After 2001, major shift in sea ice formation occured

By Rick Thoman
Alaska Climate Specialist
Alaska Center for Climate Assessment and Preparedness
International Arctic Research Center/University of Alaska
Fairbanks

Bering Strait Elders have been talking for many decades about how the timing, quality and characteristics of sea ice has been changing in the region.
From the shorter perspective of western science and with the benefit of hindsight, it’s clear through several lines of evidence that around Alaska, there was a major shift in the timing of sea ice formation after 2001.
In the Bering Sea, sea ice in the autumn nowadays forms later and takes longer to expand out from the coast, and ice moving south through the Bering Strait now happens weeks later than was typical before 2002.
This change is dramatically illustrated in this week’s Climate Watch graphic, which plots sea ice extent in the Bering Sea on November 15 each year since 1978, based on satellite data from the National Snow and Ice Data Center.
The change between autumn 2001 and 2002 we now see is in part so dramatic because the mid-November sea has never recovered to anything like what was typical in the late 20th century. It wasn’t really a gradual change at all, but rather an abrupt shift. In fact, the average November 15 sea ice extent in the most recent 24 years is 65 percent lower than the average between 1978 and 2001. This kind of sudden but sustained shift might seem surprising but is commonly seen in complex systems, both physical and cultural.