Warming Arctic sparks tundra fires

In the late summer of 2007, lightening struck a remote corner of the Arctic on Alaska’s North Slope and burned for three months. The tundra soil there was dry because the permafrost, which normally encapsulates the carbon-rich soil in an icy sealant, had melted.

The fire burned until October snowfalls put it out, but left a char the size of Cape Cod – some 400 square miles- and large enough to see from space.

Photo: Michelle Mack

Michelle Mack, a biologist from the University of Florida, and Syndonia Bret-Harte, of the University of Alaska-Fairbanks, wondered how much carbon had been released during that long, hot burn. In a paper published this week in the journal Nature, they concluded that the carbon loss from this one fire was “unprecedented.”

The amount of carbon that had been released into the atmosphere was the equivalent of 50 years of storage by the global tundra biome. That’s 2.3 million tons of carbon.

The two scientists are concerned that the incident sparks a new era in tundra fires, which in the past were relatively rare.

“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,” said Bret-Harte in a press release from the Institute of Arctic Biology.

Tundra soils store huge amounts of carbon from hundreds of thousands of years. If the frequency of fires increases from 80 to 150 years to as often as every 10 years, then the tundra has no time to recover, she said.

Conditions could get worse the more fires that occur. The fires could become a rapid positive feedback to atmospheric carbon dioxide, the scientists said.