Urban Population Share and Carbon Footprints

I am teaching Ed Glaeser's Triumph of the City to my undergrads right now; he has a chapter called "Is there anything greener than blacktop."  Just for fun, I plotted urban land share by state (source Demographia) against CO2 emissions per capita by state.  Here is what you get:

The regression line is log-linear.  An R2 of .28 on a bivariate relationship is not awful.  One should never make claims based on such things, but they are kind of fun to look at.