WASHINGTON - A man stands on a railroad track as a train rumbles closer.
"Global warming?" he says. "Some say irreversible consequences are 30 years away. Thirty years. That won't affect me."
He steps off the tracks -- just in time. But behind him is a little girl, left in front of the roaring train.
Britain on Thursday said the country's emissions of carbon dioxide, the main greenhouse gas blamed for global warming, crept up last year in the third consecutive annual increase. REUTERS/File
The screen goes black. A message appears: "There's still time."
It's just an ad, part of a campaign from the advocacy group Environmental Defense, which hopes to convince Americans they can do something about global warming, that there's still time.
But many scientists are not so sure that the oncoming train of global warming can be avoided. Temperatures are going to rise for decades to come because the chief gas that causes global warming lingers in the atmosphere for about a century.
"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.
There are limits, experts say, to how much individuals can do. The best we can hope for is to prevent the worst -- world-altering disasters such as catastrophic climate change and a drastic rise in sea levels, say 10 leading climate scientists interviewed by The Associated Press. They pull out ominous phrases such as "point of no return."
The big disasters are thought to be just decades away. Stopping or delaying them would require bold changes by people and government.
"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."
But he and other scientists say it's too late to stop people from feeling the heat. Nearly two dozen computer models agree that by 2100, the average global temperature will be 3 to 6 degrees Fahrenheit higher than now, according to 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, according to the center.
A British conference on "avoiding dangerous climate change" last year concluded that a rise of just 3 degrees would probably lead to some catastrophic events, especially the melting of the Greenland's polar ice. A study in the journal Science last month said the melting, which is happening faster than originally thought, could trigger a rise of 1 to 3 feet in global ocean levels.
Stephen Schneider of Stanford University put the odds of a massive Greenland melt at 50-50.
But Environmental Defense chief scientist Bill Chameides is more hopeful: "There's a certain amount of warming that's inevitable, but that doesn't mean that we can't avoid the really dangerous things that are happening."
Those dangerous things include: multi-century 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's possible to reduce the effects of global warming, and 59 percent think their individual actions can help, according to a poll commissioned by Environmental Defense as part of its public service campaign.
Climate scientists find themselves in the delicate position of trying to balance calculations that lead to scientific despair with an optimistic public's hope.
"You don't give up," said Schneider, co-director of Stanford's Center for Environmental Science Policy. "If you have high blood pressure, do you sit there till you die or do you take Lasix," the blood pressure medicine.
Both Barnett and Walsh said the question they get most from the public is: What can I do personally about global warming? They tell people to drive less and drive fuel-miserly cars, be more efficient about heating their homes.
But those efforts "are not going to change us from an irreversible course to a reversible one," said Walsh. "What you really want to say is: 'You can't go on like this. We can't go on like this."'
Robert Correll, a top scientist in charge of an eight-country research program into arctic problems caused by global warming, recognizes the contradictions, especially since developing nations such as China, India and those in Africa will play bigger roles in greenhouse gas pollution in the future.
The individual effort, Correll said, "is damn important, but you're not going to make much difference." That requires group or governmental action, he said.
© 2006 Associated Press