I would suggest that the first signal that needs to be there is that we'll be talking about an escalating regime. So you could start at a relatively moderate rate, let's say even $20 or $25. I think $15, frankly, by 2012, will already be too low. But it could be at around $20 and ratcheted up, with fairly clear signals as to the extent to which you're going to be ratcheting it up over the next decade or two. The Intergovernmental Panel on Climate Change estimates that carbon capture and storage will start becoming a feasible option, from a price signal perspective, if you start going above $30 to $35. For me, that's the bellwether mark, getting it to $30 to $35, and then incrementally raising it thereafter.
