The world is getting hotter. Each year more people die from extreme heat than from all other natural disasters combined. In Swelter, Bharat Venkat, the director of UCLA’s Heat Lab, tells the dramatic story of how we’ve come to understand the biology of heat. We meet a Scottish physician who unlocked the mystery of body temperature by studying a crew of sailors shipwrecked in the frigid waters of the Irish Sea, a genteel English traveller in the tropics convinced that the heat was slowly unravelling her mind, and the Harvard researchers who plunged bodies into artificial infernos to test their limits.

But alongside these scientific developments emerged a stubborn set of ideas about bodily difference – who could withstand the heat and why. Colonial physicians insisted that Indian soldiers possessed a natural tolerance that the British could never acquire. Black workers were assigned to the hottest jobs in steel mills, on the grounds that their bodies were built for it. Venkat shows how this pernicious myth spread across the globe and persists even today, and reveals a terrible calculus: the comfort and safety of some are made possible by the suffering of others.

Arguing that extreme heat is poised to become the defining public health and human rights issue of the twenty-first century, Swelter also tells us what we can do about it.