We analyse the extent to which the climate effect of unilateral climate policy in Nordic frontrunner countries may be nulli ied by the mechanics of the European Emission Trading System (ETS) in light of the recent tightening of the system. We ind that national initiatives to reduce emissions from the domestic ETS sector are likely to reduce total EU-wide emissions due to the endogeneity of the cap on ETS emission allowances. We also examine the cost-effective design of the unilateral climate policy of an EU frontrunner country, given the design of EU climate policy.Finally, we show that if the policy goal is to maximise national welfare, a uniform domestic carbon price across sectors is only optimal under special circumstances, and we highlight the importance of trade in emission rights and carbon leakage for optimal policy design.