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The localvore's dilemma

Sometimes buying local food helps in the battle against climate change. Sometimes it doesn't. And sometimes, it's just too confusing to decide.

AT VARIOUS POINTS in the coming months, a few hundred of Vermont's most ethical eaters will take the "Localvore Challenge." The actual dates of the challenge vary from town to town, but the idea is that, for a single meal, or a day, or an entire week, participants will eat only food that was grown or raised within 100 miles of where they live.

Vermont's localvores (also known as "locavores" or "locatarians") and their counterparts around the country are part of a burgeoning movement. In recent years, as large companies with globe-straddling supply networks have come to dominate organic agriculture, "local" has emerged as the new watchword of conscientious consumption. Over the past year and a half, the interest in local food has been fueled by best-selling memoirs and manifestos about local eating and dietary self-sufficiency, such as Barbara Kingsolver's "Animal, Vegetable, Miracle," Bill McKibben's "Deep Economy," and Michael Pollan's "The Omnivore's Dilemma."

The case for local food is several-fold: It tastes better, its proponents argue, and preserves species biodiversity. It shores up small-scale economies and communities in the face of globalization and cultural homogenization. It even, some of its advocates claim, protects against terrorism: a decentralized food system could limit the impact of a virus or other bio-agent introduced into the food supply.

One of the arguments most often heard, however, is about energy. And at a time of rising concern about climate change, the great distances that most of our food travels are a potent symbol of the system's profligacy and cost in greenhouse gases. For local-food activists, "food miles" have become a favored measure of environmental impact. Food activists in the US and especially in Western Europe have pushed to put the term on menus and grocery-store labels.

"[T]he typical item of food on an American's plate travels some fifteen hundred miles to get there," Michael Pollan writes in "The Omnivore's Dilemma," "and is frequently better traveled and more worldly than its eater."

But a gathering body of evidence suggests that local food can sometimes consume more energy -- and produce more greenhouse gases -- than food imported from great distances. Moving food by train or ship is quite efficient, pound for pound, and transportation can often be a relatively small part of the total energy "footprint" of food compared with growing, packaging, or, for that matter, cooking it. A head of lettuce grown in Vermont may have less of an energy impact than one shipped up from Chile. But grow that Vermont lettuce late in the season in a heated greenhouse and its energy impact leapfrogs the imported option. So while local food may have its benefits, helping with climate change is not always one of them.

"All things being equal, it's better if food only travels 10 miles," says Peter Tyedmers, an ecological economist at Nova Scotia's Dalhousie University. "Sometimes all things are equal; many times they aren't."

The new research is part of an ambitious attempt to understand how food -- and the massive, almost impossibly complex system that produces and moves it across the globe -- affects the environment. For several years in Europe, and increasingly here in the US as well, food analysts have started to adopt a methodology called Life Cycle Assessment -- a comprehensive accounting of all of the resources that go into the food network, from fertilizer and fuel to the concrete and steel used to build a packing plant and the electricity used to keep it cool.

These researchers laud the public interest in food and its environmental impact, but their work, they say, shows that "local" is not the best way to think about food and energy, or the best basis for food-buying decisions. Some of these researchers are trying to devise more accurate ways of telling consumers the climate impact of their food choices. But they are discovering that the task can be tricky. The key, they argue, is to find a way to label foods that is both accurate and simple enough for consumers to accept.

Their work also highlights a more fundamental challenge for local-food enthusiasts. Michael Pollan states this challenge starkly: "Local means local in season," he says. In places like Boston, it means not only summers of fresh berries and arugula but January diets heavy on root vegetables and canned tomatoes. Can such a movement ever find mainstream acceptance?

The American food-supply network can do certain tasks very well, and one of them is to efficiently ship things over very large distances. The costs in energy can be high: air shipping is by far the most fuel-intensive, and is the fastest growing sector of food transport. However, it still only accounts for a small minority of the food shipments into and throughout the country.

Judged by unit of weight, ship and rail transport in particular are highly energy efficient. Financial considerations force shippers to pack as much as they can into their cargo containers, whether they're being carried by ship, rail, or truck, and to ensure that they rarely make a return trip empty. And because of their size, container ships and trains enjoy impressive economies of scale. The marginal extra energy it takes to transport a single bunch of bananas packed in with 60,000 tons of other cargo on a container ship is more than an order of magnitude less than that required to move them with a couple hundred pounds of cargo in a car or small truck.

"Local food systems are often built around small-scale logistics," says Chris Foster, a research fellow at England's Manchester Business School and co-author of a December 2006 study on the environmental impacts of food production and consumption commissioned for Britain's Department for Environment, Food and Rural Affairs. "You begin to make more trips in cars. More food is shifted around in small trucks and vans, which are relatively energy-inefficient ways of moving."

