It’s already over dying hot. It’s the humidity that is the important factor. Scientifically it’s known as “wet bulb temperature”, which makes the teenager in me snigger, but the adult which I am terrified.

As I understand it, it’s the temperature/humidity combination at which the human body can no longer regulate using natural mechanisms, eg sweating. Healthy human body temperature is normally ~37C, so being somewhere which is 99% air humidity and a temperature of 40C is effectively like being in a bath of 40C water. No matter how much you sweat, the humidity overrides the cooling effect of sweat evaporating. A high fever temperature is >38C, so our bodies are incredibly temperature sensitive and any significant amount of time spent at temperatures higher than this will start to cause serious health issues and eventually death.

Thanks you for listening to my Ted talk. Sweet dreams.