Ice shelf 'hangs by a thread'

From the Sydney Morning Herald

A MASSIVE ice shelf bigger than Greater Sydney has begun to collapse in Antarctica under the pressure of climate change, new satellite images reveal.

The disintegration of the 13,680-square-kilometre Wilkins Ice Shelf began on February 28 when a large iceberg fell away. This triggered a runaway impact this month, according to scientists from the US National Snow and Ice Data Centre, when 570 square kilometres of the shelf crumbled.

The most recent satellite images taken by the centre on Easter Sunday show the ice shelf is hanging on by a single strip of ice, six kilometres wide, strung between two islands on the south-west Antarctic Peninsula....

In the past 50 years, the temperature in the western Antarctic Peninsula has risen almost three degrees, or 0.5 degrees each decade.

"The collapse underscores that the Wilkins region has experienced an intense melt season," Dr Scambos said. "Regional sea ice has all but vanished, leaving the ice shelf exposed to the action of the waves." ...

"The ice shelf is hanging by a thread," David Vaughan, of the British Antarctic Survey, said.

One of Australia's leading Antarctic scientists, Dr Ian Allison, who examined the new data yesterday, said the collapse was an indication of how quickly change can happen in the polar regions when a critical point is reached.

"This area is showing extreme warming," Dr Allison said, "The climate models all predict that with anthropogenic [human induced] warming the biggest increases are going to occur in the polar regions. And the biggest warmings we are seeing are in the Arctic and the Antarctic peninsula area."

Dr Allison said it was likely the Wilkins Ice Shelf would hold on now because winter was approaching but it would continue its collapse next January. "I expect about one-third of the ice shelf to go fairly quickly next season," he said....

Dr Allison said it was significant that the warmer temperatures were now having an effect closer to the main ice mass of the frozen continent.

If larger ice shelves start disappearing and melting starts accelerating, he said, there could be significant sea level rise over the next century.

Five more degrees further south is the start of the West Antarctic Ice Sheet, much of which lies on rock below sea level. The director of the British Antarctic Survey, Chris Rapley, said if this were to disintegrate, it would raise global sea level by about five metres. He has already described the West Antarctic sheet as an "awakened giant".

Scientists have calculated that the sheet is losing about 132 billion tonnes of ice a year.