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First the bad news. "One of the most shocking scientific realizations of all time has slowly been dawning on us," William Calvin announces in the opening words of his new book: "the earth's climate does great flip-flops every few thousand years, and with breathtaking speed." For the last 8,000 years or so, we've enjoyed an unusually stable climate. But there's no reason to suppose that it will continue indefinitely—in fact, if geological history is any guide, we can be pretty sure it won't. Imagine the disruptions associated with the Little Ice Age (a.d. 1300-1850) but on a much larger scale and concentrated in a single decade. An episode of abrupt global cooling, such as has occurred many times in Earth's history, would create massive food shortages and could easily lead to worldwide conflict—"taking much of civilization with it."
Alarmist? Absurd? Wildly apocalyptic? Calvin isn't predicting such an outcome; rather, he's suggesting that it is a real possibility, worth pondering. He observes that the last episode of abrupt global cooling, the so-called Younger Dryas, "drastically altered Europe's climate as far east as Ukraine." Starting about 15,000 years ago, the Earth had been thawing out from the last major Ice Age. But about 12,900 years ago, "just in a matter of a decade or so, the climate flipped from warm-and-wet into the cool-and-dry mode, with temperatures plunging back to what they had been in the ice ages."
Today, Europe's population of more than 650 million is fed mostly by food grown in Europe. With a climate change like the Younger Dryas, Europe might be able to support a population comparable to Canada's. Lacking present-day Europe's "winter warmth and rainfall," Calvin notes, Canada is able to support a population of only 28 million despite its huge expanse.
The good news is that we recognize the problem, and we may even be able to do something about it. "Until a dozen years ago," Calvin writes, "everyone lived in blissful ignorance about the severe climate flips that happen quickly, with just a few short years before hard times set in with a vengeance." Now there's growing awareness that the old model of very gradual climate change is defective.
Calvin was one of the first scientists to bring this new consensus to the attention of the general reader; his January 1998 Atlantic Monthly cover story, "The Great Climate Flip-Flop," provoked an enormous response (including howls of indignation and disdain from those who saw his article as the latest exercise in environmental scare-mongering). More recently, readers of Books & Culture may recall Catherine Crouch's review of Richard Alley's book, The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future. And Elizabeth Kolbert's New Yorker article, "Ice Memory: Does a glacier hold the secret of how civilization began—and how it may end?", covers some of the same territory.1 Maybe the people who made the animated feature, Ice Age, have been reading this stuff, too.
One of the purposes of Calvin's new book, A Brain for All Seasons: Human Evolution and Abrupt Climate Change, is to build on that Atlantic Monthly article, taking into account criticisms against it and knowledge gained in the interim. Much of the criticism of Calvin's article centered on the global warming debate. Yes, Calvin—like Richard Alley and many others—believes that human-caused global warming increases the likelihood of an abrupt "flip" to global cooling. Readers who saw the sequence of photographs on the front page of The New York Times for March 20 ("Large Ice Shelf in Antarctica Disintegrates at Great Speed") had good cause to feel uneasy.
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