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Home > Environmental issues > Global warming > Article

Arctic summer sea ice falls below normal for fifth year, despite a cool August

4 October 2006

The pattern of sharply decreasing Arctic sea ice continued in 2006, raising further concern that the Arctic is responding to global warming.

Matt Serreze, senior research scientist at the National Snow and Ice Data Center in Boulder, Colorado said, “If fairly cool and stormy conditions hadn’t appeared in August, slowing the rate of summer ice loss, I feel certain that 2006 would have surpassed last year’s record low for September sea ice.”

The melting season ended on September 14, the date of the sea ice minimum, when Arctic sea ice covered 5.7 million square kilometers (2.2 million sq.miles). It is the fourth lowest in the 29-year satellite record for a single day.

Arctic summer sea ice has been in steep decline since 2002 with a record 2005 low.

The average sea ice extent for the month of September was 5.9 million (2.3 million sq.miles), the second lowest on record, missing the 2005 record by 340,000

The rate of sea ice decline is now 8.6 percent per decade, or 60,421 (23,328 sq.miles) per year.  NSIDC research scientist Julienne Stroeve said, “At this rate, the Arctic Ocean will have no ice in September by 2060."

The average sea ice extent for September 2006 is shown in white.  The magenta line indicates the average September extent from 1979 to 2000.
Image from NSIDC Sea Ice Index
View larger image

Ice extent from January to mid-July 2006 was well below 2005 conditions, which if it had continued would have led to a new record low.

Low sea ice through mid-July was consistent with very warm air temperatures.  Serreze said, “high temperatures over the winter helped limit ice growth so that less ice formed. Much of the ice that did grow was probably thinner than normal. Unusually high temperatures through most of July then fostered rapid melt.”

Lower air temperatures in August broke the Arctic heat wave and slowed the melt, and storm conditions led to wind patterns that tend to spread the existing ice over a larger area.

Temperatures returned to above-normal in September. The warmer temperatures have meant a slow recovery from the September minimum.

An unusual polynya, an area of open water surrounded by ice in the center of the image, formed during the melt season in the Beaufort Sea. To the left is the coastline of Alaska, showing fall foliage color, and to the bottom right is the North Pole.
Image credit National Snow and Ice Data Center

View larger image

New development of a polynya .....

A notable feature of the 2006 melt season was the development of a large polynya, which is an area of persistent open water surrounded by sea ice, north of Alaska.

When it was near its largest area in early September, the polynya was the size of the state of Indiana.

How the polynya formed is not clear.  Unusual wind patterns may have forced the ice cover to spread apart.  Scientists also speculate that thin ice moved into the area over the winter, melting out over the summer and creating the polynya.  Another possibility is that warm waters rose to the surface.

NSIDC Lead Scientist Ted Scambos added, “Arctic sea ice is an important climate indicator because it's so sensitive to this initial warming trend.”  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 amongst 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,” Serreze said. “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.”

Data for this article was provided by the National Snow and Ice Data Center, Boulder, Colorado.

Copyright © 2006 TerraNature Trust. All rights reserved.

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