In this sweeping work of science and history, the renowned climate scientist and author of The New Climate War shows 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. Climate variability has at times created new niches that humans or their ancestors could potentially exploit, and challenges that at times have spurred innovation. But the conditions that allowed humans to live on this earth are fragile, incredibly so.There's a relatively narrow envelope of climate variability within which human civilisation remains viable. And our survival depends on conditions remaining within that range. In this book, renowned climate scientist Michael Mann arms readers with the knowledge necessary to appreciate the gravity of the unfolding climate crisis, while emboldening them - and others - to act before it truly does become too late.