chronic health conditions.

And black carbon doesn’t just affect people—it also affects the health of the Arctic as a whole. Snow and ice are very important to the Arctic because they help it stay cool by reflecting sunlight off their white surfaces back into the atmosphere –this is one of the reasons why recent ice melts in the Arctic have made the region even warmer. But when there is soot in the air, it eventually settles down in layers on the white Arctic landscape and turns it black. Now, these new black surfaces can absorb heat and trap it at ground level, which reinforces the Arctic warming cycle.

But where there’s smoke, there isn’t always fire—at least not at the surface. When peat burns, it doesn’t flare up like normal fires; instead, because it is underground, it smolders beneath the surface. These so-called “zombie fires” are still identifiable by the wisps of smoke rising from the ground, but because they burn slower and more subtly and can’t be easily extinguished, they can end up burning for much longer—even through the winter—and ultimately release much more emissions into the atmosphere. These emissions include black carbon particles, but also carbon-containing gases, which we commonly think of in the category of greenhouse gases. These gases hover in our atmosphere, where they absorb and emit heat to keep the Earth warm, like a greenhouse enveloping our planet. But when too much enters the atmosphere—like when we burn fossil fuels—these gases do their job too well and make the Earth warmer than it should be.

Arctic fires release carbon-containing gases like carbon monoxide and methane, just like cars burning gasoline. But because the chemical composition of the soil is more varied than fossil fuels, it also produces greenhouse gases like nitrous oxide that don’t contain carbon, but still trap heat. Because the Arctic contains such dense stores of carbon, fires that burn through it open the floodgates and release massive amounts of greenhouse gases into the atmosphere. One peat fire can produce 80 tons of carbon per acre, the equivalent of the annual emissions of around 20 cars. Multiply this by the millions of acres of fires cropping up each summer, and the number skyrockets. Estimates from 2019 suggest that Arctic fires produced 140 million metric tons of greenhouse gases that year; for comparison, the wildfires in California only produced 45 million metric tons. That difference is equivalent to the annual emissions of over 20 million cars.

Tracking and breaking the cycle

As the 2020 wildfire season approaches, many scientists and environmental agencies will be looking north to see if the cycle of fires continues. Based on projections from researchers, last year was not an anomaly, and we can only expect fires to burn more intensely. This year’s wildfire season is already off to a roaring start, with record-high temperatures reaching the 80s in Siberia and 1.5 million acres already burned. Predicting fires is a complex task, and scientists have to consider diverse factors, including temperature, ice melts, vegetation types and density, and human activity. Forecasting is not always accurate; for example, predictions from the last decade underestimated the fires seen last year. International weather agencies have been using satellites to monitor fires in progress by looking for characteristic smoke patterns or measuring heat output.

Arctic fires are just one emerging component of a vicious cycle of global warming (Figure 2). The poles get warmer, drying out soil and vegetation and sparking lighting, which starts fires that release greenhouse gases, further increasing atmospheric temperatures, and creating an environment to support even more fires. This makes turning the tables on Arctic fires a daunting task, but not impossible. Beyond reducing human activities that dehydrate the Arctic fringes, researchers recommend actively re-wetting the peatlands and removing plants that could fuel a fire (like spruce trees) and replacing them with mosses that can keep the ground wet. Although these measures haven’t been tested on a large scale yet, if human intervention can prevent the fires at our planet’s icy poles, it is another sign of optimism that we can keep the Earth cool for a little longer.

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Aparna Nathan is a third-year Ph.D. student in the Bioinformatics and Integrative Genomics program at Harvard University. Follow her on Twitter at @aparnanathan.

Sean Wilson is a sixth-year graduate student in the Department of Molecular and Cellular Biology at Harvard University.

Cover image: “Reflections in grey” by dracophylla is licensed under CC BY-NC-SA 2.0

For more information:

• This Wired article takes a deeper dive into the science of peat
• This video from the World Meteorological Organization walks you through the basics of how Arctic wildfires start and how meteorologists monitor them.
• Wondering what an Arctic wildfire looks like from space? These images capture some of last year’s fires from above.