| Arctic Sea Ice Decline |
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Over
the last thirty years the Arctic ice has been shrinking almost
continuously. Since the beginning of the satellite recordings in 1979
the area of the perennial ice has been steadily
decreasing at a rate of about 10% per decade. The
previous record low was that of September 2005, when the ice coverage
fell for the first time below 5.5 million square kilometers. In
September 2007 however the sea ice extent dropped to a historical
minimum of 4.3 square kilometers, 38% below the average of the last
thirty years, and a whopping 24% less than the previous record low of
2005. The northernmost edge of the ice was at 85.5 degrees north, no
more than 500 km from the geographical pole.
Of course, a one
year drop in the ice coverage usually does not mean much. There is
quite some fluctuation in the annual ice coverage, as illustrated by
the annual minimum of 1996, which actually was the highest of the
previous 13 years. But the record low of 2007 was so far below average
that it is really starting to concern scientists. The trend
in decreasing ice cover seems to be getting stronger and stronger
as time goes on.
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Polar bears are
denied their historic length of seal hunting season due to late
formation and early thaw of pack ice - Source: Bird Holidays
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The accelerating decline in sea ice may be due to changes in climate
brought on by the lack of sea ice itself. This has to do with the much
lower albedo of ocean water compared to that of ice: the paler the
object, the more it reflects the energy of the sun. Since ocean water
is much darker than ice, it absorbs more energy, and consequently adds
to the warming of the planet. This is a positive feedback system: the
more the ice melts, the warmer the polar region gets. And the longer
this process continues, the harder it will become for the ice to
recover in winter. |
Evolution of Arctic sea
ice extent in August since the beginning of the satellite measurements
in 1979. Even though the actual
minima of both 2005 and 2007 occurred in September (instead of August),
this chart clearly shows the drastic decrease
in arctic sea ice over the last 30 years. - Source: Climate Progress
The
sea ice decline is a vast problem on its own since it contributes
to global warming, but it also lies at the basis of many
other problems: it contributes to rising sea levels
and threatens the survival of polar bears.
Indirectly
the warming of the arctic region leads to the loss of
permafrost which in turn triggers arctic methane release
– methane is a greenhouse gas 20 times stronger than carbon dioxide –
and might affect ocean circulation, in
the worst case shutting down the ocean conveyor belt that allows the
Gulf Stream to bring warmer water to the Atlantic coast of North
America and Europe. This might sound contradictory, but the result
would be a cooling effect in particular areas like Iceland, Ireland,
the Nordic countries, and Britain that are warmed by the North Atlantic
drift.
After the record low in
2007, the Arctic ice sheet slowly and almost completely recovered
during the following winter, but the newly formed ice was thinner and
less dense than the ice that disappeared during the summer of 2007.
Consequently, and
because global warming has not diminished, most of this new ice again
disappeared during the summer of 2008. The annual minimum was not as
low as in the year before, but it nevertheless was second to 2007 for
the record-lowest extent of sea ice. Contributing to the near record
sea ice minimum in 2008 was a month-long period in the summer that saw
the fastest-ever rate of seasonal retreat during that period. From
August 1 to August 31, NASA data show that arctic sea ice extent
declined at a rate of 32,700 square miles per day, compared to a rate
of about 24,400 square miles per day in August 2007.
The past
winter of 2008-2009 once again was cold enough to allow most of the
area to be covered with ice – almost, since the annual maximum extent
of the ice is also declining – but once again this layer of ice was
fragile and thin compared to previous years.
This year (2009) the
melting season seems to have been less severe than the previous two
years. The slower decline is primarily due to a recent atmospheric
circulation pattern, which transported ice toward the Siberian coast
and discouraged export of ice out of the Arctic Ocean.
According to the
National Snow and Ice Data Center, the sea ice most likely reached its
minimum extent on September 12. Again the minimum was less drastic than
the one in 2007 – it was even a bit better than the minimum in 2008 –
but it’s still far lower than the mean minimum ice extent between 1979
and 2000, as you can see in the picture below.
Sources
Arctic Sea Ice Minimum 2009 - Earth Protect
National Snow and Ice Data Center
Polar Bears Go Hungry as Icy Habitat Melts Away - Inter Press Service
'Remarkable' Drop in Arctic Sea Ice Raises
Questions - NASA
Sea Ice in Retreat - New York Times
Wikipedia - Albedo - Arctic shrinkage - Thermohaline circulation - Greenhouse gas
Links
NOAA
Animation : Arctic Sea Ice Reaches 3rd Lowest Minimum Extent
Arctic
Sea Ice - Earth Observatory World of Change
Extreme Ice Survey
Projected
Losses of Arctic Sea-Ice and Polar Bear Habitat may be Reduced
if Greenhouse Gas Emissions are Stabilized
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