A gradual discovery process
How abrupt was the discovery of abrupt climate change? Many climate experts would put their finger on one moment: the day they read the 1993 report of the analysis of Greenland ice cores. Before that, almost nobody confidently believed that the climate could change massively within a decade or two; after the report, almost nobody felt sure that it could not. So wasn't the preceding half-century of research a waste of effort? If only scientists had enough foresight, couldn't they have waited until they were able to get good ice cores and settle the matter once and for all with a single unimpeachable study?
The actual history shows that even the best scientific data are never that definitive. People can see only what they find believable. Over the decades, many scientists who looked at tree rings, varves, ice layers, and such had held evidence of decade-scale climate shifts before their eyes. They easily dismissed it. There were plausible reasons to dismiss global calamity as nothing but a crackpot fantasy. Sometimes the scientists' assumptions were actually built into their procedures: When pollen specialists routinely analyzed their clay cores in 10-cm slices, they could not possibly see changes that took place within a centimeter's worth of layers. If the conventional beliefs had been the same in 1993 as in 1953--that significant climate change always takes many thousands of years--the short-term fluctuations in ice cores would have been passed over as meaningless noise.
First, scientists had to convince themselves, by shuttling back and forth between historical data and studies of possible mechanisms, that rapid shifts made sense, with the meaning of "rapid" gradually changing from millennia to centuries to decades. Without that gradual shift of understanding, the Greenland cores would never have been drilled. The funds required for those heroic projects became available only after scientists reported that climate could change in damaging ways on a time scale meaningful to governments. In an area as difficult as climate science, in which all is complex and befogged, it takes a while to see what one is not prepared to look for.
This article is based on The Discovery of Global Warming by Spencer Weart (Harvard U. Press, 2003) and was supported in part by the NSF program in history and philosophy of science. A more complete account, with full bibliographic references to the scientific work, may be found in hypertext online at
http://www.aip.org/history/climate/rapid.htm.
Spencer Weart (
[email protected]) directs the Center for History of Physics at the American Institute of Physics.
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