“The northern ice front of the Wilkins Ice Shelf has become unstable and the first icebergs have been released,” Angelika Humbert, glaciologist at the University of Muenster in Germany, said of European Space Agency satellite images of the shelf.

Ms. Humbert said about 700 square kilometres of ice, bigger than Singapore or Bahrain and almost the size of New York City, has broken off the Wilkins this month and shattered into a mass of icebergs. She said 370 square kilometres of ice had cracked up in recent days from the Shelf, the latest of about 10 shelves on the Antarctic Peninsula to retreat in a trend linked by the UN Climate Panel to global warming.

The new icebergs added to 330 square kilometres of ice that broke up earlier this month with the shattering of an ice bridge apparently pinning the Wilkins in place between Charcot island and the Antarctic Peninsula. Nine other shelves -- ice floating on the sea and linked to the coast -- have receded or collapsed around the Antarctic peninsula in the past 50 years, often abruptly like the Larsen A in 1995 or the Larsen B in 2002.

The trend is widely blamed on climate change caused by heat-trapping gases from burning fossil fuels, according to David Vaughan, a British Antarctic Survey scientist who landed by plane on the Wilkins ice bridge in January.

Ms. Humbert said by telephone her estimates were that the Wilkins could lose a total of 800 to 3,000 square kilometres of area after the ice bridge shattered.

The Wilkins shelf has already shrunk by about a third from its original 16,000 square kilometres when first spotted decades ago, its ice so thick it would have taken hundreds of years to form.

Temperatures on the Antarctic Peninsula have warmed by up to three degrees Celsius this century, Mr. Vaughan said, a trend climate scientists blame on global warming from burning fossil fuels in cars, factories and power plants. The loss of ice shelves does not raise sea levels significantly because the ice is floating and already mostly submerged by the ocean. But the big worry is that their loss will allow ice sheets on land to move faster, adding extra water to the seas.

Wilkins has almost no pent-up glaciers behind it, but ice shelves further south hold back vast volumes of ice.

The Arctic Council, grouping nations with territory in the Arctic, is due to meet in Tromsoe, north Norway, on Wednesday to debate the impact of melting ice in the north.