Sunday, September 11, 2011

A New Low for Arctic Ice

Arctic sea ice is setting new records this month. According to some measures, the ice extent is already the lowest ever recorded, and there are two more weeks of decline ahead. At the same time, the ice is more broken up than we have seen in the past, with satellite pictures showing most of the ice forming 1- and 2-kilometer pieces, the ocean water melting away the edges to form channels between them.

If the extent of ice is matching the previous record low of 2007, the ice area is the least we have ever seen. Ice thickness is harder to measure, but all indications are that it too is unusually low. Ice volume, then, is also the lowest ever, and that is the most important thing. The less ice there is, the less time it will take to melt it all away.

Svalbard provides another measure of the decline of the Arctic ice. Almost always, the northeast corner of the island group is connected to the North Pole by a near-continuous sheet of ice, even in summer. Today there is 180 kilometers of open water north of Svalbard. Farther east, the central Arctic shipping route appears to be open for the first time. That is, a cargo ship could traverse the Arctic Ocean by a route north of all of the islands. Ships are, of course, traveling the safer route closer to the Siberian coast instead, and more ships than ever are making the trip this season. The Northwest Passage through the Canadian islands has also been open since early August and is almost completely clear of ice this month, based on the satellite pictures.

As another way to look at the changes in the Arctic region, you could follow up on the ice island that broke off the Petermann glacier in northern Greenland one year ago. At the time, experts warned that such a large ice island could be a threat to Atlantic shipping for a decade or longer. Instead, it started to break up immediately and has melted rapidly. One third of the original ice island, a piece dubbed PII-B, is stuck in Baffin Bay, where it has shrunk by 13 percent since March. One fragment broke loose and is the one large piece of ice to be found in the Northwest Passage at this point. The rest of the ice island, though, has made its way south to the area of Newfoundland, where only about five pieces are still large enough to track. The two largest are still a formidable 14 square kilometers as of August 25, an obstacle to steer around for now, but sure to melt away by next year. All in all, it’s a surprisingly rapid decline for such a large block of fresh-water ice. In the meantime ice scientists are waiting for the same glacier to shed another ice island half as large, an event that is likely to happen next summer, if not sooner. That will be the last such event from that glacier, as the once ice-filled fjord that provides its outlet to the sea is now filled with sea water.

An important thing to note is that the summer of 2011 is essentially repeating the ice coverage pattern of 2007, but it is happening this time without any of the strange weather events of that summer. If Arctic ice can set a new record low during a summer of ordinary weather in the region, then we can expect it to decline further in future summers when ordinary weather occurs. It is also useful to note how far off the climate models have been in predicting this summer’s ice. None of the major climate models predicted a new record low this summer, and several predicted 50 percent more ice than there has turned out to be. My suspicion is that the climate models are not accurately reflecting the effects of declining ice thickness. These are the same climate models that predict the Arctic could be ice-free toward the end of the century. Simple extrapolations of recent ice thickness measurements suggest that it will happen much sooner than that.