Our previous podcast, “You Eat What You Are, Pt. 1,”explored how American food got so bad, how it’s begun to get much better, and who has the answers for further improvement.

Now it’s time for “You Eat What You Are, Part 2.” (You can download/subscribe at iTunes, get the RSS feed, listen via the media player above, or read the transcript here.)

In this installment, we look at the challenge of feeding 7 billion people while protecting the environment, especially from all the pollution associated with the long-distance transportation of all that food. In that regard, it would seem that going local is a no-brainer — until you start to look at the numbers.

We begin with David Cleveland, an environmental studies professor at U.C.-Santa Barbara. Santa Barbara County grows $1.2 billion worth of produce a year, putting it in the top 1 percent of U.S. counties. Cleveland started out simply trying to learn how much of the produce consumed locally was also produced locally:

CLEVELAND: This is what really shocked us: we found that when you added up all these different ways in which locally grown produce got to people in Santa Barbara County, that less than five percent of the fruits and vegetables consumed in Santa Barbara County were actually grown in Santa Barbara County, and the other ninety-five percent were imported.

Next, Cleveland wanted to know what kind of environmental and nutritional effects would result if Santa Barbara were to go totally locavore. (The resulting paper, “Effect of Localizing Fruit and Vegetable Consumption on Greenhouse Gas Emissions and Nutrition, Santa Barbara County,” can be found here.)

CLEVELAND: We wanted to look at what effect 100 percent localization of the Santa Barbara County system — which is a physically and biologically a very feasible thing to do — what effect would that have on greenhouse gas emissions? And we found that it wouldn’t make a lot of difference. Our savings in greenhouse gas emissions, per household, as a proportion of the total food system greenhouse gas emissions, was less than one percent.

Cleveland’s research built on earlier work by Christopher L. Weber and H. Scott Matthews. (You’ll hear from Weber in this episode as well; he used to teach at Carnegie Mellon and is now a researcher as the Science and Technology Policy Institute.) Their paper (PDF here) is called “Food-Miles and the Relative Climate Impacts of Food Choices in the United States.” We’ve written about it before; it argues that the vast majority of the energy associated with food production is in the production phase rather than the transportation phase, which means that relying on locally produced food as a means to limit pollution isn’t necessarily a winning battle.

You’ll also hear from economist Ed Glaeser (whom you might remember from our “Why Cities Rock” podcast). He too took notice of the Weber-Matthews argument but put his own spin on it: Glaeser is an urbanist who feels that by overvaluing ideas like local-food production (a garden in every yard, e.g.), we are potentially undervaluing the greater gains to be had by living more densely. Glaeser also talks about why we get so emotional about food in the first place:

GLAESER: The idea of there being something wrong with our food cuts to the very heart of our stomachs; of our souls, almost. So it’s not so surprising that people have these deep emotional reactions to food. And we certainly are right to worry a lot about whether or not our food is fresh, and good, and tasty, but I just keep coming back to feeling a certain amount of satisfaction that I’m eating grapes that are keeping up the standard of living in Chile.

So what’s an environmentalist to do? For starters, as Weber-Matthews suggest, stop eating so many cow products. As we put it in SuperFreakonomics :