Recent studies have implied that projections made earlier this year by the Intergovernmental Panel for Climate Change (IPCC) may badly underestimate the rate at which the oceans will rise -- and thus the devastation they could wreak.

In the first volume of a major report on global warming, published in February, the IPCC said sea levels would climb between 18 and 59 centimetres (7.2 and 23.2 inches) by 2100.

Such an increase could already threaten several small island nations and severely disrupt hundreds of millions of people living in low-lying mega deltas, especially in Asia and Africa.

But these projections did not take into detailed account the impact of any significant loss of land ice in Greenland and the West Antarctic, the IPCC acknowledged on Saturday. It therefore scrapped the upper band.

"It became apparent that, concerning the melting of the Greenland and Antarctic ice sheets, we really don't know enough," IPCC Chairman Rajendra Pachauri told AFP on Saturday in Valencia, Spain, where the body on Saturday published its keenly awaited report.

"There is a possibility, and a fair amount of literature, which suggests that it could be faster than what one has anticipated. Given the uncertainty, it was prudent, and scientifically correct, to remove the upper boundary," he said.

The IPCC is not allowed to include new studies that have not been vetted in its thorough and lengthy review process, so new data on the threat posed by these massive ice bodies were not reflected in its report.

"Over the past several years we have realized that the speed at which changes can occur -- such as ice sheet disintegration and resulting sea-level rise -- is much faster than IPCC has estimated," leading climatologist James Hansen, who heads the NASA Goddard Institute for Space Studies in New York, told AFP ahead of the Valencia meeting.

Bill Hare, one of the lead authors of the IPCC report, said it was impossible to quantify the behaviour of the ice sheets without further knowledge.

"This is why the IPCC is pulling back from giving an upper band. At present, the understanding in the scientific community on this is in flux," he said.

Were the entirety of the continent-sized iceblock covering Greenland to melt, it would lift the world's sea levels by almost seven meters (22.75 feet), swamping most coastal cities.

Western Antarctica, meanwhile, holds enough water to drive up sea levels by as much as six metres (20 feet).

Neither of these doomsday scenarios is on the agenda. But even a relatively small loss of their ice would be important. For coastal dwellers, a rise in sea levels is amplified by storm surges and exceptional tides.

In its February report, the IPCC said sea levels rose globally by 1.8 millimetres (0.07 inches) per year from 1961 to 2003 but this pace accelerated to 3.1 mm (0.12 inch) per year from 1993 to 2003.

Most of the rise was due to thermal expansion because water expands when it warms. The rest was due to runoff from glaciers and snow melting.

Recent studies have pointed to an accelerated melting of glaciers running into the sea in parts of Greenland and Antarctica, possibly because the bases of the glaciers are able to slip more easily at their base than in the past.

One theory is that water from melting ice is boring holes through the ice sheets and sits under the glacier, acting as a lubricant.

Other research, though, has said there is no perceptible change in the great Antarctic icesheet, or there may even have been a thickening of it, at least in one part.

The loss of Arctic ice, though, does not have any impact on sea levels, as this ice floats on water, displacing its own volume.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.