Extreme heat is particularly hard on older adults, and an aging population and climate change are putting ever more people at risk

Without home cooling, Phoenix's weeks with temperatures over 110 F in July 2023 became dangerous. Brandon Bell/Getty Images

Scorching temperatures have put millions of Americans in danger this summer, with heat extremes stretching from coast to coast in the Southern U.S.

Phoenix hit 110 degrees Fahrenheit (43.3 Celsius) or higher every day for over three weeks in July. Other major cities, from Las Vegas to Miami, experienced relentless high temperatures, which residents described as “hell on earth.”