At the Bloomingdale Farmers Market near 1st and R streets in Northwest D.C. there are a lot of goodies this time of year, and shopper Scott Roberts has stocked up for the week. In his arms is a veritable cornucopia of fall produce: kohlrabi, celeriac, winter squash, and radishes.
The environment is one of the reasons Roberts -- and many people -- shop for local food at markets like Bloomingdale.
"I read all the stories about the cost of energy to transport food from elsewhere and, if you can produce your food locally it's better for the environment," Roberts says.
It's true, everything at the Bloomingdale market comes from nearby. "We source from the Chesapeake watershed, that’s the rule," says Carrie Shepard, the market’s manager.
By contrast, conventional food travels an average of 1,250 miles before getting to its final destination. So why does anyone fly in food – sometimes from half a world away - and use up all that fuel when they can get lettuce or goat cheese from the next county over?
Weighing distance against other factors
The answer? Because it's more complicated than just distance, says Richard Pirog, senior associate director of the C.S. Mott Group for Sustainable Food Systems at Michigan State University. First of all, there’s not a set definition of local: many people settle on a distance of 100 miles, and in the federal government’s farm bill, "local" is defined as 400 miles. But either way, local is a measure of distance, not environmental impact.
And when it comes to assessing that environmental impact, distance must be weighed with the type of transportation used to deliver the food, as well many other farming concerns.
How did it move?
"You could have some fruits and vegetables that are trucked in from only 100 miles away and those same items could come by train from 500 miles away and train is so much more of an efficient mode of transport that the items delivered by rail take less energy and less fuel," says Pirog.
In one study, researchers compared apples shipped to the U.K. by sea with apples grown in the U.K. and stored. The sea shipping was so much more efficient than storing U.K. apples in cold storage for half a year that it was better from a greenhouse gas perspective for Brits to get their apples from New Zealand than their own back yard when the fruit was not in season.
How was it made?
Food transport is only part of the emissions picture, however, says Pirog. On average, delivery from farm to market is about 4 percent of all the emissions it takes to produce food in the U.S. By one estimate, 83 percent of our carbon footprint for food happens before that food ever leaves the farm, – so how a piece of food is produced is often more important than how it was moved.
"Local food doesn’t necessarily mean organic food," says Pirog.
In terms of energy inputs, there can be a totally different calculation. Peter Tyedmers, an associate professor at Dalhousie University in Canada, studied this using salmon farming systems in Scotland, Chile, and Norway.
For example, a hungry Edinburgh consumer could choose Scottish salmon – which is farmed – because of the lower environmental impact, Tyedmers explains. "But if you took that choice, that would have resulted in markedly higher greenhouse gas emissions and energy inputs and acidifying emissions than if you’d picked the Norwegian salmon fillet that had been frozen and trucked down to you a thousand miles away," he says.
That’s because in different regions, salmon farmers had to use more feed, and some feed is a lot more environmentally costly to produce than other feeds. So even with miles of trucking, the non-local salmon came out on top, in terms of greenhouse gas emissions.
On efficiency, the market tends to rule
If someone can produce food a thousand miles away, and ship it here, and it's still cheaper, chances are they're pretty efficient, says Rod Ludema, a professor of economics at Georgetown University.
"If there were substantial energy savings associated with local food production you should see that in the price," Ludema says. "And you don't."
Some areas are simply better at producing food, he adds. "When we import food from sunny places, we're essentially harnessing more solar energy than all the photoelectric panels in this country combined," he says. "So its very green in that sense of the word."
Imperfect decisions and trade offs
Other researchers point out that not all food is equal. It takes a lot more pollution to produce a steak than it does a bowl of rice or even a chicken breast. One study by Chris Weber and Scott Mathews calculates that if everybody in the U.S. ate 21-24% less red meat, they’d save as much greenhouse gas emissions as if everyone were to suddenly eat local.
So what does this mean for shoppers just trying to do the right thing? As Tyedmers points out, it's not that local food is any worse or better. In some cases, it may be the better choice, especially when it comes to fruits and vegetables. But it’s hard to know. It really comes down to what the consumers' values are.
"People throw up their hands, and say, ‘oh local, I really believe in local, and now you’re telling me that local may not be great,'" Tyedmers says. "My message isn’t that local is inherently inferior. We just need to learn to live with decisions that aren’t always perfect. We're always making tradeoffs in our lives."
One trade off for an unclear carbon footprint may be knowing food comes from an organic farmer, or that you are promoting biodiversity. (Local producers often have unique heirloom varieties whereas industrial crops tend to be uniform.) It may be that it’s important to a consumer to support a local farmer, to be able to visit a farm, or to promote a sense of community.
There is, of course, one last trade-off – it’s a no brainer for Lindsay Darrah at the Bloomingdale farmer’s market.
"The food here tastes better," she says.
Local food is often extremely fresh, and conventional produce is sometimes bred to last 1,000 miles in a train car rather than to maximize flavor.
So, is local food better? Depends on how you look at it. As one researcher put it, the good thing about food is that while it has a global impact, we make multiple decisions about it every day.
[Music: "Farmer's Market" by Count Basie and New York Voices from Live at Manchester Craftsmen's Guild]
Photos: Local Food