Saturday, October 3, 2009

Arctic Ice: a New Era

If it happens three times, it’s a pattern. The ice melt on the Arctic Ocean has followed almost the same pattern for the last three years, but it’s a pattern that had never been seen before 2007. It is a new era in the Arctic, and the experience of Arctic ice through 2006 can probably be disregarded, as the pattern of 2007–2009 appears to represent the new normal. Here’s how much has changed:

  • Arctic ice is generally about 1 to 2 meters thick. Previously, it was mostly 2 to 8 meters thick. Into 2007, there was a sharp distinction between first-year ice, which had just formed, and multi-year ice, which would grow thicker every winter for at least 6 years. That distinction no longer meant much by the winter of 2008, as the ocean now apparently remains warm enough in winter to melt away the underside of thicker ice.
  • Summer offshore breezes prevent ice from building up near the mainland of a continent in late summer. An onshore wind pattern may allow ice to pile up against the coast, but it will melt again when the wind blows offshore. The open coastline of Asia, Alaska, and Northwest Territories now tends to be ice-free in September. Previously, you could only count on this pattern along the European coast. Barring a persistent onshore wind pattern, the north coast of Asia is open to commercial traffic in September.
  • Arctic ice is no longer effectively anchored. Through 2006, you could count on Arctic sea ice being solidly attached to the far northern points of North American and Asia. This limited its movement, especially in winter; the wind would blow the ice around, but the ice could not go far. Since 2007, Arctic ice has been too thin to anchor effectively. When the wind changes direction, the ice can move halfway across the ocean.
  • With more ice movement, more ice is being ejected from the Arctic Ocean into the Atlantic Ocean. Previously, ice was ejected mostly east of Greenland. Now, a substantial amount of ice is also being ejected along the west coast of Greenland.
  • Summer ice that is less than 1 meter thick blows around easily and tends to jam up straits and channels. This makes cargo traffic through the Northwest Passage somewhat doubtful.
  • The ocean surface is refreezing later in the fall. One effect of this is that much of the fall snowfall is falling into the water. With less snow to provide insulation between the ice and the air, the thinnest ice can grow thicker quickly during the winter.

How long will this era of Arctic ice last? Not very long, I’m afraid. With ice only 1 to 2 meters thick it will take only one year of strange summer weather to clear substantially all of the ice out of the Arctic Ocean. This could be as simple as the wind blowing in just the right direction in July to carry the ice out to the Atlantic to melt. Or it could be a pattern of stormy weather that breaks the ice into smaller pieces and stirs it around.

There’s no telling when something like this might happen because it all depends on the weather — it could be next year, for all we know. However it happens, if most of the waters of the Arctic Ocean are directly exposed to sunlight in August and September, it will increase the ocean water temperature in a way that we’ve never seen before. New ice will still form that fall, but it will surely not look quite like the ice we are seeing now.