[Vision2020] NSIDC: "February Arctic ice extent ties 2005 for record low"

[Ted Moffett]

http://nsidc.org/arcticseaicenews/

March 2, 2011

February Arctic ice extent ties 2005 for record low; extensive snow
cover persists

Arctic sea ice extent for February 2011 tied with February 2005 as the
lowest recorded in the satellite record. Sea ice extent was
particularly low in the Labrador Sea and Gulf of St. Lawrence. In
contrast, winter snow cover remained extensive in many parts of the
Northern Hemisphere.

Overview of conditions

Sea ice extent averaged over the month of February 2011 was 14.36
million square kilometers (5.54 million square miles). This was a tie
with the previous record low for the month, set in 2005. February ice
extent remained below normal in both the Atlantic and Pacific sectors,
particularly in the Labrador Sea and the Gulf of St. Lawrence.

While ice extent has declined less in winter months than in summer,
the downward winter trend is clear. The 1979 to 2000 average is 15.64
million square kilometers (6.04 million square miles). From 1979
through 2003, the February extent averaged 15.60 million square
kilometers (6.02 million square miles). Every year since 2004 has had
a mean February extent below 15 million square kilometers (5.79
million square miles).

Conditions in context

While ice extent grew at average rates for February, the overall
extent remained anomalously low. Air temperatures over most of the
Arctic Ocean were between 2 and 4 degrees Celsius (4 and 7 degrees
Fahrenheit) higher than normal. Over the East Greenland Sea and north
towards the Pole, air temperatures were 5 to 7 degrees Celsius (9 to
13 degrees Fahrenheit) higher than normal. Colder conditions, 2 to 6
degrees Celsius (4 to 11 degrees Fahrenheit) below average persisted
over western Eurasia, east-central Eurasia and some of the Canadian
Arctic.

As air temperatures dropped in the eastern Canadian Arctic in
February, parts of the Labrador Sea started to freeze over. However,
the Gulf of St. Lawrence remained mostly free of ice. As during winter
2010, when Environment Canada reported that sea ice in the Gulf of St.
Lawrence was at the lowest level on record, the lack of ice will make
it difficult for harp seals to give birth to their pups on the sea
ice, as they normally do in February and March.

February 2011 compared to past years

February 2011 tied February 2005 for the lowest ice extent for the
month in the satellite record. Including 2011, the February trend is
now at -3.0 percent per decade.

Through most of January, the Arctic Oscillation (AO) was generally in
a strongly negative phase, similar to the pattern that dominated the
winter of 2009 to 2010. This led to very warm temperatures over the
eastern Arctic, helping to account for the low ice extents over the
Labrador Sea and Gulf of Saint Lawrence. However, toward the end of
January, the AO returned to a positive phase, and ice began to grow in
the Labrador Sea and Gulf of St. Lawrence. For more information on
current AO conditions, visit the NOAA Climate Prediction Center Web
page.

Ice motion

Typically during a negative AO phase, weather patterns favor the
retention of thick ice in the central Arctic and Canada basin, where
it can better survive the summer. The negative AO also typically leads
to a stronger Beaufort Gyre, which helps move ice from the western to
eastern Arctic. There the ice thickens, ridging and rafting against
the Siberian coast.

Last winter, the AO was in its most negative phase since at least
1951. However, slight differences from the typical AO pattern in the
location of the sea level pressure anomalies had a significant impact
on how the ice moved within and out of the Arctic Basin. During winter
2009 to 2010 the peak pressure anomalies were shifted towards the
Barents and Kara seas, which helped transport ice from the Canadian
Arctic towards the southern Beaufort and Chukchi seas. Since some of
the oldest and thickest ice in the Arctic is found north of the
Canadian Archipelago, this atmospheric pattern ended up further
depleting the Arctic of its store of old, thick ice as that old ice
melted during summer in these southerly locations.

This winter also saw a relatively strong negative AO index during
December and January.  However, as we discussed in our January 5, 2011
post, the positive sea level pressure anomalies were centered near
Iceland. This led to a more extensive anticyclonic (clockwise)
transport pattern than last winter.  This may help keep a more
extensive distribution of multiyear ice cover as summer approaches.

January and February Northern Hemisphere snow cover

Sea ice extent is only one of a number of data sets scientists use to
understand how climate is changing. Rutgers University and NOAA have
compiled a 45-year record of Northern Hemisphere snow cover extent
from NOAA snow charts. These data show that much of northern North
America, Scandinavia and northern Eurasia are snow covered between 90
and 100 percent of the time in January and February. High elevation
plains and mountains at lower latitudes, such as the southern Rocky
Mountains in the U.S. and Hindu Kush in Asia, also have extensive snow
cover.

Over this record, in January, Northern Hemisphere snow cover averages
47 million square kilometers (18.1 million square miles), and in
February it averages 46 million square kilometers (17.8 square
miles)—approximately 45 to 46 percent of the land area in the region.
While sea ice extent was below average for January 2011, this month
had the sixth-largest snow cover extent since the record started in
1966, at 49 million square kilometers (18.9 million square miles).
Snow was unusually widespread over the mid-western and eastern United
States, eastern Europe, and western China. Snow cover in February
remained above average at 47.4 million square kilometers (18.3 million
square miles), with more snow than usual in the western and central
U.S., eastern Europe, Tibet and northeastern China.

Reduced sea ice extent and extensive snow cover are not contradictory,
and are both linked to a strong negative phase of the Arctic
Oscillation (see our January 5, 2011 post). A strongly negative AO
favors outbreaks of cold Arctic air over northern Europe and the U.S.,
as many people experienced first-hand these last two winters. Whether
this is a trend, or in any way linked to ongoing climate warming in
the Arctic, remains to be seen.

Further reading

Stroeve, J.C., J. Maslanik, M.C. Serreze, I. Rigor and W. Meier. 2010.
Sea ice response to an extreme negative phase of the Arctic
Oscillation during winter 2009/2010. Geophysical Research Letters,
doi: 2010GL045662.
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Vision2020 Post: Ted Moffett