Eating Green: Food Type Trumps Distance

April 18, 2008 -- Next time you find yourself standing in the grocery store, agonizing over whether your green conscience permits you to buy the garlic shipped in from China, relax. You'll do more to reduce the greenhouse gas impact of your diet by taking the ground beef out of your cart.

That's the finding of new analysis by Christopher Weber and H. Scott Matthews of Carnegie Mellon University in Pittsburgh, Pa., who compared the greenhouse gas emissions caused by producing and transporting various categories of food in the United States.

"If you're looking across everything that you're eating, the type of food that you're choosing matters a lot more than where it comes from," Weber said.

The pair found that transporting food from the farm or production site to the store contributed only 4 percent of the total greenhouse gas emissions in the U.S. food supply, while producing the food accounted for 83 percent.

Since production dominates, choosing categories of food whose growth and processing release less greenhouse gas can make a bigger difference than becoming a strict locovore, they report. Red meat produces more greenhouse gases than any other food category -- about 2.5 times more, on average, than chicken or fish.

As a byproduct of their digestion, cows naturally produce methane, a greenhouse gas 23 times more potent than carbon dioxide. Fertilizer and manure, meanwhile, create the even-more-potent greenhouse gas, nitrous oxide (N2O).