There’s an article in today’s New York Times about PepsiCo’s effort to calculate the carbon footprint of its products, starting with Tropicana orange juice. A half-gallon of Tropicana represents the equivalent of 3.75 pounds of carbon dioxide emissions. This is roughly the same amount of carbon dioxide emitted by a 5-mile drive to the grocery store (assuming 25 mpg and 20 pounds of CO2 per gallon of gasoline). Researchers at the Lenfest Center for Sustainable Energy at Columbia University are collaborating with PepsiCo on this project (we’re among the “math experts” referred to by the NYT), so I’d like to throw a couple of ideas out there. It was a bit surprising to find that food (a.k.a. calories) was the largest source of carbon in OJ, not transport or manufacturing. If this pattern holds true for PepsiCo’s other products (life-cycle analyses for soft drinks are coming soon), what are the implications for agricultural production? Are there fertilizers that could replace nitrogen (a precursor to nitrous oxide, a greenhouse gas) without significantly lowering yields? And perhaps, how may carbon-footprinting affect our choices about what to eat?