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Why does an ice-free Arctic frighten scientists?

Doug O'Harra

Arctic sea ice shrank to the second lowest extent observed during the month of August since satellite monitoring began 32 years ago, according to the latest analysis posted by the National Snow and Ice Data Center.

"Both the Northwest Passage and the Northern Sea route appear to be open," the NSIDC reported Tuesday. "Throughout August, sea ice extent tracked near the record lows of 2007, underscoring the continued decline in Arctic ice cover."

With only a couple of weeks before the melt season ends and ice cover reaches its minimum for the year, the polar ice cap continues to flirt with breaking the all-time record set four seasons ago.

"As of September 5, ice extent had fallen below the minimum ice extents in September 2010 and 2008 (previously the third- and second-lowest minima in the satellite record)," the NSIDC reported Sept. 6. "If ice stopped declining in extent today, it would be the second-lowest minimum extent in the satellite record."

Day by day, prospects haven't been improving, the NSIDC noted.  

All summer long, scientists have found current floes thinner than previous years. The estimated total volume of sea ice (the surface footprint plus all the ice hidden beneath the waves) has spiked down to levels never seen during the 32 years of satellite eavesdropping, according to models posted by the Polar Science Center.

NASA satellite system that can resolve details almost five times smaller than the system regularly used by the NSIDC for its analysis -- a system that picks up far more of the existing open water -- suggests that the ice status may be more precarious than it appears.

According to this more sensitive system, ice extent on Sept. 5 fell below the same date in 2007, as processed by the University of Bremen. By one measure, at least, the record may have fallen already.

The NSIDC numbers calculated from its regular satellite monitoring are stark enough by themselves.

Arctic ice cover averaged of 2.13 million square miles during the month of August -- about 61,800 square miles above the minimum seen for the month in 2007, but about 830,000 square miles below the average August pack between 1979 and 2000.

By NSIDC calculations, August ice extent has declined more than 9 percent per decade since 1979. A floating ice habitat larger than Alaska, Washington and Oregon combined has now disappeared from the Arctic.

The Earth's air conditioner and marine mammal bedrock

The summer ice cap over polar ocean plays an essential role in stabilizing the Earth's climate and forms the bedrock, so to speak, of a unique marine ecosystem. As a result, tracking the fate of sea ice extent as it melts toward its annual minimum has become one of the key harbingers of long-term climate change in the Arctic.

With ice extent setting records or near records every September during the past decade -- and other indicators suggesting that the floes have lost record amounts of volume -- some scientists fear the polar sea will be virtually ice free during summer decades earlier than once thought possible.

All that open water could accelerate global climate warming because the darker ocean absorbs more solar energy than white floes. The exposed ocean then retains more heat, which slows winter freeze-up or causes even more ice to melt. This warmer, open-water Arctic will influence weather patterns and climate dynamics across the planet in unpredictable ways.

The summer loss of ice also means the destruction of one of the Earth's largest habitats -- home to a vast network of algae, plankton, fish, birds and marine mammals that concentrate on or below the ice itself. Maintaining healthy populations of polar bearswalruses and seals depends on the existence of this summer ice; when this hunting and denning platform disappears, these marine mammals must swim further or spend time on shore, making it harder to find enough to eat or avoid predators.

Seeing ice loss as so many Georgias

It's difficult to visualize the scales at work here, so for sake of argument, and a bit of levity, let's consider the current loss of Arctic ice in units of "Georgia" (the U.S. state and one of the 13 original colonies.)

At about 59,000 square miles, the Peach State would just about cover the ice deficit between August 2007 and August 2011, a significant amount of real estate that dramatizes just how bad it got four seasons ago. The Arctic of August was one Georgia above the all-time record low for the month.

But let's put that loss in perspective. In order to match the long-term average seen during the 22 Augusts that fell between 1979 and 2000, the most recent month would have needed to maintain frozen ocean covering an area 14 times larger than its distance from the record. So … the Arctic of August was 14 Georgias below average.

By Aug. 31, Arctic ice cover had shrunk even further and faster. The daily estimate was about 1.79 million square miles, or about 38,600 square miles above the record for that date.

The present Arctic ice of August -- 14 Georgias below average, maybe 23 Georgias below the maximum seen in the early 1980s -- has now melted to within half of a Georgia of breaking its previous minimum record.

Marine commerce meets open water

One near-term consequence of the near-record loss might be the unprecedented potential for marine travel. The fabled Northwest Passage over Canada is now almost entirely ice free, except for a strip of ice in Parry Channel. The southern route pioneered by the Arctic explorer Roald Amundsen opened in late August. Regular ships can now theoretically travel from the Atlantic Ocean to the Bering Sea over the top of North America.

"According to the Canadian Ice Service, sea ice extent in the western Parry Channel is now the lowest at this time of year since record keeping began in 1966 and very little multi-year ice remains," the NSIDC reported.

Online glimpses of the ice status -- the Multisensor Analyzed Sea Ice Extent (MASIE) and the European Space Agency -- show extraordinary gaps throughout the Canadian Archipeligo.

It may be there hasn't been so much open water in the Canadian Arctic for centuries.

The Northern Sea Route over Russia has been open since July, with a record number of cargo ships and tankers already making the voyage from Europe to the Pacific Ocean. All of these vessels have passed or will pass through the narrow Bering Strait off Alaska's western tip.  

More details: Researchers at the Polar Science Center this week announced that 2010 set a minimum record for the total volume of ice in the Arctic. But their latest modeling of current ice volume suggests the rate of loss has accelerated over last year, with ice volume for August about 62 percent below average and 72 percent below the volume calculated during the same month in 1979.

"Sea ice coverage remained below normal everywhere except the East Greenland Sea," the NSIDC said. "In addition, several large areas of open water (polynyas) have opened within the ice pack."

The ice-night cometh, and then what?

Air temperatures begin to fall fast in August as sunlight weakens and the length of the night grows. Melt season will soon end and the minimum extent for 2011 will be hit.

Even so, the melt rate hasn’t slowed as much as expected. During this August, about 26,100 square miles of ice disappeared each day: about 25 percent more than average. (That’s a loss of two-fifths of a Georgia every 24 hours.)  

The NSIDC reports that air temperatures were 2 degrees to 7 degrees Fahrenheit above normal, with the warmest air over the Northwest Passage. Elsewhere, weather and warm water played capriciously with the thinning ice pack.

"High pressure persisted over much of the central Arctic Ocean, associated with a wind pattern that helped to push ice from the Beaufort Sea westward into the Chukchi Sea," the agency said. "This may have slowed some ice loss in the Chukchi Sea region. However, the wind pattern also transported ice into open waters warmed during the summer, fostering melt."

So: Will a new record be set in the next two weeks? It depends. The NSIDC explains here:

The melt season for Arctic sea ice will soon draw to a close. Surface melt has already largely ended and the ocean waters are cooling. Air temperatures at the North Pole have fallen below freezing. However, with the ice cover now thinner than in years past, there is a greater potential for late-season ice loss, caused by warm water melting ice from below or winds that push the ice together.

Whether Arctic sea ice breaks a new record hinges on three factors: First, how much heat is left in the ocean to eat away at the ice edge and bottom? Second, will wind patterns blow the ice together and reduce ice extent or will they disperse the ice and expand ice extent? Finally, just how thin is the remaining ice cover? Thin ice quickly melts away when it is surrounded by warm water.

Contact Doug O'Harra at doug(at)alaskadispatch.com