"Hot and Getting Hotter: Heat Islands Cooking U.S. Cities"

"Cities are almost always hotter than the surrounding rural area but global warming takes that heat and makes it worse. In particularly days over 90°F, are associated with dangerous ozone pollution levels that can trigger asthma attacks, heart attacks, and otthe future, this combination of urbanization and climate change could raise urban temperatures to levels that threaten human health, strain energy resources, and compromise economic productivity.

Summers in the U.S. have been warming since 1970. But on average across the country cities are even hotter, and have been getting hotter faster than adjacent rural areas. ...

With more than 80 percent of Americans living in cities, these urban heat islands - combined with rising temperatures caused by increasing heat-trapping greenhouse gas emissions - can have serious health effects for hundreds of millions of people during the hottest months of the year.  Heat is the No.1 weather-related killer in the U.S., and the hottest days, her serious health impacts."

Climate Central had the story August 20, 2014.