News

It’s the meat not the miles

Diet substance has a greater impact than diet origin on greenhouse gas emissions

By
1:44pm, May 1, 2008
Magazine issue: Vol. 173 #17, May 24, 2008
Sponsor Message

Buying local certainly reduces the miles food goes before we eat. But consumers aiming to shrink their ecological footprint will get more bang for their environmental buck by eating less red meat and dairy, reports a new study. The analysis finds that transporting food to the consumer accounts for only 4 percent of food-associated greenhouse gas emissions, while production contributes a hefty 83 percent.

“There are many good reasons for going local,” comments Rich Pirog, associate director of the LeopoldCenter for Sustainable Agriculture at IowaStateUniversity in Ames. “But this study is important. Food miles alone are not a reliable indicator of environmental impact.” For the average U.S. consumer, getting the equivalent of one-seventh of a week’s calories from chicken, fish or vegetables instead of red meat or dairy will do more to reduce greenhouse gas emissions than buying all local, all the time, the researchers say. Crunching the numbers revealed that delivery to the consumer accounts for only 1 percent of red meat–associated emissions. But the production path to red meat and dairy products is clouded with nitrous oxide and methane emissions, mainly from fertilizer use, manure management and animal digestion. “Methane and nitrous oxide production are huge in agriculture,” says the study’s first author Christopher Weber of CarnegieMellonUniversity in Pittsburgh. These greenhouses gases are often left out of similar analyses, which have tended to focus solely on carbon or energy use. “That misses a huge part of the picture,” Weber says. Weber, who conducted the study with colleague, H. Scott Matthews, notes that they aren’t trying to downplay the benefits of buying local. “I shop locally,” he says. “But there’s been so much emphasis on food miles. We felt it was important to look at the whole life cycle.” Using data from the U.S. departments of Commerce, Agriculture, Transportation and other sources, Weber and Matthews modeled the total greenhouse gas emissions generated in making and moving all sorts of foods from cereals to fish to cheese. The work, to appear in the May 15 Environmental Science & Technology, paints a broad brush, cautions Weber. Because the model uses Commerce Department data, the food categories are defined by Commerce Department food sectors. So while cheese and milk are considered separately, fruits and vegetables are put in the same category. Apples and oranges aside, the paper “is an important contribution,” comments Greg Keoleian of the Center for Sustainable Systems at the University of Michigan in Ann Arbor. “More quantitative assessments like this are needed to help us understand the consequences of our choices.” The research highlights how complicated those choices are. “There is no one silver bullet way of reducing climate change,” says the LeopoldCenter’s Pirog. “These are very complex systems.” He notes that the environmental burden of food goes beyond emissions — fertilizers often impact water quality, for example. And while land use may not be as efficient on a small local farm, if that farm’s beef cattle are eating grass, they may have a lot less environmental baggage than corn-fed cattle from a conventional feedlot. Other choices, such as purchasing heirloom tomatoes, are important for maintaining crop diversity, which makes the agricultural sector less susceptible to diseases and pathogens. Weber and Matthews’ analysis looks at the hard numbers of getting food to the plate, and paying attention to that path has merit, says Keoleian. But Americans would do well to make those paths less traveled, period, he says. A 2003 study Keoleian conducted with University of Michigan colleague Martin Heller found that 26 percent of edible food in the United States is wasted, uneaten on the plate or left as offerings to the mold gods in the back of the fridge. Upgrading appliances, like refrigerators, can also substantially reduce food-related energy consumption, he says. If there’s a take-home message, it might be that one-dimensional food choices aren’t very effective, Weber says. Pirog agrees. “As we look at food purchases we need to consider health, safety, the environment, economics and community,” Pirog says. Overwhelmed? Don’t be. This new study just reemphasizes the sound advice people have been getting since elementary school, Pirog says. “Eat a healthy balanced diet, with a minimum of processed food. Eat a moderate amount of dairy and meat. Eat more whole grains and veggies. Following that advice will probably reduce your carbon footprint.”

More from Science News