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Phenomena, Comment & Notes

Iceberg armadas and flickering climates: how one good idea led to more, and we appreciated anew the world's complexity

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There are few things in life more exhilarating than getting a really good idea — one that just sings as it solves a problem that's been bothering you for God knows how long. We've all had this experience. Sometimes the ideas work out, and many illustrious careers have been built on such flashes of insight. Sometimes the ideas are total flops, in which case we bury them and move on.

The sciences are a branch of human endeavor in which ideas are the main item of commerce, the principle coin of the realm. Over the centuries, the scientific community has developed a complex set of rules about how ideas are to be evaluated, as well as some pretty definite criteria that tell you when they can be accepted. So if you want to follow the story of a good idea, what better place to look than science?

As it turns out, readers of this column already have an excellent example at hand. In the August 1993 Phenomena you met Douglas MacAyael of the University of Chicago, a young scientist who had just had a good idea about why Earth's climate developed as it did during the last ice age. Doug's idea has since gone through the scientific mill; it's time to go back and see what happened.

To refresh your memory, Doug works in glaciology. Having spent months camping on Antarctic glaciers and years trying to model their flow with computers, he knows about how ice behaves when it piles up. The problem he addressed had to do with a strange phenomenon people had found in cores drilled out of the ocean floor in the North Atlantic. Geologists were amazed to discover successive layers of rock debris and gravel that seemed out of place: the rocks in those layers appear identical to stuff you'd expect to find on land in northern Canada. Other evidence suggested that these layers, which formed every 7,000 to 12,000 years, marked periods of rapid climate change. Average temperatures climbed more than 10 degrees — the equivalent of moving the climate of Atlanta to Boston — in a few decades, followed a few thousand years later by an equally rapid return to normal. These sudden shifts in climate, accompanied by out-of-place rocks being dumped into the North Atlantic, were called "Heinrich events" after the German scientist who first discovered them.

Doug's idea was that you could understand both the origin of the rocks in the ocean bottom cores and the dramatic shift in the weather in terms of the behavior of the ice sheet that covered North America over much of the past 80,000 years. The depth of the sheet would increase as snow fell and compressed into ice, but when the ice lying on top of Hudson Bay reached to a height of about 10,000 feet, the soft rocks underneath would crumble and mix with meltwater, forming a slippery paste, and the whole thing would slough down Hudson Strait and eventually into the ocean, sending out an armada of icebergs, each with a load of crushed rocks frozen into its undersides. When the icebergs melted, the rocks were dumped (hence the strange layers). At the same time, the additional fresh water changed the patterns of ocean currents while the absence of two vertical miles of ice changed wind patterns (hence the change in climate).

"The point of the model," he told me recently, "was that everything depended on the internal behavior of the ice sheet. It was the ice driving Earth's climate, rather than vice versa." In a profession full of people who want to understand Earth's climate, a notion like this can be regarded as anything from a brilliant flash of insight to the rankest heresy. This is where the historic procedures of the scientific community come into play.

With an idea in hand, the first step is to submit a paper to a journal that in turn will vet it by a process known as peer review. The editors send the paper to one or more other scientists who evaluate it. The person submitting the paper is not told who the referees are, but normally they are chosen not just from his or her general field but from the writer's specialty. They advise the journal editor whether the paper is reasonable and worth publishing. Once the paper is published, it is subjected to a wider form of peer review. Any scientist anywhere in the world can submit a paper to the same journal calling attention to perceived inconsistencies, omissions or outright mistakes in the original paper.

In Doug's case, one of the anonymous referees realized that there was a big gap in his theory: he hadn't worked out how the sloughing ice could pick up the rocks and dump them into the ocean. A quick phone call initiated a collaboration that fixed that gap. This sort of criticism is a standard opening shot in any scientific debate, and in Doug's case it was well under way by the time his first paper was published.

The next (and more fundamental) critical step was not slow in starting. Call this the "there is another explanation for the whole thing" response. Often the most vociferous part of scientific debate, it usually consists of arguments between identifiable camps of individuals. Doug's "ice causes climate change" school was one such camp, which was opposed by a "climate change changes the ice" school, whose central idea was that it was global warming that caused the purging of the Hudson Bay ice sheet, rather than the growth of the ice sheet itself. This stage of scientific debate often resembles nothing so much as a trial in open court. It can be rancorous, it can be unsettling, but it is also necessary because, in the end, only those ideas that have been tested in this kind of fire can be trusted.

The debate is made more spirited by the very human tendency of the protagonists to believe that their particular theories explain everything there is to explain. "I was like a raccoon caught in the headlights," Doug now says with a rueful grin. "I was so obsessed with the power of the idea of ice sheet dynamics that I wanted it to be the whole picture and not just part of a larger whole. The idea was beautiful, simple and, in the end, wrong."

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