When there is some externality, the best way to deal it is with a tax (for a negative externality like pollution) or a subsidy (for a positive externality like education). Yet, I am continuously amazed how this policy using the market mechanism has found little reception in the United States. And economists are also very fond of it: it is the most efficient way to reach an objective, and in the case of a negative externality it even allows to reduce other taxes that distort the wrong way, like income taxes.
Joseph Aldy and Robert Stavins writes a survey article about how to best deal with carbon pollution, comparing a cap-and-trade of pollution permits, clean energy standards and taxation of carbon content. And the latter is the easy winner. And as argued multiple times on this blog, alternative energy should not be subsidized.