Optimal carbon taxation in EU frontrunner countries: coordinating with the EU ETS and addressing leakage

Several EU countries have targets for the reduction of CO2e emissions that go beyond the target set by the EU. We study what would be the optimal carbon tax policy in such EU frontrunner countries, focusing on two questions: 1) How should national climate policy be coordinated with the European Emissions Trading System (ETS), and 2) How should an EU frontrunner country address the risk of carbon leakage? We show that these issues are closely linked and that the answers to the two questions depend on the following factors: i) The shadow cost assigned to carbon leakage, ii) The rates of carbon leakage in the ETS and non-ETS sectors, and iii) The price of ETS emission allowances relative to the domestic marginal abatement cost of attaining the desired reduction of domestic emissions. Our analysis shows that it is preferable for an EU frontrunner country to implement a national ETS sector carbon tax that results in a higher total carbon price in the national ETS sector compared to the national non-ETS sector. We illustrate how our theoretical model can be combined with a modified version of the GTAP-E general equilibrium model of the world economy to estimate the parameters of the optimal national carbon tax scheme in an EU frontrunner country, using Denmark as an example. We find that the ETS sector should pay a total carbon price that is between 33 and 78 percent above that of the rest of the economy depending on the aversion to carbon leakage. Key policy insights It is generally optimal for an EU frontrunner country - one with a domestic emission target beyond that set by the EU - to implement a national ETS sector tax. The total national carbon price should be higher in the ETS sector compared to the non-ETS sector. Data for Denmark indicate that the total national ETS sector carbon price should be at least 33 percent higher than that of the national non-ETS sector.