Researchers at MIT warn that if climate change remains unchecked (Business As Usual-scenario = RCP 8.5) over half a billion people will, from 2070 onwards, experience humid heat waves that will kill even healthy people in the shade within 6 hours. The Wet Bulb Temperature (WBT) would exceed 35°C (95°F), at which the body – of any mammal – cannot cool itself, overheats and shuts down.
Three regions were studied: China (2018), South Asia (2017) and the Persian Gulf (2015). The researchers predict (at RCP 8.5) WBT exceeding 35°C about once every decade for the Northern Plains in China (400+ million people), at locations in the Chota Nagpur plateau, northeastern India, and Bangladesh in South Asia (70+ million people). Persian Gulf regions that would be affected include cities such as Doha, Qatar, Abu Dhabi, Dubai (UAE) and Bandar Abbas (Iran).
The total number of people affected will be higher than 0.5 billion. A study in Nature (2017) identifies regions worldwide that are likely to exceed the survivability threshold from 2070 onwards (see Fig. 2). These also include the Eastern United States, Northern Latin America and Northern Australia.
Wet bulb temperatures higher than 33.5°C for more than a few hours have not been measured in human history (yet). In 2015 there was a severe episode in South Asia with 30°C WBT. This led to 3,500 deaths. According to this article the largest hospital in Karachi was receiving 1 patient per minute and the morgue was overflowing.
Would airconditioning be to avail? Podcast Ashesashes describes that a ‘perfect storm’ will hit power supply at extreme temperatures. Airconditioning at high temperatures leads to more than 20% extra power demand, while at the same the power grid becomes less effective, nuclear and gas fuel plants provide less power because of warmer cooling water and transformers are more likely to overheat leading to power outages. Also, it is hard to see how renewable energy could meet the peak demand. Without solutions, the areas mentioned would effectively become uninhabitable.
At the Business as Usual-scenario many billions of people would experience WBT higher than 32°C on a regular (e.g. yearly) basis, which is already deadly for the less fit and makes working outside impossible.