My backyard garden is giving me mixed results this year. I did okay with the strawberries and snap peas, but the peppers are only so-so and the tomatoes are downright pathetic. Personally, I’m chalking it up to the lousy spring, not my laissez-faire attitude toward vegetables.

Still, I love it. My garden is definitely not saving the world or anything, but there’s something weirdly profound about coaxing food from the ground. (Or in my case, coaxing some dicey-looking salad greens from the planter box.) Growing food scratches some peculiar itch we have, whether it’s a glimmer of our agrarian past or a sense of self-reliance. It may even be good for us.

While eating locally is probably not the most important environmental decision we make at mealtime it often has important benefits. (More on these below the jump.) But what’s local? And can we city dwellers really sustain ourselves locally?

Enter Matt Stevenson — Sightline’s friend, periodic GIS contractor; he’s a data-fiend and map-maker. So I wasn’t surprised to see that he’d produced this map showing where you can eat on 100 mile diet if you live in Seattle:

100 miles

This 100-mile diet would be tough. There’s some good farmland—especially in the Skagit and northern Willamette Valleys—as well as some opportunity for seafood. But there’s a lot of dense forest in there; a lot of rock and ice; and a lot of development too.

Sure, fine. But Matt isn’t satisfied with general qualitative remarks like these. He crunched the numbers to figure out how much farmland we’re protecting near our urban areas—and whether it could sustain us. The news isn’t great.

  • In his blog post that accompanies the map, Matt writes:

    As it turns out there is far less acreage in cultivated crops than in hay/pasture, and within 50 miles, each acre of cultivated crops would need to feed 172 people! If we assume that all of the hay/pasture can be converted into cultivated crops, the number of people supported by one acre drops to 22. Moving out to 100 miles improves the situation, with just under 31 people per acre of cultivated crops and just under 7 per acre for all agricultural land.

     That means the numbers doen’t pencil out under any set of assumptions:

    However, according to one study, a meat-based diet requires 9 acres per person! A diet that is primarily plant-based (with some milk, cheese, and eggs) requires 3/4 of an acre.

    So even if we all became vegetarians we couldn’t sustain ourselves on the amount of farmland nearby (to say nothing of the type of farmland and local growing conditions). Not even close, although I’d be curious to know how the number change if we extended the line another 50 miles or so to capture the fertile valleys on the east slopes of the Cascades.

    Here at Sightline, we’ve written quite a bit about local food and its benefits (see here for a list). But the general tenor is that it’s very difficult—make that very, very difficult—to quantify the climate attributes of food, whether it’s local or long distance. One recent study, reported in an engaging article called Do Food Miles Matter?:

    …found that transportation creates only 11%… of the greenhouse gases… that an average U.S. household generates annually as a result of food consumption.

    I guess there are several ways to parse this. I think 11% is kind of a lot. But on the other hand, a big chunk of that transportation figure is from consumers getting to and from the store (or farmers’ market); it has nothing to do with the locality of the food source.

    Still, all else being equal, local food may shave some greenhouse gas emissions and fossil fuel consumption. Plus, not everything is about climate emissions. Eating local can have positive economic and cultural benefits: it helps sustain local farms and can encourage niche industries like troll-caught fish, organic poultry, or heirloom vegetable varieties. And at the end of the day, eating local is a bit like gardening: it’s just really, really satisfying somehow, even if you can’t put your finger on why.