Despite a slight recovery in summer Arctic sea ice in 2009 from
record-setting low years in 2007 and 2008, the sea ice extent
remains significantly below previous years and remains on a trend
leading toward ice-free Arctic summers, according to the University
of Colorado at Boulder's National Snow and Ice Data Center.
According to the CU-Boulder center, the 2009 minimum sea ice
extent was the third lowest since satellite record-keeping began in
1979. The past five years have seen the five lowest Arctic sea ice
extents ever recorded.
"It's nice to see a little recovery over the past couple of
years, but there's no reason to think that we're headed back to
conditions seen in the 1970s," said NSIDC Director Mark Serreze,
also a professor in CU-Boulder's geography department. "We still
expect to see ice-free summers sometime in the next few
decades."
The average ice extent during September, a standard measurement
for climate studies, was 2.07 million square miles (5.36 million
square kilometers). This was 409,000 square miles (1.06 million
square kilometers) greater than the record low for the month in
2007, and 266,000 square miles (690,000 square kilometers) greater
than the second-lowest extent recorded in September 2008.
The 2009 Arctic sea ice extent was still 649,000 square miles
(1.68 square kilometers) below the 1979-2000 September average,
according to the report. Arctic sea ice in September is now
declining at a rate of 11.2 percent per decade and in the winter
months by about 3 percent per decade. The consensus of scientists
is that the shrinking Arctic sea ice is tied to warming
temperatures caused by an increase in human-produced greenhouse
gases being pumped into Earth's atmosphere, as reported by the
Intergovernmental Panel on Climate Change.
Sea surface temperatures in the Arctic this season remained
higher than normal, but slightly lower than the past two years,
according to data from University of Washington Senior
Oceanographer Mike Steele. The cooler conditions, which resulted
largely from cloudy skies during late summer, slowed ice loss
compared to the past two years. In addition, atmospheric patterns
in August and September helped to spread out the ice pack, keeping
extent higher.
The September 2009 ice cover remained thin, leaving it
vulnerable to melt in coming summers, according to the CU-Boulder
report. At the end of the summer, younger, thinner ice less than
one year in age accounted for 49 percent of the ice cover. Second-
year ice made up 32 percent of the ice cover, compared to 21
percent in 2007 and 9 percent in 2008.
Only 19 percent of the ice cover was over two years old -- the
least ever recorded in the satellite record and far below the
1981-2000 summer average of 48 percent, according to the CU-Boulder
report. Measurements of sea ice thickness by satellites are used to
determine the age of the ice.
Earlier this summer, NASA researcher Ron Kwok and colleagues
from the University of Washington in Seattle published satellite
data showing that ice thickness declined by 2.2 feet between 2004
and 2008.
"We've preserved a fair amount of first-year ice and second-year
ice after this summer compared to the past couple of years," said
NSIDC scientist Walt Meier of CU-Boulder's Cooperative Institute
for Research in Environmental Sciences. "If this ice remains in the
Arctic thorough the winter, it will thicken, which gives some hope
of stabilizing the ice cover over the next few years. However, the
ice is still much younger and thinner than it was in the 1980s,
leaving it vulnerable to melt during the summer."
Arctic sea ice follows an annual cycle of melting through the
warm summer months and refreezing in the winter. Sea ice reflects
sunlight, keeping the Arctic region cool and moderating global
climate temperatures.
While Arctic sea ice extent varies from year to year because of
changing atmospheric conditions, ice extent has shown a dramatic
overall decline over the past 30 years.
"A lot of people are going to look at the graph of ice extent
and think that we've turned the corner on climate change," said
NSIDC Lead Scientist Ted Scambos of CU-Boulder's CIRES. "But the
underlying conditions are still very worrisome."
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