Ezra Klein draws attention to a study by Christopher Weber and Scott Matthews of the Carnegie Mellon University, which breaks down the carbon footprint contribution to a typical American food basket. Some interesting findings of the study are
1. 83 percent of emissions came from the growth and production of the food itself. Only 11 percent came from transportation, and even then, only 4 percent came from the transportation between grower and seller (which is the part that eating local helps cut). This means that the food shipped from far off may be better for the environment than food transported within the country -- ocean travel is much more efficient than trucking.
2. The average American household burns through about 8.1 metric tons of greenhouse gases as a result of food consumption. By contrast, if your house has a car that gets 25 mpg and you drive 12,000 miles a year (US average), that produces 4.4 metric tons of greenhouse gases. Therefore, switching to a totally local diet is equivalent to driving about 1000 miles less per year.
3. Red meat and dairy are responsible for nearly half of all greenhouse gas emissions from food for an average U.S. household. Replacing red meat and dairy with chicken, fish, or eggs for one day per week reduces emissions equal to 760 miles per year of driving. And switching to vegetables one day per week cuts the equivalent of driving 1160 miles per year.