Sigh.
Peak estimates of the carbon footprint of manufacture and transportation to point of sale for a bicycle is 150 Kg CO2 equivalent.
That's about 60 gallons of gasoline. Or less than three full tanks in an Escalade. (P.S. The Escalade didn't magically appear without a carbon footprint either. I don't know if you've checked out the weight in steel of an Escalade, but it's a wee bit heavier than a bicycle.)
Are you riding SINGLE USE bicycles? Then worry about the carbon footprint of your bicycle manufacturing. Otherwise, it's noise.
(Next, you'll be complaining about your increased methane output if you ride a bike instead of drive.)
-mr. bill