Greetings, Macaroni Munchers.
A lot of my friends are concerned about buying food from too far away, in the interests of both helping out the local economy and of reducing fossil fuel consumption. It's a scary thought about how much our food supply depends on non-renewable resources like transportation fuel, and it's appealing to have the visceral connection to what you eat that you can get only from being able to visit the place where your food grows.
Agriculture and the Developing World
The unfortunate consequence of favoring domestic produce, however, is that you deprive the developing world of the much-needed foreign exchange which comes from agricultural exports. In fact, in non-industrialized areas of the third world, pretty much the only thing they produce that we consume is food.
A typical Nicaraguan farm worker earns about $.25 an hour (a quarter the minimum wage of neighboring Costa Rica). The cost of living there may be quite low, but still I'm disgusted by the fact that they could pick coffee for 8 hours and not earn enough money for a singe espresso shot in an American café.
By insisting on buying domestic food, we're just driving developing-world wages down farther. There are plenty of options for Americans: they don't all need agricultural work to stave off extreme poverty. Giving meaningful work to developing nations promotes the sense of coöperation which leads to good feelings and peace.
Dependence on developing nations for food can also lead to peace-making policy. You're less likely to invade another country if you need the food they produce to survive.
Aside: I'm being overly-dramatic. Americans consume on average 3790 calories per day (although some of that is spoilage), so losing even a third of food imports wouldn't spell widespread famine. At the same time, you're less likely to go to war with an entrenched trading partner; the European Union may have ushered in an age of post-historicism, now that individual countries are so economically entwined that it would be sillier than ever to go to war.
Fuel Costs by Sea and Land
Trade and peace aside, many of my friends want to consume as little fossil fuel as possible in getting their food delivered, so they're careful to buy only from locally-grown produce. However, raw distance-from-home is a poor tracker of fuel consumed, since freight by sea is so much more efficient than by land. Let's figure out just how much more efficient it is to ship a container one mile by sea than by land.
By land, a typical mileage rating for a semi truck carrying a 53-foot trailer is about 6 miles per gallon. Page 5 of this document has all of the relevant information: an ultra-sized container ship traveling at 22.5 knots burns 180 tonnes of fuel per day, and carries 10 000 twenty foot-equivalent units of cargo. After a little math, we find the ship transports the same 53-ft container at 44 miles per gallon.
A ship coming to the United States from Chile burns about the same amount of fuel per container as a semi truck traveling about 700 miles, and if people drive 8 miles to the grocery store to buy 50 lbs of groceries in a car rated at 30 miles per gallon, they burn as much fuel per grocery item as that container ship from Chile.
Before jumping on the "local food" bandwagon, please consider the impact of shunning the developing world. Also, consider biking, busing or walking to the grocery store when possible if you're really interested in reducing fossil fuel consumption.