Can We Survive Extreme Heat? Humans have never lived on a planet this hot.

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2. And outside arid areas, it's the wet-bulb temperature

95 F wet-bulb is the upper limit of human survivability when the humidity goes up

As humidity increases, so does the wet-bulb temperature. Because we never hit a wet-bulb temperature of 95 degrees Fahrenheit in today’s climate, it’s hard to say what the societal effects would be. But wet-bulb temperatures between 84 degrees and 88 degrees Fahrenheit (29–31ºC) have been responsible for tens of thousands of deaths around the world. A wet-bulb temperature of 86 degrees Fahrenheit (30ºC) was recorded during a heat wave in 2015 in the southeastern coastal Indian state of Andhra Pradesh that killed at least 2,500 people.

The risks are starkest for places that already see high heat and humidity, like the Persian Gulf and the Tropics. And some of the regions most at risk of these spikes are the most densely populated — places like Northeast India, East China, West Africa, and the Southeastern U.S.