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Arctic sea ice resumes big meltdown

Doug O'Harra

With only a month to go before melt season ends and the Arctic Ocean starts to refreeze, the polar ice cap has begun shrinking fast again and now covers the second smallest area ever observed for this time of year, according to a new update just posted by the National Snow and Ice Data Center.

“With about a month left in the sea ice melt season, the amount of further ice loss will depend mostly on weather patterns,” the NSIDC said.

Satellite imagery showed that ice covered about 2.15 million square miles on Aug. 14 — about 815,000 square miles below the average for that date but about 84,900 square miles above the record minimum seen on the same day in 2007.

“Sea ice is low across almost all of the Arctic, with the exception of some areas of the East Greenland Sea,” the NSIDC reported. “It is exceptionally low in the Laptev and Kara Sea areas.”

The Northern Sea Route over Russia had already opened to shipping traffic earlier than ever before, with some tankers already successfully traveling from Europe to Asia through the Bering Strait. But more ships will soon be steaming across.

The Russian gas producer Novatek plans to send the 120,000-ton tanker Vladimir Tikhonov along Russia’s Arctic Coast to the Bering Strait in August — the largest ship of its kind to ever traverse the Northern Sea Route, the Barents Observer reported last week. “Novatek plans to ship a total of 420,000 tons of gas condensate through the NSR in 2011.”

Other satellite coverage (and here) suggests that the southern route of the Northwest Passage over Canada has also now gone ice free and could, theoretically, be navigated by ship.

The new data offers a glimpse of how shifting weather has played capriciously with the fate of the thinning floes across the region. First a month of clear, calm skies shrank the cap to the smallest extent ever recorded for the month of July, pulling off the Asian coast and opening  the Northern Sea Route. Then colder and stormier conditions slowed the rate of loss and spread out the floes so that the total ice extent slipped behind the 2007 season in its race to the bottom.

“During early summer, a high-pressure cell persisted over the northern Beaufort Sea, promoting ice loss,” the NSIDC explained. “This weather pattern broke down toward the end of July, slowing ice loss but spreading out the ice pack, making it thinner on average.

“The weather has now changed again, bringing another high-pressure pattern. Winds associated with this pressure pattern generally bring warm temperatures, and tend to push the ice together and reduce overall extent.”

The ice pack, while more spread out, is now thinner than it was in 2007, the scientists say, and the total volume of ice has never been lower. While it’s not possible to directly measure the volume of floating ice across the Arctic, the Polar Science Center at the University of Washington has posted several alarming estimates here and here that illustrate a startling, downward trend.

It gets worse. The satellite data normally analyzed by the NSIDC comes from a system that can resolve ice pack details as small as 15.5 miles across — and that’s the data the agency uses to make comparisons back to 1979. But a different, more sophisticated system that can resolve ice pack details down to 3.88 miles suggests that there may be even less ice than appears and 2011 has been “tracking” 2007 far more closely than previously thought.

That system “can detect small but widespread areas of open water within the ice pack in the Beaufort and East Siberian seas, because of its resolution,” the NSIDC explained.

Buoys anchored around the Arctic on thick multi-year floes — and monitored by the U.S. Army Cold Regions Research and Engineering Lab — are also confirming that the ice pack has thinned substantially.

“Data from six of these buoys through July 20 show that this year, the ice surface is melting faster than the underside of the ice,” NSIDC reported. “As the sun starts to sink on the horizon, surface melt will slow. However, ocean waters warmed during the summer will continue to melt the ice from below, reducing ice thickness and extent into September.”

The Earth’s ice cap plays an essential role in stabilizing the world’s climate, and its summer-time loss directly contributes to climate change because darker open water absorbs more solar energy than white floes. The exposed ocean then stores heat that, in turn, causes even swifter melt.

Summer sea ice also provides habitat necessary to maintain healthy populations of polar bears, walruses and seals. When this hunting and denning platform disappears, marine mammals must swim further or spend time on shore, making it harder to find enough to eat or avoid predators. The United States has listed the polar bear as threatened under the Endangered Species Act due to the ever-shrinking summer ice pack north of Alaska.