Thursday, July 3, 2008

Stirring the Arctic

The Arctic Ocean’s ice cover is melting earlier and faster this year, mainly because the ice is thinner.

Thin ice melts faster, of course, and it turns out that a mix of thick and thin melts almost as fast as thin ice by itself. The wind breaks that ice up and blows it around. The ice eventually ends up somewhere warmer, where it melts. The only ice that is safe is a near-solid sheet of thick ice wedged against land.

And there is only one of those left in the Arctic. It’s a band of ice 300 kilometers wide that stretches northwest of the Arctic coast of Greenland in a straight line that goes most of the way to the Yukon coast.

This thick ice bypasses the North Pole, raising the likelihood that the central Arctic and the waters from there to Alaska, Asia, and Europe could be substantially free of ice by September.

Steve Conner at The Independent raised a sensation a week ago with his news story, “Scientists warn that there may be no ice at North Pole this summer.” The story, though, basically repeats data and analysis from the U.S. National Snow and Ice Data Center (NSIDC), and it offers very cautious opinions from scientists. Throwing caution to the wind, I can say that the Northwest Passage may not matter so much after all. Before too long, it could be possible to sail in almost a straight line from Norway to the Bering Strait.

The ice map shown in the Independent seems to show that multi-year ice still covers a third of the Arctic Ocean. But the NSIDC May 19 map shows that most of that area is covered by a mix that includes at least 40 percent single-year ice. There was only the one band of 61–80 percent multi-year ice remaining, and that remaining ice is far more fragile than it would have been a decade ago when multi-year ice covered most of the ocean. When the wind changes direction and starts blowing away from the islands where the ice is anchored, that ice too will blow away and melt. That will happen at some point, though perhaps not this year, as the result of weather patterns that we can predict only a week in advance. And that would seem to be the only major event remaining before the Arctic Ocean can be substantially ice-free.

In yesterday’s NSIDC report, we see ice moving around the Arctic more than last year. One way to see this is that while the daily ice coverage is higher than last year, the monthly ice coverage is lower — the result of ice moving from place to place during the month. The ice movement is one of the reason scientists say the ice must be substantially thinner than it was last year.

Yesterday’s report also emphasizes how early the surface melt of Arctic ice began this year, something that is easy to see when you compare the maps of the last four years. Surface melt starts with the warm air and sunshine melting the snow cover on top of the ice. The snow melt runs off and forms puddles which speed up the melting process. Surface melt started about three weeks earlier this year than last year, and the extra three weeks of melting are expected to lead to more melting than ever during July and August, the months of the most rapid ice melt every year in the Arctic.

Until recently, the conventional scientific view was that the Arctic Ocean would remain substantially ice-covered. Then the consensus was that it would become ice-free in summer between 2100 and 2200. Then it was 2050. One year ago, the prediction from one model that the Arctic could be ice-free around 2013 seemed like a mistake. Now we are asking if it is possible that almost the entire ocean could be ice-free later this year — and the best answer we can offer is that it depends on the weather.