Climate Watch

For years, western scientists did not pay too much attention to changes in Bering Sea ice because the maximum extent did not show much change. In fact, as recently as 2015 the Bering Sea was sometimes cited as an example of a region bucking the trend of declining ice. Of course, that viewpoint was based on just one single measure: Maximum areal extent. No consideration was given to ice quality, thickness or seasonality. But regional Elders have been talking about these kinds of chances for many years now. Some important characteristics of ice, its quality for example, are very difficult to measure from satellites in space and measuring the thickness of ice less than several feet thick is still a challenge. Changes in seasonality have been easier to see even from the ice extent information for at least ten years. In the Bering Sea, the change when autumn ice develops or moves in is one of the most obvious. When is there enough ice to buffer crashing waves from autumn storms? When is it safe to work and travel on the ice?

The graphic shows the date when the Bering Sea ice extent first covered an area about the size of the Seward Peninsula in autumn, since 1978. I use this as a measure of autumn ice development because this is well above the satellite measurement error but also once there gets to be this much ice, it generally is here to stay.

What we find is that in the late 1970s a typical autumn would first have ice cover of about 19,000 square miles around November 5, of course some years earlier and some later. Nowadays, we typically have to wait until November 26 to see the same level of ice, and this fall that date was not reached until December 5.

So, this year the ice is one month later than we would have expected it to be back in the late 1970s.