''We certainly aren't going to stop that 18-wheeler that's rolling down the hill. In the short term, I'm not sure that anyone can stop it," said John Walsh, director of the Center for Global Change and Arctic System Research at the University of Alaska in Fairbanks.
''The big payoff is going to be for our children," said Tim Barnett, a senior scientist at the Scripps Institution of Oceanography in California.
''Together, if we take a concentrated action as a people, we might be able to slow it down enough to avoid these surprises," Barnett added.
Nearly two dozen computer models agree that by 2100, the average yearly global temperature will be 3 to 6 degrees higher than now, said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research.
Even if today the world suddenly stops producing greenhouse gases, temperatures will rise 1 degree by 2050, the organization said.
A British conference with an aim, it said, of ''avoiding dangerous climate change" concluded last year that a rise of just 3 degrees would probably lead to some catastrophic events, especially the melting of Greenland's polar ice.
A study in the journal Science last month said that the melting, which is happening faster than originally thought, could trigger a 1- to 3-foot rise in global ocean levels.
Stephen Schneider of Stanford University put the odds of a massive Greenland melt at 50-50.
But the chief scientist for the nonprofit ecological group Environmental Defense, Bill Chameides, expressed more hope. ''There's a certain amount of warming that's inevitable, but that doesn't mean that we can't avoid the really dangerous things," he said.
Those dangerous things include multicentury melts of polar ice sheets and an accompanying major sea-level rise, abrupt climate change from a dramatic slowing of the ocean current systems, and the permanent loss of glacier-fed ancient water supplies for China, India, and parts of South America.
Despite what scientists say, 70 percent of Americans think it is possible to reduce the effects of global warming, and 59 percent say their individual actions can help, according to a poll commissioned by Environmental Defense as part of its public service campaign.
