How Green Is My Orange?

How much does your morning glass of orange juice contribute to global warming?

AP PepsiCo is tracking the carbon footprint of making orange juice.

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.

PepsiCo finally came up with a number: the equivalent of 3.75 pounds of carbon dioxide are emitted to the atmosphere for each half-gallon carton of orange juice. But the company is still debating how to use that information. Should it cite the number in its marketing, and would consumers have a clue what to make of it?

PepsiCo’s experience is a harbinger of the complexities other companies may face as they come under pressure to calculate their emission of carbon dioxide, a number known as a carbon footprint, and eventually to lower it.

“The main thing is helping us figure out where the carbon is in the chain,” said Neil Campbell, president of Tropicana North America, a division of PepsiCo. While acknowledging that protocols for measuring greenhouse emissions are far from perfect, Mr. Campbell said, “you can end up doing nothing if you let that stop you.”

PepsiCo, a manufacturer of soda, salty snacks and cereal based in Purchase, N.Y., is among a growing number of companies that hope to get ahead of potential government mandates and curb their energy use as prices and long-term supply grow less certain.

They also want to promote supposedly low-carbon products to consumers anxious about rising global temperatures; such labeling has already appeared in Europe.

The list of companies that have taken steps to reduce carbon emissions includesI.B.M. , Nike , Coca-Cola and BP , the oil giant. Google , Yahoo and Dell are among the companies that have vowed to become “carbon neutral.”

PepsiCo is among the first that will provide consumers with an absolute number for a product’s carbon footprint, which many expect to be a trend. The information will be posted on Tropicana’s Web site. The company has not yet decided if it will eventually put it on the package.

While carbon reduction efforts are generally welcomed by environmentalists, some complain that the marketing claims are backed by fuzzy numbers and dubious assumptions.

Standards exist for determining a carbon footprint, but companies can apply them in different ways. They can decide how rigorous they want to be in counting emissions in the supply chain, and what data sources they should use in the process.

“Any time people are making a legitimate effort to reduce emissions directly or indirectly with their product and services, most of us would think that is a good thing,” said Michael Gillenwater, dean of the Greenhouse Gas Management Institute, a nonprofit organization that teaches greenhouse gas management and accounting.

“The trick is when you try to put a strict label that has implications for comparing your product to another product, or implying that you have no climate change impact,” he said.

Nancy Hirshberg, vice president for natural resources at the yogurt maker Stonyfield Farm, said measuring a carbon footprint is a “fabulous tool” for pinpointing areas to reduce emissions. For instance, her company was surprised to learn that milk production was a far bigger contributor to greenhouse gas emissions than its factory.

But she said there were so many variables in determining a carbon footprint that an absolute number was meaningless as a marketing tool.

“I’m thrilled that people are thinking about their carbon footprint, but to put a number on a package is misleading at best,” she said.

PepsiCo’s interest in determining the carbon footprint of its products began in England, where carbon anxiety is further advanced than in the United States. In 2007, Walkers, a PepsiCo brand, published the carbon footprint of its potato chips on its Web site and on the package.

Mr. Campbell, who ran the Walkers brand, championed the idea when he came to Tropicana at the beginning of 2008. As was the case with Walkers, Tropicana hired an outside auditor, the Carbon Trust, to review its calculations and certify its footprint. The Carbon Trust was set up by the British government to accelerate progress toward a low-carbon economy.

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Making orange juice is relatively straightforward: the oranges are picked by hand, trucked to the plant, squeezed, pasteurized and packed into cartons and shipped by train to distribution points around the country. Early on, company officials roughed out the carbon footprint of Tropicana juice. But when the Carbon Trust came back with its own calculations, that initial estimate was off by more than 20 percent.

Growing the oranges accounted for a larger share — about a third — than PepsiCo had expected, almost entirely because of the production and application of fertilizer.

Now, PepsiCo managers said they planned to work with their growers and with researchers at the University of Florida to find ways to grow oranges using less carbon. And they are starting to grapple with ways to teach the public how to interpret the carbon footprint of a product.

PepsiCo is scheduled to announce its Tropicana results on Thursday, and will publish carbon-footprint numbers for products including Pepsi, Diet Pepsi and Gatorade. Said Bryan Lembke, a PepsiCo manager on the project: “If you don’t measure it, you can’t improve it.”

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