There's a New York Times article that explains how Andy Revkin chatted with Ed Begley, Jr. about the energy that was needed for the cabbie to power a pedicab. "Walking is not zero emission because we need food energy to move ourselves from place to place," says Chris Goodall (author of "How to live a low-carbon life" and the same person behind this argument when it surfaced last August). The key is that we have to take in account the energy used to make our food. If you replace your calories with, let's say, a cup of milk, you have to take in consideration the cow's methane emissions and the CO2 used for transport until your house. Of course, using a home-harvested baked potato, or even better, a home-grown raw carrot, actually makes your walking cleaner from a CO2 perspective.
To go even further, Michael Bluejay, from Bicycleuniverse states that someone who eats the standard American diet does more environmental damage by walking compared to a car that gets better than 24 mpg. Although the best option is using a bicycle, which is more efficient over a distance.
This by no means should justify the use of cars over other means of transport, as Goodall himself adds a comment to the NYT article: "The food supply chain is about 20 percent of UK emissions, about the same as private transport. Motor vehicle fuel efficiencies are improving in Europe, driven by regulatory fiat. There is no similar push to improve the CO2 performance of the food supply chain. World meat consumption is expected to double by 2050. (source NYT Feb 24 2008). This is incompatible with a stable climate."
- ABC's Boston Legal says walking is more polluting than driving
- Here's a new one: walking is worse for the environment than driving