If you think the weather is crazy now, be glad it isn't normal. Agriculture, civilization, and the lifestyles we now take for granted developed during 10 millenniums of unusual climatic calm.
Greenland's glaciers and other geophysical records tell us the norm for the past 110,000 years featured wild swings between hot and dry or cold and wet conditions, whose unpleasantness ranged far beyond anything in our cultural memory. So much for Texas' drought, or Europe's harsh winter.
As Richard Alley notes in this provocative little book, the climate we love to hate "is about as good as it gets." We better learn to love it enough to make the considerable effort it will take to understand our climate system: how to make the most of it and how not to upset it.
The Pennsylvania State University geophysicist channels this scientific insight into a compelling tale of climate sleuthing. His technical detail skillfully avoids ennui.
Greenland's glaciers record climatic history in terms of dust layers, ice structure, and other natural hieroglyphs. If you can read them as Alley and his fellow sleuths do, you can trace air-temperature trends and precipitation back 100,000 years.
Greenland ice that records this history layer upon layer - the "time machine" of the title - tells us much about what has happened to climate.
But Alley connects its record with histories recorded in sea and lake sediments, cave deposits, and other repositories around the planet. Taken together, they tell a story of climatic caprice that has disabused scientists of their old assumption that significant change takes millenniums to occur.
The record clearly shows erratic swings between climate extremes within decades, or even from year to year. As Alley puts it, it's as though an impish child were playing with a switch that throws the climate system into different modes.
This puts concern over human-made global warming in a new perspective. The switch lies somewhere in the complex interplay of air, land, sea, and biosphere. The child stands for natural factors that give this system a small push. Sometimes the push leads nowhere. Other times it throws the climate switch. The disturbing - although not yet proven - implication is that human activity now may join in the impish play.
Concern over global warming has focused on climate change over the next half century or longer. Humanity could, with great effort, adapt to that. It could slow the change by curbing emission of carbon dioxide and other heat-trapping gases.
The new concern is the possibility that, curbed or not, human tinkering may throw the switch, bringing undesirable climate change suddenly upon us.
Alley does a service by injecting this issue into the global-warming debate. He is authoritative without being dogmatic, concerned without being alarmist. His bottom-line questions say it all:
"Will nature, or humans, return the climate to the 'normal' condition of wild jumps rather than the 'anomalous' stability that we now enjoy? And, if such a return seems likely, is there anything we can do about it?"
Finding answers is a work in progress. We can be grateful that Alley - as lucid in a press conference as he is in this book - will help keep us informed.
Robert C. Cowen writes about science for the Monitor.
The Two Mile Time Machine: Ice cores, Abrupt Climate Change, and Our Future
By Richard Alley Princeton University Press 229 pp., $24.95
(c) Copyright 2001. The Christian Science Monitor