North Pole Sea Ice Minimum Third-Lowest Since 1979

by Emily Gertz

categories: Arctic & Antarctic, Science

Published September 19, 2009 @ 05:16PM PT

Watch this space...I'll be blogging all week, next week, from both the UN Climate Summit and related happenings, and the G20 meeting in Pittsburgh, in partnership with Grist and the Voice Project.

On Sept. 12, the sea ice cap covering the North Pole most likely hit its yearly low, according to federal scientists.

Poor ol' 2009 didn't quite make the record books: The sea ice did not recede to the record minimum of 2007.  But it's still much reduced compared to historic averages.

According to the National Snow and Ice Data Center, on Sept. 12 the  ice covered 2.97 million square miles (5.10 million square kilometers ) of the Arctic Ocean.  That's about 24% less than the average sea ice minimum from 1979 (when satellite measurements began) to 2000 was  4.17 million square miles (6.71 square kilometers).

The 2009 sea ice minimum extent was just under 1 million square kilometers below average. According to the NSIDC, this is the third lowest since the start of satellite measurements in 1979. The only two years with less sea ice were 2007 and 2008.  The chart below illustrates the trends in context:

Does the slight upward trend indicate a cessation of human-caused climate changes?  Very, very unlikely, unfortunately -- because there's a parallel trend of older, thicker ice melting and not returning.  NSIDC researchers say that while the sea ice extent receded less far than in the past two years, the Arctic Ocean ice is now "dominated by younger, thinner ice, which is vulnerable to melting."

What are the non-human-propelled factors affecting the how much the sea ice shrinks and grows?  As New York Times reporter Andrew Revkin wrote on his DotEarth blog this week,

...the small global network of  ice, climate and ocean specialists trying to make sense of ice behavior at both poles are — as always — working to use each year’s data to refine their still crude models. Many readily acknowledge that the Arctic is an extraordinarily complicated system in which ice conditions are determined by winds, currents and both air and sea temperature. It is a system that can amplify either a human warming influence or a natural one, making the task of disentangling a signal of human influence from other forces exceedingly tough.

In short, it's complex.  Although it's important to note:  Given both the overall speed of the human-propelled global warming, and its intensified affects in the Arctic, it's very, very unlikely that there are any natural trends in the works that would spark a major recovery of Arctic sea ice.  Bummer.

In an ideal world, this degree of unknowns would argue for a taking a more truly conservative approach to the climate, by slowing the human-propelled greenhouse gas pollution that's contributing to Arctic complexity and fragility.

Something to keep in mind in the coming weeks and months of international climate negotiations -- from next week's UN Climate Summit in New York City to December's formal treaty talks in Copenhagen.