From the Jan/Feb '09 issue of Sierra Magazine:
Recently many concerned eaters, worried about the number of "food miles" their meals have to travel between farm and fork, have sought to eat as locally as possible. While there are many fine reasons for doing so, the transportation of food turns out to account for only 11 percent of its greenhouse-gas emissions. According to Christopher Weber and H. Scott Matthews of Carnegie Mellon University, food production is a much greater factor--especially that of red meat, because of the high energy and fertilizer use required. Switching from beef to veggies one day a week, the researchers figure, would reduce your carbon footprint more than if you bought all of your food locally.
The graph above measures various foods by metric tons of carbon dioxide equivalent per household annually. Non-CO2 gases include methane, which cows burp, and nitrous oxide, released in the growing of cattle feed. —Paul Rauber