Will rising heat reverse population growth in hot U.S. counties?
Core argument: The U.S. county at the 90th percentile of heat averaged about 62 days per year above 80°F daily average temperature over 1951–1980, rising to 72 days over 1991–2020.
The link between extreme heat and population growth was strongly positive in the 1980s. That relationship weakened substantially over the subsequent two decades and vanished entirely over 2010-2020. The projections for the decades ahead show a continuation of this pivot. “Hot” climate counties have gotten considerably hotter - to a point where they are no longer as tolerable. The 90th percentile county over 1951-1980 averaged about 62 days per year of daily average temperatures above 80◦F. That number grew to 72 days from 1991-2020. The projected climate changes are predicted to cause a general shifting of population from the Southeast and parts of the Southwest to the North, the Mountain West, and most of the Pacific coastline.




