This guest post is an excerpt from Cooler Smarter: Practical Steps for Low-Carbon Living, written by the Union of Concerned Scientists and published by Island Press. Find out more at www.coolersmarter.org
If the verdict is still out on organic food, what about food produced locally? Can we reduce our carbon emissions by buying local food? Are "food miles"—the miles traveled by our dinner from farm to table—a good measure of global warming impact?At first glance, it sounds as if local must be better. If the choice is between identical food identically grown nearby or far away, local food is certainly the clear winner because it entails fewer transportation emissions. But suppose the local food is produced on a farm with higher emissions; how does that compare with the savings in transportation? In northern states, for instance, is it better to buy tomatoes grown in local, heated greenhouses or those grown in open-air fields hundreds of miles away?
To answer this question, researchers at Carnegie Mellon University studied food miles and the emissions resulting from U.S. food purchases. They calculated the total transportation requirements—and transportation emissions—of food production, not just delivery of food from farm to retail but also delivery of fertilizer, equipment, and other inputs to the farm.
Their results show that transportation accounts for only 11 percent of the carbon emissions caused by food production. Of that amount, so-called upstream transportation of inputs to the farm (or to farm suppliers) accounts for some seven percent of overall food-related transportation emissions. Most notably, perhaps, final delivery—the trip from the farm to the supermarket—accounts for just 4 percent of total food emissions on average. By comparison, production of the food accounts for 83 percent of the carbon emissions, with warehousing and wholesale and retail operations making up the small remainder.
What does this mean for you? The emissions from producing food are so much greater than those from transporting it that transportation makes up only a tiny part of your carbon "foodprint." Even if local food eliminated all the emissions from transportation, long-distance food produced on a farm with 5 percent lower emissions might actually contribute less to global warming.
An extreme example of this effect can be seen in farm products shipped to Europe or the United States from New Zealand. Several New Zealand researchers crunched the numbers to show that the carbon emissions from producing and delivering lamb, apples, and dairy products from New Zealand to the United Kingdom were actually lower than the emissions from the same foods produced locally in the United Kingdom. Why? The study no doubt sought to put New Zealand goods in the best possible light, but the numbers are still compelling: As these researchers demonstrated, not only do New Zealand farmers use less chemical fertilizer than their British counterparts, but also more than half of New Zealand's electricity derives from hydropower, which produces no carbon emissions. Those two differences, as it turns out, are enough to offset the emissions from 11,000 miles of ocean shipping.
However, it is important to note that the mode of transportation does make a difference in this calculation. Mile for mile the volume of emissions from air freight is about four times the emissions caused by truck transport and nearly 50 times more than that of ocean transport. It is certainly well worth trying to be aware of food items transported by air. Examples include fresh seafood from far away, premium cheeses, and highly perishable items such as fruits, berries, vegetables such as asparagus, and cut flowers. If something commands a premium price and is highly perishable, it is very likely air freighted. Similarly, it can be helpful to consider tropical fruit and cut flowers as an occasional treat rather than an everyday necessity. Fruits such as pineapples are typically air freighted, for instance. Bananas and other tropical fruit are shipped, but usually in refrigerated boats and then long-haul trucks. In all these examples, "food miles" make a more significant difference to carbon emissions, so it makes sense to pay special attention to air-freighted items and to encourage your supermarket to publicize information for customers about air-freighted items.
The bottom line when it comes to food miles: As the well-known food author Michael Pollan has noted, there is much to be said for serving food you know "the story behind," which is much easier to accomplish by buying locally. Buying local food is an excellent way to support farmers in your area and to ensure freshness and quality. But other strategies are more effective in reducing the global warming emissions resulting from your diet.
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