The “comparability” of climate mitigation efforts undertaken by developed countries can be assessed in many different ways. Some relevant factors such as emissions, population, and GDP are readily quantified and compared; others, such as a country’s geography, economic structure, or trade profile, are not. Given the multiplicity of factors at play, parties are unlikely to agree on an explicit formula to determine, or to assess the comparability of, their respective efforts. Rather, efforts are likely to be agreed through political bargaining in which countries emphasize the metrics and national circumstances that most favor their positions. The outcome will likely rest on parties’ mutual assessments of one another’s efforts, employing the criteria they deem most relevant.