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?

Alley's answer: For the last ten thousand years or so, during which humans developed agriculture and industry, Earth's climate has been unusually stable and hospitable. However, over the past hundred thousand years, and indeed over most of its four-billion-year history, Earth has experienced repeated abrupt, significant climate change. Our understanding of the reasons for these abrupt changes suggests that temperature increases of even a few degrees could upset the stable climate in which we currently live and set off catastrophic changes.

How could this happen? In brief, glossing over much of the detail that is clearly and carefully explained by Alley, models verified against the climate records indicate that Earth's climate is controlled by many factors, involving the oceans as well as the atmosphere, which incorporate myriad forms of positive and negative feedback. Positive feedback, whether in electronic circuits or a planet's climate system, greatly amplifies a small disturbance (the unpleasant feedback whines in loudspeaker systems are seeded by very quiet sounds). Most of the negative feedback mechanisms in Earth's climate act more slowly than the positive feedback mechanisms, so while negative feedback prevents Earth's climate from spiraling completely out of control over millions of years, it does not prevent abrupt changes over decades or centuries. As Alley explains in the two "punch lines" of part 4:

1. Climate in the past has been wildly variable, with larger, faster changes than anything industrial or agricultural humans have ever faced.

2. Climate can be rather stable if nothing is causing it to change, but when the climate is "pushed" or forced to change, it often jumps suddenly to very different conditions, rather than changing gradually.

Furthermore, changes in temperature are inextricably linked to changes in rainfall and humidity, so even small changes in temperature can profoundly alter whether land is arable or even habitable.

As for simplicity, a great deal of the media coverage of climate science suggests that there is widespread disagreement in the scientific community about the likelihood of human-induced climate change, with results about as reliable as those little weather forecasts in The Old Farmer's Almanac. But Alley documents the remarkably broad consensus among scientists that human activities are altering the climate, and if we don't slow down or stop, the results are likely to be disastrous.[1]

Alley makes a thorough and compelling case for the importance of reducing greenhouse emissions. He also argues that catastrophic climate change will affect the poor and developing nations of the world far more severely than the industrialized nations, both because most wealthy nations are in parts of the globe less prone to climate-related disaster and because wealth brings with it the infrastructure to cope with drought, floods, severe storms, and acute heat or cold. In the light of the U.S. disavowal of the Kyoto Treaty without an obvious commitment to developing an alternative, this is sobering reading.

But as valuable as The Two-Mile Time Machine is as an introduction to the findings and implications of paleoclimatology, it is probably even more valuable as a rare view of the culture and practice of science. In his description of the weeks spent at the Greenland Ice Sheet Project 2 research station, Alley gives the lie to the hopelessly outdated image of scientists as lonely geniuses spurred by competitive frenzy: the collegiality and teamwork common in scientific research come across clearly. The atmosphere of the research station is one of community and camaraderie, as research staff are united by their common scientific mission. Although few scientific teams spend six weeks at a time working and camping together in subzero temperatures, partnership and good humor are the rule rather than the exception in most laboratories.

Alley's description of climate science also illustrates the painstaking process of obtaining and verifying scientific results. There is no single measurement on which the climate record rests. Rather, the record is constructed using several different kinds of data, and is considered believable only insofar as all the different lines of evidence are consistent with one another. For example, the ice cores are made up of visibly distinct layers, each layer coming from a single season's snowfall, and dating the layers is an important first step in analyzing the climate record. This requires several independent measurements, including electrical resistance, dust content, chemical composition, isotopic ratios, and simply counting layers in the same manner that one would count rings in a tree trunk. Furthermore, the measurements themselves are only trusted if several different researchers can independently arrive at the same results.

The Two-Mile Time Machine restores some of the joy of discovery that has always been present in scientific work, but is often lost amidst today's furious research pace and compressed news cycles. As such, it should be accessible and appealing to nonscientists, even if they skip over a few of the more intricate explanations of Alley's research methods. (More technically inclined readers, or those who want to confirm the author's conclusions, can consult an extensive bibliography.) This book should certainly be read by anyone concerned about climate change (though it is probably too much to hope that policy makers themselves will find time for it); but perhaps it will also be read by some future scientists whose imagination will be kindled by Alley's enthusiasm.

Catherine H. Crouch is a postdoctoral fellow in applied physics at Harvard University.

1. A recent article in Science (January 26, 2001, p. 566), "It's Official: Humans Are Behind Most of Global Warming," reports the consensus opinion of the hundreds of environmental scientists participating in the United Nations-commissioned Intergovernmental Panel on Climate Change.

NOTE: For your convenience, the following book, which was mentioned above, is available for purchase:

• The Two-Mile Time Machine, by Richard B. Alley

Copyright © 2001 by the author or Christianity Today/Books & Culture Magazine.
Click here for reprint information on Books & Culture.