Climate Change: Prediction Perils

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.

But in any case, climatologists now are mostly agreed that human impacts will swamp the effects of the Milankovitch cycles. The question has been, which specific impacts? In the mid-1970s, scientists were focusing on an increase of dust and "aerosols" (suspended droplets of liquid, mostly sulfuric acid) in the atmosphere. These, the result of increased agriculture and burning of coal in power plants, lower the Earth's temperature by reflecting sunlight back into space. Ironically, clean-air laws in North America and Europe had the effect of reducing aerosols (which cause acid rain), so the predominant influence on climate now is the buildup of carbon dioxide—which traps the Earth's heat in the lower atmosphere and contributes to global warming.

As late as 1992, in a story that for some reason has gotten far less attention, NEWSWEEK revisited the Ice Age threat, this time posing it as a perverse consequence of the greenhouse effect. Citing the theories of an "amateur scientist and professional prophet of doom named John Hamaker," the article raised the specter that a small increase in air temperature could cause more snow to fall in places like northern Greenland, where the ground is often bare. (Extremely cold air doesn't hold enough moisture for a good snowfall.) Increased snow cover, by reflecting more sunlight back into space, could trigger a return of the glaciers to North America. Although the intricate web of positive and negative feedbacks that control climate are still not fully understood, that particular scenario hasn't gotten much attention in the last decade.

The point to remember, says Connolley, is that predictions of global cooling never approached the kind of widespread scientific consensus that supports the greenhouse effect today. And for good reason: the tools scientists have at their disposal now—vastly more data, incomparably faster computers and infinitely more sophisticated mathematical models—render any forecasts from 1975 as inoperative as the predictions being made around the same time about the inevitable triumph of communism. Astronomers have been warning for decades that life on Earth could be wiped out by a collision with a giant meteorite; it hasn't happened yet, but that doesn't mean that journalists have been dupes or alarmists for reporting this news. Citizens can judge for themselves what constitutes a prudent response-which, indeed, is what occurred 30 years ago. All in all, it's probably just as well that society elected not to follow one of the possible solutions mentioned in the NEWSWEEK article: to pour soot over the Arctic ice cap, to help it melt.