Arctic Sea Ice Season Shortening by 5 Days Per Decade

The Arctic sea ice season is shortening by five days per decade, with the appearance of sea ice becoming delayed by warmer weather, according to new research.

Writing in the journal Geophysical Research Letters, University College London Earth sciences professor Julienne Stroeve and her colleagues report their analysis, which used satellite data, indicates that the Arctic Ocean is absorbing more of the Sun's energy in the summer, leading to a delayed appearance of autumn sea ice.

In some Arctic regions, the freezing is occurring up to 11 days per decade later than it has in the past.

However, Stroeve noted that the headline figure of five days per decade hides a lot of variability in the iceless season.

"From year to year, the onset and freeze-up of sea ice can vary by about a week," she said. "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."

The research has implications for tracking the effects of climate change, as well as practical applications for the logistical planning of shipping operations through Arctic waters and Arctic oil exploration missions.

"The extent of sea ice in the Arctic has been declining for the last four decades, and the timing of when melt begins and ends has a large impact on the amount if ice lost each summer," Stroeve said. "With the Arctic region becoming more accessible for long periods of time, there is a growing need for improved prediction of when the ice retreats and reforms in winter."

A compounding effect can be observed over the years. A trend of higher temperatures across all months in the Arctic means more ice is melting than is being re-frozen in winter. Ice is a more reflective surface than water, so less ice leads to a lower albedo, or reflection, which in turn leads to more absorbed head from the Sun.

"This means that 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," University College London said in a statement.

Additionally, multi-year ice - ice that survives the melting season and remains frozen - is diminishing. Multi-year ice has a higher albedo than single-year ice, which is beneficial because it reflects heat away from Earth. However, the proportion multi-year ice has fallen, from about 70 percent of all Arctic ice in the 1980s to about 20 percent today.

The results of this study are closely in line with other, similar research, which supplies added confidence that models used to predict Arctic ice patterns are broadly correct.