MELTING Antarctic ice is adding so much fresh water into the oceans every year that it could fill Loch Ness 18 times over, according to scientific research published yesterday.
Previously it was thought that the massive ice sheet would actually help mop up some of the sea level rise caused by global warming, because rising temperatures would increase the amount of snow falling on the continent.
However the latest survey - using a new technique to measure the mass of ice with NASA satellites - has become the first to suggest that overall it is in "significant decline". They found it was losing 36 cubic miles a year, enough to raise global sea level by 0.4 millimetres a year.
The Antarctic ice sheet contains 70 per cent of the world's fresh water and if all of it was to melt - along with the more vulnerable Arctic and Greenland ice sheets - sea levels would rise by a catastrophic 84 metres.
Environmentalist campaigners urged the world to go on a "war footing" to fight climate change by reducing greenhouse gas emissions before it was too late.
However, other experts sounded a note of caution about the study, saying that it had been carried out over a relatively short period that might not reflect the overall trend.
The report's chief author, Dr Isabella Velicogna of Colorado University, said: "This is the first study to indicate the total mass balance of the Antarctic ice sheet is in significant decline.
"It showed the glaciers in the west were accelerating and losing more mass. In the east, there have been surveys showing there is growing mass in the interior. What our study showed was the east is in balance between what's growing and what is being lost at the edges."
Two satellites, launched in 2002, orbit the Earth at an altitude of 310 miles, flying one behind the other exactly 137 miles apart. The constant gap between the satellites allows scientists to measure the variation in gravity caused by the massive ice sheet. This can then be used to calculate the mass of ice in particular regions.
A previous report by the Intergovernmental Panel on Climate Change (IPCC), a United Nations' body, predicted that the Antarctic ice sheet as a whole would gain ice as a result of global warming.
Dr Velicogna said: "What we found is the ice sheet is losing mass quite a bit, so we should pay attention. I think we have to be careful. It's unlikely this is going to stop tomorrow."
Dr Richard Dixon, of WWF Scotland, has maintained an optimistic stance - despite warnings from several leading environmentalists who believe global warming is now irreversible - that something can be done to stave off the worst effects of climate change.
But findings of the Colorado study, which appeared yesterday in the online journal Science Express, were further evidence of the need for drastic action, he said. "This is more bad news and very significant. The situation is desperately urgent and really we should be setting things on a war footing. The economy should be switched over to fighting climate change," Dr Dixon said.
"We have got about ten years to get really serious. In 15 years' time, if [greenhouse gas] emissions globally aren't going down instead of going up, then we're in very serious trouble."
However, Professor David Vaughan, of the British Antarctic Survey, said the figures produced were not radically different from previous estimates, despite being produced using a totally different method. Normally scientists base their calculations on measurements of the height of the ice.
And he added: "The record [showing the loss of ice] that's been published is over a very short period. We'd really like several decades of record to be confident the changes we're seeing are long-term trends."
Professor Vaughan said the east Antarctic ice sheet would not be lost completely "within the next few millennia".