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PEOPLE HIGHLIGHT the extensively transport-ed nature of our food supply with the concept of “food miles.” In the U.S., food travels an average of 1,500 miles, usually by truck, to reach the din-ner plate. “Locavores” advocate eating only food produced much closer than a half-continent’s trip away. But if climate impact is the main driver behind their decision, locavores may be taking the wrong approach.

According to a study by research assistant professor Christopher L. Weber and associate professor H. Scott Matthews, both in the de-partment of civil and environmental engineer-ing at Carnegie Mellon University, transporta-tion and food miles make a relatively minor contribution to the total climate impact of the American diet (Environ. Sci. Technol. 2008, 42,3508). By their calculation, transportation over-all reflects only 11% of food-related greenhouse gas emissions, with the final distribution from producer to retailer accounting for 4%. Instead, it’s pollution associated with produc-tion that constitute the major source of food-related greenhouse gas emissions, and those emissions vary by type of food.

Looking at the different food categories, red meat is by far the biggest contributor to greenhouse gas emissions, thanks to the inefficient conversion of plant energy into animal-based energy. Plus, there are the methane emissions produced by ruminant ani-mals such as cattle, sheep, and goats. Those same methane emis-sions catapult dairy products past poultry and fish to a surprise second-place on the greenhouse gas list.

When people change the types of food they eat, they wield a big-ger environmental impact than they could by changing the origin or the distance their food travels. So people will reduce the climate effects of their diet far more by switching to a vegetarian diet than by becoming even an extreme locavore. “Our study shows defini-tively that if you are trying to reduce the greenhouse gas impacts of your food consumption, ‘buying local’ should be secondary to changing your diet,” Matthews says.

What does that mean for someone like me? I’ve been a dairy- and egg-eating vegetarian since 1997. The initial reason for that dietary sea change was a knee-jerk response to a sausage-filled trip to Ger-many. I also wanted to prove to myself that I could actually do it. If I were in the same situation today, I hope that the environmental impact of the meat eater’s diet would play a role in my decision.

Therefore, the study by Matthews and Weber suggests that I made my biggest contribution to the cause when I became a vegetar-ian. If I want to make a significant impact from this point, the study suggests I have to give up dairy products as well.

Which brings me back to eating locally. Other than becoming

a vegan, worrying about food miles is just about the only way to decrease the environ-mental impact of my diet.

Novelist Barbara Kingsolv-er, trained in environmental

science and a frequent writer of environmental essays, is among the more prominent people who have committed themselves to eating local-ly. She chronicles her family’s one-year experi-ment in the book “Animal, Vegetable, Miracle.”

Kingsolver acknowledges that eating locally is not easy—even for people living on a farm. Her family grows a large garden, she raises heirloom turkeys, and her younger daughter, Lily, keeps a flock of egg-laying chickens. Each family mem-ber was allowed one nonlocal item, such as cof-fee, as long as he or she agreed to research ways to obtain it that were environmentally respon-

sible and fair to the producers.Kingsolver’s book challenges readers to be more aware of the

food they eat. Not everybody has the luxury—if it can be called that—of living on a farm, but most people have access to one of the many farmers’ markets that have cropped up around the country.

Eating locally might not offer quite the climate payoff that people thought, but there may be other reasons for eating locally. There’s something to be said for simply knowing where your food comes from. The recent Salmonella scare in tomatoes and jalapeño peppers certainly highlights that.

Matthews notes that he and Weber have taken heat from people who buy locally produced food. “Nowhere in our paper do we say people should stop doing those things,” Matthews says. “Supporting locally grown produce is a great way to make an economic and per-sonal contribution to improving” one’s region, he adds.

But food miles are only part of the whole equation. “People should not be focused in on food miles or any other metric without broadly understanding the sources of their impact, CO2 or otherwise,” Mat-thews says. “In general, the average household’s activities that lead to the most greenhouse gas emissions are heating/cooling their resi-dence and transportation. Food is in general third or fourth.”

All of this encourages me to be more mindful of my own food-purchasing habits and the provenance of my food. I’m taking baby steps, but I still have a long way to go. In the winter, I still buy food that has made the long journey from warmer climes, but in the summer, I buy my produce at my local farmers’ markets—and I ride my bicycle to get there.

Views expressed on this page are those of the author and not necessarily those of ACS.

Eating As An Environmentalist

WHAT YOU EAT matters more than how far it traveledCELIA HENRY ARNAUD, C&EN WASHINGTON

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markets can help people be vegetarian and eat locally.

SCIENCE & TECHNOLOGY INSIGHTS