The Arctic melt season is averaging five days longer with each passing decade, a new study by NASA and the National Snow and Ice Data Center reveals. And with more ice-free days, the water (which is darker than the surrounding ice) is absorbing the sun’s heat and accelerating the process. This means the Arctic ice cap has shrank by as much as four feet.
The sobering news comes following a study of satellite data from 1979 to 2013. By the end of this century, scientists believe, there will be a fully melted Arctic Ocean during the entire summer. And the news also comes in the same week that the Intergovernmental Panel on Climate Change (IPCC) released its own report on global warming.
“The Arctic is warming and this is causing the melt season to last longer,” stated Julienne Stroeve, a senior scientist at NSIDC, Boulder and lead author of a new study. “The lengthening of the melt season is allowing for more of the sun’s energy to get stored in the ocean and increase ice melt during the summer, overall weakening the sea ice cover.”
The research further revealed that solar radiation absorption depends on when the melt season begins; this is particularly true since the sun rises higher during the spring, summer and fall than in the winter. It’s still hard to predict when things will melt or freeze, however, since this depends on weather.
“There is a trend for later freeze-up, but we can’t tell whether a particular year is going to have an earlier or later freeze-up,” Stroeve said. “There remains a lot of variability from year to year as to the exact timing of when the ice will reform, making it difficult for industry to plan when to stop operations in the Arctic.”
Data was collected with NASA’s (long deceased) Nimbus-7 Scanning Multichannel Microwave Radiometer and instruments aboard Defense Meteorological Satellite Program spacecraft.
“When ice and snow begin to melt, the presence of water causes spikes in the microwave radiation that the snow grains emit, which these sensors can detect,” NASA stated. “Once the melt season is in full force, the microwave emissivity of the ice and snow stabilizes, and it doesn’t change again until the onset of the freezing season causes another set of spikes.”
The research has been accepted for publication in Geophysical Research Letters.