Shortening snow cover is heating up the Arctic
The observed increase in summer temperatures in Alaska is due to a reduction in the winter snow cover period. This not only reduces the cooling reflection of the white surfaces, but also allows the floor to warm up more quickly and over a longer period of time. This in turn promotes local snowmelt and delays the formation of snow cover in autumn.
Since the 1960s, snowmelt has started earlier in the region by an average of 2.3 days per decade. Accordingly, the soil thaws earlier and the first plants sprout. The warmer temperatures and longer growing season also allow trees and shrubs to expand their range northward. Since these in turn support the warming because they absorb solar radiation more than the low tundra flora, there are positive feedbacks. These can also affect, for example, microbial life in the soil, which breaks down organic matter deposited under warmer conditions more quickly and thus provides growth-boosting nutrients.
Terry Chapin from the University of Alaska at Fairbanks and her colleagues evaluated satellite data on temperature and cloud density and compared them with observations of vegetation development and snow cover, as well as albedo measurements. They found that changes in atmospheric circulation, the extent of sea ice, or cloud cover could not explain the observed warming of up to three degrees over the past twenty to thirty years. According to the results of the analyses, the decisive factor was the duration of the snow cover, followed by changes in the plant world: almost 12,000 square kilometers of tundra have turned into forest in the last fifty years.
The Arctic summer is now the warmest it has been in at least four centuries. Locally, the temperature rose at a rate expected for a doubling of carbon dioxide concentrations in the atmosphere.
