For months, Siberia has been experiencing extreme heat due to a combination of persistent sunny weather and human-caused climate change. In addition to producing Arctic temperatures that cracked 100 degrees in June, the heat has fueled an enormous outbreak of wildfires, including fires on tundra underpinned by permafrost—normally frigid soil that is likely becoming even less frozen this year.

This rash of fires on landscapes that are typically too cold, wet, and icy to burn is raising alarms for ecologists and climate scientists, who fear it’s yet another sign that the Arctic is undergoing rapid changes that could tip off a cascade of consequences both local and global.

If fire becomes a regular occurrence on Siberia’s thawing tundra, it could dramatically reshape entire ecosystems, causing new species to take over and, perhaps, priming the land for more fires. The blazes themselves could also exacerbate global warming by burning deep into the soil and releasing carbon that has accumulated as frozen organic matter over hundreds of years.

"This is not yet a massive contribution to climate change," says Thomas Smith, an environmental geographer at the London School of Economics who has been tracking the Siberian fires closely. "But it’s certainly a sign that something different is happening."

More superheated fires

Siberia is no stranger to large summertime wildfires, including fires north of the Arctic Circle in the region’s expansive boreal forests. But so far, 2020 has been a banner year for fire in the Russian Arctic.

Mark Parrington, a senior scientist with the European Center for Medium-Range Weather Forecasts, says that the fires started to spread across Siberia around the middle of June. Daily levels of "fire radiative power," a measure of the fires’ heat output, rival those seen in 2019 (another extreme fire year) and far exceed anything else the Arctic has experienced since at least 2003. Russia’s Forestry Agency estimates that millions of acres of land have gone up in flames in eastern Siberia’s Sakha Republic, Chukotka, and Magadan regions.

In addition to flames being extremely intense and widespread, scientists are struck by how far north fires are burning and the types of ecosystems that are igniting. Smith has been investigating this using a combination of land cover maps and satellite data. He’s found that in addition to the huge number of fires scorching northern boreal forests, many are burning even further north on the tundra and in carbon-rich peatlands. In all cases, the ecosystems that are burning sit atop frozen soils that comprise permafrost.

While tundra fires are not unprecedented—scientists have documented a handful of large ones on Alaska’s North Slope in recent history—it’s unusual to see so many at once over such a large area, Smith says.

Several of the fires might even be setting geographic records. In late June, the European Space Agency’s Sentinel-2 satellite detected a series of fires at latitudes close to 73 degrees north—the northernmost fires in records going back to 2003, according to satellite remote sensing expert Annamaria Luongo. The most recent one, spotted by Sentinel-2 on June 30, flared up just a few miles from the shores of the Laptev Sea, a part of the Arctic Ocean.

"I was a little shocked to see a fire burning 10 kilometers south of a bay of the Laptev Sea, which is like, the sea ice factory of the world," says Jessica McCarty, a fire researcher at Miami University in Ohio. "When I went into fire science as an undergraduate student, if someone had told me I’d be studying fire regimes in Greenland and the Arctic, I would have laughed at them."

Heat is the underlying cause of these fires. Since December, temperatures across Siberia have been way above normal due to a persistent ridge of high pressure air parked over the area that has produced warm, sunny weather, melting the snowpack early. The heat has backed off slightly since mid-June, when the Siberian town of Verkhoyansk experienced a record-breaking 100-degree day, but it’s far from gone: The same day that a fire was spotted on the shores of the Laptev Sea, air temperatures in the area reached 94°F.

"To me what’s really shocking is how warm it’s been relative to average for so many weeks and months," says Zack Labe, a climate scientist at Colorado State University.

All of this is on top of the long-term, climate change-driven warming trend, which is causing the Arctic to heat up at more than twice the globally averaged rate.

McCarty says the hot, dry weather likely dried out tundra vegetation, priming it to burn. Layers of partly decomposed organic material on the ground, called duff, have been warming and drying too. Smith suspects that the recent heat has also caused some additional thawing and drying deeper down in the permafrost, which contains a seasonally thawing "active layer" atop soil that typically remains frozen year round. "The heat wave just really brings everything up to a level where it can burn," he says.

Unlocking the carbon

A key concern of Arctic scientists is that some of these fires are burning not just across the surface of the tundra, but also down into the soil, through layers of carbon-rich organic matter accumulated over many centuries.

"By how big they are and how hot they are, I would say there’s no way they’re not burning down," says Amber Soja, an associate research fellow with the National Institute of Aerospace and an expert on Siberian wildfires. As the fires eat their way underground, climate-warming greenhouse gases are released into the atmosphere, ultimately triggering more Arctic warming and more permafrost thaw. More immediately, ground fires give off heat, which can drive additional thawing and burning of the permafrost, Soja says.

While it’s unclear how much carbon is being released by this year’s fires or how much permafrost is thawing because of them, scientists are keen to investigate these questions. Longer term, the fires might also degrade the permafrost by removing upper layers of soil that act as an insulating barrier, a process that has been well documented in boreal forests. Permafrost deterioration can cause the ground to collapse in on itself and melted ice to pool up on the surface in lakes, something scientists witnessed in the wake of a large tundra fire on Alaska’s North Slope in 2007.

How these fires alter the Arctic’s delicate ecological balance is another important question to be answered. Soja says that severely scorched boreal forests sometimes transform into "pyrogenic tundra" after a fire kills off the trees and burns out the seeds stored in the soil, allowing grasses to take over. Fires on land that was already tundra, meanwhile, can sometimes make it easier for shrubs to take root, darkening the landscape, which absorbs more heat and makes it more fire prone in the future. And as climate change keeps encouraging the treeline to creep north, even more fire fuel is being added to Arctic landscapes.

"In terms of ecology, I don’t know what’s going to happen," Soja says. "This is pretty far north. I think the damage is extensive. And I think it will take a long time to recover. Maybe not at all."