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MADELEINE BRAND, host:

This is Day to Day. I'm Madeleine Brand.

ALEX CHADWICK, host:

I'm Alex Chadwick. There's so much attention these days on being green, buy a hybrid car, or, like Madeleine's husband, put in a veggie diesel burner, use fluorescent light bulbs, recycle plastic bottles, what about what you eat?

Unidentified Woman #1: Food contributes a third of the world's greenhouse gasses.

Unidentified Man #1: What happens on your plate is how we change the landscape, the atmosphere.

Unidentified Man #2: These strawberries are grown 30 miles from here.

Unidentified Woman #2: What can I do with my food choices?

BRAND: Well, this week, we bring you a series of conversations about the environmental costs of our food, and, remember, we asked you to send us the questions that most interest you about this topic? Now, we try to answer those questions, and to help us out, we brought in an expert.

CHADWICK: Doctor Gina Solomon is a senior scientist with the Natural Resources Defense Council. She is speaking with us from San Francisco. Dr. Solomon, welcome to Day to Day.

Dr. GINA SOLOMON (Senior Scientist, Natural Resources Defense Council): Thank you.

CHADWICK: Before we go to our listener questions, would you please just give me an idea of how much carbon or other greenhouse gases, like methane, how much of that is associated with the production of food compared to, say, cars, what comes from cars?

Dr. SOLOMON: Worldwide, about 18 percent. So nearly one fifth of the human-produced greenhouse gas pollution comes from animal agriculture. That's significantly more than what comes from automobiles. One pound of beef generates the equivalent of over 36 pounds of carbon dioxide.

CHADWICK: When you say animal agriculture, do you mean animals or animals and grain production?

Dr. SOLOMON: The grain that the animals eat is definitely part of the picture, and so, when the United Nations came up with their one fifth figure, they put together the fertilizer manufacturing to grow the animal feed, the energy use on the farm, the transport of the feed, the transport of the animals, the processing of the animals, and even the changes in land use as a result of animal agriculture.

CHADWICK: But just to be clear, you're talking about just raising animals. This isn't what goes into growing vegetables or grain for human consumption?

Dr. SOLOMON: No. Vegetables and grains have a much smaller carbon footprint than animal agriculture. There's a big difference.

CHADWICK: OK, a surprising figure to me. 20 percent of the carbon accumulation of the world is associated with raising animals for food. Now, here's some listener questions. Listeners wondering about the environmental impact of a strictly vegan and vegetarian diet versus a diet with meat and dairy.

Dr. SOLOMON: That's a great question because there are carbon calculators on the web, and I could give you a URL for a good one.

CHADWICK: OK, we'll post a link to that on our website, but go ahead.

Dr. SOLOMON: What you can do with the carbon calculator is put your money into either fruits and vegetables or into dairy products and meat, and see what the difference in your greenhouse gas emissions turn out to be. If you are a typical family of four, and you switch from eating a diet with meat and dairy and also some fruits and vegetables to a exclusively vegan diet, you reduce your carbon emissions by about a million metric tons per year.

CHADWICK: Is there some difference in food processing? And I'm thinking of the processing required to make fake bacon out of tofu, or I'm not quite sure what you make it out of, as opposed to processing real bacon.

Dr. SOLOMON: The costs of the processing are relatively small, in my opinion, compared to the costs of the entire life cycle and production of the meat. Now, bacon is interesting, though, because it comes from pigs, which is actually smaller source of greenhouse gas emission than cows. That's because cows are major emitters of methane and nitrous oxide, which are very powerful greenhouse gases.

CHADWICK: I have another question from a listener here, but, from you've said already, maybe I already know the answer. Here it is. What is the most energy intensive food? I'm guessing it goes moo.

Dr. SOLOMON: Yeah, the most energy intensive food is pretty much anything that comes from a cow.

CHADWICK: OK, here's a question, and this is from us here at Day to Day. What are the challenges that we are all going to face in trying to assess just the carbon impact of food production, a kind of question we're setting for ourselves this week.

Dr. SOLOMON: Assessing the true full life cycle carbon impact or greenhouse gas impact of anything is very difficult. But people are getting better and better at it, really taking the entire life cycle of a product, and that's been done reasonably well for meat agriculture, which is why we now know that we can point to the cow as a big source of the problem. And the amount of beef that most people eat in a year generates at least a third as much pollution as their car generates in a year and, in some cases, more.

CHADWICK: Do you know, and this is a listener question, do you know what the carbon impact of soy is? And you talk about the life cycle of these products, what about soy?

Dr. SOLOMON: Soy requires fertilizer to grow, and it does also create some land use changes. You know, a lot of it depends on where the soy is grown, but I can tell you that the main problem with soy is that a lot of it is fed to animals, so that the direct human consumption of soy is a smaller problem than the fact that most of it goes into animal feed.

CHADWICK: Doctor Gina Solomon. She's a senior scientist with the Natural Resources Defense Council. They have all sorts of online tools to help you figure out the carbon cost of food. We'll link to them at npr.org. Doctor Solomon, thank you.

Dr. SOLOMON: Thank you.

BRAND: And tomorrow our series on the environmental footprint of food continues. Cafeterias across the country are serving up something different.

Unidentified Woman #3: We're not saying don't eat beef and cheese. We're saying, can it be a quarter of the volume on your plate versus half or two thirds?

BRAND: It's the low carbon diet tomorrow on Day to Day.

CHADWICK: It's Day to Day from NPR News. Stay with us.

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