A new study says 2 billion to 3.5 billion people in 50 years will be living in a climate that historically has proven just too hot to handle.
Monday's international study calculates the ideal climate niche where humanity has flourished and then looked at areas projected to get hotter and more crowded by the year 2070. Right now, 20 million people live in areas where the annual average temperature is 84 degrees or hotter.
In half a century that will likely be way past 1 billion people, and in an unlikely but worst-case scenario 3.5 billion people. And most of these people will be in poor nations, unable to afford air conditioning.