To be more specific, the figure of merit is the wet-bulb temperature. http://en.wikipedia.org/wiki/Wet-bulb_temperature http://en.wikipedia.org/wiki/Wet-bulb_t

To be more specific, the figure of merit is the wet-bulb temperature. http://en.wikipedia.org/wiki/Wet-bulb_temperature http://en.wikipedia.org/wiki/Wet-bulb_temperature There are a great many places where people live that regularly exceed 45 C in the summer. However, these places also tend to be very dry. So it's misleading to think "it only hits 105 in Memphis but it crosses 120 in Las Vegas, so Memphis will be fine". In reality the wet-bulb temperature in Vegas is usually lower than in Memphis. Human beings cannot survive when the wet-bulb temperature goes above 35 C. There are a number of cities that occasionally see wet-bulb temperatures above 32 C, which could become deadly heat waves in a severe warming scenario. This is particularly true near the warmest seas -- the Gulf of California, the Red Sea and the Persian Gulf. (Mazatlan in June is absolutely miserable.) There was a recent study published in Science about it: https://advances.sciencemag.org/content/6/19/eaaw1838 https://advances.sciencemag.org/content/6/19/eaaw1838