locality of food matters far less that what you eat
Eating "local" is a trendy thing these days, with hipsters making much of going to the farmers' market and "Locavore" bumper stickers all over the place. And certainly, all else being equal, it's more energy efficient and gives fresher produce to choose apples from an orchard within 100 miles than to buy apples shipped over from New Zealand.
But, as is often the case, when we look more closely we see that all other things are not necessarily equal.
First off, food coming from far away will tend to use highly efficient rail transport, or moderately efficient tractor-trailers, while your local farmer is probably delivering his goods in a panel van or pickup truck.
The difference is enormous. I got curious, so I ran some rough numbers.
As you may have heard in those CSX ads, rail can move one ton of cargo 436 miles on a gallon of fuel; that works out to moving a pound of food (or other stuff) 872,000 miles on one gallon of fuel. A typical tractor-trailer might haul 50,000 pounds at 5 mpg: that's one pound moved 250,000 miles on one gallon. Now consider a panel truck that gets 20 mpg, carrying a two tons of food: it moves one pound only 80,000 miles on one gallon. (Pretend the panel truck runs on diesel, but since these are back-of-the-envelope calculations it doesn't really matter.)
The tractor-trailer and the panel truck both have to make empty return runs, while the train picks up new cargo for the next leg of its loop; so we should half the numbers for both types of truck.
Rail: 872,000 pound-miles per gallon.
Tractor-trailer: 125,000 pound-miles per gallon.
Panel truck: 40,000 pound-miles per gallon.
That means that, for the same amount of fuel it takes a small farmer to move food 100 miles in their truck, rail transport might move that same food over 2,000 miles! Of course, it has to be moved to and from the train depot, but this illustrates the issue: it's quite possible for food coming from far away to use the same or less energy to transport, than "local" food.
(Of course the most local food is what you garden or forage yourself; there's no transportation cost when I walk out front and pick a few leaves of kale, and I'm thinking of trying some experiments with the plantain that's taking over the yard...)
So in terms of transportation efficiency, local food may not be a big win, or indeed a win at all. But more than that, transportation is a small piece of agricultural energy usage, as this WorldWatch article explains. Final delivery from producer or processor to the point of sale accounts for only 4 percent of the U.S. food system's greenhouse gas emissions; add in "upstream" miles and transport of things like fertilizer, pesticides, and animal feed, and transport still only accounts for about 11 percent of the food system's greenhouse gas emissions.
80 to 90% of greenhouse gas emissions from the food system come from agricultural production. So reducing those is far more important than reducing transport emissions. And how can we shift to more efficient food production? You know what I'm going to say: plant-based diets.
The UN Food and Agriculture Organization has estimated that 18 percent of total greenhouse gas emissions come from livestock, a bigger share than the total of all transport. Livestock account for about 20 percent of the total terrestrial animal biomass. Grazing occupies a stunning 26 percent of the Earth's land area, while about a third of all arable land is devoted to feed crops for livestock.
According to Tara Garnett of the Food Climate Research Network, "Broadly speaking, eating fewer meat and dairy products and consuming more plant foods in their place is probably the single most helpful behavioral shift one can make" to reduce food-related greenhouse gas emissions.
And Christopher Weber and H. Scott Matthews of Carnegie Mellon University computed that replacing red meat and dairy with vegetables one day a week would give you the same greenhouse gas savings as driving 1,160 miles less per year. Therefore, they suggest that "dietary shift can be a more effective means of lowering an average household's food-related climate footprint than 'buying local.'"
There are certainly good reasons to choose local produce: what gets to you quicker, is fresher. And it usually implies eating seasonally available and less-processed foods, which are definite energy wins.
But often, only going local is a way for people to avoid making the hard choice to make a meaningful change in how they eat. Eating the flesh of a chicken raised and slaughtered 50 miles away rather than that of one raised and slaughtered 250 miles away, is the easy way out. The hard thing -- but the healthy, compassionate, and sustainable thing -- to do, is to reduce, or even eliminate, consumption of animal foods.