January 19, 2009
Wilkins Ice Shelf On Borrowed Time
A large ice shelf is near collapse in Antarctica, held together only by a small strip of ice as global warming continues to alter the map of the frozen continent.
"We've come to the Wilkins Ice Shelf to see its final death throes," glaciologist David Vaughan of the British Antarctic Survey (BAS) told Reuters after his red Twin Otter plane landed near the shelf's narrowest section.
The large, flat-topped ice shelf extends 65 ft. out of the sea off the Antarctic Peninsula, and is held together by a narrowing 25-mile ice strip that has dwindled to an hourglass shape of just 1640 ft. wide at its narrowest point.
In 1950, the shelf was over 60 miles wide, covering 6,000 square miles. Since then, temperatures on the Antarctic Peninsula have warmed by about 3 Celsius (5.4 Fahrenheit), the fastest rise anywhere in the southern hemisphere. Other parts of the continent show little sign of warming.
Wilkins, named after Australian George Hubert Wilkins, an early Antarctic aviator, has lost nearly a third of its area since 1950, but is still about the size of Connecticut. Once the strip breaks up, much of the remaining ice will likely be swept away by the sea. Already, large icebergs the size and shape of shopping malls, which are often used by seals to bask in the sunshine, surround the area.
After an aerial survey a year ago, the BAS said that Wilkins was "hanging by a thread."
"Miraculously we've come back a summer later and it's still here. If it was hanging by a thread last year, it's hanging by a filament this year," Vaughan noted.
Nine other shelves around the Antarctic peninsula have collapsed or receded during the past half century, many quite suddenly such as the Larsen A in 1995 or the Larsen B in 2002. The phenomenon is widely blamed on global warming caused by heat-trapping CO2 gases from the burning of fossil fuels.
"This ice shelf and the nine other shelves that we have seen with a similar trajectory are a consequence of warming," said Vaughan.
In total, roughly 9,650 square miles of ice shelves have been lost, enough to alter maps of Antarctica. Some shelves are believed to have been in place for more than 10,000 years, according to indications from ocean sediments.
Working on behalf of Dutch scientists, Vaughan attached a GPS monitoring station to a long metal pole that was stuck in to the Wilkins ice shelf. This will allow scientists to monitor ice movements via satellite.
The disintegration of ice shelves does not substantially raise sea levels because the ice is floating and already mostly submerged by the ocean. But scientists are concerned that their loss will allow land-based ice sheets to move more rapidly, adding extra water to the seas.
And while Wilkins has almost no pent-up glaciers behind it, ice shelves further south restrain enormous volumes of ice.
"When those are removed the glaciers will flow faster," Vaughan said.
"It's very unlikely that our presence here is enough to initiate any cracks," Vaughan said, referring to the hour he spent on the shelf, accompanied by BAS scientists and two Reuters reporters.
"But it is likely to happen fairly soon, weeks to months, and I don't want to be here when it does."
The United Nations Climate Panel, of which Vaughan is a senior member, forecasted in 2007 that the world's sea levels would rise by 7 to 23 inches this century. However, that prediction did not account for the possible acceleration of ice loss from Antarctica, and even a small change could dramatically affect sea levels. The continent's ice sheets contain enough water to raise world sea levels by 187 feet.
Nearly 190 nations have agreed to establish a new U.N. treaty by the end of the year to slow global warming through the reduction of emissions from the burning of fossil fuels in power plants, factories and cars.
On the Net: