Whats to stop people just buying more petrol (and so busting the cap)?
At the petrol pump, there are no controls at all – except for the price. The cap cannot be busted because there are only a fixed number of certificates issued, hence a fixed amount of petrol in circulation, corresponding to the cap. If people (the whole population taken together) want to buy more petrol than this, the price goes up until they dont. That is what supply and demand means. Its like land – there is only a finite, fixed supply of this too. I can always buy some more land (provided I have the money) – but this doesnt cause more land to be created.
