The trend of disappearing summer sea ice in the Arctic is clear even though there is always some variability from year to year. Severe winter weather underscores the importance of keeping track of significant trends. Here are the numbers, according to Julienne Stroeve, of the National Snow and Ice Data Center in Boulder, Colo., as reported in the Economist in February:
“Between 1953 and 2014, the average area of the Arctic sea ice shrank by 48,000 square kilometers a year.”
“Between 1979 and 2014, it shrank by 87,000 square kilometers a year.”
“Between 1996 and 2014, the rate rose to 148,000 square kilometers.”
The accelerating rate is explained in part by the fact that ice reflects sunlight but water, which is darker, absorbs it. So as water replaces ice, more heat is retained. Heat transported from lower latitudes could also be part of the explanation.