Quietly, but with increasing force, consensus is building among many scientists that international action may be needed to avert a profound increase in global temperatures during the next century. The predicted shift would result from a buildup of carbon dioxide (CO2) and other gases in the atmosphere. The process has been dubbed the ``greenhouse effect,'' because the gases trap solar heat energy in the atmosphere much like a greenhouse.
Earlier this week, the Senate Subcommittee on Toxic Substances and Environmental Oversight held hearings on the greenhouse effect. Sen. Albert Gore Jr. (D) of Tennessee said he planned to introduce legislation to expand research into the greenhouse effect and declare an ``international year of scientific study'' of the effect.
There have been sharp disagreements among scientists over what the greenhouse effect could lead to: Some suggest it could melt part of the polar icecaps, sending world sea levels catastrophically upward, and dramatically rearrange the global distribution of deserts and vegetation, all in the next century.
Others say those warnings are greatly exaggerated and don't take into account vital factors about the earth and its climate, of which little is currently known. ``We can't actually prove a lot of these things scientifically,'' states Dr. Charles Bowen, a University of Wisconsin glaciologist.
Researchers calling for development of public policies to deal with potential effects of the greenhouse phenomenon agree that many of the most complex and subtle aspects of Earth's climate still elude understanding. But after years of measuring atmospheric gas levels and concocting and refining equations, they add that enough pieces of the puzzle have been put in place to suggest a certain picture of the way the greenhouse process will affect Earth.
``Of course, there is a possibility we could be wrong,'' says Dr. Syukuro Manabe, a meteorologist with the National Atmospheric and Oceanic Administration. ``But let me put it this way: If after all the carbon dioxide we have been pumping into the atmosphere, the climate doesn't change by the next century, I'll be a very, very suprised person.''
Since the 19th century, researchers have warned that burning fossil fuels like coal and oil might pump enough CO2 into the air to alter the atmosphere's makeup. Only in the past decade or so, however, have researchers predicted that the amount of CO2 in the atmosphere will double from its pre-industrial-age levels some time during the second half of the next century. Based on complex mathematical models, they say, that could mean that the average surface temperature on Earth could increase between 3 to 10 degrees Fahrenheit, beginning around the turn of the century.
This fall, scientists from 29 countries convened in Villach, Austria, to weigh the available body of scientific evidence on the greenhouse effect. They concluded that world temperatures would perhaps rise higher than any on record, and that subsequent melting of polar ice caps and rising sea levels would come in the first half of the 21st century. They said that governments should begin developing economic and social plans based on those assumptions, and that ``it is a matter of urgency to refine estima tes of future climate conditions.''