I just got off a fascinating interview with Dr. Gidon Eshel, a geophysicist who studies the greenhouse gas impact of food. He's probably best known for being co-author on a paper about how reducing meat in U.S. diets (or flat-out going vegetarian) could make a big improvement on this country's emissions footprint. In other words, he's usually the guy telling you to stop eating beef.

But I wanted to know whether all vegetables were created equal. If you really care about reducing your carbon footprint, are there veggies or fruits you should be shunning along with the cows? The answer, according to Eshel, is emphatically "yes".

Depending on where you live, eating baby spinach or arugula is almost like eating a burger, in terms of greenhouse gas emissions. It's that intense. Sure, if you live in the Central Valley of California, or in Florida, not so. But most people live very far from those places. If you live east of longitude 100 [Draw a line through the middle of the Dakotas—MKB] and north of, say, Jesse Helms country, you have no business eating greens at all between October and June. Again, you know, you're free to do whatever you want, but if you want to be really careful about your greenhouse gas footprint, this is what you should do.

The reason boils down to the huge amounts of energy needed to run the greenhouses that grow our local baby salad mix in winter, and, to a lesser extent, the fuel burned by trucking in California-grown salad. Although, Eshel says, you'd be way better off, from an emissions standpoint, buying the California greens than buying local—if buying local means greenhouse-grown.

Want to avoid interrogating your salad supplier all winter? Eshel recommends switching to cabbage as a planet-friendly salad base alternative.

Image courtesy Flickr user timlewisnm, via CC