Cracking up: the ice shelf as big as Northern Ireland

It is one of the biggest in Antarctica and, for the past century, the massive Wilkins ice shelf appeared to have escaped the ravages of global warming. But now, enormous cracks have appeared in this floating ice platform the size of Northern Ireland. Scientists say it is breaking apart at an unprecedented rate after warmer temperatures weakened it.

A thin strip of ice is all that now prevents the Wilkins shelf from disintegrating and breaking away from the landmass of the Antarctic peninsula, scientists said yesterday. The peninsula is the fastest-warming region in the Antarctic and has seen some of the largest temperature rises on earth (0.5C per decade) which is why the Wilkins ice shelf is on the verge of disappearing completely, said one of the scientists.

Observers at the British Antarctic Survey (BAS) in Cambridge and the US National Snow and Ice Data Centre in Colorado said they were astonished to discover just how fast the ice shelf was breaking apart since the first cracks were seen in February.

"Wilkins is the largest ice shelf yet on the Antarctic peninsula to be threatened, said David Vaughan of the BAS. "I didn't expect to see things happen this quickly. The ice shelf is hanging by a thread - we'll know in the next few days or weeks what its fate will be.

"In this case things are happening more rapidly than we thought. We didn't really understand how sensitive these ice shelves are to climate change," said Dr Vaughan, who predicted in the 1990s that it would take 30 years for the ice shelf to break up.

Ice shelves form along the coasts and, because the ice is already floating on water, their disintegration does not affect sea levels. However, scientists believe that their rapid disappearance could lead to the faster movement into the ocean of the massive, land- based ice sheets and glaciers - which do raise sea levels.

The Wilkins ice shelf covers an area of about 5,282 square miles and satellite images taken at the end of February revealed that the rapid disintegration began after an iceberg the size of the Isle of Man broke away from its western edge.

Ted Scambos, of the snow and ice data centre, spotted the development and alerted colleagues at the BAS in Cambridge, who immediately dispatched a Twin Otter reconnaissance aircraft to map the Wilkins ice shelf with a series of aerial photographs.

"I had never seen anything like this before - it was awesome," said Jim Elliott, who was on board the aircraft. "We flew along the main crack and observed the sheer scale of movement from the breakage. Big, hefty chunks of ice, the size of small houses, looked as though they've been thrown around like rubble - it was like an explosion."

Dr Scambos said: "We believe the Wilkins has been in place for at least a few hundred years. But warm air and exposure to ocean waves are causing a break-up ... the collapse underscores that the Wilkins region has experienced an intense melt season. Regional sea ice has all but vanished, leaving the ice shelf exposed to the action of waves."

Several ice shelves on the peninsula have retreated in recent years and six of them - the Prince Gustav Channel, Larsen Inlet, Larsen A and Larsen B, the Wordie, Muller and the Jones ice shelves - have collapsed completely.

The Wilkins ice shelf is important because it is farther south on the Antarctic peninsula, where temperatures are generally colder than at the northern tip. "Climate warming in the Antarctic peninsula has pushed the limit of viability for ice shelves further south - setting some of them that used to be stable on a course of retreat and eventual loss," Dr Vaughan said.

"The Wilkins breakout won't have any effect on sea level because it is floating already, but it is another indication of the impact that climate change is having on the region."

The two biggest ice shelves in Antarctica - the Ross and the Ronne - lie on the edges of the Antarctic mainland farther south and so far show no signs of melting, Dr Vaughan added.

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