[corrected update] A 2007 wildfire in the Arctic was the largest such fire ever recorded, releasing into the atmosphere the equivalent of a year’s worth of stored carbon (“annual net C sink”) from the entire Arctic tundra biome. An increase in frequency of such fires could accelerate warming in the region, leading to a positive feedback effect.
NOTE TO MY READERS: the original title of this post stated that “50 year’s worth of carbon” was release by the fire. this is/was an error in the interpretation of the carbon-dated age of the burned tundra (“50 years old”), as reflected in the Alaska Dispatch article’s title (see end references), which was erroneously duplicated here. My apologies (see comments below for more info on this).
For the past 11,000 years or so, the Arctic’s boreal forests and tundra have remained mostly free of wild fires. But in 2007, the largest fire ever recorded in the Arctic swept across the Alaskan Northern Slope region, releasing an estimated 2.1 teragrams (2.3 million tons) of carbon into the atmosphere. According to a recently published paper in the journal Nature, this is an amount “two orders of magnitude larger than annual net C (carbon) exchange in undisturbed tundra.”
Ecosystem researchers from the University of Alaska, Fairbanks and the University of Florida assessed 20 MAT (moist acidic tundra) sites one year after the Anaktuvuk River fire (which lasted over two months and burned over 1000 square km / 400 sq miles of tundra). Additionally, 10 unburned sites were assessed for comparison. Based on these assessments, the researchers estimated that the release of carbon was an “amount similar in magnitude to the annual net C sink for the entire Arctic tundra biome averaged over the last quarter of the twentieth century.” (emphasis added).
Normally, a tundra fire does not cause great concern amongst ecologists, as the wet vegetation and soil (which is under-layered by permafrost ) tends to constrain the fire’s spread. However, that year the tundra soil was unusually dry; a lightning strike hit the area in July, ignited the fire that would continue to burn for over two months, boosted by strong September winds. The researchers found that 40% of that burn met the classification for “severe burn”, which is a large percentage for any tundra fire.
“The frequency of tundra fires is increasing, probably as a response to climate warming,” says ecologist and co-author Syndonia “Donie” Bret-Harte of the UAF’s Institute of Arctic Biology.
Wet soil and low vegetation act as an insulator for the permafrost (soil that stays frozen for a year or more) below it; as fires become more frequent and severe, this insulation effect is lost, and the permafrost begins to thaw. Decomposition of this soil (which is rich in organic matter), releases large quantities of carbon dioxide, nitrogen and even methane gas from accelerated bacterial decomposition of plant matter.
The scientific team used radiocarbon dating of samples from the sites to fix the maximum age of the soil carbon emitted from the fire at 50 years. They further estimate that the Anaktuvuk River fire doubled the cumulative area of tundra burned since 1950.
According to the paper’s authors, if the intervals between large fires stays around 80 to 150 years, then the burned tundra can recover (and maintain its critical carbon sequestration function). If, however, the frequency increases to every ten years, or perhaps less, then the tundra will have little chance of recovery.
Similar to recent theories of “CO2 fertilization”, there is the “Arctic greening” theory which posits that current warming conditions will increase vegetation cover in the Arctic (evidence does exist of increased vegetation growth), thanks to more CO2, creating a massive carbon “sink” (i.e., a mechanism of absorbing CO2), and providing a negative feedback effect to off-set CO2 induced warming.
However, the “wild card” in that scenario is the drying out of the surface tundra, making conditions ripe for wild fires. This impact will more than compensate for any putative “canceling out” of climate forcings by increased vegetation growth.
Quoting from the paper’s abstract:
‘The magnitude of ecosystem C lost by fire, relative to both ecosystem and biome-scale fluxes, demonstrates that a climate-driven increase in tundra fire disturbance may represent a positive feedback, potentially offsetting Arctic greening and influencing the net C balance of the tundra biome.’
“These fires could be a radical and very rapid positive feedback to atmospheric carbon dioxide,” says co-researcher Michelle Mack, Department of Biology, Univ. of Florida.
Other researchers participating in this study were: Teresa N. Hollingsworth, Randi R. Jandt, Edward A. G. Schuur, Gaius R. Shaver, David L. Verbyla. Check out the July 27, Nature paper Carbon loss from an unprecedented Arctic tundra wildfire
Also check out the original July 28 Alaska Dispatch source article 2007 Arctic wildfire released 50 years of stored carbon into atmosphere by Doug O’Harra
top photo: BLM:
second photo: M. Sydonia Bret-Harte; source: Supplementary Information, linked/cited paper (above)
bottom diagram: source: Supplementary Information, linked/cited paper (above)