DATE: August 27, 2019

SNIP: The Arctic is transforming before our eyes: the ice caps are melting, the tree-line is shifting northwards, starving polar bears wander into cities. The region is warming twice as fast as the rest of the planet due to climate change, largely due to changes in albedo – the loss of sunlight-reflecting ice and snow, replaced by sunlight-absorbing ocean and soil. This is driving a dangerous positive feedback cycle where heating spirals into more heating.

And, now, the Arctic isn’t only losing its ice. It is being set ablaze.

Gargantuan forest fires in Siberia, which burned for more than three months, created a cloud of soot and ash as large as the countries that make up the entire European Union. More than four million hectares of Siberian taiga forest went up in flames, the Russian military were deployed, people across the region were choked by the smoke, and the cloud spread to Alaska and beyond. Fires have also raged in the boreal forests of Greenland, Alaska and Canada.

Though images of blazing infernos in the Arctic Circle might be shocking to many, they come as little surprise to Philip Higuera, a fire ecologist at the University of Montana, in the US, who has been studying blazes in the Arctic for more than 20 years.

“I’m not surprised – these are all the things we have been predicting for decades,” he says.

A key tipping point, he says, is an average July temperature of 13.4C over a 30-year period. Much of the Alaskan tundra has been perilously close to this threshold between 1971 and 2000, making it particularly sensitive to a warming climate. The number of areas near to and exceeding this tipping point are likely to increase as the climate continues to warm in the coming decades, says Higuera.

“Across the circumpolar Arctic, the take-home message is that there are distinct thresholds above which you start to see the tundra burning – it’s like a binary switch,” says Higuera. “This threshold relationship is part of what makes the Arctic so sensitive: areas will stay below this threshold for years, off our radar for fire activity – and then all of a sudden with a change in temperature it will start to burn.”

Fires in the Arctic also have huge implications for the global climate. Boreal forests and Arctic tundra cover 33% of the global land surface, and hold an estimated 50% of the world’s soil carbon – more carbon than is stored in all the world’s vegetation, and equal in size to the amount of carbon in the atmosphere.

Because conditions in the north are so cold, microbial growth and decomposition are much slower than in the tropics, so carbon is stored in layers of permafrost rather than recycled back into the nutrient cycle through vegetation growth.

In other words, if the forests burn and tundra melts, we could dramatically increase the amount of carbon in our atmosphere – essentially rendering useless even the most coordinated global attempts to cut global emissions.

Now, we are seeing that once solid ground itself burn. Fires on the peatland are dominated by flameless smouldering combustion, which move overland through the leaf litter at the snail’s pace of half a metre a week, rather than the speedy rate of 10km per hour in a forest fire.

“These aren’t flames licking up into the trees like in Bambi,” says Merritt Turetsky of the University of Guelph, in Ontario, Canada. “These are slow-moving edges of ignition that move through the moss, the leaf biomass, and everything else that has fallen onto the forest floor.”

These smouldering fires not only are ignited much more easily than fiery flames by lightning strikes – they also can persist through cold and wet conditions much longer, largely because the peat holds vast stores of the combustible gas methane. As the climate warms, northern soils and peat dry out, making smouldering fires much more likely.

In a research paper from 2015, Turetsky explains how smouldering fires are actually a much greater threat to the global climate. They burn for much longer, so they can transfer heat much deeper into the soil and permafrost, overall consuming twice as much carbon-rich fuel as normal fires.

“You need a huge amount of precipitation to fall to put these out – but if you get just a moderate amount of rain, that often comes with lightning, which can just blow things up thanks to the methane in the peat, and just make it worse,” she says.

If conceiving of fires in the Arctic wasn’t enough of a paradigm shift, an even greater psychological hurdle is understanding that much of the fire in the Arctic is actually underground.

Capable of smouldering beneath the surface, these subterranean fires can persist through the winter and pop up in spring in completely unexpected locations. Hence their nickname: “zombie fires”. They’re neither dead nor alive.

Taken together, melting permafrost, methane release, drying peat, vanishing ice, simmering zombie fires and of course a warming climate are all combining into an unprecedented setting for dramatic changes in the Arctic.