I just scored a copy of
How Bad are Bananas at the library and have been completely engrossed.
To my surprise, the author provides the following information about riding a bike 1 mile.
If your cycling calories come from cheeseburgers, the emissions per mile are about the same as two people driving in an efficient car
The good news is that cycling that mile under the influence of a banana has a footprint of about a quart of the cheeseburger. I believe powering with oatmeal calories emit even fewer grams of carbon dioxide.
I guess I have been pretty smarmy about cycling vs motoring, but now will remind myself that it is only an efficient means of transportation if my diet is also not too wasteful of food resources.