This provocative article by Ed Glaeser reminds me of my frustrations about Stockton's General Plan settlement.
Restricting development in your city may reduce your city's global warming contribution, but can increase greenhouse gases if it displaces development to other areas. Glaeser argues that global warming would be helped if more people lived in California, and less in Boston. Of course, CA has other resource/environmental constraints to population growth, namely water. But that would be helped if there were fewer cows in CA and more in Massachusetts.
Encouraging density within a city can help (and the Stockton plan settlement isn't all bad), but global warming can only be seriously addressed with large-scale regional plans - not city plans.