Wednesday, August 3, 2011

Record Low Arctic Sea Ice for July

The NSIDC reports a record low July Arctic sea ice extent. Ice extent has declined more slowly during the last two weeks, but age, thickness, and concentration continue to decline well below historic norms. One researcher’s map of sea ice age from two weeks ago shows only isolated patches of multiyear ice, but the good news is that this ice seems to be protecting some of the newer ice from melting.

Sea ice extent is declining more slowly in part because so much ice is flowing away from the central Arctic into the Atlantic and the western Canadian islands. This pattern of outflow boosts the extent numbers but does nothing to reduce the rate of ice melting. Any ice that flows south in August will melt within a few weeks. To make the situation worse, it is some of the oldest ice that is flowing south in the Canadian islands and west of Greenland, and it is the most concentrated ice that is flowing out in unusually large volume along the east coast of Greenland.

The Siberian coast shipping route is already passable — a tanker ship tested the route in the first half of July with little difficulty — and it is likely to remain so for the next seven weeks. The Northwest Passage is probably passable too, although cargo ships there can proceed with more confidence if they wait until more of the ice melts.

It is too early in the season to say that ice in some areas of the Arctic Ocean might avoid melting. The satellite pictures continue to show ice moving large distances from one day to the next, at rates faster than the flow of a river. With thin, free-flowing ice, there is plenty of time for any particular block of ice to move into a position to melt, or for the thicker ice to move north and out of danger if the winds blow in that direction.