Monday, August 27, 2012

Arctic Sea Ice Is Dying

There is an exclamation point on today’s NSIDC Arctic sea ice extent map.

It is not just that the ice extent has reached a shocking all-time record low three weeks before the usual end of the ice melting season. You can see the shape of an exclamation point at the top of the ice pack on the map.

The exclamation point is formed by two polynyas, areas of water surrounded by ice. The dot, making its first appearance on the map today, is a new polynya that formed at 86° north latitude. This is an event that is remarkable in itself. Polynyas don’t form easily so far north. If ice is not safe in this spot, 400 kilometers from the North Pole, it is not safe anywhere in the Arctic.

Polynyas also do not usually form this late in August, with the sun so low in the sky, but then, for Arctic sea ice, this is no ordinary August. In the past, we would expect to see rapid ice melt in June and July. Then in August, melt slows, coming almost to a stop by the end of the month. Not so this year. Melt has continued at a July-like pace right through August.

This year is also not a repeat of 2007, the previous record low year. That summer had the kind of sunny weather you would see once in 8 years to promote rapid melting. This summer’s weather was more average and should have protected the ice better. Yet the extent graph shows almost a straight-line descent from the beginning of June to the present.

The ice is thinner than ever, and this is a special irony. This year, we thought we would finally get good data on ice thickness. Alas, the ice is too thin for the radar models to work.

At the beginning of the summer I said that this would not be the year when the Arctic ice would melt out completely, because there was not enough open water in the Arctic Ocean to soak up the sun in May. Open water is key to ice melt because the sun is high in the sky in May (into July) and water, being darker, absorbs at least five times as much solar heat as ice does. I was expecting the ice extent data to follow along the lines of 2007 and 2010, and until July, it did. But it’s easy to see that something new is happening now.

We have reached the turning point where a warmer ocean surface is rejecting the ice. The Arctic sea ice is dying.

The warmer ocean also means a weak fall re-freeze, with perhaps only 11 weeks from January to March for new ice to build up. Some observers believe the volume of ice at the peak in March or April 2013 could be no larger than what has melted already this year. If they are correct, then all the ice could easily melt away next summer, and every summer from then on. And the ice that forms in winter will be more like the ice in the Atlantic Ocean than what we are used to seeing in the Arctic.

Ice takes heat away when it melts, so the loss of Arctic sea ice will affect weather all over the Northern Hemisphere. Of special concern to me:

  • Greenland: without sea ice to keep things cool, the entire Greenland ice sheet could melt away in 150 years. This will result in a sea level rise that will swamp most of the world’s coastal cities. There will be thousands of earthquakes along the East Coast of North America.
  • The heartland: areas in central North America far from the coasts are likely to get less regular rain, and will likely no longer be suitable for growing crops like corn.

These future consequences are speculative. We don’t have enough historical data to guide us on the specifics. Alas, what the latest sea ice data says is these changes are upon us now, whether we understand them or not.