Thursday, May 20, 2010

Volcanic Ash Meets Arctic Ice

The airport at Svalbard was closed yesterday, though it has now reopened, as an ash cloud from the Eyjafjallajökull volcano in Iceland moved north and spread out across the Arctic Ocean. The southerly winds were good news for travelers in Europe, where airports reopened and hundreds who had been waiting a day or two got clearance to fly to North America. But it is not good news for Arctic sea ice.

At this time of year, the whole ocean north of Svalbard is covered with ice in all directions, to the left or to the right. Air tends to sink at high latitudes, so volcanic ash clouds don’t stay elevated for long in the Arctic. Probably half of the ash cloud will be settling today across a broad area of ice north of Svalbard and Greenland, where it will make the ice melt faster. Much of it will reach the coast of Siberia, but winds could carry this part of the cloud offshore again before it reaches the surface.

Ash is much darker than the snow pack that normally protects the Arctic ice cover from the sun. The ash will absorb heat from the sun and melt the snow and then the ice, much the same way that cinders and grit are traditionally used to treat snow-covered surfaces where I live in Pennsylvania. But while we want to remove winter snow and ice from the roads here, no one wants the Arctic sea ice to melt away.

It is hard to predict the magnitude of the ash effect; the importance of soot on the Greenland ice sheet has been recognized only recently, and we don’t have much experience to go on to guess the mass of the ash that is being deposited on the Arctic today. However, we do know that even tiny specks of industrial soot have significant effects on ice melt in Greenland. Some scientists who doubt the magnitude of the effect of carbon dioxide levels on polar ice melt argue that particulate matter, such as soot, is having a greater impact on the Arctic ice than the increasing carbon dioxide levels are having. It is safe to say that any particulate matter that falls on ice in sunlight will melt many times its own weight in ice. The volcanic ash from Eyjafjallajökull is light gray when dry but turns into a sticky black goo when wet, and it won’t take long at all to get wet as soon as it lands on the snow. Once there, I have to imagine it will stay in place until the ice melts through far enough to break up and tip over.

This volcanic ash event comes in a year when the North Pole ice is only about 1 meter thick, much less than the traditional 5 meters. The thicker ice blew away in the late winter, moving first toward Alaska, then turning toward Chukotka, where much of it has piled up against the coast to melt. The ice in the area of the North Pole is mostly first-year ice that formed last fall off the Siberia coast. Even without the addition of volcanic ash, it had a chance of melting through and breaking up this summer. With the arrival of volcanic ash just at the period of maximum sunlight and most rapid melting, the chance of that happening is increased. Coincidentally, today is also the day when 24-hour sunlight reaches Svalbard, so there will be no nighttime at all for the next two months in any place where the ash falls today. And the distance from Iceland to Svalbard is similar to the distance from Iceland to the European mainland, so on any given day, there is a chance that Eyjafjallajökull and the winds could send another ash cloud in that direction.