He said that he would launch a carbon cap-and-trade system, and that he would auction off the credits. One of the big arguments in regard to cap-and-trade, is whether to allow businesses that currently emit to start off in the system holding credits -- "grandfathering" them in. (This is tied up with Bush administration's efforts to make expanding an existing dirty business not trigger "new source review".) If folks know that in a year or two they're going to have to bid in an auction for the right to continue their current businesses, we're going to see much faster reductions in CO2 emissions.
In other global-warming news, Chris Dodd came out foursquare in favor of a carbon tax. I guess an advantage of having no chance, is you can say things like that...