The Greenness of Cities

March 5, 2008
Edward Glaeser (Glimp Professor of Economics, Harvard University) Matthew Kahn (Professor, UCLA)

This paper was originally released at the March 2008 conference, "Green Cities: Lessons from Boston and Beyond," at the Boston Public Library.

Over the past 50 years, automobileoriented suburbs have grown much more quickly than denser urban areas, and over the past six years, the four fastest growing American metropolitan areas have been Atlanta, Dallas, Houston and Phoenix—all hot places that use an impressive amount of electricity to create a pleasant year-round climate. Cars and air conditioners both lead to significant emissions of carbon dioxide, which an increasing body of evidence has linked to potentially dangerous climate change. If this evidence is correct, then there are serious social costs associated with new forms of development that tend to be extremely energy intensive. These findings do not imply that there is one right form of urban development. However, they do suggest that low-density development, particularly in the South, is associated with far more carbon dioxide emissions than higher density construction. If, as a society, we are seeking to reduce our carbon emissions, then it might make sense for us to consider steps that would make it relatively more attractive to build up areas with a lower carbon footprint and less attractive to build more homes in places where emission rates are particularly high.