Sunday, June 13, 2010

Record Decline in Arctic Sea Ice

The widespread Arctic sea ice of April, with sea ice extent barely below the long-term average, gave way to the fastest May melt ever recorded, with ice extent declining at a June-like pace. Now that June is here, the rapid rate of melting continues in almost a straight line on the graph. One reason is warm weather over most of the Arctic Ocean, 1 to 5 degrees above the average for May, according to NOAA. But another reason, more significant in terms of what may happen this summer, is unusually thin ice. By most indications, the ice on the Arctic is the thinnest it has ever been, but it is certainly thinner than it was before 2007.

If you’ve seen pictures of the ice in Greenland, it is hard to understand how thin the ice on the Arctic Ocean is. The area of the Arctic Ocean is several times that of Greenland, but it holds about 1/200 as much ice as there is in Greenland.

At the same time, there are factors that ought to be slowing down the ice melt. For example, weather has been relatively calm, with few storms to break up the ice.

I’ve been looking for any indication that the volcanic ash that fell across areas of the Arctic Ocean last month is accelerating ice melt, but there is nothing so far to indicate that. The ice along the Siberian coast where the heaviest ash probably fell is melting through in areas, but in a pattern that is not obviously different from the past three years.

One other marker I look for is a path of clear water north of Svalbard, previously a rare occurrence. From the satellite picture, the ice north of Svalbard is significantly broken up already, and it could open up with little warning.