We study clean energy subsidies in a quantitative climate-economy model. Clean en-ergy subsidies decrease carbon emissions if and only if they lower the marginal product of dirty energy. The constrained-efficient subsidy equals the marginal external cost of dirty energy multiplied by the...

"Prices versus quantities" (Weitzman 1974), a hugely influential paper, is widely cited (and taught) in current debates about the best policy to reduce greenhouse gas emissions. The paper's criterion for ranking policies suggests that technological uncertainty favors taxes over cap and trade....

We introduce a "smart" cap and trade system that eliminates the welfare costs of asymmetric information (“uncertainty”). This cap responds endogenously to technology or macroeconomic shocks, relying on the market price of certificates to aggregate information. It allows policy makers to...