Scientists detect huge increase in Antarctic ice melt

Global warming has caused annual ice loss from the Antarctic ice sheet to surge by 75 percent in a decade, according to the most detailed survey ever made of the white continent's coastal glaciers.

In 2006, accelerating glaciers spewed an estimated 192 billion tonnes of Antarctic ice into the sea, scientists calculate.

The West Antarctica ice sheet lost some 132 billion tonnes, while the Antarctic Peninsula, the tongue of land that juts up towards South America, lost around 60 million tonnes.

But there was a "near-zero" loss in East Antarctica, the world's biggest ice sheet, the paper says.

Investigators from five countries, led by Eric Rignot of NASA's fabled Jet Propulsion Laboratory, used interferometry radar from four satellites to build a picture of the periphery of Antarctica.

They sought to measure the velocities of glaciers that shift ice to the coast from the massive sheets that cover Antarctica's bedrock.

They built up a picture of around 85 percent of Antarctica's coastline thanks to the data supplied by the European Space Agency's two Earth Remoting Sensing satellites, the Canadian Radarsat-1 and Japan's Advanced Land Observing satellites.

"Over the time period of our survey, the ice sheet as a whole was certainly losing mass, and the mass loss increased by 75 percent in 10 years," said the study, published online by the specialist journal Nature Geoscience.

"Most of the mass loss is from the Pine Island Bay sector of West Antarctica and the northern tip of the Peninsula, where it is driven by ongoing, pronounced glacier acceleration.

"In East Antarctica, the loss is near zero, but the thinning of its potentially unstable marine sectors calls for attention," it said.

The loss of 192 billion tonnes is more than twice the annual flow of the river Nile when it reaches the sea, according to a calculation by AFP.

Seen by another yardstick, it is equivalent to an annual rise in global sea levels of about 0.5 mm, if factors such as evaporation and effects on precipitation are not factored in.

By comparison, sea levels rose by between 10cm and 20cm from 1900 to 2006, the Nobel-winning Intergovernmental Panel on Climate Change (IPCC) reported last year.

It forecast a rise of at least 18cm by 2100, mainly as a result of thermal expansion, because water expands when it warms.

The IPCC declined to set an upper figure to this estimate specifically because of uncertainty about ice melt from Antarctica and Greenland.

The new study says glaciers are likely to determine whether these vast stores of frozen water remain stable or leak.

From 1980 to 2004, snowfall over Antarctica was unchanged or was even above normal in the regions where there was the biggest ice loss, it notes.

Previous research has found two big factors that can cause a glacier to build up speed.

One is the loss of ice shelves, on the coast. These act rather like corks, bottling up the movement of the glacier.

When the shelf breaks up as a result of warmer seas, the glacier can flow into the sea unimpeded.