the ice caps are melting...still
Arctic sea ice extent averaged over
As in February, the Arctic Oscilla-
the month of March 2011 was 14.56
tion (AO) mainly stayed in its positive
million square kilometers (5.62 million
phase, which tends to bring lower-
square miles). This is the second-low-
than-average pressure over much of
est March extent on record, after 2006.
the Arctic, and higher-than-normal
In March, ice extent remained below
pressure in middle latitudes. For more
normal in both the Atlantic and Pacific
information on current AO conditions,
sectors of the Arctic, particularly in
visit the NOAA Climate Prediction
the Labrador Sea and the Gulf of St.
Center Web page.
Lawrence Ice extent showed little change
arctic sea ice extent (area of ocean with at least 15% sea ice)
Every year at the start of the melt season, scientists look at sea ice age,
through the month of March, as is typi-
using data from satellites and buoys.
cal this time of year. The ice reached
Older ice that has survived several
its winter maximum extent on March
summer melt seasons tends to be
7, and over the next few weeks, ice
thicker, while newer ice is thinner and
extent declined only slightly. New ice
more vulnerable to melt in summer.
was still growing in some areas, but it
Over the past several decades, the
was melting in others. Overall, the ice
spring ice cover has become increas-
changes in these regions canceled each
ingly dominated by younger and
other out.
generally thinner ice, because of strong
Archipelago into the Beaufort and
summer melting in recent years that
Chukchi Seas, in a region that used to
increased, though not above the previ-
has reduced the amount of ice surviv-
be dominated by old ice that usually
ously reported level of March 7. This
ing into winter.
survived the summer melt season. A
Late in the month, extent again
late increase is due mainly to increases
This year the older, thicker ice has
similar tongue of old ice appeared in
of extent in the Kara, Barents, and
increased somewhat over last year,
March 2010, which almost completely
Greenland Seas. The Greenland Sea in-
although it remains younger than the
melted away during the summer
crease is likely due primarily to ice that
1979 to 2000 average ice age. Data
of 2010. Whether the tongue of old
was exported from the Arctic Ocean to
through the third week of March shows
ice seen this spring melts away this
the Greenland Sea by winds and ocean
an increase in sea ice one to two years
summer will depend largely on ocean
currents, though some ice growth is
old, and older than two years old,
temperature and the weather patterns
also apparent. The increase in the Kara
compared to recent years. However,
that set up over the next six months.
and Barents Seas appears primarily
the amount of older ice remains much
due to ice growth resulting from unu-
lower than in the mid-1980s, and there
recently recalculated their entire series
sually cold weather in the region.
is still almost none of the oldest ice,
of ice age data based on a minimum
older than four years old, that used to
of 15% concentration. The old version
the Arctic Ocean were above average,
dominate much of the Arctic Ocean.
used a 40% minimum. The repro-
reaching 7 to 9 degrees Celsius (13 to
The distribution of old and young
cessed ice age data is therefore more
16 degrees Fahrenheit) above average
ice at the end of March 2011 also looks
consistent with other measures of sea
over the Chukchi Sea. Below-average
different than the standard compari-
ice, including NSIDC sea ice extent
temperatures were found over Green-
son period of 1981 to 2000. Winds and
data, which use a threshold of 15%.
land, the Norwegian Sea and part of
ocean currents this winter resulted in
Canada which does not bode well for
an unusual tongue of old ice extend-
breaking of temperature records in
the safety department.
ing from north of the Canadian Arctic
the American west this fall, as well as
Air temperatures over almost all of
James Maslanik and colleagues
Other changes of note include the