The paper considers an endogenous growth model with climate change as well as three R&D sectors dedicated to energy, CCS (Carbon Capture and Storage) and backstop efficiency. First, we characterize the set of decentralized equilibria: a particular equilibrium is associated with any vector of policy instruments including a carbon tax and a subsidy to each R&D sector. Second, we show that it is possible to express any equilibrium as the solution of a maximization program. Third, we solve the first-best optimum problem and thereby deriving the optimal instruments. Finally, we illustrate the theoretical model using calibrated functional specifications. In particular, we investigate the effects of various combinations of policy instruments (including the optimal ones) by determining the deviation of each corresponding equilibrium from the "laisser-faire" benchmark. We find notably that introducing an R&D subsidy hardly affects emissions when a carbon tax is already implemented, thus revealing a complementary effect between these two policy instruments.