How Green Is your Orange

BRADENTON, Fla. — How much does your morning glass of orange juice contribute to global warming?

PepsiCo, which owns the Tropicana brand, decided to try to answer that question. It figured that as public concern grows about the fate of the planet, companies will find themselves under pressure to perform such calculations. Orange juice seemed like a good case study.

PepsiCo hired experts to do the math, measuring the emissions from such energy-intensive tasks as running a factory and transporting heavy juice cartons. But it turned out that the biggest single source of emissions was simply growing oranges. Citrus groves use a lot of nitrogen fertilizer, which requires natural gas to make and can turn into a potent greenhouse gas when it is spread on fields.