Briefly, just to correct what I said, almost all economists agree that a carbon tax is the most cost-effective way to reduce greenhouse gas emissions.
I would like to say a couple of things. We've heard from a couple of people this idea that there's a choice between putting a price on carbon and spurring technology innovation. It's actually not a choice. The two are integrally related. You need both. Part of what spurs technology innovation is the idea that you may actually sell that technology someday. What helps you sell that technology is having a price on pollution.
Part of the reason we don't see adequate levels of clean innovation, even though carbon and other kinds of pollution are a real cost, is that pollution is not priced by the economy. This is what economists call an “externality”. Even a conservative right-wing economist like Milton Friedman used to tell his University of Chicago students that his free market theories don't work when it comes to pollution, because private markets don't price pollution.
Putting a price on carbon is one of the critical things you need to drive the invention and the adoption of these clean technologies. It's not the only thing, but it's vital.