NSIDC: Arctic sea ice extent neared record lows during summer 2011
- 06 Oct 2011, 10:30
- Verity Payne
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.
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.