In July 2007, lightning sparked a fire on the dry, warming tundra of Alaska’s North Slope that dumped 2.3 million tons of carbon into the atmosphere — in a stroke, feeding back to the climate system as much carbon as all the Arctic’s tundra absorbs in a year.
At 400 square miles, the blaze in the watershed of the Anatktuvuk River was the largest tundra fire in thousands of years, researchers say, although the size of this single fire does not concern them so much as the signal it sends that more probably are on the way.
“These fires could be a radical and very rapid positive feedback to atmospheric carbon dioxide,” warns Michelle Mack, a University of Florida biologist, whose study of the fire, with colleagues from Florida and the University of Alaska-Fairbanks, appears in the new issue of the journal Nature.
“Fire has been largely absent from tundra for the past 11,000 or so years, but the frequency of tundra fires is increasing, probably as a response to climate warming,” observes co-author Syndonia “Donie” Bret-Harte, a University of Alaska ecologist, observes on a UA release.
Across much of the ice-free Arctic, tundra is the soft, peaty, usually-moist, carbon-rich mat of soil that insulates permanently frozen ground — permafrost — from the summer atmosphere. In a climate of increasing summer temperatures, the loss of Arctic sea ice catches the eyes of the world more readily than their effects on the land environment — until lightning strikes.
A tundra wildfire is different from the wilderness blazes that char the forests and brush lands in temperate zones. In a tundra fire, it is the ground itself that burns.
In the wake of the fire, a thinner layer of tundra protects the permafrost. The tundra’s blackened condition also absorbs more heat from the sun.
“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,” said Mack. “If that huge stock of carbon is released, it could increase atmospheric carbon dioxide drastically.”
IMAGE: Some 400 square miles of tundra burn through Alaska’s Anatktuvuk River in the summer of 2007. CREDIT: Alaska Fire Service