Thawing Permafrost Likely to Boost Global Heating

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“Some warming-related trends in Arctic regions, such as the
encroachment of trees into tundra, may cause absorption of carbon
dioxide and thus partly counter the effects of thawing permafrost.
But Schuur and colleagues’ new assessment indicates that thawing is
likely to dominate known countervailing trends.”
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Public release date: 1-Sep-2008
American Institute of Biological Sciences

Contact: Jennifer Williams
jwilliams@aibs.org
202-628-1500

After noon EST on September 2, the full text of the article will be
available for free download through the copy of this Press Release
available at http://www.aibs.org/bioscience-press-releases/.

Thawing permafrost likely to boost global warming
Greenhouse gas emissions from previously frozen organic carbon in
soil are seen as larger than previously believed

The thawing of permafrost in northern latitudes, which greatly
increases microbial decomposition of carbon compounds in soil, will
dominate other effects of warming in the region and could become a
major force promoting the release of carbon dioxide and thus further
warming, according to a new assessment in the September 2008 issue of
BioScience. The study, by Edward A. G. Schuur of the University of
Florida and an international team of coauthors, more than doubles
previous estimates of the amount of carbon stored in the permafrost:
the new figure is equivalent to twice the total amount of atmospheric
carbon dioxide. The authors conclude that releases of the gas from
melting permafrost could amount to roughly half those resulting from
global land-use change during this century.

Schuur and his colleagues refine earlier assessments by considering
complex processes that mix soil from different depths during melting
and freezing of permafrost, which occur to some degree every year.
They judge that over millennia, soil processes have buried and frozen
over a trillion metric tons of organic compounds in the world’s vast
permafrost regions. The relatively rapid warming now under way is
bringing the organic material back into the ecosystem, in part by
turning over soil. Some effects of permafrost thawing can be seen in
Alaska and Siberia as dramatic subsidence features called
thermokarsts.

Schuur and his colleagues acknowledge many difficulties in estimating
carbon dioxide emissions from permafrost regions, which hold more
carbon in the Arctic and boreal regions of the Northern Hemisphere
than in the Southern Hemisphere. Data are limited, and emissions are
influenced by the amount of surface water, topography, wildfires,
snow cover, and other factors. Thawing, although believed to be
critical, is hard to model accurately.

Some warming-related trends in Arctic regions, such as the
encroachment of trees into tundra, may cause absorption of carbon
dioxide and thus partly counter the effects of thawing permafrost.
But Schuur and colleagues’ new assessment indicates that thawing is
likely to dominate known countervailing trends.

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