A natural outcome of the emerging pledge and review approach to international climate change policy is the interest in comparing mitigation efforts among countries. Domestic publics and stakeholders will have an interest in knowing if "comparable" or "peer" countries are undertaking (or planning to undertake) "comparable" effort in mitigating their greenhouse gas emissions. Moreover, if the aggregate effort is considered inadequate in addressing the risks posed by climate change, then this will

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... likely prompt interest in identifying opportunities for greater effort by individual countries -an assessment that requires metrics of effort and comparisons among countries. We propose a framework for comparing mitigation effort, drawing from a set of principles for designing and implementing informative metrics. We present a template for organizing metrics on mitigation effort, for both ex ante and ex post review of effort. We also provide preliminary assessments of effort along emissions, price, and cost metrics for post-2020 climate policy contributions by China, the European Union, and the United States. We close with a discussion of the role of academics and civil society in promoting transparency and facilitating the evaluation and comparison of effort. JEL Codes: Q54, Q3, Q52