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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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