Is The Earth Warming Up?

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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.