In a recent post citing our data on metro cap-and-trade costs, Free Exchange, the blog of the Economist, feared that people are moving from “clean” metropolitan areas with low carbon emissions to “dirtier” ones with higher emissions. As evidence, the author points to a recent paper by Ed Glaeser and Matthew Kahn, who argue that cleaner cities have set up the most onerous barriers to population growth.

There are two empirical problems here, but before getting into those, it is worth affirming the link between reform efforts related to exclusionary zoning and the environmental movement. Denser areas, with less suburban sprawl, which is created in large part by zoning, not only provide more economic opportunities for minorities and the poor, but they also reduce emissions by shortening commutes and facilitating public transportation. Reform efforts should seek the elimination of anti-density barriers, as part of an effort to reduce carbon emissions.

Now for the problems: Are people really flocking to “dirty” metros? Not any more than they are moving to clean metros. There is an insignificant positive correlation between emissions and housing supply growth at the metropolitan level. Using growth data from 1990 to 2000 for the 50 largest metros, I find that the relationship disappears completely if you adjust for initial population density, which is negatively correlated with both growth and emissions. A graph in Glaeser and Kahn’s paper also demonstrates the absence of a significant relationship between emissions and growth using data from 2000 to 2006.