Posted on April 24, 2008

Rich Pirog, associate director of the Leopold Center at Iowa State University [1] and one of the pioneers of the concept of "food miles [2]," is the first to concede that it's smarter to assess the environmental impact of a food item over its entire lifetime. That means looking not only at transportation impacts but also those of production and distribution.

But not a few commentators have gone further, suggesting food miles do not matter at all. For example, Dr Adrian Williams of the National Resources Management Centre at Cranfield University [3], told reporters for the Guardian [4] newspaper in the United Kingdom ("The Observer," 23 March 2008): "The concept of food miles is unhelpful and stupid. It doesn't inform about anything except the distance traveled."

Pirog has just pointed out to me three recent studies, however, which underscore that food miles still matter enormously.

The first study comes from the University of Washington in Seattle. It compares two plates with identical amounts of salmon, potato, asparagus, and apple. One is locally produced; the other isn’t. The researchers perform a Life Cycle Assessment [5] (LCA) on each plate, and find that the nonlocal plate contributed 50% more of the greenhouse gases (GHG) responsible for climate disruption than the local plate did. ("Seattle Food System Enhancement Project: Greenhouse Gas Emissions Study [6].")

Interestingly, salmon dominates both sides of the analysis because fishermen – local and nonlocal, for aquaculture and wild catch – use prodigious amounts of diesel fuel. Even so, what ultimately tips the climate scales against the nonlocal plate is transportation. The study found foreign producers of fruits and vegetables are slightly more efficient in their use of chemicals and farm fuels, but the transportation of the nonlocal plate produces six times more GHG than transportation for the local plate. Overall, the nonlocal fruits and vegetables produced nearly two times as much GHG as the local alternatives.

Somewhat different conclusions come from a team of researchers at the Catholic University in Leuven, Belgium. ("Energy Lifecycle Inputs in Food Systems: A Comparison of Local versus Mainstream Cases [7]," Journal of Environmental Policy & Planning, March 2007.) The study finds that local food systems can produce more greenhouse gases than mainstream food systems. For example, if local means a household makes a car trip to a community supported agriculture [8] farm several times each week, rather than one trip to a supermarket, the associated energy consumption is relatively high.

But the Belgian study also suggests the best GHG strategy is to localize intelligently. Walk or ride a bike when you go shopping. Choose food products that are in season (and avoid GHG burdens of heated greenhouses). Plan ahead to minimize storage and packaging requirements.

And think regionally. Interestingly, the tiny size of Belgium means that even its mainstream food system could easily fit within many U.S. states. In other words, their mainstream would look relatively local here. And some of the reasons mainstream systems in Belgium perform better – such as making sure delivery trucks are full –would certainly apply to many metropolitan food systems in the United States.

The Belgian study, like several others, suggests that some imported foodstuffs can minimize their GHG emissions by sea-based shipping, since boats are believed to have a relatively low carbon footprint. If you ship by land for very long distances, say a coast-to-coast trucking haul in the United States, that footprint gets larger. And if you ship by air freight, that footprint gets huge.

The problem is that this assumption about the lower carbon footprint of sea shipping turns out to be wrong. A new study from the United Nations Intergovernmental Panel on Climate Change [9], leaked to the Guardian newspaper ("True Scale of CO2 Emissions from Shipping Revealed [10]," 13 February 2008), has concluded that the actual GHG emissions from sea freight are three times greater than previously estimated.

In fact, the UN report calls into question nearly every study finding modest GHG benefits for certain imports. Take, for example, the widely publicized study from New Zealand suggesting that its lamb exports had a quarter of the carbon footprint as local lamb in the United Kingdom. As I’ve pointed out elsewhere ("On the Lamb [11]," The Ethicurian, 10 August 2007), that study, commissioned by New Zealand lamb exporters, is riddled with incomplete data and didn’t even look at local New Zealand lamb. Now we know that even if these problems were fixed, the study's conclusion is obsolete.

Again, measuring "food miles" cannot fully determine the carbon footprint of what we eat. But it remains an important tool – and one that will continue to remind us of the GHG advantages of localization.

By Michael H. Shuman [12]