14 Jan 2008, 1952 hrs IST,AFP

PARIS: Global warming has caused annual ice loss from the Antarctic ice sheet to surge by 75 per cent 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 icesheet, the paper says.

Investigators from five countries, led by Eric Rignot of NASA's fabled Jet Propulsion Laboratory (JPL), 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 per cent of Antarctica's coastline thanks to the data supplied by the European Space Agency's two Earth Remoting Sensing (ERS) 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," according to 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, but the thinning of its potentially unstable marine sectors calls for attention."

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 news agency.

Seen by another yardstick, it is equivalent to an annual rise in global sea levels of about 0.5 mm (0.02 of an inch), if factors such as evaporation and effects on precipitation are not factored in.

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

It forecast a rise of at least 18 cms (17.2 inches) by 2100, mainly as a result of thermal expansion, for water expands when it warms. The IPCC declined to set an upper figure to this estimate specifically because of uncertainty about icemelt 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 1980-2004, 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.

Another factor is water from melted snow that penetrates the glacier through cracks and shafts known as moulins. The water then acts as lubricant beneath the glacier, enabling it to move faster.

David Vaughan, a professor at the British Antarctic Survey (BAS), said a consensus was emerging, after several years of doubt and debate, that Antarctica was contributing to sea-level rise.
"For the future, we will need more of this type of study quantifying the change, and more studies out on the ice, to determine why the changes are occurring, so we can predict whether they will increase in future."

Around 70 per cent of the world's fresh water is stored in Antarctica. The loss of either of the continent's icesheets or of Greenland would drive up ocean levels by many metres (feet), drowning highly-populated delta regions and low-lying states and amplifying dangerous storm surges.

But that is a doomsday scenario which does not feature in any of the IPCC's projections.

Loss of water from ice sheets on land adds to sea levels, whereas loss of sea ice does not. Ice that floats on the ocean -- such as at the North Pole -- displaces its own volume.

Link to original article: http://timesofindia.indiatimes.com/Opinion/Planet_SOS/Global_Warming/Ice_loss_is_accelerating/articleshow/2699841.cms