This article in today’s NYT highlights new research that shows that locally produced food in some instances may actually be more energy intensive than food imported from hundreds or thousands of miles away. While this may surprise many environmentalists, it shouldn’t.
A lot of factors contribute to the total energy/carbon footprint of food, and the distance the food travels is only one dimension. But there are many other reasons to question the "local is always better" logic.
For example, importing grains can be an amazingly efficient way for areas lacking in water to conserve water resources. Dried grain is light, doesn’t require refrigeration, and is nutritious. Areas like the Midwest that receive lots of rainfall are great areas for grain production, while deserts in California are not.
There is an added dimension as well. Many developing countries rely on agricultural exports to generate foreign currency so that they can buy medicines, cellphones, clothes, and all sorts of goods that help them improve their material standard of living. If everyone in the developed world suddenly stopped importing their food, they would be further impoverished.
None of this is to suggest that food miles are not something to be conscious of, but they aren’t the only thing. One of the insights from economic analysis is always to focus on the root of a problem, because of the law of unintended consequences. If energy consumption or carbon emissions is the real problem, then policies aimed directed at energy or carbon costs are the best way to address the issue, not a secondary dimension such as food miles.