GREENING OF THE ARCTIC: As permafrost thaws at Eight Mile Lake in Alaska, tundra vegetation will shift from sedges to shrubs, soaking up some--but not all--of the carbon released by the warming soil.
Image: Hanna Lee
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When permafrost thaws, microbes convert ancient organic matter in the frozen soil into climate-warming gases, like carbon dioxide and methane, potentially triggering a positive feedback loop that further melts the Arctic.
But the once-barren soil also spouts new—and larger—shrubs that can act as a carbon sink, and scientists have wondered what the net effect of permafrost thawing would be on atmospheric carbon balance. A new study published this week in Nature suggests that changing landscape can counterbalance the release of permafrost carbon—but only for a little while.
"The greening of the Arctic will not compensate for the huge amount of permafrost carbon that will be released," says lead author Ted Schuur, an ecosystem ecologist at the University of Florida in Gainesville.
Permafrost contains approximately 98 petagrams (98 quadrillion grams, or 108 billion tons) of carbon—or one sixth the total amount currently in the atmosphere. In order to understand how rapidly this carbon would be released into the air, Schuur and his group have been measuring carbon dioxide absorption and emission by plants and soil at the Eight Mile Lake watershed in the northern foothills of the Alaska Range across what they call a "gradient of thaw." Then, they use radiocarbon dating to determine how long the greenhouse gas had been trapped as carbon in the permafrost.
Not surprisingly, the researchers found that more extensively thawed soils emit carbon at a higher rate than recently thawed soils. But when the researchers looked at sites that had been thawing for about 15 years, they found that the increased plant growth more than compensated for their old carbon emissions. After 15 years, however, these soils were losing much more old carbon than the new plants were able to soak up.
"This is the first real study to put numbers on these things," says David Lawrence, an Earth systems scientist at the National Center for Atmospheric Research who was not involved in the study. "Data like this are critical." He is eager to incorporate the new findings in the Community Land Model used for climate simulations.
Lawrence points out, however, that not all permafrost will thaw in the same way. The study was conducted on a type of ground called thermokarst, which allows water to drain away as it melts. In wetter areas, Lawrence explains, permafrost has the potential to turn into a peat land and remain a long-term carbon sink, but that could also lead to increased methane emissions. "From a global warming perspective," he says, "that could still turn around and be positive feedback."
Schuur agrees with this assessment. "We can't say its going to be 15 years in every place," he says, "but we can say [that] in the initial decade of thaw permafrost will be acting as a carbon sink, and by 30 years it will be a carbon source."
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9 Comments
Add CommentThen why use such a backward, misleading title?
Reply | Report Abuse | Link to thisMaybe to go with the misleading article.
Reply | Report Abuse | Link to thisSo, if its gonna cause problems why not burn it in our cars?
Reply | Report Abuse | Link to thisit could replace coal and oil, much better than doing nothing
perhaps.
I used to look forward to my Scientific American all through undergrad and grad school. I watched with great sadness as it diverged from a science publication to a political publication. I refused to renew about 1.5 years ago. I can see I haven't missed anything.
Reply | Report Abuse | Link to thisWhat's with you nitwits posting here? This an informative article based on good science that exactly explains the title statement. You guys are going to feel real foolish in a few years.
Reply | Report Abuse | Link to thisMaybe because this is a low on facts article that is high in phd BS.
Reply | Report Abuse | Link to thisYou miss the point:
Reply | Report Abuse | Link to thisFor instance, there is an area six times the size of Germany containing about 540 billion tons of carbon off the Siberian coast. That submarine permafrost is perilously close to thawing. Three to 12 kilometers from the coast the sea sediment is just below freezing. The permafrost has grown porous, there is a loss of rigor in the frozen sea floor, and the surrounding seawater is highly oversaturated with solute methane.
"...Researchers were investigating "alarming" reports in the last few days of the release of methane from long frozen Arctic waters, possibly from the warming of the sea& --"Arctic sea ice drops to 2nd lowest level on record," AP, 27 Aug '08
If the Siberian (submarine) permafrost-seal thaws completely and all the stored gas escapes, the methane content of the planet's atmosphere would increase twelve fold. The result would be catastrophic global warming. --"A Storehouse of Greenhouse Gases Is Opening in Siberia," Spiegel, 17 April '08
The article only considers surface permafrost, not submarine permafrost.
pgtruspace: The article is simply reporting the finds of the study in question in short form. Plenty of facts, no BS. Your right wing fear of science is showing.
Reply | Report Abuse | Link to thisGeological studies in Europe show that during the ice ages, permafrost was up to 600 feet deep. Since the end of the last glaciation, permafrost in Britain has all melted, since mean annual weather temperatures are now some 11°C, and the geothermal gradiants increase temperatures as you dig down.
Reply | Report Abuse | Link to thisSo it should be born in mind that deep permafrost melting may be occuring now...