End of the line: A Note on Environmental Policy and Innovation when Governments cannot Commit

It is widely accepted that one of the most important characteristics of an effective climate policy is to provide firms with credible incentives to make long-run investments in R&D that can drastically reduce emissions. Recognizing that a government may be tempted to revise its policy design after innovations become available, this note shows how the performance of two policy instruments –prices (uniform taxes) and quantities (tradeable pollution permits)– differ in such a setting.I also discuss the gains from combining either instrument with subsidies to adopting firms.