In very simple terms, it means that you do more than you have to do because you gain from it. The market approach of the cap-and-trade system should awaken the entrepreneurial spirit in every business person who has a cap, and drive him to reduce more than he can, to make his enterprise more efficient from an energy and a process point of view. In the process, he will eliminate the greenhouse gas emissions because he can monetize those greenhouse gas emissions. He can compare the cost of investing in reduction processes with the price he'd get for those reductions in the market.
So it's a very simple cost-benefit analysis. There's nothing magic about it.
In the deck I've provided here, you can see the numbers from American Electric Power. These numbers show that emissions between 1995 and 1999 were allowed to be 33.2 million tonnes, but the actual emission was 26.2 million tonnes, for a net sulphur dioxide benefit of 7 million tonnes.
Now, that is quite a significant reduction, and that doesn't come from somebody in the green movement; it comes from the largest carbon-emitting company in the United States.