What we referred to in the Turning the Corner plan was an anticipated price of carbon of $65 a tonne by, I think, 2018. The complexity of this, as I understand it, is that the price of carbon under almost any plan that is a pathway to medium- and long-term targets is in any given year not going to be the same. It will be a price that can be set implicitly by fiat, it can be a market-determined price, and it's very difficult to project what that price is going to be.
Then that price, in interacting with other economic circumstances--energy prices may be influenced by the world oil price and so on--will directly combine to influence the cost to the economy of any given regulatory or cap and trade system. So it's very difficult to know what the price will be at any given point. Indeed, the whole world--those who are contemplating national policy that would put a price on carbon--is grappling with these same issues.