FEATURE - Antarctic ice riddle keeps sea-level secrets

By Alister Doyle, Environment Correspondent

TROLL STATION, Antarctica (Reuters) - A deep freeze holding 90 percent of the world's ice, Antarctica is one of the biggest puzzles in debate on global warming with risks that any thaw could raise sea levels faster than U.N. projections.

Even if a fraction melted, Antarctica could damage nations from Bangladesh to Tuvalu in the Pacific and cities from Shanghai to New York. It has enough ice to raise sea levels by 57 metres if it melted, over thousands of years.

A year after the U.N.'s Intergovernmental Panel on Climate Change (IPCC) projected sea level rises by 2100 of about 20 to 80 cms, a Reuters poll of 10 of the world's top climatologists showed none think that range is alarmist.

Six experts stuck by the projections, saying the response of ice sheets in Antarctica and Greenland was still unclear, and four other experts, including one of the authors of the IPCC report, projected gains could be 1 or even 2 metres by 2100.

"Most people looking at it are thinking more in terms of a metre," said John Moore of the Arctic Centre at the University of Lapland. "Insurance companies don't know to a factor of 100 where to set their insurance premiums for coastal areas in Florida."

Some island nations, such as the Maldives in the Indian Ocean, are building defences costing millions of dollars and want to know how high to build.

"I think it will be...certainly at the high end of the range," said Kim Holmen, research director of the Norwegian Polar Institute, at the Troll Station 250 km from the coast in Antarctica.

Set amid jagged mountains like the mythical homes of troll giants, this part of east Antarctica is the world's deep freeze with no sign of a thaw. Temperatures were about minus 15 Celsius at the height of the Antarctic summer.