Ice loss could push sea levels above estimates: report

David Fogarty, Reuters 12 Jun 09;

SINGAPORE (Reuters) - Increasing loss of ice from Antarctica and Greenland could cause sea levels to exceed U.N. estimates by 2100, an Australian government-backed report says, with the extent of the rise still uncertain.

The U.N. Climate Panel says seas could rise by 18-59 cm (7-24 inches) by 2100. It also raised the possibility of an additional 20 cm rise if polar ice sheets dumped ever greater amounts of ice into the ocean.

That assessment was based on scientific knowledge up to 2005.

"There is now emerging evidence that sea level rise by 2100 might exceed this," says the report released on Friday that reviews the latest science and is meant to guide policy-makers.

"Although it is unlikely that total sea level rise by 2100 will be as high as 2 meters, the probable upper limit of a contribution from ice sheets remains uncertain," said the report by the Antarctic Climate and Ecosystems Cooperative Research Center in Hobart, Tasmania.

A rise of even one meter would force millions along Bangladesh's low-lying coast to move inland and trigger mass migration in Vietnam's Mekong Delta. Major coastal cities around the globe would need taller sea defenses or risk being swamped.

"The ice that's being lost is Antarctica is being lost not by surface melt. The continent is very cold. But it's being lost by increasing discharge from glaciers," Ian Allison, one of the report's authors, said in an online briefing on Friday.

"Some of the large glaciers in West Antarctica have sped up and they are pushing more ice out into the ocean," said Allison, leader of the Australian Antarctic Division's ice, ocean, atmosphere and climate program.

The same was also occurring in Greenland, in addition to increased melting of ice near the coast.

SHRINKING SEA ICE

The report says sea levels were rising at the upper end of U.N. climate panel projections and that evidence suggested the Greenland and Antarctic icesheets were contributing more to present sea-level rise than was previously estimated.

The total ice stored in ice sheets on both landmasses would raise sea levels by nearly 65 meters if it all melted.

East Antarctica, where most of the ice is locked up, remains stable for now, studies show.

But in West Antarctica, much of the ice sits on bedrock up to 2 km below sea level and was at great risk of collapse if warming seas eroded protective ice shelves.

The ice would be susceptible to rapid decay if it thinned and progressively began to float away, the report said, which called for greater research to better estimate how much the loss of ice would raise sea levels.

A study released last month showed that a meltdown of West Antarctica's ice sheet would raise sea levels by 3.3 meters, half what was previously thought, but the impact would still be catastrophic, especially for U.S. coastal cities.

The center, in a separate report released on Friday, also warned of the risks from shrinking sea ice at the poles.

Floating sea ice helps regulate the climate by reflecting large amounts of solar radiation and drives ocean circulation patterns.

It is also crucial to seals, polar bears, penguins and as a refuge for tiny creatures called krill, a key component of the food chain.

"In response to a warming climate, sea ice is forecast to reduce by 24 percent in extent and 34 percent in volume by 2100," said the study.

The Arctic has already suffered rapid loss in the extent of summer sea ice and some scientists estimate it could be ice-free as early as 2013.

(Editing by Sugita Katyal)