Another global warming feedback loop, and it’s not good
By Summit Voice
SUMMIT COUNTY — Tundra fires have the potential to dramatically boost levels of carbon dioxide in the atmosphere in a very short time, according to researchers who studied the 2007 Anaktuvuk River fire, which burned 401 square miles as the largest tundra fire on record.
Tundra fires have been highly unusual during the past 11,000 years, but have become frequent in recent decades as the climate warms. The study of the Anaktuvuk River fire on Alaska’s North Slope revealed how rapidly a single tundra fire can offset or reverse a half-century worth of soil-stored carbon. The fire releases 2.3 million tons of carbon into the atmosphere.
Tundra soils store huge amounts of carbon hundreds to thousands of years old. Intact, the layers of organic soil insulate the permanently frozen ground, called permafrost, below.
“The amount of carbon released into the atmosphere from this fire is equivalent to the amount of carbon stored by the global tundra biome,” said lead author Michelle Mack, a biologist from the University of Florida. “This was a boreal forest-sized fire.”
Little is known about the effects of fire on carbon storage and cycling in tundra ecosystems. Cool, wet soils underlain by permafrost are thought to restrict fires to aboveground plants and ground-level plant litter leaving the carbon stored in soils relatively intact. As arctic summers get warmer and dryer, so too do the soils, which are highly flammable and able to burn more deeply when dry.
“If the frequency of these fires remains at long intervals, 80 to 150 years, then the tundra has time to recover,” said Syndonia “Donie” Bret-Harte, an ecosystem ecologist at the University of Alaska Fairbanks Institute of Arctic Biology. “If these fires occur more frequently, say every 10 years or so, then the landscape cannot recover.”
The Anaktuvuk River fire was started by a lightning strike in July 2007.
“Normally we would expect the fire to go out in the moist soil, but this summer was so dry that the fire didn’t go out and strong winds in September caused it to burn a very large area,” said Bret-Harte, who noted that 40 percent of the fire was classified as a severe burn – high for a tundra fire. The fire was visible 24 kilometers south at the IAB Toolik Field Station, where the scientists were working, as a wall of smoke on the horizon.
In addition to the direct release of carbon into the atmosphere, tundra fires are important because of the potential feedbacks to global climate change. “These fires could be a radical and very rapid positive feedback to atmospheric carbon dioxide,” said Mack.
Fire removes organic material that insulates permafrost from warm summer temperatures. Insufficient insulation can lead to thawing permafrost, destabilization of the ground surface and exposure of deep soil carbon to decomposition and release into the atmosphere – ultimately amplifying high-latitude warming.
According to the authors, their observations of carbon loss from the Anaktuvuk River fire support the idea that tundra fires have the potential to release large amounts of carbon and decrease landscape carbon stocks, having an immediate impact on atmospheric carbon and climate.