Our species likes it cold.
Homo sapiens evolved in — and still inhabits — one of Earth’s rare and fragile ice ages, periods distinguished not by an abundance of saber-toothed cats and woolly mammoths but by ice caps at the poles. For most of its 4.5-billion-year history, our planet was too warm for polar ice. Tyrannosaurus rex’s steamy Cretaceous kingdom 66 million years ago was in many ways a more representative slice of history than our own. Back then, reefs blanketed the beds of shallow seas as warm as bathwater, and jungle creatures watched the southern lights dance behind gaps in the thick canopies of Antarctic rainforests.