escribes the important contributions that geology has made to our understanding of climate change since the 1830s. 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. But how could we be on the cusp of another ice age when all indications point to a warming climate? Though much is uncertain, this book clearly shows that major climate shifts can be appallingly rapid--occurring over as little as twenty or thirty years. Dumping greenhouse gases into the atmosphere may increase the chance that this "climate switch" will be thrown in one direction or the other, with catastrophic effects on worldwide agriculture. All the more reason to take the threat of climate change seriously.Now available in paperback with a new epilogue by the author, this accessible and engagingly written book is essential reading for anyone looking to understand one of our most important contemporary debates.