Antarctic ice shelf crumbling.

• Author: O'Meara, Molly

The Antarctic Peninsula's Larsen B ice shelf retreated past its historical minimum in March 1998 when a 200 square kilometer block of ice collapsed into the sea. Scientists believe the ongoing loss of such massive quantities of ice has permanently destabilized the ice shelf. According to U.S. National Snow and Ice Data Center (NSIDC) research associate Ted Scambos: "this could be the beginning of the end" for Larsen B.

Measuring 12,000 square kilometers, about the size of Jamaica, Larsen B may soon be the largest of a series of ice shelves to completely collapse. David Vaughan and Christopher Doake of the British Antarctic Survey (BAS) have documented the dramatic retreat of five smaller peninsular ice shelves in the past 50 years. Most stunning was the rapid disintegration in January 1995 of the 1,300 square kilometer Larsen A, which used to lie to the north of Larsen B.

Nearly a year before NSIDC's satellite images revealed the retreat of Larsen B, Doake and his colleagues used computer models to predict the shelf's demise. Their conclusions were published in the February 1998 journal Nature just weeks before the big iceberg broke away. "Larsen B...exhibits a stable pattern," they wrote, "but if the ice front were to retreat by a further few kilometres, it too is likely to enter an irreversible retreat phase."

The...