While humans can survive temperatures of well over 50C when humidity is low, when both temperatures and humidity are high, neither sweating nor soaking ourselves can cool us. What matters is the “wet-bulb” temperature – given by a thermometer covered in a wet cloth – which shows the temperature at which evaporative cooling from sweat or water occurs. Humans cannot survive prolonged exposure to a wet-bulb temperature beyond 35C because there is no way to cool our bodies. Not even in the shade, and not even with unlimited water.
A 35C wet-bulb temperature was once thought impossible.
But last year scientists reported that locations in the Persian Gulf and Pakistan’s Indus river valley had already reached this threshold, although only for an hour or two, and only over small areas.
As climate change drives temperatures upwards, heatwaves and accompanying unliveable temperatures are predicted to last longer and occur over larger areas and in new locations, including parts of Africa and the US south-east, over the decades to come.
What can governments, companies and citizens do?
