Andrew Martin in the New York Times notices a new study that adds a few wrinkles to the locavores’ “local is better” equation with food. As with any simple equation that attempts to summarize an endlessly complex system, it has nuances.

Gail Feenstra, a food system analyst at the [University of California at] Davis campus, says her group hopes the research will help consumers decide if buying local is better than buying organic food that has traveled hundreds of miles. “Maybe you can buy organic within a certain geographic range, and outside of that the trade-offs won’t work anymore,” Ms. Feenstra said.

At some point, the ethical maze can make you dizzy. But there was one line of inquiry from the California researchers that hit particularly close to home: the carbon impact of shoppers themselves.

Some people walk or take the subway to buy their groceries and then compost what they don’t use. But, let’s face it, most of us drive and toss the leftovers into the garbage disposal or the garbage can. In doing so, we may be contributing nearly a quarter of the greenhouse gases associated with our food, research has shown.

Here’s why: Instead of going to the grocery store once a week and stocking up, many consumers are driving for groceries several times a week, if not every day, to all sorts of different stores.

(BTW, UC Davis makes olive oil from street trees on campus. How cool is that?)