Lately, I've been eating a lot of tofu in an attempt to cut back on my meat consumption. But tofu doesn't exactly grow on trees—I'm guessing it takes a lot of energy to turn fresh soy beans into soft, white stuff. Am I really helping global warming by switching from chicken breasts to bean curd?

The Lantern loves tofu, but the kind she grew up with was often smothered in pork. While that particular dish may not satisfy either environmental or ethical concerns, it is true that switching from meat to tofu should help you cut back on your greenhouse gas emissions. How significant are those savings, exactly? That depends on your current eating habits.

Let's start with a meat recap. As we've discussed before, the production of livestock takes a heavy toll: According to an extensive 2006 report from the United Nations' Food and Agricultural Organization, raising animals uses more land than any other industry. It's also a bigger source of greenhouse gas emissions than the entire transportation sector. That's why many experts have advocated going meat-free one day a week as a strategy for combating global warming.

Not all meat is created equally when it comes to environmental impacts. Producing a calorie of chicken protein requires only a fraction of the energy that it takes to churn out a calorie of beef protein. Chickens also produce significantly lower levels of greenhouse gases, thanks in part to their dainty diet and the fact that, unlike ruminant animals, they don't go around expelling methane from their mouths and rear ends.

So where does tofu fit into this picture? Soybeans themselves are a highly efficient source of protein: According to one recent study, it takes about 0.2 calories of fossil fuels to make a calorie of soybean protein, a little more than one-thirtieth of the total for chicken. Soy is also much better from a global-warming perspective: In conventional production, a kilogram of raw beans generates about 150 grams to 300 grams of carbon-dioxide equivalent, as opposed to 2,500 grams for the equivalent quantity of edible chicken meat. (Organic soybeans should produce even less CO2 equivalent. [PDF])

But then, we're not talking about eating soybeans in their natural form. As you note in your question, it takes some work to make beans into tofu. Soybeans are soaked in large tanks and ground into a slurry that then gets heated, filtered, and coagulated into slabs before being chopped up, packaged, and pasteurized. All of these steps require energy—and they dramatically increase tofu's carbon footprint.

Last year, the Dutch government commissioned a study of the environmental effects of vegetarian "meat substitutes," including veggie burgers, Quorn, and tofu. According to the analysis, a kilogram of tofu sold in the Netherlands produces about two kilograms of carbon-dioxide equivalent (PDF) from the farm to the supermarket. That's only a little less than Dutch chicken, at 3 kilograms of CO2-equivalent per kilogram of meat. Mackerel, herring, pollock, and mussels—some of which the Lantern has already championed as low-carbon options for seafood lovers—scored about the same or better than tofu. That's a much smaller difference than the Lantern would have expected.

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