Previous models had shown that efforts to cut greenhouse gas emissions would only slightly slow the Earth's warming by the year 2100, but had not looked further out, said Aiguo Dai of the National Center for Atmospheric Research in Boulder, Colo.

Dai's study on the future of Earth's climate appears in the Dec. 1 issue of Geophysical Review Letters.

"The thing I think is striking is that you see a lot more effect from controlling carbon dioxide (a greenhouse gas) over the next hundred years (from 2099 to 2199)," said Robert Dickinson, a climate modeler at the Georgia Institute of Technology.

And while that's good news, it can only happen if people start reducing greenhouse gas emissions today, he pointed out.

"You're talking about long-time scales," said Dickinson. "This is part of the problem of getting political will (to make changes today)."

Dai's computer-powered peephole into the 21st and 22nd centuries also provided some cautionary news. When the model was run with the assumption that nothing is done to control current greenhouse gas emissions — conditions he calls Business As Usual — global temperatures continue to rise unabated.

In both scenarios, the areas hardest hit by rising temperatures are at high latitudes. And while some people might not consider warmer weather in Alaska, for instance, to be a problem, said Dickinson, the melting of permafrost under buildings, the flood of rainwater into dams that that once fell as snow and the rise in sea level could pose major problems worldwide.

There are several reasons that climate modelers have not previously looked beyond the year 2100, said Dai. One reason is that it takes an awful lot of computer power to run a model into another century. There's also a lot less confidence in the results from a model that ventures too far into the unknown, said Dai.

One of the few areas that's understood well enough to risk such long-range study is global temperature, he said. Climate models can also predict changes in rainfall, winds and storm tracks, but these are less certain when extended beyond 2100, he said.

The take-home message, said Dai, is that there are clear benefits for reducing greenhouse emissions today, for which our great-great-great grandchildren no doubt will be grateful.