Many efforts to address greenhouse gas emissions combine a cap-and-trade system with other measures such as a renewable portfolio standard. In this paper we use a computable general equilibrium (CGE) model, the MIT Emissions Prediction and Policy Analysis (EPPA) model, to investigate the effects of combining these policies. We find that adding an RPS requiring 20 percent renewables by 2020 to a cap that reduces emissions by 80% below 1990 levels by 2050 increases the net present value welfare cost of meeting such a cap by 25 percent over the life of the policy, while reducing the CO2-equivalent price by about 20 percent each year.