In this sweeping work of science and history, the renowned climate scientist and author ofThe New Climate Warshows us the conditions on Earth that allowed humans not only to exist but thrive, and how they are imperiled if we veer off course.For the vast majority of its 4.54 billion years, Earth has proven it can manage just fine without human beings. Then came the first proto-humans, who emerged just a little more than 2 million years ago—a fleeting moment in geological time. What is it that made this benevolent moment of ours possible? Ironically, it’s the very same thing that now threatens us—climate change.The drying of the tropics during the Pleistocene period created a niche for early hominids, who could hunt prey as forests gave way to savannahs in the African tropics. The sudden cooling episode known as the “Younger Dryas” 13,000 years ago, which occurred just as Earth was thawing out of the last Ice...