In the first decade of this century, for the first time in history, the majority of the planet's population resided in cities. We are an urban planet. If ongoing changes in climate are to have an impact on the human species, most of these impacts will play out in cities. This fact was brought into full relief in the summer of 2003, when more than 70,000 residents of Europe perished in one of the most prolonged and intense heat waves in human history....