When it comes to heat, the human body is remarkably resilient — it’s the humidity that makes it harder to cool down. And humidity, driven in part by climate change, is increasing.
A measurement of the combination of heat and humidity is called a “wet-bulb temperature,” which is determined by wrapping a completely wet wick around the bulb of a thermometer. Scientists are using this metric to figure out which regions of the world may become too dangerous for humans.
A term we rarely hear about, the wet-bulb temperature reflects not only heat, but also how much water is in the air. The higher that number is, the harder it is for sweat to evaporate and for bodies to cool down.
At a certain threshold of heat and humidity, “it’s no longer possible to be able to sweat fast enough to prevent overheating,” said Radley Horton a professor at Columbia University’s Lamont-Doherty Earth Observatory.