Globally, cities are the source of over 70 percent of the world's greenhouse gas emissions. Cities are also the engines of the global economy, concentrating more than half the world’s population, and they are where the middle class is rapidly expanding. Indeed, by the year 2050, two-thirds of...

Globally, cities are the source of over 70 percent of the world's greenhouse gas emissions. Cities are also the engines of the global economy, concentrating more than half the world's population, and they are where the middle class is rapidly expanding. Indeed, by the year 2050, two-thirds of...