Is Earth really getting too hot for people to survive?

Many countries have seen extremely hot weather lately, but in most of the inhabited world, it’s never going to get “too hot for people to live here,” especially in relatively dry climates. When it’s hot outside in dry places, most of the time our bodies can cool off by evaporating water and heat from our skin as sweat. However, there are places where it occasionally gets dangerously hot and humid, especially where hot deserts are right next to the warm ocean. When the air is humid, sweat doesn’t evaporate as quickly, so sweating doesn’t cool us the way it does in drier environments. In parts of the Middle East, Pakistan and India, summer heat waves can combine with humid air that blows in off the sea, and this combination can be truly deadly. Hundreds of millions of people live in those regions, most without access to indoor air conditioning. Scientists like me use a “wet bulb thermometer” to get a better sense of this risk. A wet bulb thermometer allows water to evaporate by blowing ambient air over a damp cloth. If the wet bulb temperature is over 95 F (35 C), and even at lower levels, the human body...