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Largely natural ups and downs in a weather system centered near
Iceland have contributed to regional variations and an overall decrease
in Arctic sea ice cover over the last twenty years, according to new
As this semi-permanent low-pressure system intensifies and weakens,
it affects the amount of air (generally warm) being brought into the
Arctic to the east of the low and the amount of air (generally cold)
being swept out of the Arctic to the west. These changes in turn affect
the amount of ice cover in the respective regions, adding to the effects
of climate warming.
Claire L. Parkinson of NASAs Goddard Space Flight Center in
Greenbelt, Md., highlights the changes in Arctic sea ice and their
possible connection to the Icelandic low-pressure system in a paper
appearing in the most recent issue of Polar Geography.
Parkinson plotted the extent of sea ice using satellite
passive-microwave data from 1979 through 1999. Data were analyzed from
the Nimbus 7 satellite and three satellites of the Defense
Meteorological Satellite Program (DMSP). Results confirm an overall
decline in Arctic ice extent that has been connected with climate
warming, but also show regional differences that suggest there are other
The Icelandic Low is a key to bringing a greater or
lesser amount of warm air into the Arctic depending on the intensity of
the system, and is part of a larger weather pattern called the North
Atlantic Oscillation (NAO). NAO is the name for changes in the
difference of air pressure between the semi-permanent low-pressure
system centered near Iceland (the Icelandic Low) and a semi-permanent
high-pressure system centered near the Azores Islands (better known as
the Bermuda-Azores High).
On average, both of these systems are present all year; however, both
are strongest in winter. When both the high and the low intensify and
fluctuate in pressure relative to one another, they change the
circulation of cold and warm air in the region.
When the Icelandic Low is strong, it forces cold Arctic air southward
to the area west of Iceland and Greenland, setting the stage for
increasing sea ice cover in Baffin Bay, the Labrador Sea, Hudson Bay and
the Gulf of St. Lawrence. At the same time, to the east, warm air that
is swept northward reduces ice extent. This warmer air contributes to
the reduced ice extents east and north of Greenland, and the reduced
extent of ice in the entire Arctic overall. When the Icelandic Low is
weak, it will still bring warm air northward to the east of Iceland, but
not as much as when the Icelandic Low is strong, Parkinson said.
In the Arctic, sea ice extent fluctuates with the seasons. It reaches its peak extent in March, near the end of Northern Hemisphere winter, and its minimum extent in September, at the end of the summer thaw. In September 2007, Arctic sea ice extent was the smallest area on record since satellites began collecting measurements about 30 years ago.