Massive Antarctic ice shelf set to break loose

Yahoo News 3 Apr 09;

PARIS (AFP) – A Jamaica-sized ice shelf is close to wrenching itself away from Antarctica, following dramatic weakening of an ice "bridge" linking it to the continent, the European Space Agency (ESA) reported Friday.

The icy umbilical cord tying the Wilkins Ice Shelf to two islands on the Antarctic peninsula "looks set to collapse," ESA said.

The evidence comes from radar pictures taken on Thursday by its Envisat Earth-monitoring satellite, the Paris-based agency said in a press release.

Scientists have been keeping a worried eye on this ice shelf for years.

For many, it is a barometer of global warming, which has hit the Antarctic peninsula harder than almost any region on Earth.

The Wilkins Ice Shelf was stable for most of the last century, covering around 16,000 square kilometres (6,000 square miles) before it began to retreat in the 1990s.

By May 2009, an ice bridge, about 2.7 kms (1.7 miles) wide on average and just 900 metres (yards) at its narrowest point, was all that connected it to Charcot and Latady islands.

Over the past year, the ice shelf has lost about 1,800 square kilometres (700 square miles), or about 14 percent of its size, in further breakup events, ESA said.

New pictures show "the beginning of what appears to be the demise of the ice bridge" itself, it added.

This week, rifts formed along the central axis of the bridge and a large chunk of ice broke away. The stress patterns are now expanding rapidly, pointing to a likely imminent collapse of the link.

Ice shelves are ledges of thick ice that float on the sea and are attached to the land. They are formed when ice is exuded from ice sheet on land.

In the past 20 years, Antarctica has lost seven shelves.

The process is marked by shrinkage and the breakaway of increasingly bigger chunks before the remainder of the shelf snaps away from the coast.

It then disintegrates into debris or into icebergs that eventually melt as they drift northwards.

Scientists are especially puzzled that the Wilkins has suffered big breakups during the southern hemisphere's winter, when atmospheric temperatures are at their lowest.

One theory is that relatively warm currents from the Southern Ocean are scouring the underside of the shelf, thinning it rapidly from underneath.

In the past 50 years, the peninsula -- the tongue of Antarctica that juts up towards South America -- has experienced warming of 2.5 degrees Celsius (4.5 degrees Fahrenheit), which is many times higher than the global average.

In the early 1990s, many experts predicted that it would take 30 years for a shelf as vast as the Wilkins to be lost.

Antarctica is the world's biggest store of freshwater. Its ice, located on land in two vast slabs and on the peninsula, holds enough water to raise global sea levels by 57 metres (185 feet).

The Antarctic ice shelves do not add to sea levels when they melt. Like the Arctic ice cap, they float on the sea and thus displace their own volume.

Wordie Ice Shelf has disappeared: scientists
Reuters 3 Apr 09;

WASHINGTON (Reuters) - One Antarctic ice shelf has quickly vanished, another is disappearing and glaciers are melting faster than anyone thought due to climate change, U.S. and British government researchers reported on Friday.

They said the Wordie Ice Shelf, which had been disintegrating since the 1960s, is gone and the northern part of the Larsen Ice Shelf no longer exists. More than 3,200 square miles (8,300 square km) have broken off from the Larsen shelf since 1986.

Climate change is to blame, according to the report from the U.S. Geological Survey and the British Antarctic Survey, available at pubs.usgs.gov/imap/2600/B.

"The rapid retreat of glaciers there demonstrates once again the profound effects our planet is already experiencing -- more rapidly than previously known -- as a consequence of climate change," U.S. Interior Secretary Ken Salazar said in a statement.

"This continued and often significant glacier retreat is a wakeup call that change is happening ... and we need to be prepared," USGS glaciologist Jane Ferrigno, who led the Antarctica study, said in a statement.

"Antarctica is of special interest because it holds an estimated 91 percent of the Earth's glacier volume, and change anywhere in the ice sheet poses significant hazards to society," she said.

In another report published in the journal Geophysical Letters, the National Oceanic and Atmospheric Administration reports that ice is melting much more rapidly than expected in the Arctic as well, based on new computer analyses and recent ice measurements.

The U.N. Climate Panel projects that world atmospheric temperature will rise by between 1.8 and 4.0 degrees Celsius because of emissions of greenhouse gases that could bring floods, droughts, heat waves and more powerful storms.

As glaciers and ice sheets melt, they can raise overall ocean levels and swamp low-lying areas.

(Reporting by Maggie Fox; Editing by Xavier Briand)