Let me make a few observation which firmly put all of that research into mad science department.
- Worrying about the carbon footprint of human metabolism is silly for two reasons. First, unless you want to consider killing humans, we cannot do much about metabolism itself. It continues even while we sleep. Second, this carbon footprint comes mostly from food production, so we should work on making food production cleaner, not stop walking around, as the paper seems to suggest.
- Among those who try to achieve a greener lifestyle, walking is not considered an alternative to driving. Environmentally friendly alternatives to driving are living closer to work, taking commuter trains and using bicycles (which are 3-5 times more efficient than walking).
- People need exercise to stay healthy. That's why people should take a walk instead of driving (that, and fresh air).
- Even if all of us walk all day long, we will only increase the pollution levels by a minuscule amount.