High-tech experiments may show Antarctica sea rise risks

Dismayed by ice and storms, British explorer Captain James Cook had no regrets when he abandoned a voyage searching for a fabled southern continent in 1773.

Finding only icebergs after he was the first to cross the Antarctic Circle, he wrote ruefully that if anyone ventured further he would find a "land doomed by nature... to lie for ever buried under everlasting ice and snow":

"I shall not envy him the honour of discovery, but I will be bold to say that the world will not be benefited by it."

Things may be worse than he thought.

Climate change is turning Antarctica's ice into one of the biggest risks for coming centuries. Even a tiny melt could drive up sea levels, affecting cities from New York to Beijing, or nations from Bangladesh to the Cook Islands - named after the mariner - in the Pacific.

Scientists are now trying to design ever more high-tech experiments - with satellite radars, lasers, robot submarines, or even deep drilling through perhaps three kilometres of ice - to plug huge gaps in understanding the risks.

"If you're going to have even a few metres it will change the geography of the planet," Rajendra Pachauri, head of the UN Intergovernmental Panel on Climate Change, said of the more extreme scenarios of fast ocean rise.

"Greenland and Antarctica are two huge bodies of ice sitting on land that could really have very serious implications for the levels of the seas," said Mr Pachauri. Eventually discovered in 1820, Antarctica locks up enough water to raise sea levels by 57 metres. Greenland stores the equivalent of seven metres.

Worries about sea level rise are among the drivers of 190-nation talks on a new UN deal to combat climate change, mainly by a shift away from fossil fuels, due to be agreed in Copenhagen in December.

Scientists are concentrating on the fringes, where the ice meets a warming Southern Ocean. "It's the underside of the ice sheets that's crucial," said David Carlson, a scientist who headed the International Polar Year from 2007-08.

Warmer seas may be thawing ice sheets around the edges, he said, and allow ice to slide off the land into the sea more quickly, adding water to sea levels. But it is hard to be sure because of a lack of long-term observations.

"The same things that defeated Cook - ice and bad weather - are still problems," Dr Carlson said.

About 10 ice shelves, extensions of ice sheets that float on the ocean and can be hundreds of metres thick, have collapsed on the Antarctic Peninsula in the past 50 years. Part of the Wilkins Ice Shelf snapped in April.

And recent studies indicate a slight warming trend in Antarctica, teased out from computer studies of temperature records. Still, most of Antarctica is not going to thaw - the average year-round temperature is -50˚C.

One possibility is to look far back into history. Studies indicate that in the Eemian about 125,000 years ago, for instance, temperatures were slightly higher than now, hippopotamuses bathed in the Rhine - and seas were four metres higher.

"We need to know where the extra four metres came from," said David Vaughan, a glaciologist at the British Antarctic Survey, adding that one possibility was that West Antarctica's ice had collapsed.

He said that an operation to drill through ice - about three kilometres thick to bedrock - could help find out. West Antarctica is vulnerable because its ice rests on rocks below sea level and holds enough ice to raise sea levels by three to six metres.

A sample of rocks beneath the ice would reveal if and when they had last been exposed to cosmic rays - which cause chemical changes that can be read like a clock. There could also be fossils or ancient sediments under the ice to fix dates.

If the ice had collapsed in the Eemian or during other warm periods between - Ice Ages, it would set off global alarm bells about risks of a fast rise in sea levels, Dr Vaughan said. A finding that the ice had been stable would be a huge relief.

In early September, UN Secretary-General Ban Ki-moon said world sea levels could rise by between 0.5 and two metres this century, far higher than most experts have forecast.

Dr Pachauri spoke of a rise of between 18 and 59 centimetres by 2100, excluding a possible acceleration of a thaw of Antarctica or Greenland. Seas rose 17 centimetres in the past century.

And another complicating issue is that experts have found lakes under ice sheets in recent decades, but no one understands whether they might lubricate the slide.