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 peer countries are undertaking (or planning to undertake) comparable efforts in mitigating their greenhouse gas emissions. Moreover, if the aggregate efforts are considered inadequate in addressing the risks posed by climate change, then this will likely prompt a broader interest in identifying those countries where greater efforts are arguably warranted based on comparison with their peers. Both assessments require metrics of efforts and comparisons among countries. We propose a framework for such an exercise, drawing from a set of principles for designing and implementing informative metrics. We present a template for organizing metrics on mitigation efforts, for both ex ante and ex post review. We also provide preliminary assessments of efforts along emissions, price, and cost metrics for post-2020 climate policy contributions by China, the European Union, Russia, 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 efforts

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