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Thawing Subarctic Permafrost Increases Greenhouse Gas Emissions
The permafrost in the bogs of subarctic Sweden is undergoing dramatic changes. The part of the soil that thaws in the summer, the so-called active layer, has become thicker since 1970, and the permafrost has disappeared altogether in some locations.
This has lead to significant changes in vegetation and to a subsequent increase in emission of the greenhouse gas methane. Methane is 25 times more potent than carbon dioxide as a greenhouse gas.
Behind these new findings is an international research team led by the GeoBiosphere Science Centre at Lund University in Sweden. The results were published 20 February in Geophysical Research Letters. The researchers say their results are unique, as there are very few places in the circumpolar North where comparison of observations over a period of decades is possible.
The Abisko region in subarctic Sweden, which they studied, has long-term records of climate, permafrost and other environmental variables, they say. The Abisko area is recognized by UNESCO as part of the international network of Man and the Biosphere Reserves.
In the present study, airborne infrared images were used to compare the distribution of vegetation in 1970 with that of 2000. Dramatic changes were observed, and the scientists relate them to the climate warming and decreasing extent of permafrost that was observed over the same period.
The exchanges of carbon dioxide and methane between land and atmosphere has been studied for a long time in Abisko. Carbon dioxide can either be released from the bogs, or mires, to the atmosphere or absorbed from the atmosphere into the mires. But these mires predominantly release methane into the atmosphere, the researchers say.
Methane is released from the breakdown of plant material under wet soil conditions. The disappearance of permafrost and subsequent wetter soil conditions have lead to the observed increases in methane emissions.
"At a particular mire, Stordalen, we have been able to estimate an increase in methane emissions of at least 20 percent, but maybe as much as 60 percent, from 1970 to 2000," says the lead researcher, Torben R. Christensen of Lund University's GeoBiosphere Science Centre.
Despite methane being an important greenhouse gas, it is often forgotten in discussions of the greenhouse effect, the scientists say. Methane is released from rice agriculture and meat production, but the largest single source of methane is the natural wetlands.
If what is seen in subarctic Sweden is representative of the circumpolar North, this could mean an acceleration in the rate of predicted climate warming, they say.
The annual mean temperature in Abisko is -0.7 degrees Celsius [30 degrees Fahrenheit], but during recent years it has often been above zero Celsius [32 degrees Fahrenheit].
"One might imagine the cold subarctic ecosystems as very static, but in areas where the mean annual temperature is around zero [Celsius; 32 degrees Fahrenheit], the ecosystems may be extremely sensitive. The ecosystems are dynamic and their response to climate change is very rapid. This we have seen clearly here in Abisko," says Christensen.
Title: "Thawing sub-arctic permafrost: Effects on vegetation and methane emissions" Authors: Torben R. Christensen, Torbjoern Johansson, H. Jonas Aakerman, and Mihail Mastepanov, Department of Physical Geography and Ecosystems Analysis, GeoBiosphere Science Centre, Lund University, Sweden Nils Malmer, Department of Ecology, Plant Ecology and Systematics, Lund University, Sweden Thomas Friborg, Institute of Geography, Copenhagen University, Denmark Patrick Crill, Complex Systems Research Center, University of New Hampshire, USA Bo H. Svensson, Department of Water and Environmental Studies, Linkoeping University, Sweden Citation: Christensen, T. R., T. Johansson, H. J. Aakerman, M. Mastepanov, N. Malmer, T. Friborg, P. Crill, and B. H. Svensson (2004), Thawing sub-arctic permafrost: Effects on vegetation and methane emissions, Geophys. Res. Lett., 31, L04501, doi:10.1029/2003GL018680.
American Geophysical Union
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Open-Air Experiment Could Deflate Hopes Forests Will Alleviate Global Warming
Seattle - Feb 16, 2004
A futuristic Duke University simulation of forest growth under the carbon dioxide-enriched atmosphere expected by 2050 does not reinforce the optimism of those who believe trees can absorb that extra CO2 by growing faster, said a spokesman for the experiment.