"Urban heat islands have hotter days, far hotter nights, and more extremely hot days each summer than adjacent rural areas," said Alyson Kenward, lead author of the report and senior scientist with Climate Central. The concrete, asphalt and shingled roofs of buildings, roads and other infrastructure in urban environments usually make cities much hotter than surrounding rural areas.
On average, U.S. summer temperatures have increased nearly 2 degrees since 1970, the National Climate Assessment reported earlier this year. "Thanks to the dual action of urbanization and climate change, cities are not just hotter, they are getting hotter faster: 45 of 60 cities we analyzed were warming at a faster rate than the surrounding rural land," Kenward reported.
About 80% of Americans live in metropolitan areas. Cities also tend to have many more extremely hot days each year, on average, than nearby rural areas, the report found. Over the past 10 years, cities had an average of at least eight more days over 90 degrees each summer, compared to nearby rural areas.
Hotter summer temperatures have been correlated with higher ozone pollution, and the hottest days of the year often had ozone levels exceed the safe standard established by the Environmental Protection Agency....