Environmental activists are encouraging Americans to buy more locally grown products to lower climate-changing emissions. But could a shift in the American diet be even more effective? Yes, according to a study published in the journal Environmental Science and Technology.  As VOA's Rosanne Skirble reports, the study found that red meat and dairy products are responsible for nearly half of all greenhouse gas emissions from the food an average American household consumes. 

There is an environmental cost in just moving food from the farm to your table. The farther food travels, the greater the emissions from the truck or boat or plane that carries it. The argument goes, if you could minimize that energy use, you could minimize the associated carbon dioxide emissions, says Christopher Weber, associate professor of environmental and civil engineering at Carnegie Mellon University  and the study's lead author.

"This isn't just transporting from the pig farm to the person, but transporting the feed from the corn field to the pig, transporting the fertilizer from the fertilizer manufacturer to the corn field and vice versa, going all the way back to, say, moving the oil from Saudi Arabia to the U.S.," he says.

The researchers looked at the total life cycle of greenhouse gases emitted to produce the food consumed by an average American household.  It turns out that transportation as a whole is not the main offender. It accounts for about 11 percent of those food-related emissions, with only 4 percent in the final delivery stage from producer to retailer. Agricultural and production practices are responsible for almost all the rest.

Weber says methane and nitrous oxide from farm animals - in their manure - is far more polluting than the most familiar greenhouse gas, carbon dioxide.  

"These animals are producing a lot of manure which, if it is not handled correctly, which more often than not in this country is true, it produces methane and nitrous oxide, which are 20 and 200 times as potent as CO2," he says.

Simply put, red meat is far more greenhouse-gas-intensive than all other foods, and Weber says, "You can have a much bigger impact by eating less grain-fed red meat and dairy in your diet than you can by eating locally."

Weber says a shift from beef to chicken, fish or eggs, or a vegetable-based diet just one day a week would have more impact on the environment than buying all household food locally for an entire year.

"That would reduce your total impact by about 1,000 miles [1,600 kilometers] a year in a standard car," he says.

If the average household were to shift totally away from red meat and dairy toward a vegetarian diet or one with some chicken, fish and eggs in it, that would amount to driving 8,000 fewer miles, or 13,000 kilometers.

Weber has taken that message to heart. He eats no red meat and prepared his vegetarian Thanksgiving dinner with locally grown produce, knowing his carbon footprint would be lighter.

"I haven't actually gone and done the actual calculations of how this would compare to a traditional meal, but I am fairly confident that it would be considerably lower," he says.  

Weber says in the next step of his research, he hopes to address the emissions impact of land use and different agricultural practices.