A study by the prolific Carnegie Mellon University researcher Christopher Weber found that food transport accounts for only 11 percent of food-associated greenhouse gas emissions, while production contributes a whopping 83 percent. Specifically, nitrous oxide and methane -- mainly byproducts of fertilizer use, manure management and animal digestion -- make up a far bigger piece of the emissions pie than emissions from transporting our food from faraway places.

The study noted that U.S. consumers can do more to reduce greenhouse gases by eating one-seventh of a week's calories from chicken, fish or vegetables instead of red meat or dairy than buying all local foods.