Earth has a global climate system made up of interconnected parts, constantly changing. This wasn't always known, however, and over the past 150 years this idea was forged by scientists working independently, studying water in its myriad forms. Linking the history of the planet with the lives of those who studied it, Sarah Dry follows the exploits of remarkable scientists like Louis Agassiz, John Tyndale, and James Croll, whose discoveries coalesced into a unified working theory of our planet's climate. We now call this field climate science, and Dry examines why in recent years it has provoked great passions, anxieties, and warnings.