Temperatures have been off the charts across the country this summer, and America's cities are particularly hard-hit.
Cities are heating up "about twice as fast as the rest of the planet," writes Richard Harris for NPR. The reasons are varied, but mostly boil down to evaporating water: There just isn't much of it in cities, where pavement and the built environment don't allow water to stand and evaporate. As a result, there isn't much cooling in cities.
See the story at NPR.