You are correct that me riding a bike (by myself) has no measurable effect on the world, which is another reason why I ride for me, not the rest of the world. Millions of additional cyclists could have measurable effects on the price of fossil fuels. However, I think it is realistic to expect people to continue to burn fossil fuels until extracting these fuels becomes a zero sum gain (until it burns as much energy to extract than you get out of it). We are near or at peak oil now, so, unless you can convince the entire world to abandon use of fossil fuels, cyclists, will have no real effect on the rate of consumption. We can't consume fuel any faster than we are now. If hundreds of thousands of Americans abandon the car in droves, others will willingly consume whatever we save. Therefore, I do not believe that cycling to save the earth is a worthwhile endeavor. There are better reasons to cycle.

Recycleable shopping bags are a good thing, I agree. I think my point is that most "green" marketing suggests that you can save the earth without really altering your lifestyle. To have a real global impact, serious lifestyle alterations, by millions and millions of people are necessary. It is unlikely that millions upon millions of people will do this willingly. More likely, resource scarcity, will force these changes at some point in the future. If and when that happens, it will be painful. For the people who are least dependent on fossil fuels, the transition will still be painful, but less painful.