Summer sea ice
fell below normal for the fifth straight year in 2006, according to the
National Snow and Ice Data Center (see “Summer Sea Ice Continues to
Shrink,” page 39). A notable feature of the 2006 melt season was the
development of a large polynya, or area of persistent open water
surrounded by sea ice, north of Alaska in the Beaufort Sea.
The polynya formed in mid-August and continued to grow through early
September. By Sept. 11, 2006, the area of open water had grown to
roughly the size of the state of Indiana—about 38,000 square miles
(100,000 square kilometers). The Moderate Resolution Imaging
Spectroradiometer (MODIS) on NASA’s Aqua satellite took the background
picture above on the same day.
How the polynya formed isn’t clear. Unusual wind patterns may have
forced the ice cover to spread apart. Scientists also speculate that
thin ice moved into the area during the winter, melting out over the
summer and creating the polynya. Another possibility is that warm waters
rose to the surface, helping melt the ice.
The team felt it would be irresponsible to attribute the polynya to
greenhouse warming. “However, as the ice continues to thin with
increasing climate warming, we may see features like this more often,”
says Meier.
According to NSIDC, as sea ice melts in response to rising temperatures,
it creates a positive feedback loop: melting ice means more of the dark
ocean is exposed, allowing it to absorb more of the sun’s energy,
further increasing air temperatures, ocean temperatures and ice melt.
The observed changes in the ice cover indicate that this feedback is now
starting to take hold. Sea ice is only one indicator of Arctic change
among many, such as warming of permafrost, changing patterns of
vegetation from tundra to shrubs, a warming ocean and accelerated melt
of the Greenland ice sheet.
“I’m not terribly optimistic about the future of the ice,” says NSIDC
Senior Research Scientist Mark Serreze. “Although it would come as no
surprise to see some recovery of the sea ice in the next few years—such
fluctuations are part of natural variability—the long-term trend seems
increasingly clear. As greenhouse gases continue to rise, the Arctic
will continue to lose its ice. You can’t argue with the physics.”
