Does It Really Matter Whether Your Food Was Produced Locally?
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But, say Weber and Matthews, we should also take into account food production, which requires that other materials (for example, fertilizer, fuel and animal feed) be hauled a total of another 9,000 ton-kilometers per year per household! In sum, transportation for production plus delivery comes to 12,000 ton-kilometers annually. That consumes a lot of energy and produces a lot of greenhouse emissions; however, transportation has far from the biggest climate clout in the food business. Final-delivery food miles, the focus of many localization efforts, account for only 4 percent of the food system's total emissions.
How food is grown and processed and how it travels would seem to be much more important that how far it travels. Per ton of cargo, modes of transportation differ greatly in their global-warming potential and other environmental impacts. Hauling a ton of food one mile by truck emits 16 times the emissions created by hauling a ton of grain for a mile by oceangoing ship, or nine times the emissions from hauling it by river barge. Importation of food into the United States rose a staggering 25 percent between 1997 and 2004. But because international trade is dominated by ocean-shipping, food-miles emissions increased by only about 5 percent during that period.
Local or not, some types of foods account for a far bigger share of total emissions than do others. Factory-farmed beef and pork, for example, are spectacularly climate-unfriendly. Weber and Matthews concluded that by shifting only about 20 percent of its red-meat consumption to grains and vegetables, a household could achieve the same emissions reductions that would result from totally eliminating final-delivery food miles with a radically local diet.
The Wandering Sandwich
In the United Kingdom and other northern European countries, where diets are more import-heavy than in the United States, food miles have been a topic of intense debate and research for years. In a 2004 review of the evidence ( pdf), the UK's Department for Environment, Food and Rural Affairs (DEFRA) concluded, "The impacts of food transport are complex, and involve many trade-offs between different factors. A single indicator based on total food kilometers traveled would not be a valid indicator of sustainability."
That complexity is exemplified by foods whose local production is highly resource-intensive; hauling such products long distances can actually reduce climate impacts. According to DEFRA, a UK grocery chain that imports field-grown tomatoes from Spain causes only one-third the carbon dioxide emissions that it would cause by buying domestic, greenhouse-grown tomatoes.
Last year, Caroline Saunders and colleagues at Lincoln University in New Zealand reported that because of the large quantities of energy required to raise lambs in northern Europe relative to New Zealand, UK residents could reduce their carbon emissions associated with lamb-eating more than three-fourths by buying meat raised in New Zealand rather than in the UK--even when the carbon cost of shipping meat halfway around the world was accounted for. Obtaining dairy products and out-of-season apples from New Zealand (with its reverse seasons) rather than producing and storing them for months in the UK could, they projected, cut the resulting greenhouse emissions as much as 50 percent.
One conclusion to be drawn from such studies is that given current production systems, eating red meat or out-of-season fresh fruits and vegetables is going to generate a lot of climate-altering emissions, whatever distance they travel.
Large British grocery chains now ship virtually all of their goods through their own regional distribution centers (RDCs), greatly increasing average food miles but giving small-scale food-growers a boost. By hauling their vegetables to the nearest RDC, says DEFRA, "smaller producers can gain access to national chains of shops, substantially expanding their market areas."