Iceberg close to record size

The break-up of the Antarctic's ancient ice sheets is continuing. In the latest development, a slab of ice covering 4,000 square miles - the size of counties Mayo and Donegal combined - has snapped free of the Ross marine ice shelf.

The iceberg's progress is being monitored by the University of Wisconsin-Madison's Antarctic Meteorological Research Centre. "This is a very big iceberg, close to a record, if not a record," stated Dr Matthew Lazzara of the Centre. "It's not often that you see them of this magnitude."

Pieces of ice have been breaking off the Ross and Larsen B ice shelves for some years. A slab that would have stretched from Dublin to Drogheda, in a strip three miles wide, broke free in 1998 from the Larsen B. This new iceberg is 55 times larger, however, and if it drifts northwards into shipping lanes, as others have done before, it will be a serious hazard to navigation for years.

It won't have an impact on sea levels, however. Ice shelves are thick masses which float on the sea surface, projecting miles out from the Antarctic coastline. Like ice cubes floating in a glass, their release will not raise sea levels.

The break-up of the ice sheets which blanket the Antarctic continent itself would be a different matter. Loss of land ice would throw hundreds of millions of tonnes of water into the sea, pushing up levels around the world.