Friday, December 19, 2008

Arctic greening linked to retreating sea ice

University of Alaska, Fairbanks: An interdisciplinary group of scientists led by Donald “Skip” Walker of the Institute of Arctic Biology at the University of Alaska Fairbanks has strongly linked sea ice changes to changes in Arctic land-surface temperatures and increased tundra greenness….If the Arctic continues to warm as predicted, large changes in vegetation will have important consequences for the status of permafrost, depth of the thaw layer, snow patterns, hydrological cycles, wildlife and human uses of arctic landscapes. There will also be significant feedbacks to climate through changes in the carbon flux and in the amount of light and heat reflected by the land.

Walker’s group combined information from Earth-orbiting satellites with ground-based studies and climate analyses to examine the trends of sea ice, land temperatures and vegetation using a simple numerical indicator of greenness called the Normalized Difference Vegetation Index. Vegetation reflects near-infrared light and absorbs visible light, Walker said: the greater the difference between the infrared and visible channels, the greater the density of green vegetation. The index also accounts for things like shadow and slope-aspect.

After examining 28 years of sea ice, land temperature and NDVI data, Walker’s group found that between 1982 and 2007, summer sea-ice cover declined by 27 percent in a 50-kilometer band along Arctic Ocean coastlines. Corresponding changes in the greening index varied, ranging from a relatively large 24-percent increase along the Beaufort Sea in northern Alaska and Canada to a 12-percent decline along the Laptev Sea in Russia....

Coastal tundra in Alaska, US Fish and Wildlife

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