Two Wheels vs. Four [SLATE]

How far do I have to ride my bike to pay back its carbon footprint?

Bike commuting. Click image to expand.I'm thinking about switching my daily commute from four wheels to two. But I'm concerned about all the energy it takes to manufacture and ship a new bicycle. How many miles would I need to substitute a bike for my car before I've gone "carbon neutral"?
It's tough to say exactly how much greenhouse gas making a bicycle requires, since none of the major manufacturers has released data on their energy consumption. Independent analysts have used a couple of different measures. Shreya Dave, a graduate student at MIT, recently estimated that manufacturing an average bicycle results in the emission of approximately 530 pounds of greenhouse gases (PDF). Umbra Fisk, a research associate at Grist, came up with a total carbon footprint of one ton of carbon dioxide-equivalentsfor every $1,000 of manufacturing cost. These two estimates intersect at a bike that costs $265 to build—well within the range of manufacturing costs for the wide variety of bicycles on the market.