Climate Change Book Review

Doug Macdougall, Frozen Earth: The Once and Future Story of Ice Ages, (University of California Press, 2004), pages 256

For those interested in global warming and climate change, this is a chilling reminder of other possibilities.

MacDougall does an excellent job about the evolution of the theory of ice ages. The theory evolved through several steps. The initial step was to realize that only massive ice ages could explain the scared landscape, the glacial deposits, and "erratics" - rocks and large boulders moved many miles from their place of origin in the northern hemisphere. The next step was to understand the nature of the recent ice ages, and most specifically, that they advanced and retreated many times. The final step was to understand and explain the cycles. The leading theory was subtle changes in Earth's orbit, wobble, and tilt. However, it was only in the mid 1970s that it was possible to date the cycles of recent ice ages with sufficient accuracy to understand the relationship between ice age cycles and orbit, wobble and tilt.

The result was surprising. Ice ages did not occur because of extreme cold in the northern hemisphere. Instead, they were the product of relatively cool summers and relatively warm winters. The warm winters encouraged precipitation at the top of the ice cap, and fueled its growth. The summers meant the snow cover persisted later into spring and started earlier in the fall - both events making the earth's surface reflect more of the income radiation, and therefore cooling it.

Having explained the theory of recent ages, Macdougall proceeds to explain some of the more ancient ice ages.

Macdougall does an excellent job of explaining the scientists behind the theories, the scientific debates along the way, and ultimately the theory of ice ages.

In the final chapter, Macdougall speculates about the future potential for ice ages. He notes that based on orbit, wobble and tilt considerations, Earth should head into another ice age in about 30,000 years. The addition of greenhouse gases into the atmosphere could delay the onset of another ice age, or it could postpone. Interesting questions.

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