One Gigantic Wild Card In Global Warming

NEW YORK, Feb. 3, 2007 — -- The findings in the new report are sobering enough -- that the world's scientists agree global warming is "unequivocal" and irreversible: Manmade greenhouse gases are shooting up -- driving the rise in earth's temperature and sea level, and the decline in earth's snow cover.

But there's a massive unknown worrying the scientists: Sea levels could rise in the coming decades faster than anyone thought.

Ominous news in the fourth unanimous assessment in 20 years by the IPCC [Intergovernmental Panel on Climate Change], just finalized at a plenary session in Paris, sets the stage: The human-induced warming has now reached down more than a mile to normally frigid deep ocean currents -- currents that for millions of years have acted as a massive cooling system for the planet.

Water expands as it heats up, so scientists can now calculate that sea level will rise up between seven inches and nearly two feet before the end of the century.

But there's also an enormous wild card: It's the Greenland Ice Sheet, two miles thick at its center and containing enough ice to raise the world's oceans 23 feet.

It's melting so fast lately that the scientists in Paris couldn't settle on any predictions for it.

"We don't know what the likelihood is that part of those ice sheets might suddenly destabilize," climate scientist Richard Somerville, standing not far from the Eiffel Tower, told ABC News.

Somerville, one of the grandfathers of accurate global warming prediction, had just emerged from a week of intense IPCC consensus-seeking among scientists and public officials from 113 nations.

He described the slow, inclusive and painstaking IPCC assessment process as unprecedented in the history of the world's science, and "the gold standard" for climate prediction.

Back in the United States, NASA-Goddard glaciologist Waleed Abdalati, who has been watching Greenland for years, confirms the possibility that Greenland could well hold unpleasant surprises.