The Uninhabitable Earth: Life After Warming

by David Wallace-Wells

Overwhelmingly, of course, the viruses and bacteria making homes inside us are nonthreatening to humans—at present. Presumably, a difference of a degree or two in global temperature won’t dramatically change the behavior of the majority of them—probably the vast majority, even the overwhelming majority. But consider the case of the saiga—the adorable, dwarflike antelope, native to central Asia. In May 2015, nearly two-thirds of the global population died in the span of just days—every single saiga in an area the size of Florida, the land suddenly dotted with hundreds of thousands of saiga carcasses and not one lone survivor. An event like this is called a “mega-death,” this one so striking and cinematic that it gave rise, immediately, to a whole raft of conspiracy theories: aliens, radiation, dumped rocket fuel. But no toxins were found by researchers poking through the killing fields—in the animals themselves, in the soil, in the local plants. The culprit, it turned out, was a simple bacteria, Pasteurella multocida, which had lived inside the saiga’s tonsils, without threatening its host in any way, for many, many generations. Suddenly it had proliferated, emigrated to the bloodstream, and from there to the animals’ liver, kidneys, and spleen. Why? “The places where the saigas died in May 2015 were extremely warm and humid,” Ed Yong wrote in The Atlantic. “In fact, humidity levels were the highest ever seen in the region since records began in 1948. The same pattern held ...