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The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future, by Richard B. Alley, Princeton University Press, 2000, 240 pp.; $24.95
If there is one thing that distinguishes the beginning of this century from the beginning of the last, it may be the ability of the average educated person to accept fantastical scientific achievements, not to mention new scientific jargon, without a second thought. Physicists talk about tiny particles with weird names; biologists have just unveiled a complete map of the human genome; environmental scientists make sweeping claims about climate change. But how, exactly, do scientists get this information? A great deal of contemporary science explores things too remote in space or time (or both), or too tiny, to permit direct observation. You can't simply put your finger under a microscope and read off your genetic code.
Much of the ingenuity of science lies in figuring out how to figure things out. The multicolored "map" of the genome came only after a maddeningly complex, and highly automated, process of separating DNA molecules from all the rest of the biochemical stew that fills cell nuclei and performing a lengthy series of chemical reactions that identified, one by one, the sequence of the four possible constituents of DNA. Identifying the fundamental building blocks of the universe—bizarre particles such as the top quark and the Higgs boson—involves accelerating beams of more ordinary particles such as protons to speeds nearly that of light (a heroic experimental task in itself), colliding these high-speed particles together, measuring the paths followed by the particle debris from these collisions, and—from those paths—inferring properties such as mass and charge of the particles under investigation.
So it is also with our current understanding of Earth's climate, the subject of Richard Alley's superb book, The Two-Mile Time Machine. As Alley explains in the introduction ("Setting the Stage"), assessing the impact of human-induced climate change—the "global warming" we've been hearing so much about, for instance—requires models of how Earth's climate works. Developing and verifying these models requires comparing the predictions of models to an actual record of climate. Thus studies of past climate are an essential ingredient for addressing concerns about the future by a complex process of inference. We can't directly observe Earth's climate in the distant past, but we can analyze ice samples drilled from as much as two miles below the surface in Greenland or Antarctica (hence Alley's title).
Part 2 of Alley's book, "Reading the Record," explains how records of past temperature, atmospheric composition, oceanic circulation, and other important information about the past hundred thousand years of climate are extracted from Greenland ice cores. Part 3 then gives an overview of the climate record determined from these measurements, and part 4 describes current models of what determines Earth's climate. The final part of the book is titled "Coming Craziness?" and subtitled "What might happen to Earth's climate in the future—and what we might do about it."
Alley demonstrates that the scientific understanding of climate is both a lot more complex, and a lot simpler, than public perceptions might indicate. As for its complexity, popular discussion tends to center on findings that, due to the human-produced increase in atmospheric greenhouse gases, the average global temperature is a few degrees higher than it was a century ago, without clear explanation of why this might be of serious concern. How could a few degrees one way or another really matter?
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