Is walking worse for greenhouse gases than driving?

It appears it could be depending on how you get your calories.

These posts at Freakonomics, pointing to a long post calculating the impact of walking versus driving goes some way to turning conventional wisdom on its head. Here's the story: walking requires energy. The fuel for this energy is food. The amount of food required to replenish the calories burnt walking can require more energy and produce more externalities than driving.

I love economics because of its ability to confound conventional wisdom. And no where, perhaps, does conventional wisdom need more confounding than in confronting the very real challenges of climate change.