A recent study by a pair of researchers at Carnegie Mellon University came up with a surprising result, though. While transporting food long distances definitely contributes to greenhouse gases, that amount is tiny compared to the impact of red meat and dairy.
...engineers Christopher Weber and H. Scott Matthews of Carnegie Mellon University in Pittsburgh have found that although most foods in the U.S. are transported over long distances, the process of making the food dominates greenhouse gas emissions. Indeed, they traced 83 percent of the average household's food-related footprint of greenhouse gases to the origins of the food itself. Transportation only contributes 11 percent of greenhouse gas emissions on average—with the transportation leg from producer to retailer accounting for just 4 percent.The big culprit is, of course, cattle. Not only do they crank out vast amounts of methane (and methane is a much more potent greenhouse gas than CO2), but other aspects of the production process are also GHG intensive.
The start-to-finish process of raising and distributing red meat causes more greenhouse gas emission than any other food group, with dairy products coming in second. Animal products create the greatest amounts of nitrous oxide, emitted as a result of soil fertilization and management, because animals are inefficient at using plant energy. Producing red meat and dairy also causes the bulk of all methane emissions, which are put out by ruminant animals and manure fertilizer.The scale is such that, for the average household, just cutting a little over a day's worth of red meat and dairy would totally balance out the buy-local effect.
Which isn't to say that buying local isn't a worthy goal - it is. But encouraging people to cut out meat and dairy is even better. Even one meatless day can have a big impact; cutting our red meat entirely would be as good, from a GHG perspective, as driving a more fuel efficient car or cutting out a couple of airplane flights.
For perspective, food accounts for 13% of every U.S. household's 60 t share of total U.S. emissions; this includes industrial and other emissions outside the home. By comparison, driving a car that gets 25 miles per gallon of gasoline for 12,000 miles per year (the U.S. average) produces about 4.4 t of CO2. Switching to a totally local diet is equivalent to driving about 1000 miles less per year, Weber says.Another good point - ocean shipping is much more efficient than trucking. So food brought in by boat from Chile to San Francisco has a fairly low impact - better than potatoes trucked in from Idaho.
Which is good news for us, since we eat no red meat, but are addicted to mangoes and coconuts...
