USA Today: Scientists, for the first time, have a clearer picture of what causes the "urban heat island" effect, a common phenomenon that makes cities swelter by as much as 22 degrees more than the nearby countryside, especially at night in the summer. Previously, researchers thought that evaporation was the main reason why rural areas stay cooler than cities. (Evaporation, which absorbs heat energy, is greatly reduced when cement and concrete replace grass, trees and plants.) Study lead author Lei Zhao of...