The difference can be dramatic, according to Rich Pirog, a food-systems researcher at Iowa State University's Leopold Center for Sustainable Agriculture. A bag of potatoes shipped from Idaho to Boston by rail, he estimates, is likely to require less energy in transit than the same bag of potatoes driven from Maine to Boston in a farmer's truck. In recent decades, the national food-distribution system has shifted from rail to trucking, so fuel use has risen, but that still doesn't necessarily make local the best energy option.

A study Pirog did of Iowa's food supply in 2001 suggested that a transition to a more localized food system, at least in Iowa's case, would cut fuel use over today's international system. But the same study found that a multi-state regional system would be better still. The trucks transporting food in that model would be bigger and more efficient per unit of food than in the local model, while not traveling as far as in a national model.

How food travels, in other words, matters as much as how far it travels, and what happens on the farm or in the kitchen can leave a much bigger energy footprint than what happens between them.

"Often it's those activities and behaviors at the two ends of the production system that tend to dominate," says Peter Tyedmers. Food analysts point out that, per pound of food, the grocery shopper's drive home from the store or farmer's market can often use more energy than the entire rest of the supply chain.

Life Cycle Assessment -- in essence an exhaustive itemization of a product's every environmental impact -- was originally developed by engineers and chemists in the late 1960s for durable goods like cars and household appliances. Only in recent years has it started to be applied to food. Most of the food research has been done in Europe, where energy costs are higher than in the US and climate change has been a less contentious issue.

A few LCA studies -- of tomatoes in Sweden, of apples and lettuce in Great Britain -- suggest that in certain situations and certain seasons, the imported option is more energy-efficient than the local one.

During the European winter, it takes far less energy to grow produce outdoors in a warm climate like Spain or North Africa or New Zealand than in a heated greenhouse in Sweden or England. The energy that goes into heating that greenhouse, the studies found, or to storing locally grown fruit at a temperature cold enough to keep it for any length of time beyond the end of the growing season, can easily outweigh the energy required to ship produce from a warmer country.

One of few comprehensive studies done in North America compared the energy used to bring consumers British Canadian farmed salmon and Alaskan wild salmon, according to Tyedmers, who led the work. The results have yet to be published, but Tyedners says that he found that everything from the method of fishing to the source of a region's electricity to the form in which the fish was transported ended up being more important factors than shipping distance.

And for cattle, the greatest climate impact comes not from hauling cows and milk and steaks around the country, but from cow burps. Cows are impressive emitters of methane, a greenhouse gas that is 20 times more potent than carbon dioxide (contrary to popular belief, most of it comes out the front of the cow, not the rear). A cow with a bit of indigestion can contribute as much to global warming in a day as the average SUV.

But if "food miles" are such a crude measure, what's an environmentally concerned grocery shopper to look to? Some food activists are targeting the ends of the food production process -- farmers both in the US and Europe are looking at ways to heat greenhouses with renewable energy, or to avoid heating them at all even during winter, and both the British government and Ben & Jerry's recently announced efforts to modify cow feed to reduce methane production. Others are working to wring inefficiencies out of the local food-distribution system by getting farmers to consolidate their produce into larger trucks making fewer trips.

More broadly, though, some food analysts are trying to introduce LCA thinking to consumers. The Swedish government, as well as the British retailer Tesco, has announced plans to affix products with "carbon labels" that announce just how much carbon was emitted in production and distribution. Here in the US, Bon Appetit Management Company, a corporate caterer that serves Yahoo!, MIT and others, plans to introduce a similar measure next spring.

Rich Pirog sees this as a start. Ultimately, he envisions a series of labels: In addition to nutrition information, a box of cereal or a bunch of green beans would bear stickers relaying their carbon emissions along with their fair-trade credentials. The risk in such a scheme, however, is that consumers, given too much information, absorb none of it.

For their part, some localvores are suspicious of such labeling proposals. "To me the whole idea of calculating out the carbon impact way overcomplicates something that should be pretty simple," says Robin McDermott, co-founder of the Mad River Valley Locavores. Even if it turned out that an imported bunch of tomatoes were somehow more environmentally friendly than a local one, she says, she'd still go with local. "There's the taste," she says, "and you're supporting local farmers."

Michael Pollan hastens to point out that eating locally is only part of a larger food ethic. The problem isn't merely, he argues, that we ship our lettuce across the country; the problem is that people living in New England, a place naturally unfriendly to large-scale lettuce production, feel entitled to eat lettuce in February. Before World War II, he points out, Americans ate locally and in season because they had no choice.

"It's a new idea," he says, "this expectation that we can have a salad all year round."

Drake Bennett is the staff writer for Ideas. E-mail