The paper considers a growth model with climate change and three R&D sectors dedicated to energy, backstop and CCS(Carbon Capture and Storage) efficiency. First, we characterize the set of decentralized equilibria: to each vector of public tools, a carbon tax and a subsidy to each R&D sector, is associated a particular equilibrium. Second, we solve the first-best optimum problem and we implement it by computing the vector of optimal tools. Finally, we illustrate the theoretical model using some calibrated functional specifications. In particular, we investigate the effects of various combinations of public policies (including the optimal ones) by determining the deviation of each corresponding equilibrium from the "laisser-faire" benchmark.