In what could be an early sign of global warming, scientists reported an Antarctic ice shelf has rapidly disintegrated over the past 20 years, apparently due to localized temperature increases.

Two researchers with the British Antarctic Survey said Wednesday satellite photos clearly show the Wordie Ice Shelf breaking apart into icebergs and shrinking from an estimated 800 square miles in 1966 to only 280 square miles in 1989."We suggest that breakup was triggered by a climatic warming," said C.S.M. Doake and D.G. Vaughan in a paper published in the scientific journal Nature.

In an accompanying commentary, a NASA scientist warned against interpreting the demise of the Wordie Ice Shelf as a foreshadowing of widespread melting of the polar ice cap. He noted Wordie was affected by a regional warming trend that had not been observed in other parts of Antarctica.

However, he said the new study showed how greater warming could hasten the melting of the West Antarctic Ice Sheet, a massive layer of continental ice with the potential to substantially raise sea levels worldwide.

Doake and Vaughan said the Wordie ice shelf was weakened by increasing cracks and melt water caused by warming air temperatures over Marguerite Bay, the small body of water into which the shelf extends.

The result, the researchers said, was accelerated iceberg calving - when enormous chunks of ice break off.