Well, not directly. They respond to the same peer reviewed study that Dubner cites in his blog, namely "Food-Miles and the Relative Climate Impacts of Food Choices in the United States," by
The paper does note that the last miles to the table are not the major source of greenhouse gas emissions... agricultural inputs are. So you make more of a "green" impact by reducing consumption of red meat (since you're using a lot less agricultural inputs (fertilizer) to grow soy and corn which is fed to methane-producing cattle) than by buying local.
Ethicurean doesn't disagree. But their analysis of the paper doesn't lead them to the conclusion that local isn't better. There are other quality of life reasons for eating locally (which Dubner doesn't address... since he sticks to simple economics).
Ethicurean also stands up to Salon's recent attack on localvores here:
A dissenting commenter on this latter post dismisses the food miles issue and notes: "I buy food at farmers markets. Mostly for the reason you mention: it's picked later and thus tastes better."