If climate change is unchecked (RCP 8.5) South Asia will experience heat waves that “exceed the survivability threshold” (sic!) from 2070 onwards. Researchers at MIT conclude in a 2017 study that 4% of the South Asia-population, about 70 million people, would face heatwaves of humid heat that will kill even healthy people in the shade within hours. The wet bulb temperature (WTB) would reach 35°C, which means that the human body cannot cool itself and shuts down.
Three quarters (1.3 billion people) in South Asia would experience at least one heatwave before the end of the century with wet bulb temperatures of 31°C, conditions of ‘extreme danger’. To compare: In 2015 there was a severe episode in wich 30°C WTB was measured. This led to 3,500 deaths in South Asia. According to this article the largest hospital in Karachi was receiving 1 patient per minute and the morgue was overflowing.
Wet bulb temperatures currently rarely exceeds 31°C. 35°C WTB has never been measured yet.