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The precise chemical process is still uncertain, but the central role of CFCs is undeniable. Last month Barney Farmer, an atmospheric physicist at the Jet Propulsion Laboratory in Pasadena, Calif., announced that his ground-based observations as a member of the 1986 Antarctic National Ozone Expedition pointed directly to a CFC-ozone link. "The evidence isn't final," he said, "but it's strong enough." Earlier this month, results from NASA's Punta Arenas project confirmed the bad news. Not only was the ozone hole more severely depleted than ever before -- fully 50% of the gas had disappeared during the polar thaw, compared with the previous high of 40%, in 1985 -- but the CFC connection was more evident. Notes Sherwood Rowland, a chemist at the University of California at Irvine: "The measurements are cleaner this time, more detailed. They're seeing the chemical chain more clearly."
Atmospheric scientists have long known that there are broad historical cycles of global warming and cooling; most experts believe that the earth's surface gradually began warming after the last ice age peaked 18,000 years ago. But only recently has it dawned on scientists that these climatic cycles can be affected by man. Says Stephen Schneider, of the National Center for Atmospheric Research in Boulder: "Humans are altering the earth's surface and changing the atmosphere at such a rate that we have become a competitor with natural forces that maintain our climate. What is new is the potential irreversibility of the changes that are now taking place."
Indeed, if the ozone layer diminishes over populated areas -- and there is some evidence that it has begun to do so, although nowhere as dramatically as in the Antarctic -- the consequences could be dire. Ultraviolet radiation, a form of light invisible to the human eye, causes sunburn and skin cancer; in addition, it has been linked to cataracts and weakening of the immune system. Without ozone to screen out the ultraviolet, such ills will certainly increase. The National Academy of Sciences estimates that a 1% drop in ozone levels could cause 10,000 more cases of skin cancer a year in the U.S. alone, a 2% increase. These dangers were enough to spur representatives of 24 countries, gathered at a United Nations-sponsored conference in Montreal last month, to agree in principle to a treaty that calls for limiting the production of CFCs and similar compounds that wreak havoc on the ozone.
Potentially more damaging than ozone depletion, and far harder to control, is the greenhouse effect, caused in large part by carbon dioxide (CO2). The effect of CO2 in the atmosphere is comparable to the glass of a greenhouse: it lets the warming rays of the sun in but keeps excess heat from reradiating back into space. Indeed, man-made contributions to the greenhouse effect, mainly CO2 that is generated by the burning of fossil fuels, may be hastening a global warming trend that could raise average temperatures between 2 degrees F and 8 degrees F by the year 2050 -- or between five and ten times the rate of increase that marked the end of the ice age. And that change, notes Schneider, "completely revamped the ecological face of North America."