Growing kinda cooler or growing really cooler?

I've previously posted on the recent National Research Council report on the linkage between compact development, vehicle miles traveled (VMT), and carbon emissions. Now the authors of Growing Cooler, a previous study conducted for the Urban Land Institute, have offered a response.

Both sides agree that the built environment and energy use are correlated enough to necessitate federal, state, and local policy responses in favor of compact development, but the two groups disagree on the magnitude of the effect. The NRC sees a moderate correlation, while the Growing Cooler authors project a much greater environmental impact from development patterns. The NRC report predicts a metropolitan area VMT reduction of 1 - 11% by 2050 from more compact development. Growing Cooler expects 12 - 18% reductions.

The details of this difference are too numerous and complex to get into here, but it mostly comes down to different predictions about the future. Will 2050 look much like now only further down the same trends, or will changes in energy prices, demographic composition, consumer preferences, environmental consciousness, etc. alter the underlying conditions more substantially?

On this note, Witold Rybczynski says pretty much the same thing with less numbers and more gusto in this month's Atlantic. Check out the Green Case of Cities:

"Being truly green means returning to the kinds of dense cities and garden suburbs Americans built in the first half of the 20th century. A tall order—but after the binge of the last housing boom, many Americans might be ready to consider a little downsizing."