The local wits in Salina, Kansas, like to say the easiest way to for us “eat locally” around here is to heat up a Tony’s® frozen pizza. It’s not just that Tony’s has a large plant on the west side of town. Salina is also surrounded by wheat fields and is home to a large flour mill. Our local pizza, at least theoretically, could be assembled on a local crust.

But our hometown pizza can be considered local only if we ignore the many miles ingredients like tomato sauce, cheese, pork and beef travel to reach the plant. To that should be added the highway or rail miles logged by the cattle and hogs who gave their lives for the pizza; the distances that feed grains and soybean meal traveled to reach the feedlots, dairy farms and hog-confinement facilities where the animals were raised; the trips that tomatoes took to the sauce factory, and the miles that fertilizers and other inputs were hauled to reach the fields where the tomatoes were grown.

We eat lots of high-mileage meals. In 1997, the distance traveled by an average food item from its site of production to the average U.S. grocery store (counting only the delivery distance, not the transportation involved in production) was 980 miles. In the next few years, food imports shot up dramatically; as a result, by 2004, the average food item was traveling 1,230 miles.

That is widely viewed as an undesirable, if not absurd, situation. The Seattle Times, for instance, advises, “Transportation of food requires copious amounts of fossil fuels and other resources that contribute to global warming and pollution, so the lower the food mileage we rack up, the better.”

In a report stressing the need for more localized food, Iowa State University’s Leopold Center analyzed two healthful vegetarian dinners consisting of rice, stir-fried vegetables and salad. The first was prepared with ingredients from a family garden, a farmers’ market, and a food co-op; the second was put together from fresh, store-bought ingredients. Adding up the lengths of trips taken by all 13 ingredients from farm to kitchen, the first meal–despite efforts to localize–had logged 3,445 miles. It scored well, however, compared with the second, conventionally prepared meal, which had traveled 22,100 miles–circling the earth, figuratively speaking. But does that Iowa meal teach a useful lesson about the national or global food system? In other words ….

Do Food Miles Even Matter?

With rising demand for localization of food production, the concept of “food miles”– first formulated in the early 1990s and generally understood as the sum of miles a given quantity of food travels from the point of production to the point of final sale or consumption — remains a popular indicator of sustainability. A quick news search last week turned up 70 articles in the previous month that included the term “food miles.”

Reducing food miles, local-food advocates argue, will not only reduce carbon emissions by shrinking transportation networks but will also help ensure that food is produced more responsibly and is of high quality. Although food from nearby sources is desirable for many such reasons, research over the past few years has shown that simply calculating food miles in the absence of other information does not capture the complexity of the food system in a way that is useful to the well-intentioned eater.

In a much-cited 2008 paper (pdf), Christopher Weber and Scott Matthews of Carnegie-Mellon University calculated that per U.S. household, the shipping of food from farms to retail outlets racks up 3,000 ton-kilometers per year (which could be accumulated by any combination of weight and distance — for example, by hauling three metric tons of food 1,000 kilometers). This is what they called the “final delivery” leg of the food chain, the part normally used in calculations of food miles.

But, say Weber and Matthews, we should also take into account food production, which requires that other materials (for example, fertilizer, fuel and animal feed) be hauled a total of another 9,000 ton-kilometers per year per household! In sum, transportation for production plus delivery comes to 12,000 ton-kilometers annually. That consumes a lot of energy and produces a lot of greenhouse emissions; however, transportation has far from the biggest climate clout in the food business. Final-delivery food miles, the focus of many localization efforts, account for only 4 percent of the food system’s total emissions.