Tundra fire's massive carbon release prompts warming worries

Jul 27, 2011, 22:48 GMT

Washington - A massive tundra fire in Alaska in 2007 released as much carbon into the air as a city the size of Miami emits in two years, a study released Wednesday said.

The findings have triggered growing concern among scientists about the escalating effect of ever more frequent tundra fires on global warming.

'The 2007 fire was the canary in the coal mine,' said Michelle Mack of the University of Florida, whose team contributed to the study. 'It's a wakeup call that the Arctic carbon cycle could change rapidly, and we need to know what the consequences are.'

A study on the 2007 Anaktuvuk River fire will be published Thursday in the journal Nature. The largest recorded tundra fire in the circumpolar arctic region burnt up 1,039 square kilometres.

It released an estimated 2.1 million metric tons of carbon, most of it carbon that had been stored in the tundra in the past 50 years.

It burned up the actual peat-like soil, which has dried out due to global warming, and removed a layer of insulation for the perma-frost. But it also blackened the large area, making that area of the tundra even more susceptible to thawing from solar warmth, the authors said.

'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 Syndonia Bret-Harte, an ecosystem ecologist at the University of Alaska Fairbanks Institute of Arctic Biology.

Under normal conditions, cool, wet soils on top of permafrost have limited fires to above-ground vegetation, but as Arctic summers get warmer and dryer, so do the soils, the authors said.

The fire was triggered by a lightning strike in July 2007.

The release of carbon emissions into the atmosphere, through burning of fossil fuels and organic matter, is blamed by scientists for global warming and the rapid melting of ice cover in the Arctic region.

Bret-Harte said that the tundra can recover if it has 80 to 150 years between fires. 'If these fires occur more frequently, say every 10 years or so, then the landscape cannot recover,' she said.

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