The buildup of scientific evidence has heightened the sense of urgency about responding to the greenhouse threat, and it's no longer just environmentalists who are talking the loudest. Among the advocates of action are representatives of the insurance industry, which could be financially devastated by more frequent killer storms. Says Kaj Ahlmann, president of Employers Reinsurance Corp. of Overland Park, Kansas: "Global climatic change is probably the single most important issue facing the world today."

So far, the world's governments have paid mostly lip service to the idea of heading off global warming. The goal of the climate agreement forged at the 1992 Earth Summit, in which nations pledged to work toward cutting their greenhouse-gas emissions back to 1990 levels by the year 2000, is seen as wholly inadequate and no longer possible to achieve anyway. That puts the onus on a U.N. meeting this December in Kyoto, Japan, where delegates will try to seal a much stronger climate treaty. The European Union has declared that greenhouse emissions should be 15% below their 1990 levels by the year 2010.

That won't happen, however, without the leadership of the U.S., the biggest producer of greenhouse gases. With only 4% of the world's population, America is responsible for 22% of the carbon emissions. President Clinton has vowed that the U.S. will agree to "binding limits" on the amount of gas it spews into the atmosphere but has been slow to offer specifics. The challenge for the U.S. and other countries is to curb the greenhouse effect without stalling their economies. The most forceful approach--hiking taxes on the use of fossil fuels--has little chance to win approval in the American Congress. But Mike MacCracken, director of the White House's Interagency Office of Global Change Policy, contends that the U.S. can slash greenhouse emissions 30% with a host of strategies that everyone could support, including the planting of trees to absorb carbon dioxide, the development of more fuel-efficient cars and the installation of electricity-producing solar panels on 1 million American roofs by the year 2010.

At the moment, though, the dangerous plumes of heat-trapping gases are still increasing in volume. And the longer the world's nations wait to respond, the more costly the response will be. The future will always be full of uncertainties that scientists can never fully resolve, but after studying all the evidence pointing to global warming, many researchers are convinced of the immediate need to act. "Time," warns Santer, "is a luxury we may not have."