NASA satellite data reveals how this year's minimum sea ice extent, reached on Sept. 9 as depicted here, declined to a level far smaller than the 30-year average (in yellow) and opened up Northwest Passage shipping lanes (in red). (Credit: NASA Goddard's Scientific Visualization Studio)
Last month the extent of sea ice covering the Arctic
Ocean declined to the second-lowest extent on record. Satellite data
from NASA and the NASA-supported National Snow and Ice Data Center
(NSIDC) at the University of Colorado in Boulder showed that the
summertime sea ice cover narrowly avoided a new record low.
The Arctic ice cap grows each winter as the sun sets for several
months and shrinks each summer as the sun rises higher in the
northern sky. Each year the Arctic sea ice reaches its annual minimum
extent in September. It hit a record low in 2007.
The near-record ice-melt followed higher-than-average summer
temperatures, but without the unusual weather conditions that
contributed to the extreme melt of 2007. "Atmospheric and oceanic
conditions were not as conducive to ice loss this year, but the melt
still neared 2007 levels," said NSIDC scientist Walt Meier. "This
probably reflects loss of multiyear ice in the Beaufort and Chukchi
seas as well as other factors that are making the ice more
vulnerable."
Joey Comiso, senior scientist at NASA's Goddard Space Flight Center in
Greenbelt, Md., said the continued low minimum sea ice levels fits
into the large-scale decline pattern that scientists have watched
unfold over the past three decades.
"The sea ice is not only declining, the pace of the decline is
becoming more drastic," Comiso said. "The older, thicker ice is
declining faster than the rest, making for a more vulnerable
perennial ice cover."
While the sea ice extent did not dip below the 2007 record, the sea
ice area as measured by the microwave radiometer on NASA's Aqua
satellite did drop slightly lower than 2007 levels for about 10 days
in early September, Comiso said. Sea ice "area" differs from extent
in that it equals the actual surface area covered by ice, while
extent includes any area where ice covers at least 15 percent of the
ocean.
Arctic sea ice extent on Sept. 9, the lowest point this year, was 4.33
million square kilometers (1.67 million square miles). Averaged over
the month of September, ice extent was 4.61 million square kilometers
(1.78 million square miles). This places 2011 as the second lowest
ice extent both for the daily minimum extent and the monthly average.
Ice extent was 2.43 million square kilometers (938,000 square miles)
below the 1979 to 2000 average.
This summer's low ice extent continued the downward trend seen over
the last 30 years, which scientists attribute largely to warming
temperatures caused by climate change. Data show that Arctic sea ice
has been declining both in extent and thickness. Since 1979,
September Arctic sea ice extent has declined by 12 percent per
decade.
"The oldest and thickest ice in the Arctic continues to decline,
especially in the Beaufort Sea and the Canada Basin," NSIDC scientist
Julienne Stroeve said. "This appears to be an important driver for
the low sea ice conditions over the past few summers."
Climate models have suggested that the Arctic could lose almost all of
its summer ice cover by 2100, but in recent years, ice extent has
declined faster than the models predicted.
NASA monitors and studies changing sea ice conditions in both the
Arctic and Antarctic with a variety of spaceborne and airborne
research capabilities. This month NASA resumes Operation IceBridge, a
multi-year series of flights over sea ice and ice sheets at both
poles. This fall's campaign will be based out of Punta Arenas, Chile,
and make flights over Antarctica . NASA also continues work toward
launching ICESat-2 in 2016, which will continue its predecessor's
crucial laser altimetry observations of ice cover from space.
In a taped version of a live broadcast, NASA Cryosphere Program Manager Tom Wagner shares his insights on the 2011 minimum. (Credit: NASA's Goddard Space Flight Center)
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