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These are all worst-case scenarios, and the report's authors acknowledge that plenty of uncertainties remain in their analysis. For example, as the world warms up, it should get cloudier; depending on what sort of clouds predominate, their shadows could offset the warming effect. And nobody knows how the deep ocean currents--which play a major but still murky role in world climate, channeling heat from one part of the globe to another--would respond to global warming.
Some researchers argue that even with these caveats the report overstates the case. Says Richard Lindzen, an atmospheric scientist at M.I.T.: "The margin of error in these models is a factor of 10 or more larger than the effect you're looking for."
Even if Lindzen is wrong and the IPCC report is right, there might not be much anyone could do. Slashing emissions of greenhouse gases to stave off global warming would be straightforward enough, but that doesn't mean it would be easy. Among the strategies recommended in the new report: switching from coal and oil to natural gas, turning to nuclear and solar energy, slowing deforestation, altering land-use and traffic patterns, curbing automobile use, changing life-styles and employment patterns.
In other words, people in the developed world would have to completely transform their society, and rich countries like the U.S. would have to subsidize poor but fast-developing nations like China. And that's just to roll CO2 emissions back to 1990 levels, the goal most environmentalists endorse. To stave off global warming completely, Lindzen maintains, "you would have to reduce emissions to where they were in 1920." Despite noble proclamations issuing from meetings like the 1992 Earth Summit in Rio, that is virtually inconceivable. As economist Henry Jacoby of M.I.T.'s Sloan School of Management puts it, "If you said, 'Let's design a problem that human institutions can't deal with,' you couldn't find one better than global warming."
Even a Democrat-controlled, Al Gore-inspired Congress would shrink from passing draconian emissions-control measures. And the current Republican House and Senate are unlikely to consider such regulations no matter how many scientists are convinced that global warming is real. Other industrial nations probably won't do much better, and poor countries can't afford to try. A more realistic strategy, some scientists argue, is to spend what research money there is figuring out how best to deal with global warming when it comes. It's already too late, they say, to do much else.
--Reported by David Bjerklie/New York and Michael Riley/Washington