Since the human body is basically a robot fuelled by food, and the production of food produces greenhouse gasses (as well as other negative things (namely farmed animals)), I wonder: 

what is the E^[1]($MtC{O}_{2}e$^[2] per meter walked) of walking? 

Or maybe some other measurement of the cost of walking? (For example, E(USD spent per meter walked).)

How does this change when, say, on a bicycle? or a scooter? or on a train? etc.

(If you did not do research on this, and do not plan on doing research on this, don't do research on this. I do not need to know this information. I just figured it would be nice to know.)

1. ^{^}

   E(X) is the expected value of some random value X, or "if you were to randomly generate different values of X, and take the arithmetic mean of them all, as the number of X's you generate gets larger, the arithmetic mean of them all approaches E(x)."

2. ^{^}

   $MtC{O}_{2}e$ means "the amount of [metric tons of [carbon dioxide]] that would be needed to produce the same impact on the environment.", or "the environmental impact, in terms of [metric tons of carbon dioxide]". (Not to be confused with "the environmental impact of ONLY the $C{O}_2.$")