Not that this article contradicts my previous post, since the latter focused on the healthfulness of the food, not just its environmental impact, but this article raises lots of great questions and helps undo the simple-minded, “local is best” mindset. I am obviously in favor of local food, especially that grown ~20 ft. from my kitchen (!), but there are SOOOO many complicating factors. This article lays them bare.
I find this a perfect example of why a carbon tax on energy is the best way to go. As you inflate the price of CO2 producing energy, the price alone helps you account for the CO2 impact and you will naturally avoid the high-CO2 producing foods.