Saturday, June 21, 2008

MoreTrees in The Arctic Could Mean...Worsening Climate Change


greening tundra
Image from EOS

While we'd usually be the first to welcome the appearance of more trees, it may not be the most favorable outcome in the high Arctic, reports ScienceNews' Janet Raloff. That is because the advance of boreal forests, which have begun to supplant the region's tundras, threatens to accelerate the impact of global warming by reducing the region's albedo effect.

polar urals
Image from synchroswimr

When the sun's rays hit either snow or ice, they are reflected back into space instead of being absorbed, reducing heat collection (Lloyd described this type of feedback loop last year). The spread of forests, which both creates more dark surfaces and removes white ones, would thus result in more sunlight being absorbed. This would only compound warming in the region, which is already moving at a fast clip due to the thinning of ice sheets and record melting of sea-surface ice.

It couldn't come at a worst time. According to the University of Alaska Fairbanks' F. Stuart Chapin, temperatures in the Arctic Circle are already rising at roughly twice the global average. A new report to be published in Global Change Biology reveals that the leading edges of conifer forests have already creeped 20-60 meters up Siberia's Ural Mountains over the last century -- overrunning tundra in some places. Forests are now located in areas where no tree has grown over the last millenium, says Frank Hagedorn, one of the authors.

The end result could be a "big Arctic carbon bomb" going off, explains Andy Bunn of Bellingham's Western Washington University. The release of the roughly 200 petagrams (or 200 trillion kilograms) of carbon stored in the top meter of Arctic tundra would greatly undermine any global climate change mitigation effort, Bunn warns.

Via ::ScienceNews: Forest Invades Tundra (magazine)

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