The Real Reason Cities Can Be So Much Greener Than Other Places

For those who do research on the sustainability of cities, there's a tantalizing puzzle. Per capita, cities are greener than other places; urban residents have a much smaller ecological footprint.

In our current models, we understand only about half of that difference, perhaps even less. To be sure, some of the greenness of cities is not so hard to explain. For example, people drive less in bigger cities because it's harder to drive, and because it's easier to get around without a car. Other factors are small in themselves, but add up: the closer spacing of buildings results in lower transmission losses and pumping energy; there's less embodied energy in roads and other infrastructure; urban residences tend to be more compact and energy-efficient.