Optimal emission pricing in the presence of international spillovers: Decomposing leakage and terms-of-trade motives

Carbon leakage provides an efficiency argument for unilateral climate policy to differentiate emission prices in favor of emission-intensive and trade-exposed sectors. At the same time, differential emission pricing can be (mis-)used as a beggar-thy-neighbor policy to exploit terms of trade. Using an optimal tax framework, we propose a method to decompose the leakage motive and the terms-of-trade motive for emission price differentiation. We employ our method for a quantitative impact assessment of unilateral climate policy based on empirical data. We find that the leakage motive yields only small efficiency gains compared to uniform emission pricing. Likewise, the terms-of-trade motive has rather limited potential for strategic burden shifting. We conclude that the simple first-best rule of uniform emission pricing remains a practical guideline for unilateral climate policy design.