If global temperatures increase by 1 degree Celsius (1.8 degrees Fahrenheit) over current levels, each year billions of people will be exposed to heat and humidity so extreme they’ll be unable to naturally cool themselves. If the increase is 2 C above pre-industrial levels, the 2.2 billion residents of Pakistan and India’s Indus River Valley, the one billion people in eastern China and sub-Saharan Africa’s 800 million will annually experience many hours of heat surpassing human tolerance. With warming 3 C above pre-industrial levels, heat and humidity too high would affect the Eastern Seaboard and middle of the U.S. from Florida to New York and Houston to Chicago as well as South America and Australia.
www.psu.edu/news/health-and-human-development/story/climate-driven-extreme-heat-may-make-parts-earth-too-hot-humans/