How can walking damage the environment more than driving?

John Tierney paraphrases Chris Goodall, the author of “How to Live A Low-Carbon Life”:

How can that be? Because Mr. Goodall takes into account something that a lot of environmentalists don’t: the human energy expended in averting fossil-fuel use. “Walking is not zero emission because we need food energy to move ourselves from place to place,” he writes. “Food production creates carbon emissions.” Now, you could argue that most people are overweight and so could use the exercise anyway, but that doesn’t mean that they’re not going to consume calories to replace the ones they’ve burned. In fact, some experts argue that most people do in fact simply eat more to compensate (which is one reason so many people remain overweight). And judging from the fitness of the pedicab drivers I’ve seen, they don’t have much weight to lose anyway.

If you walk 1.5 miles, Mr. Goodall calculates, and replace those calories by drinking about a cup of milk, the greenhouse emissions connected with that milk (like methane from the dairy farm and carbon dioxide from the delivery truck) are just about equal to the emissions from a typical car making the same trip. And if there were two of you making the trip, then the car would definitely be the more planet-friendly way to go.

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