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{{BNR-table|scienticity=5|readability=5|hermeneutics=5|charisma=5|recommendation=5}}
Richard B. Alley, ''The Two-Mile Time Machine : Ice Cores, Abrupt Climate Change, and Our Future''. Princeton, New Jersey : Princeton University Press, 2000. 229 pages, with appendices, "Sources and Related Information", and index; illustrated.

Here is a fascinating, well-written, and accessible book that sheds a great deal of light on what we know about climate change in the history of the Earth. I expect all readers will not agree with me but I thought Alley wrote with a maximum of objectivity and a minimum of emotional heat.

These paragraphs from the introductory chapter indicate the author's direction:
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The history of this climatic craziness is written in cave formation, ocean and lake sediments, and other places. But the record is probably clearest and most convincing in the ice of Greenland. This incomparable, 110,000-year archive provides year-by-year records of how cold and snowy Greenland was, how strong the storms were that blew dust from Asia and salt from the ocean, end even how extensive the wetlands of the world were. [pp. 3—4]
<br>[...]<br>
This book is a progress report on abrupt climate changes. We will discuss what has been learned, how this knowledge was gained, and what it might mean to us. The existence of abrupt climate changes casts a very different light on the debate about global warming, so we will examine the greenhouse arguments under this new light. We won't find all of the answers—many are not known yet--but we will frame the questions, and we may gain some clues to our future. [p. 5]
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Popular discussions of anthropogenic climate change usually refer to "global warming" as though that sums up the potential problems, but an increase in temperature through increasing carbon emissions and greenhouse effects in the atmosphere is only the beginning of the story, a mere trigger to possible effects. The main concerns over "global warming" relate to the relatively large amounts of atmospheric carbon dioxide we are pouring into our atmosphere: the historic record shows that rapid and large climate shifts have occurred in our deep past accompanied by small changes in atmospheric carbon dioxide and that it looks likely that a change in atmospheric carbon dioxide can trigger shifts.

It's a complicated question and, although getting a good picture of this context for climate change is not so difficult, it takes time to work through the deductions and absorb the conclusions. For my taste Alley covered all the necessary ground at just the right pace and with enough detail to give a clear understanding of the numerous scientific findings that fit together to create a remarkably complete and coherent record of climate change and many of its possible causes and effects.

The author worked with pioneering scientific expeditions to Greenland that pulled two-mile long ice cores from the Greenland ice cap and then analyzed those samples to establish the history of Earth's climate changes over the past 100,00 (or so) years. Describing the massive job of understanding and decoding the clues contained in the ice is a grand scientific adventure that the author uses as the backbone to telling his larger story about the history of climate change. Along the way he exhibits an abundance of scientific rationale and deduction in an excellent example of how science works to arrive at difficult but solid deductions.

After the first third of the book discussing all of the data that could be gleaned through sophisticated and clever analyses of the ice cores, Alley pauses to reflect before moving  on to build the historic record of climate change from those results.

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By now I hope that you are convinced that a dedicated team of drillers, pilots, cooks, scientists, and other can pull a two-mil-long piece of ice out of Greenland, cut up the ice, analyze it, and tell you how and when the climate changed in Greenland and in many other places. Our friends can analyze trees and mud from other regions, and tell you much about the past climates where the threes grew and the mud settled. The stories from these studies, and what they might mean, are the reason the government paid for us to go to Greenland, and form the rest of this book. I'll give you the punch lines first, and then discuss them. There are many punch lines, and all have something to tell us. The two biggest are:
   <br><br>
1. Climate in the past has been wildly variable, with larger, faster changes than anything industrial or agricultural humans have ever faced. <br>
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. You might think of the climate as a drunk: When left alone, it sits, when forced to move, it staggers. <br>
3. The "pushes" that have caused climate changes is the past probably have included drifting continents, wiggles in Earth's orbit, surges of great ice sheets, sudden reversals in ocean circulation, and others. <br>
4. Small "pushes" have caused large changes because many processes in the Earth system amplify the pushes. Greenhouse gases have probably been the most important amplifiers. <br>
5. Humans can foul our own nest—and we can clean it up. [pp. 83—84]
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Looking deep into the history of Earth's climate is exciting and filled with surprises. Perhaps it's no longer surprising that there have been numerous periods of climate fluctuations accompanied by large temperature changes in some regions, the coming and going of ice coverage, changes in rain-fall patterns, and other large-scale patterns. More surprising is to find that climate changes with rather large effects have also happened on numerous occasions over surprisingly short timescale, sometimes as little as 10 years, maybe at times 1 or 2 years. But the fluctuations are not equally distributed and our current quiescent period may give false security.
<blockquote>
With one partial exception about 8,200 years ago, the ice-core records show no similarly large, abrupt changes in snow-fall, temperature, dust, or methane since the end of the Younger Dryas [cold event, about 11,500 years ago]. The millennia over which agriculture and industry rose have been calm and constant by comparison. True, climate changes have contributed to the rise and fall of empires, lured the Vikings to Greenland and then driven them out, and otherwise affected human lives. But these changes that have affected historical humans appear as slow one-degree shifts in the ice-core records, not as abrupt ten-degree jumps. The large effects that small climate changes have had on humans, and the unequivocal records of much larger climate changes, are enough to make some people think deeply, and eve to make them a little nervous. [p. 118]
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In the final chapters of the book Alley looks at consequences of the climate model as it is currently emerging, including what we know with certainty and what we surmise with less (but growing) certainty.
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Ice cores and other sediments show that large, rapid, and widespread climate changes have been common on Earth for most of the time for which we have good records, but have been absent during the critical few millennia during which agriculture and industry arose. At least some of those large changes appear to have been triggered by increased fresh-water delivery to the north Atlantic. Climate jumps have been especially common when changes were occurring in important parts of the climate system, including summer sunshine in the north, carbon dioxide in the atmosphere, and ice-sheet size.
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The critical questions for us are: Will nature, or humans, return the climate to the "normal" conditions 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? [p. 169]
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I found this book exciting to read. Exciting in that the author wrote a great tale of scientific adventure, excited for the excellent scienticity of his writing, excited about the accessibility and depth of his exposition on climate change, and excited because this book could serve as a powerful antidote to the frustrations and futility of climate-change debate by soundbite.

{{Notesby|JNS}}

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