Tuesday, August 23, 2011

Thawing permafrost could release vast amounts of carbon and accelerate climate change by the end of this century

Dan Krotz in the Lawrence Berkeley National Labotatory News: Billions of tons of carbon trapped in high-latitude permafrost may be released into the atmosphere by the end of this century as the Earth’s climate changes, further accelerating global warming, a new computer modeling study indicates. The study also found that soil in high-latitude regions could shift from being a sink to a source of carbon dioxide by the end of the 21st century as the soil warms in response to climate change.

The research was led by Charles Koven of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). He conducted the research with a team of scientists from France, Canada, and the United Kingdom while he was a postdoctoral researcher at France’s Laboratoire des Sciences du Climat et de l’Environnement. The modeling was conducted at a supercomputing facility run by France’s Alternative Energies and Atomic Energy Commission.

...Their findings counter results from a comparison of models that was included in the Intergovernmental Panel on Climate Change’s 2007 fourth assessment report. The comparison found that climate change will spark a growth in high-latitude vegetation, which will pull in more carbon from the atmosphere than thawing permafrost will release.

But unlike earlier models, the new model includes detailed processes of how carbon accumulates in high-latitude soil over millennia, and how it’s released as permafrost thaws. Because it includes these processes, the model begins with much more carbon in the soil than previous models. It also better represents the carbon’s vulnerability to decomposition as the soil warms.

As a result, the new model found that the increase in carbon uptake by more vegetation will be overshadowed by a much 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.”...

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.

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