Is The Earth Warming Up?

By David Brand

The Great Plains has become a dust bowl, and people are moving north into Canada's uplands to seek work. Even in Alaska, changing ocean currents are boosting the fish catch. New York is sweltering in 95 degrees weather that began in June and will continue through Labor Day. In the Southeast the hot spell started six weeks earlier . . .

That picture of the future is all too familiar to many meteorologists. To some, it makes the drought that is crippling the nation's midsection seem an ominous harbinger of things to come. Because of the greenhouse effect, a process by which natural and man-made gases trap solar heat in the earth's atmosphere, the gradual warming of the globe is inevitable, in the view of many scientists. But until now, most had cautiously avoided definitive statements about precisely when such an effect might take place.

Testifying before a congressional committee last week, James Hansen, an atmospheric scientist who heads NASA's Goddard Institute, riveted Senators with the news that the greenhouse effect has already begun. During the first five months of 1988, he said, average worldwide temperatures were the highest in the 130 years that records have been kept. Moreover, Hansen continued, he - is 99% certain that the higher temperatures are not just a natural phenomenon but the result of a buildup of carbon dioxide (CO2) and other gases from man- made sources, mainly pollution from power plants and automobiles. Said Hansen: "It is time to stop waffling and say that the evidence is pretty strong that the greenhouse effect is here."

His findings were based on monthly readings at 2,000 meteorological stations around the world. The data showed that temperatures over the past century had increased in winter more than in summer, and that areas in high latitudes like Paris and New York had warmed up more than regions near the equator. That was consistent with computer models. "These are all expected signatures of the greenhouse effect," Hansen said. Still, he and other leading scientists warned against concluding that the greenhouse effect is directly responsible for the heat wave that is parching areas of the U.S. "Why didn't we have a drought last summer?" he asks. "You can only say that the probability of drought is increased by the greenhouse effect."

The phenomenon that Hansen describes is actually a natural, beneficial atmospheric process that many scientists believe has gone awry -- perhaps irreversibly. Without the greenhouse effect, life on earth would be a nightmare of subzero temperatures. Instead, naturally produced CO2 and other gases, mainly from plant and animal life, behave in the atmosphere like the glass in a greenhouse: they let the visible warming rays of the sun in but inhibit the escape of infrared rays back into space.

Since the Industrial Revolution, however, increased production of CO2 and other gases, such as nitrous oxide, has made the protective atmospheric shroud even denser. If scientists are correct, the atmospheric blanket of pollutants is now capturing far more of the earth's excess heat, resulting in global warming.

Hansen contends that over the past century worldwide temperatures have risen by about 1.2 degrees F, compared with the natural variation over such a period of only 0.4 degrees F. "Warming has been sufficient that it is unlikely to have been accidental," he notes. But other scientists question whether this can be attributed to the greenhouse effect. Stephen Schneider of the National Center for Atmospheric Research in Boulder agrees with Hansen that this has been the warmest decade on record and that the planet is gradually heating up. But the evidence, he says, is circumstantial. Contends Schneider: "It doesn't prove the greenhouse effect."

Other scientists note that global climate moves in broad historical cycles of warming and cooling tens of thousands of years long. Astronomical cycles, volcanoes, the interplay of deserts, oceans, cloud cover, even the methane produced by termites, can affect the density of the atmospheric greenhouse. Declares Chester Ropelewski, a climate specialist with the Maryland-based Climate Analysis Center: "It's still not clear whether this is the CO2 signal. The hard evidence isn't there."

Whether the greenhouse effect has arrived or not, some scientists calculate that global temperatures could increase between 3 degrees and 9 degrees F by the year 2050. If that happens, even hotter, dryer summers are on the way, probably accompanied by a gradual melting of polar ice caps and glaciers that will cause sea levels to rise several feet by mid-century. By then it is probable that more CO2 production, from sources as diverse as industry and rampant deforestation, will play an increasingly important role in heating up the earth. Even Hansen's scientific critics hope his testimony, however premature, will prod people into taking measures to ease the greenhouse effect by conserving energy and cutting back on burning fossil fuels. The alternative, though, may be even less pleasant for many. As Democratic Senator Wendell Ford of Kentucky pointed out last week, the only major energy source that might replace fossil-fuel plants is nuclear power.

With reporting by Andrea Dorfman/New York and Dick Thompson/Washington