After I wrote a column critical of Illinois’ local-food law, a couple of readers accused me of ignoring the energy used in shipping food. A comment from Oni, for example, said:

Shipping food all over the place has several problems not mentioned in the article (go figure). The “free market” is not the answer to everything.

When you look into the scholarly literature, though, buying food from far away isn’t actually a problem, carbon-footprint-wise. Tim Harford, author of The Undercover Economist, said in a Forbes column last year that the locavore movement exaggerates the amount of food that travels by air. And even when food is air-freighted, he calculates, the carbon cost is tiny:

You’d need to fly a lot of Chilean grapes to emit a ton of carbon dioxide: about 350 pounds of Chilean grapes, to be precise. Even taking into account the evidence that carbon dioxide is more damaging when emitted by aircraft, the carbon cost of flying a half-pound bunch of grapes to your region is almost certainly less than 25 cents, perhaps less than one cent.

Two Carnegie Mellon University engineering professors, Christopher L. Weber and H. Scott Matthews, also concluded that the food-distance problem isn’t much of a problem. Most of food’s carbon footprint comes in the growing and processing, not the shipping. Weber and Matthews write:

Transportation as a whole represents only 11% of life-cycle GHG (greenhouse gas) emissions, and final delivery from producer to retail contributes only 4%.

Even if you vowed to buy 100 percent of your food from local growers — an unrealistic goal if you like, say, bananas or oranges — you wouldn’t be doing much for the planet. There are more effective ways to reduce your dietary carbon footprint, Weber and Matthews say:

Shifting less than one day per week’s worth of calories from red meat and dairy products to chicken, fish, eggs, or a vegetable-based diet achieves more GHG reduction than buying all locally sourced food.

Finally, Time’s Joel Stein didn’t delve into the economics or the physics of the issue before deciding to concoct a “distavore” meal in which everything came from at least 3,000 miles away. It does sound tasty, though, and Stein includes a blistering indictment of the locavore folks:

The local-food movement is deeply Luddite, part of the green lobby that measures improvement by self-denial more than by actual impact — considering shipping food in containers is often more energy-efficient than a local farmer trucking small amounts that are then purchased on a separate weekend farmers’-market trip you take in your SUV. So I’m going to keep buying food from my foreign neighbors. Because it’s the only way we Americans learn about other countries, other than by bombing them.