The regions that would likely be hardest hit include India, Bangladesh and Pakistan, home to more than a billion people.
The evidence has been gathered using data that shows deadly effects of hot weather are associated with a combination of high temperature and high humidity. These levels are recorded using a measurement known as “wet-bulb temperature,” which basically “reflects the ability of moisture to evaporate,” according to BBC’s report on the matter. When these “wet bulb” temperatures reach 35 degrees Celsius, the human body simply cannot cool itself on its own anymore, and can only survive a few hours.
Nowadays, wet-bulb temperatures rarely rise above 31 Celsius, but in 2015, when these temperatures reached the limit, 3,500 people were killed by heat in India and Pakistan. According to professor Elfatih Eltahir, one of the authors of the study published in the journal Science Advances, by 2100 around 70 percent of the population of India could be exposed to 32C wet-bulb temperatures.