Thursday, October 10, 2013

(Not So) Solid Ice

While the U.S. government shutdown and debt ceiling crisis are taking up virtually all the media attention other things are happening and should be pointed out. Despite contextually questionable claims by climate change deniers that Arctic ice increased by 29% (Initial figures published on the NSIDC on their web site were incorrect. Rose initially claimed a 60% increase.) from last year that are technically true but leave out that it still leaves the extent of ice up north well short of historical averages, news from the poles isn't all that encouraging if you really pay attention. It is true that compared to last years minimum Arctic ice extent this year's wasn't as bad. But the NSIDC points out:
Overall, 10.03 million square kilometers (3.87 million square miles) of ice were lost between the 2013 maximum and minimum extents. This was the seventh summer that more than 10 million square kilometers of ice extent were lost; all but one of the seven (the summer of 1990) have occurred since 2007. ... September average sea ice extent for 2013 was the sixth lowest in the satellite record. The 2012 September extent was 32% lower than this year’s extent, while the 1981 to 2010 average was 22% higher than this year’s extent. Through 2013, the September linear rate of decline is 13.7% per decade relative to the 1981 to 2010 average.
NSIDC also discusses another meaningful metric when they report on ice. Thickness.
The pattern of ice thickness for the summer of 2013 is similar to what has been seen in recent years. According to data from the European Space Agency CryoSat-2 radar altimeter, the spring melt season started with an Arctic ice cover thinner than in any recent year. This corroborates thickness information inferred from a calculation of ice age that showed first-year ice, which is thinner and more vulnerable to melt, over a significant part of the Arctic Ocean as the melt season started (see our earlier post).
Then we move to the part that is really beloved by the "skeptics". The Antarctic. It had another record extent in sea ice this year. The details from the NSIDC are:
Antarctic sea ice extent reached 19.47 million square kilometers (7.52 million square miles) on September 22, a record high maximum extent relative to the satellite record, and slightly above the previous record high set last year. This year’s maximum extent was 3.6% higher than the 1981 to 2010 average Antarctic maximum, representing an ice edge that is 35 kilometers (approximately 22 miles) further north on average. Overall, Antarctic September sea ice extent is increasing at 1.1% per decade relative to the 1981 to 2010 average. This increase is likely due to a combination of factors, including winds and ocean circulation. A recent paper by our colleague Jinlun Zhang at the University of Washington concludes that changes in winds are resulting in both more compaction within the ice pack and more ridging, causing a thickening of the pack and making it more resistant to summer melt.
On the other hand there's a new discovery that makes me wonder how well this will hold up. That sea ice in western Antarctica has gouges in it. Gouges that come up into the ice from the bottom and are as tall and wide as the Eiffel Tower. New research hints that these gouges are related to water flow from melting ice. What that might mean to further increases in ice extent is something we'll have to wait and see, though it doesn't bode well for it, I'd think. Cross posted to The Moderate Voice