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The changing weather is apparently connected with differences in the amount of energy that the earth's surface receives from the sun. Changes in the earth's tilt and distance from the sun could, for instance, significantly increase or decrease the amount of solar radiation falling on either hemisphere—thereby altering the earth's climate. Some observers have tried to connect the eleven-year sunspot cycle with climate patterns, but have so far been unable to provide a satisfactory explanation of how the cycle might be involved.
Man, too, may be somewhat responsible for the cooling trend. The University of Wisconsin's Reid A. Bryson and other climatologists suggest that dust and other particles released into the atmosphere as a result of farming and fuel burning may be blocking more and more sunlight from reaching and heating the surface of the earth.
Climatic Balance. Some scientists like Donald Oilman, chief of the National Weather Service's long-range-prediction group, think that the cooling trend may be only temporary. But all agree that vastly more information is needed about the major influences on the earth's climate. Indeed, it is to gain such knowledge that 38 ships and 13 aircraft, carrying scientists from almost 70 nations, are now assembling in the Atlantic and elsewhere for a massive 100-day study of the effects of the tropical seas and atmosphere on worldwide weather. The study itself is only part of an international scientific effort known acronymically as GARP (for Global Atmospheric Research Program).
Whatever the cause of the cooling trend, its effects could be extremely serious, if not catastrophic. Scientists figure that only a 1% decrease in the amount of sunlight hitting the earth's surface could tip the climatic balance, and cool the planet enough to send it sliding down the road to another ice age within only a few hundred years.
The earth's current climate is something of an anomaly; in the past 700,000 years, there have been at least seven major episodes of glaciers spreading over much of the planet. Temperatures have been as high as they are now only about 5% of the time. But there is a peril more immediate than the prospect of another ice age. Even if temperature and rainfall patterns change only slightly in the near future in one or more of the three major grain-exporting countries the U.S., Canada and Australia global food stores would be sharply reduced. University of Toronto Climatologist Kenneth Hare, a former president of the Royal Meteorological Society, believes that the continuing drought and the recent failure of the Russian harvest gave the world a grim premonition of what might happen. Warns Hare: "I don't believe that the world's present population is sustainable if there are more than three years like 1972 in a row."