People die from falling asleep in saunas because they are unable to lose heat due to high humidity. This is also a problem in caves with high humidity, and people have died in relatively cool temperatures because they are unable to cool themselves with perspiration.

There are growing numbers of "death zones" across the planet where human life is impossible without air conditioning because wet bulb temperatures are so high that it is physically impossible for the body to radiate enough heat to keep from cooking itself to death; as planet temperatures rise, inevitably there will be a power failure in one of these death zones and there will be catastrophic loss of life on a monstrous scale.