[asa] Record Ice Loss in August

From: Rich Blinne <rich.blinne@gmail.com>
Date: Fri Sep 05 2008 - 12:36:23 EDT

http://nsidc.org/arcticseaicenews/

Following a record rate of ice loss through the month of August, Arctic sea ice
extent <http://nsidc.org/cgi-bin/words/word.pl?ice%20extent> already stands
as the second-lowest on record, further reinforcing conclusions that the
Arctic sea ice cover is in a long-term state of decline. With approximately
two weeks left in the melt season, the possibility of setting a new record
annual minimum in September remains open.

Overview of conditions

Arctic sea ice extent on September 3 was 4.85 million square kilometers
(1.87 million square miles), a decline of 2.47 million square kilometers
(950,000 square miles) since the beginning of August.

Extent is now within 370,000 square kilometers (140,000 square miles) of
last year's value on the same date and is 2.08 million square kilometers
(800,000 square miles) below the 1979 to 2000 average.

*Conditions in context*

In a typical year, the daily rate of ice loss starts to slow in August as
the Arctic begins to cool. By contrast, in August 2008, the daily decline
rate remained steadily downward and strong.

The average daily ice loss rate for August 2008 was 78,000 square kilometers
per day (30,000 square miles per day). This is the fastest rate of daily ice
loss that scientists have ever observed during a single August. Losses were
15,000 square kilometers per day (5,800 square miles per day) faster than in
August 2007, and 27,000 square kilometers per day (10,000 square miles per
day) faster than average.

This August's rapid ice loss reflects a thin sea ice cover that needed very
little additional energy to melt out.

*Regional ice loss contributes to decline*

What part of the Arctic contributed most strongly to the rapid August
decline? Through spring and early summer, ice losses were largest in the
Beaufort Sea. In August, the pattern of ice loss changed, with the greatest
ice losses shifting to the Chukchi and East Siberian Seas.

The shift in location of maximum ice losses was fueled by a shift in
atmospheric circulation. A pattern of high pressure set up over the Chukchi
Sea, bringing warm southerly air into the region and pushing ice away from
shore. August air temperatures in the Chukchi Sea (at 925 millibars
pressure, roughly 750 meters [2,500 feet] in altitude) were 5 to 7 degrees
Celsius (9 to 13 degrees Fahrenheit) warmer than normal. Ice loss in the
Chukchi and East Siberian Seas averaged 14,000 square kilometers (5,400
square miles) per day faster than in 2007.

Sea ice also experienced an unusual retreat north of Ellesmere Island during
August. Partial collapse of ice shelves in the region attended this
retreat. Visit the Trent University press release at:
http://www.trentu.ca/newsevents/newsreleases_080903iceshelf.php.

*Warm ocean temperatures*

Mike Steele and Wendy Ermold from the University of Washington's Applied
Physics Laboratory Polar Science Center <http://psc.apl.washington.edu/> have
been closely monitoring sea surface temperatures in the Arctic.

Positive sea surface temperature anomalies for August 2008 correspond with
areas of ice retreat. When the ice melts, it exposes open water that absorbs
solar energy; the warm ocean waters then favor further sea ice melt. An
interesting phenomenon, in this regard, is that sea ice this August has been
drifting into the Beaufort Sea only to melt when it encounters these warm
ocean waters.

As autumn comes to the Arctic, the ocean will begin to lose its heat back to
the atmosphere. This means that regions of high sea surface temperatures
seen in August will be manifested as above-average air temperature in
corresponding regions as autumn unfolds.

*August 2008 average extent compared to past Augusts*

Arctic sea ice extent averaged over the month of August was 6.03 million
square kilometers (2.33 million square miles). This is 1.64 million square
kilometers (633,000 square miles) below the 1979 to 2000 August average,

However, August 2008 was still 670,000 square kilometers (260,000 square
miles) above August 2007, despite the record-breaking rate of decline over
the past month. Why would this be? The best explanation for this is that
this summer did not experience the "perfect storm" of atmospheric conditions
seen throughout the summer of 2007.

Even though August ice extent was above that of August 2007, the downward
trend for August ice loss has now gone from -8.4% per decade to -8.7% per
decade.

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Received on Fri Sep 5 12:36:47 2008

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