Edward Glaser makes the perceptive observation that goes against the conventional wisodom in urban planning, "If you want to take good care of the environment, stay away from it and live in cities". Densified cities are an ideal example of a marriage between good economics and even more good environmental activism.
Comparing densified citiy centers and urban sprawls, Prof Glaeser and Mathew Kahn have found that in almost every metropolitan area, the central city residents emitted less carbon than the suburban counterparts. They also find that emissions from driving, public transit, home heating, and household electricity are lowest for city centers. They write, "There is a strong negative association between emissions and land use regulations. By restricting new development, the cleanest areas of the country would seem to be pushing new development towards places with higher emissions... Higher-density suburban areas, which are still entirely car-dependent, still involve a lot less travel than the really sprawling places."
Prof Glaeser also finds that the electricity usage for heating (and cooling) purposes is much less in cities than in suburbs. He writes, "Living surrounded by concrete is actually pretty green. Living surrounded by trees is not." The prescription that comes from these findings is unmistakable - Green Cities, Brown Suburbs. In other words, it is both green and economically efficient to build sky-scrapers and promote densified city centers.
Prof Glaeser's conclusion is revealing, "Americans who settle in leafy, low-density suburbs will leave a significantly deeper carbon footprint, it turns out, than Americans who live cheek by jowl in urban towers. And a second paradox follows from the first. When environmentalists resist new construction in their dense but environmentally friendly cities, they inadvertently ensure that it will take place somewhere else—somewhere with higher carbon emissions. Much local environmentalism, in short, is bad for the environment."
I have also argued about the benefits of densified, vertical development here.