Posted on February 4, 2011 - by admin
The milk that you poured into your cereal this morning, do you know where it came from? Was it delivered to your doorstep by hand? Trucked from a large dairy farm in a neighboring city? Packaged and flown across the country? Which of these results in the least amount of carbon emissions?
When it comes to sourcing our food, we are often told that it is best to eat locally to minimize the environmental impacts of food production. To illustrate this, food miles are one metric used to quantify how local your food is. Simply put, food miles measure the distance a food travels from its origin to your plate. So, an apple from a local orchard may have only 10 food miles behind it, but a frozen pizza could have been shipped 3,000 miles from a distant manufacturing plant. Moreover, the average distance that your meal travels before arriving to you has been rising. American consumers are buying processed foods more frequently, and demand seasonal produce all year long.
Intuitively, it seems like a food with lower food miles should be more environmentally friendly than a food from a more distant location. But is this really the best way to assess the environmental impact of a food?
A Red Herring
For all the attention that has been paid to carbon emissions from transportation, the truth is that they make up only a small portion (11%) of greenhouse gases generated over the lifetime of a food product. In reality, the bulk of greenhouse gases stem from production, with 83% of emissions occurring before the food even leaves the farm (World Watch). Hence, focusing solely on food miles is like mending the fence while the rest of the house is on fire.
For instance, it takes more energy to produce vegetables off-season in greenhouses than in warmer climates. Researchers in Sweden concluded that it was better for Swedes to buy Spanish tomatoes instead of locally-grown Swedish tomatoes, since the local tomatoes were grown in greenhouses warmed by fossil fuels, as opposed to the Spanish crops grown in open fields (Carlsson-Kanyama, 1997). Another example of energy-intensive processing is local produce that is kept frozen throughout winter versus a product that is shipped fresh from another place.
Not All Miles Are Equal
Meanwhile, the nuances of transportation methods throw additional kinks into the story. Trains are 10 times more efficient than trucks at transporting freight, which means you could truck a product 100 miles or move it by train 1,000 miles with the same carbon emissions impact (World Watch). In general, air transport produces the greatest amount of greenhouse gas emissions, followed by small road vehicles, large road vehicles, rail and sea freight (Pirog et al, 2009).
Let’s not forget the miles we add by traveling to and from the point of purchase. Local transportation by car and small trucks is highly inefficient compared to mass transport, and food systems that integrate bulk deliveries can be more environmentally friendly than farmers markets. One study found that driving more than 7.4 km (4.6 miles) to the farmers market to buy locally-grown food would produce more carbon emissions than purchasing from a large-scale box supplier that uses cold storage, packaging and transportation (Blouin et al, 2009).
Taking all these factors into account, you get some eyebrow-raising results when tabulating the true environmental impact of foods. Researchers found that one ton of lamb raised on New Zealand’s clover-filled pastures and transported to the U.K. by boat produced only 1,520 pounds of carbon emissions, versus 6,280 pounds for lamb raised in Britain on feed (NYT).
Blast, it appears that serious investigation of the food mile reveals that it cannot be used to make a cut-and-dried case for greener consumption. So what should the time-strapped, socially-conscious consumer do? Stay tuned next week for part two of “What’s in a Food Mile?”.