NSIDC: Arctic sea ice extent neared record lows during summer 2011
Image - NSIDC Sept Arctic SI 20111004 (note)
The National Snow and Ice Data Center (NSIDC) have released their latest figures on Arctic sea ice extent for summer 2011:
“Average ice extent for September 2011 was 4.61 million square kilometers (1.78 million square miles), 2.43 million square kilometers (938,000 square miles) below the 1979 to 2000 average. This was was 310,000 square kilometers (120,000 square miles) above the average for September 2007, the lowest monthly extent in the satellite record. Ice extent was below the 1979 to 2000 average everywhere except in the East Greenland Sea, where conditions were near average.”
Since satellite records began in 1979, Arctic sea ice extent has been declining, and these latest figures confirm that Arctic sea ice loss is continuing, as shown in the graph below.
Image - NSIDC Sept Arctic SI2 20111004 (note)
Arctic sea ice varies seasonally, growing during the winter when it is coldest, and retreating during the warm summer. However, this seasonal variation does not mask the overall trend of declining Arctic sea ice which has been observed over the last three decades. If the ice loss continues we can expect the Arctic sea ice extent to reach new record lows in future summers.
Summer 2011 saw much speculation by scientists and the blogosphere that this year would bring a new record summer sea ice low. Media attention peaked in September when scientists from the Polar Science Center, University of Washington, published data showing that Arctic sea ice volume reached a new record minimum in 2010. This was swiftly followed by an announcement by German researchers that Arctic sea ice reached a “new historic minimum” on September 8th. The NSIDC (who use a slightly different technique) subsequently put Arctic sea ice extent as reaching its annual minimum on September 9th, and now describe the satellite data for 2011 as showing that “sea ice cover narrowly avoided a new record low”.
The previous record Arctic summer sea ice low, reached during September 2007, has been put down to a very specific set of weather conditions which exacerbated the increase in melting associated with global warming. Similar weather conditions were only present at the start of this summer, yet this year’s Arctic summer sea ice levels were comparable with those reached in 2007. So what could have caused this year’s unusually low extent? The NSIDC speculate that this could be due to the Arctic sea ice being thinner, as it continues to lose older, thicker (‘multi-year’) ice. As Joey Cosimo, NASA senior scientist, puts it:
“The sea ice is not only declining; the pace of the decline is becoming more drastic. The older, thicker ice is declining faster than the rest, making for a more vulnerable perennial ice cover.”
The decline in Arctic sea ice is now happening faster than IPCC models projected for the 2007 AR4 report. This has led to suggestions that we could see ice-free Arctic summer seas in just a few decades if the current rate of decline continues.