Concrete and steel more enviromental than grass and trees?

Grow a forest. Protect it from axes that hack.
Then the Lorax and all of his friends may come back.--Dr. Seuss

From Ed Glaeser's The Lorax Was Wrong (via Greg Mankiw):

But cars represent only one-third of the gap in carbon emissions between New Yorkers and their suburbanites. The gap in electricity usage between New York City and its suburbs is also about two tons. The gap in emissions from home heating is almost three tons. All told, we estimate a seven-ton difference in carbon emissions between the residents of Manhattan’s urban aeries and the good burghers of Westchester County. Living surrounded by concrete is actually pretty green. Living surrounded by trees is not.

Maybe Dr. Seuss got his doctorate at the same place Dr. Ruth got hers.