I got down-voted heavily on reddit for this idea, but I still think it's genius: Everybody gets a card with their yearly CO2 budget stored on it. For filling up your car at a gas station, but also for consuming electricity, taking a plane or buying stuff (except low CO2 food) a corresponding amount will be withdrawn from your card.

The card is credited weekly, so you can't overspend too much of it. Your saved credits will decline slowly over time. Of course all has to be balanced considering socio-economic factors.

The great thing is you can sell your credits to rich people, so it would even reward you for staying at home giving you sort of a minimal income.