Climate is what you expect; weather is what you get — so goes the pocket distinction between the two broad categories of meteorology. Only now...

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“Climate Crash: Abrupt Climate Change and What It Means for Our Future”
by John D. Cox
Joseph Henry Press, 224 pp., $27.95

Climate is what you expect; weather is what you get — so goes the pocket distinction between the two broad categories of meteorology. Only now, thanks to an emerging theory known as abrupt climate change, we find out that climate is really not what we expected, after all.

Instead of shifting gradually in nice smooth graphable curves, Earth’s past climate has repeatedly and suddenly lurched into radically different temperature and precipitation regimes — heat spikes of nearly 13 degrees Fahrenheit in just 20 years, followed by equally rapid plunges back to Ice-Age-cold.

Scientists have taken to comparing the way climate swings without warning out of a relatively stable state to tipping a boat — it rocks and rocks and then all of a sudden it capsizes — or, more alarmingly, to rousing a drunk out of a stupor. “When left alone, it [i.e., climate] sits,” as one climatologist puts it in “Climate Crash: Abrupt Climate Change and What It Means for Our Future”; “when forced to move, it staggers with abrupt changes in direction.”

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No, abrupt climate change does not manifest itself in the instantaneous orgy of meteorological mayhem depicted in last summer’s disaster pic “The Day After Tomorrow” — remember the herd of tornadoes that decimated Los Angeles in an afternoon, and the ice age that gripped Manhattan in the course of rush hour? But, as author John D. Cox notes in this absorbing and sobering new book on the subject, the makers of that much-ridiculed movie did get one basic idea “just right”: “Climate change can be dangerous, even catastrophic.”

Cox, a veteran science journalist and the author of a superb collection of profiles in meteorological courage called “Storm Watchers,” devotes the bulk of this book to the story of how the notion of abrupt climate change emerged over the past seven decades from a series of grueling research projects in inconvenient places. It’s a classic case of data ignored or dismissed because they went against the grain of received wisdom.

As Cox puts it in one of his many inspired metaphors, the idea of abrupt climate change is “so counterintuitive and so elusive that it is like a concert being played at a pitch beyond the range of human hearing.”

Cox structures his chapters around the “holy crap!” moments that capped the major research endeavors:

• The 1930 German expedition to Greenland led by doomed meteorologist Alfred Lohar Wegener (an early proponent of the theory of continental drift).

• A U.S.-sponsored Cold War-era Greenland ice-drilling experiment under the direction of the Swiss-born geologist Henri Bader and the young American geologist Chester C. Langway Jr.

• The breakthrough that American geo-chemist Wallace S. Broecker scored when he merged his two research paths (paleoclimatology and ocean circulation) and suddenly realized that ocean currents play a key role in climate change.

Comparing data from a much-ballyhooed 1992 Greenland ice-drilling project with evidence from ocean sediments, one scientist stated baldly that in the course of 20 years, “a threshold was crossed, and the climate of much of the world shifted abruptly from cold to warm.”

Cox works hard to thread the climatological breakthroughs into a taut, suspenseful narrative line, but it’s tough sledding, given the material. Though the implications of abrupt climate change are enormous, the story of how scientists teased out millennia of shifting weather patterns from bubbles trapped in shelves of ice and flecks of pollen at the bottom of lakes is simply not as gripping as the making of the atomic bomb or the race to determine longitude. Unless you’re a specialist in the field or a serious weather geek, you may find yourself glazing over, as haggard geologists and paleoclimatologists wave their arms over yet another plunge in the mercury 45,000 years ago.

Actually, as Cox makes clear at the end of the book, the fact that the most dramatic changes happened so long ago turns out to be intriguing in its own right. Even with the recent global warming, the climate of the past 8,000 years — the entire history of human civilization — has been strangely stable compared with the preceding 240,000 years.

Climatewise, we’re in a prolonged, precarious lull — a lull that may well be shattered by the greenhouse gases we’re spewing into the atmosphere. In the final pages, Cox connects the dots between human-induced global warming and the likelihood of another lurch into abrupt climate change.

When confronted with the recent warming that already has altered life on Earth, our current political leaders shrug, obfuscate or write it off as natural variation. “Prove that we’re responsible,” they demand. But as Cox notes in his conclusion, if and when the switch gets thrown on our climate again — and there are “ominous signs” that abrupt change may already be underway — it won’t matter a whit who or what caused it.

David Laskin, who writes frequently about weather and climate, is the author of “The Children’s Blizzard,” “Braving the Elements” and “Rains All the Time.”