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Arctic sea ice could melt by summer of 2013
mongabay.com
December 12, 2007
Melting in the Arctic is occurring faster than most scientists predicted, according to research presented at the fall meeting of the American Geophysical Union in San Francisco.
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After record retreat in September 2007, Arctic sea ice had been making a slow winter recovery. Mean sea ice extent remained at record-low levels in October 2007, but beginning in late October, sea ice grew by more than 150,000 square kilometers (about 58,000 square miles) per day for about 10 days—the fastest regrowth observed in the satellite record. Despite this rapid growth, sea ice extent remained below normal for November, though it was not a record low.
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These images show Arctic sea ice on November 14, 2007 (top), and the record low on September 16, 2007 (bottom). White indicates 100 percent sea ice concentration, and deep blue indicates no sea ice. In each image, the yellow line encompasses the area in which there was at least 15 percent ice cover in at least half of the Novembers in the record (median sea ice extent). The images are based on observations by the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) aboard NASA's Aqua satellite. The long term record is based on satellite observations collected between 1979 and 2002 by sensors on the Nimbus-7 satellite and three Defense Meteorological Satellite Program satellites.
NASA image created by Jesse Allen, using data obtained courtesy of the National Snow and Ice Data Center (NSIDC). Caption courtesy of NASA.
In the mosaic image above, created from nearly 200 images acquired in early September 2007 by the Advanced Synthetic Aperture Radar (ASAR) instrument aboard ESA's Envisat satellite, the dark gray colour represents the ice-free areas while green represents areas with sea ice. The most direct route of the Northwest Passage (highlighted in the top mosaic by an orange line) across northern Canada is shown fully navigable, while the Northeast Passage (blue line) along the Siberian coast remains only partially blocked. To date, the Northwest Passage has been predicted to remain closed even during reduced ice cover by multi-year ice pack — sea ice that survives one or more summers. However, according to Pedersen, this year's extreme event has shown the passage may well open sooner than expected.
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Both Greenland and Arctic sea ice are melting at record rates, with Greenland's ice sheet losing 19 billion more tons of ice than ever recorded and summertime Arctic sea ice volume declining by 50 percent over the past four years. While just a year ago scientists predicted an ice-free Arctic sea by 2040, they now say the Arctic Ocean could be nearly ice-free at the end of summer by 2012.
"The Arctic is often cited as the canary in the coal mine for climate warming," NASA climate scientist Jay Zwally told the Associated Press. "Now as a sign of climate warming, the canary has died. It is time to start getting out of the coal mines."
The Arctic is particularly sensitive to changes in the extent of sea ice, which helps reflect sunlight back into space, cooling the region. When sea ice melts, the dark areas of open water absorb the sun's radiation, trigger a positive feedback loop that worsens melting.
Melting in the Arctic was so extensive this year that the fabled Northwest Passage was open to navigation for the first time on record. Scientists say the Northeast Passage -- north of Russia -- may soon also be navigable due to disappearing sea ice.
The melting has set off a scramble between Canada, Russia, the U.S., Denmark, Sweden and Norway which are all seeking to claim rights to the Arctic's rich mineral and gas deposits.
Environmentalists are concerned that the loss of summer sea ice could have dramatic implications for wildlife -- like polar bear and walrus -- that depend on pack ice for feeding.
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