In the publicity surrounding global warming, climate scientists are usually the experts consulted by the media. We rarely hear from geologists, who for almost two hundred years have been studying the history of Earth's dramatic and repeated climate revolutions, as revealed in the evidence of rocks and landscapes. This book, written by a geologist, describes the important contributions that geology has made to our understanding of climate change. What emerges is a much more complex and nuanced picture than is usually presented. While the average person often gets the impression that the Earth's climate would be essentially stable if it weren't for the deleterious effects of greenhouse gases, in fact the history of the earth over many millennia reveals a constantly changing climate. As the author explains, several long cold eras have been punctuated by shorter warm periods. The most recent of these warm spells, the one in which we are now living, started ten thousand years ago; based on previous patterns, we should be about due for the return of another frigid epoch. Some scientists even think that the warming of the planet caused by man-made greenhouse gasses tied to agriculture in the past few thousand years may have held off the next ice age. Though this may be possible, much remains uncertain. But what is clearly known is that major climate shifts can be appallingly rapid--occurring over as little as twenty or thirty years. One danger of dumping greenhouse gases into the atmosphere is that they may increase the chance that this "climate switch" will be thrown, with catastrophic effects on worldwide agriculture. Besides her discussion of climate, the author includes chapters on how early naturalists pieced together the complicated geological history of Earth, and she teaches the reader how to interpret the evidence of rock formations and landscape patterns all around us. Accessible and engagingly written, this book is essential reading for anyone looking to understand one of our most important contemporary debates.