• Choose a category
• All
• Classic-Fiction

One of my personal heroes in science is Richard B. Alley, an outstandingly accomplished glaciologist and professor of geosciences at Penn State University. Not only has he cranked out one landmark idea after another, published nearly forty times in Science and Nature, been elected to the National Academy of Sciences, and written a wonderful popular book explaining it all for the rest of us,487 he is also about the nicest and most enthusiastic guy one could ever hope to meet.

In 1994, Alley came to deliver a guest lecture at Cornell University, where I was a lowly second-year graduate student. Everyone was abuzz that Richard Alley was coming, because he had just published a pair of back-to-back articles in Nature that had stunned the climate-science community.488 Even my thesis advisor—who was pretty famous himself, having written the paper putting together the theory of plate tectonics489—was talking about them. But a great thing about academia is that it is on open, democratic affair even when it comes to its pop icons. Visiting celebrities will hang out for a day or two happily chatting with whomever, even lowly second-year graduate students. Landing a meeting with one is largely a matter of getting to the sign-up sheet first, which of course I did.

When my time slot arrived I went to meet Alley, armed with a list of questions about his Nature papers so I could hear more from the great man himself. That lasted about forty-five seconds, before he insisted on hearing all about my work. I couldn’t believe it. It was a dumb little side project of my research, but Alley’s enthusiasm was totally contagious. We relocated to my lab hole, where he huddled alongside me, giving all manner of helpful advice and inspiration. By the time he ran off late to his next appointment, I was so excited about my project I barely remembered I’d forgotten to ask more about his. That’s just the kind of guy he is.490

What had everyone gabbling was what Alley and his colleagues had dug out of the Greenland Ice Sheet. The U.S. National Science Foundation had funded construction of a drilling and laboratory camp on top of it to extract a two-mile-long ice core called GISP2, an enormous task taking about four years.491 Preserved in the upper sections of ice cores are annual layers, like the rings of a tree. Each one contains the compressed equivalent of a full year’s worth of snow accumulation falling on the ice sheet surface (cores are drilled from deep ice sheet interiors where it never melts). By counting the layers down-core and measuring their thickness and chemistry, a very long reconstruction of past climate variations is obtained. We even get tiny samples of the ancient atmosphere, by cracking into air bubbles trapped in the ice. From these high-resolution annual measurements in Greenland, Alley and his colleagues had discovered that around twelve thousand years ago, just when we were pulling out of the last ice age, the climate began shuddering wildly.

The shudders happened faster than anyone had dreamed possible. Our climatic emergence from the last ice age, it seems, was neither gradual nor smooth. Instead it underwent rapid flip-flops, seesawing back and forth between glacial and interglacial (warm) temperatures several times before finally settling down into a warmer state. These large temperature swings happened in less than a decade and as quickly as three years. Precipitation doubled in as little as a single year. Around Greenland, at least, there was no gradual, smooth transition from a cold ice age to the balmy interglacial period of today. Alley’s team had shown that climate could sometimes teeter as well, like a “flickering switch,” between two very different states. Furthermore, it had happened other times in earlier millennia, so this was not a totally isolated event. The extreme rapidity of these changes, concluded Alley, implied “some kind of threshold or trigger in the North Atlantic climate system.”492

Thus was born a brand-new subfield of climate science known today as “abrupt climate change.” Twenty years ago