The Arctic melt season is increasing by an average of 5 days per decade, according to a new study from University College London.
Satellite data going back over 30 years has confirmed that the Arctic Ocean is absorbing more of the sun's energy during the summer months due to an increase in open water, which has a lower albedo than the lighter colored sea ice and snow.
This map below charts the change in the melt season over the past quarter century. Red areas see lengthened melt seasons. In a handful of areas (in blue) the melt season has shortened. Credit: Julienne Stroeve (UCL Earth Sciences/National Snow and Ice Data Center)
Since the region is absorbing more heat energy in the summer the appearance of sea ice in the autumn has been increasingly delayed on average.
Key excerpts from the UCL report.
While temperatures have been increasing during all calendar months, trends in melt onset are considerably smaller than that of autumn freeze-up.
....even a small change in the extent of sea ice in spring can lead to vastly more heat being absorbed over the summer, leading to substantially later onset of ice in the autumn.
....multi-year ice (which survives through the summer without melting) has a higher albedo than single-year ice that only covers the sea in winter. Since the 1980s, the proportion of the Arctic winter ice that is made up of multi-year ice has dropped from around 70% to about 20% today,
“The headline figure of five days per decade hides a lot of variability. From year to year, the onset and freeze-up of sea ice can vary by about a week. There are also strong variations in the total length of the melt season from region to region: up to 13 days per decade in the Chukchi Sea, while in one, the Sea of Okhotsk, the melt season is actually getting shorter.”
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