Antarctica lost more ice in last 10 years: study

Deborah Zabarenko, Reuters 14 Jan 08;

Antarctica's contribution to global sea level rise was about 0.02 inch in 2006, compared to about 0.01 inch in 1996.

WASHINGTON (Reuters) - Antarctica lost billions of tons of ice over the last decade, contributing to the rising seas around the world, a climate researcher said on Monday.

The ice melted from two particular parts of the southern continent, according to Eric Rignot and colleagues, who wrote about the phenomenon in the journal Nature Geoscience.

Using satellites to monitor most of Antarctica's coastline, the scientists estimate that West Antarctica lost 132 billion tons of ice in 2006, compared to about 83 billion tons in 1996. The Antarctic Peninsula, which stretches toward South America, lost about 60 billion tons in 2006.

To put this in perspective, 4 billion tons of ice would be enough to provide drinking water to the more than 60 million people of the United Kingdom for a year, fellow author Jonathan Bamber of the University of Bristol said in a statement.

This ice loss is not from the so-called ice sheets that cover the water around the continent. This melting occurred in the glaciers that cover much of the Antarctic land mass, and when that melts, it contributes to sea level rise in a way that sea ice does not.

"One immediate consequence (of the melting Antarctic ice) is to raise sea level," Rignot, of the Jet Propulsion Laboratory, said in an e-mail interview. Antarctica's contribution to global sea level rise was about 0.02 inch in 2006, compared to about 0.01 inch in 1996.

Rignot noted that the U.N. Intergovernmental Panel on Climate Change figured Antarctica would not contribute at all to sea level rise, and in fact predicted a growth of the big ice sheet the covers much of the continent from enhanced precipitation.

This prediction was supposed to come from increased evaporation from the oceans as the planet warmed up, but this has not been observed so far in Antarctica, Rignot said.

"In some regions the ice sheet is close to warm sources of water. ... The parts of Antarctica we are seeing change right now are closest to these heat sources," he said.

These findings are in line with what is happening to the Greenland ice sheet, which melted at a record rate last year, and with studies of Arctic sea ice, which ebbed to its lowest level ever measured in 2007.

A study last week by researchers at the University of Colorado at Boulder found that older, thicker Arctic sea ice that lasts from year to year is giving way to younger, thinner sea ice that is more susceptible to melting.

(Editing by Jackie Frank)

Loss of Antarctic ice has soared by 75 per cent in just 10 years
Steve Connor, The Independent 14 Jan 08;

Parts of the ice sheets covering Antarctica are melting faster than predicted, with the net loss of ice probably accelerating in recent years because of global warming, a study has found.

A satellite survey between 1996 and 2006 found that the net loss of ice from Antarctica rose by about 75 per cent as the movement of glaciers towards the sea speeded up.

Scientists estimate that that the West Antarctic Ice Sheet lost about 132 billion tons of ice in 2006, compared with a loss of 83 billion tons in 1996. In addition, the Antarctic peninsula lost about 60 billion tons of ice in 2006.

"To put these figures into perspective, 4 billion tons of ice is enough to provide drinking water for the whole UK population for one year," said Professor Jonathan Bamber, of the University of Bristol. "We think the glaciers of the Antarctic are moving faster to the sea. The computer models of future sea-level rise have not really taken this into account."

Sea levels are estimated to have risen by 1.8mm a year on average during the 20th century, but data from the past decade or so suggest that the average rise is now about 3.4 mm per year.

Computer models used by the Intergovernmental Panel on Climate Change (IPCC), which predict that sea levels will rise by no more than about 50cm by 2100, are based largely on the stability of the Antarctic ice sheets. But many scientists now believe this forecast is too restrained. "I agree with a number of scientists who feel the IPCC is likely to have underestimated the upper bound of predicted sea-level rise by the end of the century – 50 cm is probably too conservative," Professor Bamber added.

There are two key factors in estimating the net loss of Antarctic ice. The first is the flow of glaciers towards the sea; the second is the build-up of snow over the vast landmass of the frozen continent. The IPCC models imply that global warming will increase the moisture content of the atmosphere and so may actually increase snowfall over Antarctica, much of which is too cold to be affected by rising global temperatures. This would suggest a net build-up of ice. However, Professor Bamber believes the IPCC's models have not taken into account the complex, dynamic interaction between the ocean and the ice shelves of West Antarctica and the Antarctic Peninsula, which are warmer than East Antarctica.

Eric Rignot, who led the latest study published in the journal Nature Geoscience, said the findings indicated a rapid loss of ice to the sea rather than a net gain. "We have determined that the loss is increasing with time, quite rapidly at 75 per cent in ten years," Dr Rignot said. "We have also established that most of this loss, if not its entirety, is caused by glacier acceleration. The IPCC focussed on the surface mass balance component. We find this component is not indicative of the true mass balance."

The acceleration in ice loss over the past 10 years could increase in coming decades, he added. "As some of these glaciers reach deeper beds, their speeds could double or triple, in which case the contribution to sea-level rise from Antarctica could increase quite significantly beyond what it is now. Many people suspect Antarctic ice to be immune from changes. We are finding this is not the case.

"The future is the big question. The potential exists for ice speed to increase two or three times, which will result in a doubling of the mass deficit from Antarctica."

Melting into history

* July 1985: UK scientists detect hole in ozone layer

* January 1995: Larsen A ice shelf disintegrates

* July 1998: Evidence suggests future collapse of West Antarctic ice sheet

* March 2000: An iceberg 183 miles long and 22 miles wide breaks adrift

* February 2002: Larsen B ice shelf collapses

* October 2003: World's largest iceberg splits

* March 2006: Research shows shrinking ice has raised sea levels by 1.2mm

* September 2007: Sea ice covering Antarctica melts back to record low