Antarctic ice shelf 'hanging by thread': European scientists

Yahoo News 10 Jul 08;

New evidence has emerged that a large plate of floating ice shelf attached to Antarctica is breaking up, in a troubling sign of global warming, the European Space Agency (ESA) said on Thursday.

Images taken by its Envisat remote-sensing satellite show that Wilkins Ice Shelf is "hanging by its last thread" to Charcot Island, one of the plate's key anchors to the Antarctic peninsula, ESA said in a press release.

"Since the connection to the island... helps stabilise the ice shelf, it is likely the breakup of the bridge will put the remainder of the ice shelf at risk," it said.

Wilkins Ice Shelf had been stable for most of the last century, covering around 16,000 square kilometres (6,000 square miles), or about the size of Northern Ireland, before it began to retreat in the 1990s.

Since then several large areas have broken away, and two big breakoffs this year left only a narrow ice bridge about 2.7 kilometres (1.7 miles) wide to connect the shelf to Charcot and nearby Latady Island.

The latest images, taken by Envisat's radar, say fractures have now opened up in this bridge and adjacent areas of the plate are disintegrating, creating large icebergs.

Scientists are puzzled and concerned by the event, ESA added.

The Antarctic peninsula -- the tongue of land that juts northward from the white continent towards South America -- has had one of the highest rates of warming anywhere in the world in recent decades.

But this latest stage of the breakup occurred during the Southern Hemisphere's winter, when atmospheric temperatures are at their lowest.

One idea is that warmer water from the Southern Ocean is reaching the underside of the ice shelf and thinning it rapidly from underneath.

"Wilkins Ice Shelf is the most recent in a long, and growing, list of ice shelves on the Antarctic Peninsula that are responding to the rapid warming that has occurred in this area over the last fifty years," researcher David Vaughan of the British Antarctic Survey (BAS) said.

"Current events are showing that we were being too conservative, when we made the prediction in the early 1990s that Wilkins Ice Shelf would be lost within 30 years. The truth is, it is going more quickly than we guessed."

In the past three decades, six Antarctic ice shelves have collapsed completely -- Prince Gustav Channel, Larsen Inlet, Larsen A, Larsen B, Wordie, Muller and the Jones Ice Shelf.

Antarctic Ice Shelf All But Lost
LiveScience.comT, Yahoo News 10 Jul 08;

A vast shelf of ice in Antarctica is hanging on to the continent by a thread and is not expected to survive, scientists announced today.

The Wilkins Ice Shelf is experiencing further disintegration that could collapse an ice bridge connecting the shelf to Charcot Island. Since the connection to the island helps to stabilize the ice shelf, it is likely the breakup of the bridge will put the remainder of the ice shelf at risk, the researchers said.

The disintegration is evident in images from the European Space Agency's Envisat satellite.

The Wilkins Ice Shelf, a broad plate of floating ice south of South America on the Antarctic Peninsula that is connected to Charcot and Latady Islands, had been stable for most of the last century before it began retreating in the 1990s. A major breakup was spotted in May, the second this year.

This third significant breakup is puzzling because it occurred in the Southern Hemispheric winter. It's also behaving differently than previous breakups.

"The scale of rifting in the newly-removed areas seems larger, and the pieces are moving out as large bergs and not toppled, finely-divided ice melange," said Ted Scambos from the U.S. National Snow and Ice Data Center.

The Antarctic Peninsula's atmosphere has experienced more warming than any other part of the southern-most continent; in the past 50 years, it has experienced 4.5 degrees Fahrenheit (2.5 degrees Celsius) of warming. The warming has been so drastic because the peninsula is sandwiched between a region with substantially rising air temperatures and a warming ocean.

But warm water seems to be at least partly to blame for the recent disintegration, Scambos said.

In the past 20 years, seven ice shelves along the peninsula have retreated or come apart, including the spectacular 2002 breakup of the Larsen B Ice Shelf. The entire Wilkins shelf, before the recent breakups, covered about 6,180 square miles (16,000 square kilometers - about the size of Northern Ireland).

"Wilkins Ice Shelf is the most recent in a long, and growing, list of ice shelves on the Antarctic Peninsula that are responding to the rapid warming that has occurred in this area over the last fifty years," said David Vaughan of the British Antarctic Survey. "Current events are showing that we were being too conservative when we made the prediction in the early 1990s that Wilkins Ice Shelf would be lost within thirty years - the truth is it is going more quickly than we guessed."

Meanwhile at the top of the world, melting has become so rapid that scientists say the North Pole could be ice-free this summer.