The Wet-Bulb Bottleneck; No, We Won't "Adapt", And Neither Will Lot Of Other Life Forms

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And it doesn’t get any better after 2050. But forecasts about the disintegration of society are social and political speculations and have nothing to do with mass extinctions. Huber is more interested in the hard limits of biology. He wants to know when humans themselves will actually start to disintegrate. His 2010 paper on the subject was inspired by a chance meeting with a colleague.

“I presented a paper at a conference about how hot tropical temperatures were in the geological past and [University of New South Wales climate scientist] Steve Sherwood was in the audience. He heard my talk and he started asking himself the very basic question: ‘How hot and humid can it get before things start dying?’ It was literally just an order of magnitude kind of question. I guess he thought about it and realised that he didn’t know the answer and wasn’t sure anyone else did either… Our paper really wasn’t motivated by the future climate per se, because when we started we didn’t know if there was any kind of realistic future climate state that would fall within this habitability limit. When we started, it was just like, ‘We don’t know. Maybe you have to go to, like, 50C global mean temperature.’ Then we ran a whole set of model results and it was rather alarming to us.”

Sherwood and Huber calculated their temperature thresholds using the so-called wet-bulb temperature, which basically measures how much you can cool off at a given temperature. If humidity is high, for instance, things like sweat and wind are less effective at cooling you down and the wet-bulb temperature accounts for this. “If you take a meteorology class, the wet-bulb temperature is calculated by basically taking a glass thermometer, putting it in a tight wet sock and swinging it around your head,” he said. “So when you assume that this temperature limit applies to a human, you’re really kind of imagining a gale force wind, blowing on a naked human being, who’s doused in water, and there’s no sunlight, and they’re immobile and actually not doing anything other than basal metabolism.”

Today, the most common maximums for wet-bulb temperatures around the world are 26C to 27C. Wet-bulb temperatures of 35C or higher are lethal to humanity. Above this limit, it is impossible for humans to dissipate the heat they generate indefinitely and they die of overheating in a matter of hours, no matter how hard they try to cool off. “So we were trying to get across the point that physiology and adaptation and these other things will have nothing to do with this limit. It’s the easy-bake oven limit,” he said. “You cook yourself, very slowly.” What that means is that this limit is likely far too generous for human survivability.

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https://www.theguardian.com/environment/2017/sep/09/this-is-how-your-world-could-end-climate-change-global-warming