I have a contrasting opinion about this "SCREW YOU CO2" bicycle t-shirt. Riding bikes increases the air's carbon dioxide. More than a car? I highly doubt it, but certainly enough that riding a bike does not go as far as to say "screw you".
Telling people to stop raising animals, to have smaller families, and that they must plant trees on their own property, are all non-starters politically, but those are the best answers.