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Thursday, August 25, 2011

Thawing Arctic Permafrost Likely to Release Large Amounts of Carbon

New research which contradicts 2007’s Intergovernmental Panel on Climate Change’s assessment suggests that billions of tons of carbon dioxide trapped in high-latitude permafrost may be released into the atmosphere by the end of this century if the temperatures continue to rise apace, which in turn will only further and quicken global warming.

A sink becomes a source, as revealed by these two simulations of net CO2 fluxes due to climate change at the end of 21st century. The control simulation on the left did not include permafrost processes. The permafrost simulation on the right included processes that depict how carbon accumulates in soil and how it decomposes. In the latter simulation, large carbon losses are seen in central Canada where substantial permafrost stocks exist that are vulnerable to warming. Units are in grams of carbon per square meter per year.
Additionally, the study found that the soil would become a source of carbon dioxide, rather than a sink, by the end of the century as the soil warms in response to the climate change.
These findings run contrary to what the Intergovernmental Panel on Climate Change’s assessment had suggested, which was that with increased temperatures the vegetation in the Arctic would increase, subsequently increasing the amount of carbon drawn into the soil.
But according to the new research, led by Charles Koven of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), those models used by the IPCC did not include detailed processes of how carbon accumulates in high-latitude soil over millennia, and therefore started out with less carbon in the soil for their simulations.
The new model does include these detailed processes, and begins with much more carbon in the soil than the previous models ever did. It also better represents the carbon’s vulnerability to decomposition as the soil warms.
As a result, the model run by Koven and his colleagues found that the uptake of carbon by increased vegetation would be thoroughly overwhelmed by the larger amount of carbon released into the atmosphere.
“Including permafrost processes turns out to be very important,” says Koven, who joined Berkeley Lab’s Earth Sciences Division as a staff scientist earlier this year. “Previous models tended to dramatically underestimate the amount of soil carbon at high latitudes because they lacked the processes of how carbon builds up in soil. Our model starts off with more carbon in the soil, so there is much more to lose with global warming.”
In the end, the simulations suggested a climate-induced loss of between 25 and 85 petagrams of carbon. The best estimate from the simulations found that 62 petagrams of soil carbon would be released into the atmosphere by 2100, which amounts to approximately 68 billion US tons, equivalent to an addition 7.5 years of manmade emissions at today’s rate.

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