A mysterious phenomenon is causing four major glaciers in the Antarctic to shrink in unison, causing a significant increase in sea levels, scientists have found.

Deji Cuonu, a young Tibet woman carries her baby as they endure a snowstorm at the foot of the 7,191 metre Nojing Kangtsang glacier where she raises yaks and sells tourist books as part of a small collective. Although the melting of Tibet's massive glaciers threatens to have dire global repercussions, climate change remains a vague concept for the people of this Himalayan region 04 March 2007 with experts saying that if global warming trends continue, up to a third of the world's highest glaciers could melt away by 2050 and half will disappear by 2090.(AFP/Peter Parks)

The rise in atmospheric temperatures caused by global warming cannot account for the relatively rapid movement of the glaciers into the sea, but scientists suspect that warmer oceans may be playing a role.

"There is a possibility that heat from the ocean is somehow flowing in underneath these glaciers, but it is not related to global warming," said glaciologist Duncan Wingham of University College London. "Something has changed that is causing these glaciers to shrink.

"At this rate the glaciers will all be afloat in 150 years or so."

Satellite measurements have shown that the Antarctic glaciers are retreating in a uniform manner, suggesting a common cause. Air temperatures over Antarctica are much too cold for any significant surface melting, which suggests that the flow of the glaciers into the sea is being aided by melting at their base, lubricating their movement into the ocean.

In a study in the journal Science, Dr Wingham and colleague Andrew Shepherd of Edinburgh University found that the Greenland and Antarctic ice sheets have together contributed a sea level rise of 0.35mm a year over the past decade - about 12 per cent of the current global trend.

While the retreat of the Greenland ice sheet can be linked to melting of the glaciers' surface, the same it not true of the four major glaciers in the Antarctic identified by Wingham and Shepherd.

"These glaciers are vulnerable to small changes in ocean temperature," he said. "A rise of less than 0.5C could have triggered the present imbalance."

However, it would take about 200 years for extra heat from the ocean to reach the underside of the glaciers, which makes it difficult to believe that the present shrinkage is due to global warming, Dr Wingham said.

© Copyright 2007 Independent News and Media Limited

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