A human body may be able to adapt to extremes of dry-bulb temperature (commonly referred to as simply temperature) through perspiration and associated evaporative cooling provided that the wet-bulb temperature (a combined measure of temperature and humidity or degree of ‘mugginess’) remains below a threshold of 35 °C. (ref. 1). This threshold defines a limit of survivability for a fit human under well-ventilated outdoor conditions and is lower for most people. We project using an ensemble of high-resolution regional climate model simulations that extremes of wet-bulb temperature in the region around the Arabian Gulf are likely to approach and exceed this critical threshold under the business-as-usual scenario of future greenhouse gas concentrations. Our results expose a specific regional hotspot where climate change, in the absence of significant mitigation, is likely to severely impact human habitability in the future.* OK, without airconditioning. Although, it's actually pretty incredible to me that people lived there at all before airconditioning. Here's the summary from phys.org:
It would still be rare, and cities such as Abu Dhabi, Dubai and Doha wouldn't quite be uninhabitable, thanks to air conditioning. But for people living and working outside or those with no air conditioning, it would be intolerable, said Eltahir and Pal. While Mecca won't be quite as hot, the heat will likely still cause many deaths during the annual hajj pilgrimage, Eltahir said.