Book excerpt: When we think "climate change," we think of man-made global warming, caused by greenhouse gas emissions. But natural climate change has occurred throughout human history, and populations have had to adapt to its vicissitudes. Tony McMichael, a renowned epidemiologist and a pioneer in the field of how human health relates to climate change, is the ideal guide to this phenomenon, and in his magisterial Climate Change and the Health of Nations, he presents a sweeping and authoritative analysis of how human societies have been shaped by climate events.