Under a variety of methods, estimates of the world's population exposed to extreme heat indicate very large and growing numbers and an increase since pre-industrial times. For example, Li et al.  estimate that globally, 1.28 billion people each year experience heatwave conditions similar to that of the lethal Chicago 1995 event, compared with 0.99 billion people that would be similarly exposed under a pre-industrial climate. Further, for the 150 most populated cities of the world, a 500% increase in the exposure to extreme heat events occurred over the 1980-2017 period , while for the 1986-2005 period, the total exposure to dangerous heat in Africa's 173 largest cities was 4.2 billion person-days yr-1 . Globally the present exposure to heatwave events is estimated to be 14.8 billion person-days yr-1, with the greatest cumulative exposures measured in person-days occurring across southern Asia ,
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report