The rapid breakdown of the floating ice shelves observed in recent years, the experts said, could destabilize land-based ice sheets and glaciers behind them and cause faster melting and rise in sea levels than anticipated.

Current projections for rises in sea levels do not take into account the new hypothesis, said Peter Clark, professor of geosciences at Oregon State University.

"We may be more vulnerable to sea level rise than we thought and it may be more rapid than we have anticipated," Clark said. "This is an issue we should take very seriously."

Current projections in climate models suggest that global warming during the next century or two will cause thermal expansion of water and some melting of glacial ice chiefly in Greenland.

However, that may be largely offset by increased precipitation and glacial buildup in Antarctica, leading to increased sea level of about 50 centimeters

(20 inches) the scientists said.

The breakdown of glaciers currently being studied, said Clark, could double the sea level rise to a full meter.

And in a span of about 1,000 years, he added, the Greenland ice sheet may disappear, raising Earth's sea level by about six meters (20 feet). Glacial breakdown mechanisms currently being studied could speed that up considerably.

"It's become clear that the West Antarctic Ice Sheet, much of which sits on land that's actually below sea level, is one of the most vulnerable in the world to these types of rapid breakdowns," Clark said.

"The real problem would occur if these smaller glacial breakups trigger larger ones, and rising sea levels by themselves might cause a feedback mechanism which would further speed up the process," the scientist added.