After 10,000 fire-free years, the Arctic tundra is again experiencing wildfires, and they're contributing significantly to the world's carbon dioxide levels.
A new University of Florida study quantifies the amount of soil-bound carbon that was released into the atmosphere in 2007's Anaktuvuk River fire, which covered more than 400 square miles on the North Slope of Alaska’s Brooks Range.
And the 2.1 million metric tons of carbon released in the fire – twice the amount of greenhouse gases emitted by Miami in a year - is significant enough to impact the global climate, says ecologist Michelle Mack.
"The 2007 fire was the canary in the coal mine," she says. "In this wilderness, hundreds of miles away from the nearest city or source of pollution, we’re seeing the effects of a warming atmosphere. It’s a wakeup call that the Arctic carbon cycle could change rapidly, and we need to know what the consequences will be."
As well as pumping greenhouse gases into the atmosphere, the fire consumed up to 30 percent of the insulating layer of organic matter that protects the permafrost beneath.
Because the Arctic tundra has a carbon-rich, peaty soil, the ground itself is combustible, and when the fire recedes, some of the soil is gone. Afterwards, the permafrost is not only more exposed, but also covered by blackened ground, which absorbs more of the sun’s heat and could accelerate thawing.
"When the permafrost warms, microbes will begin to decompose that organic matter and could release even more carbon that’s been stored in the permafrost for hundreds or thousands of years into the atmosphere," says Mack. "If that huge stock of carbon is released, it could increase atmospheric carbon dioxide drastically."
Using radiocarbon dating, the team found that carbon up to 50 years old had been burned in the 2007 fire.
"This fire was a big wakeup call, and it can happen again, not just in Alaska but in other parts of the Arctic, like Canada and Russia," says Mack.
"Suppressing a fire in the wilderness is costly, but what if the fire causes the permafrost to melt? We need to have that discussion."