Ice loss could push sea levels above estimates - report

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

The UN Climate Panel says seas could rise by 18-59 cm 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 yesterday, 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 two metres, the probable upper limit of a contribution from ice sheets remains uncertain," said the report by the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart, Tasmania.

A rise of even one metre 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 defences 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," remarked Ian Allison, one of the report's authors, yesterday.

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

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

The report says sea levels were rising at the upper end of UN climate panel projections and that evidence suggested the Greenland and Antarctic ice sheets 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 metres 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 two kilometres 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.