Global warming should add to the ice in Antarctica rather than make it melt, but world sea levels are still expected to rise by up to three feet over the next century, United Nations experts say.

The experts say it is so cold in Antarctica that it cannot snow much, so warmer temperatures will allow more snow to fall and be pressed into ice."If you have cold temperatures, you don't get much snowfall," explained John Houghton, chief executive of Britain's Meteorological Office.

Houghton chaired a U.N. working group which concluded that higher snowfall in Antarctica would outweigh any increase in the summer melt along its coast.

But the panel of scientists also concluded that the Greenland ice sheet and glaciers in the northern polar region would start to shrink.

Despite an increase in snowfall in Greenland, the summer melt would be bigger than in Antarctica because of the island's lower latitude, lower average altitude and longer coastline.

The working group said shrinkage of the Greenland ice cap, together with an expansion of the oceans due to warming, would still lead to higher sea levels and the potential flooding of coastal lowlands.

Houghton said the U.N. panel estimated that the accumulation of extra ice in Antarctica would balance out the net loss in Greenland.

But melting glaciers elsewhere would cause about 40 percent of the expected rise in sea levels and the expansion of sea water due to higher temperatures would account for the rest.

The panel said that unless action was taken to curb the greenhouse gases such as carbon dioxide, the seas would rise by between 12 to 39 inches by 2100.

Their best estimate was a rise of 26 inches.