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Remember Global Cooling?
Why scientists find climate change so hard to predict.
Imaginechina (left); detail from 4/28/1975 Newsweek article
Oct. 23, 2006 - In April, 1975, in an issue mostly taken up with stories about the collapse of the American-backed government of South Vietnam, NEWSWEEK published a small back-page article about a very different kind of disaster. Citing "ominous signs that the earth's weather patterns have begun to change dramatically," the magazine warned of an impending "drastic decline in food production." Political disruptions stemming from food shortages could affect "just about every nation on earth." Scientists urged governments to consider emergency action to head off the terrible threat of . . . well, if you had been following the climate-change debates at the time, you'd have known that the threat was: global cooling.
More than 30 years later, that little story is still being quoted regularly—as recently as last month on the floor of the Senate by Republican Sen. James Inhofe, chair of the Environment and Public Works Committee and the self-proclaimed scourge of climate alarmists. The article's appeal to Inhofe, of course, is not its prescience, but the fact that it was so spectacularly wrong about the near-term future. Even by the time it appeared, a decades-long trend toward slightly cooler temperatures in the Northern hemisphere had already begun to reverse itself—although that wouldn't be apparent in the data for a few years yet—leading to today's widespread consensus among scientists that the real threat is actually human-caused global warming. In fact, as Inhofe pointed out, for more than 100 years journalists have quoted scientists predicting the destruction of civilization by, in alternation, either runaway heat or a new Ice Age. The implication he draws is that if you're not worried about being trampled by a stampede of woolly mammoths through downtown Chicago, you don't have to believe what the media is saying about global warming, either.
But is that the right lesson to draw? How did NEWSWEEK—or for that matter, Time magazine, which also ran a story on the subject in the mid-1970s—get things so wrong? In fact, the story wasn't "wrong" in the journalistic sense of "inaccurate." Some scientists indeed thought the Earth might be cooling in the 1970s, and some laymen—even one as sophisticated and well-educated as Isaac Asimov—saw potentially dire implications for climate and food production. After all, Ice Ages were common in Earth's history; if anything, the warm "interglacial" period in which human civilization evolved, and still exists, is the exception. The cause of these periodic climatic shifts is still being studied and debated, but many scientists believe they are influenced by small changes in the Earth's orbit around the Sun (including its "eccentricity," or the extent to which it deviates from a perfect circle) and the tilt of its rotation. As calculated by the mathematician Milutin Milankovitch in the 1920s, these factors vary on interlocking cycles of around 20,000, 40,000 and 100,000 years, and if nothing else changed they would be certain to bring on a new Ice Age at some time. In the 1970s, there were scientists who thought this shift might be imminent; more recent data, according to William Connolley, a climate scientist at the British Antarctic Survey who has made a hobby of studying Ice Age predictions, suggest that it might be much farther off.
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