Sunday, August 15, 2010

The Arctic Ice Cat

Arctic ice cat

NSIDC 2010-08-13

The Arctic sea ice map has formed into a cat face shape again this year. This time, the ice extends more toward Alaska, where much of the thicker ice ended up in March and April, but the ocean is not so cold there, and the melt in the remainder of this month could take much of that away.

The “Arctic Ice Cat” forms because of thin ice in the Arctic Ocean — about a foot thick, too thin to stand up to the Atlantic currents on the right side of the map, the Siberian rivers at the top, or the warmer waters of the southern Arctic on the left side. At the same time, it is just strong enough to hold its own, to triangulate between the Asian and North American islands and hold a somewhat stable position.

The high mobility of the ice around the edges makes shipping tricky. Loose ice tends to blow into the straits of the Northwest Passage and is a threat to pile up against the Siberian coast with little advance warning, potentially pinning a cargo ship there.

Meanwhile, the picture of stability should not provide much reassurance. The ice could be highly stable in this shape, but realistically, it is just barely holding together. It would only take a big summer storm to blow the ice every which way, melting most of it. Or, an unusually warm summer would make the ice so thin that it could pile up on the shore and melt on the beach. There is no sign of either event happening this year, but even so, the Arctic sea ice is on track to repeat the record low extent of 2007.

The Arctic ice cat is a reminder that what used to be a reliable geographical feature, the “Arctic Ice Cap,” now depends on the weather. At this point, no one can say whether the Arctic Ocean will be open for shipping next month — but anyone who is interested can follow the weather reports.