Calculating “food miles” — the distance a particular food item travels from the farm to the consumer — has become a kind of shorthand for a particular food’s “greenness,” at least in terms of its greenhouse-gas emissions. The lower the number, the better; hence, the popularity of the “100-mile diet,” in which you consume only foods produced within 100 miles of your home.

Fighting food milesBut the concept has, inevitably, been attracting some skepticism and criticism, to which can now be added The Locavore’s Dilemma, a book by Pierre Desrochers and Hiroko Shimizu, published in 2012, which is critical of the concept and the importance that some people have attached to it. Of food miles, they write, “Despite its popularity, the concept and its underlying rationale have been convincingly debunked in numerous Life Cycle Assessment studies, a methodology that examines the environmental impact associated with all the stages of a product’s life cycle, from raw material extraction to disposal of the finished product. Not surprisingly, it turns out that food miles can only be taken at face value in the case of identical items produced simultaneously in the exact same physical conditions but in different locations — in other words, if everything else is equal, which is obviously never the case in the real world.”

The major shortcoming, they continue, is that transportation turns out to be nowhere near the largest source of emissions for most food. They point to U.S. research showing that transportation contributes only about 4 percent of total emissions related to most groceries, while the production phase accounts for about 83 percent of households’ carbon dioxide footprint in terms of food. The bottom line: It makes little sense to deploy intensive inputs — such as heat and lights, for example, to grow tomatoes in a cold, dark climate — to produce a food that could be produced in another region with less technology applied and then transported in bulk quantities.

In a July 2 interview with Grist magazine, the authors spoke of local-food movements throughout history, which all failed: “There was a local-food movement in the British empire in the 1920s, and it turns out that even the British empire was not big enough to have a successful local-food movement. The First World War cut Germany off from the rest of the world, so they had to revert to local food. And, of course, people starved there, and they had a few bad crops and all the problems that long-distance trade had solved came back with a vengeance.”

Nevertheless, the authors said their goal was not to do away with the idea of local food, just to shift the focus away from transportation to areas like production where a real difference could be made. “You should stick to what you’re doing best, and then trade with others, and that way everybody will be better off,” they said. “And don’t pretend that [local food] is helping the Earth — [it’s] just producing a niche product for upper-crust consumers.”