The Paris Agreement on climate change is built around a pledge-and-review system, wherein countries submit nationally determined pledges of mitigation commitments. While the agreement’s flexible design has attracted broad participation, its lenient informational requirements for pledges have also engendered considerable ambiguity in countries’ commitments. What are the implications of commitment ambiguity on the credibility of compliance and treaty effectiveness more broadly? This article sheds light on these questions by evaluating the relationship between commitment ambiguity and ambition in countries’ Paris pledges. We introduce a model that disentangles commitment ambiguity into two distinct forms: structural and strategic. We argue that structural ambiguity, which arises from constraints on the information necessary for governments to accurately assess their commitment potential, dampens the ambition levels of pledges. This prudence effect is driven by compliance concern: the anticipation of audience costs in case of non-compliance induces policymakers to adjust ambition downwards. Our empirical analysis of countries’ Nationally Determined Contributions demonstrates that ambiguous pledges exhibit lower ambition than precise ones. In line with our theory, this prudence effect of ambiguity is mainly pronounced among democracies, which face higher domestic audience costs in case of non-compliance with pledges than autocracies. This article contributes a novel theory of ambiguity and ambition in international institutions, which shows how audience-based compliance concerns can discipline cheap talk. Moreover, the article’s empirical findings provide insight into the credibility of countries’ climate pledges under the Paris Agreement, with implications for the treaty’s overall effectiveness prospects.

关于气候变化的《巴黎协定》是围绕承诺和审查系统建立的，其中各国提交国家确定的减缓承诺。虽然该协议的灵活设计吸引了广泛的参与，但其对承诺的宽松信息要求也导致各国的承诺相当模糊。承诺模糊性对更广泛地遵守条约的可信度和条约有效性有何影响？本文通过评估各国在巴黎承诺中承诺模糊性与雄心之间的关系来阐明这些问题。我们引入了一个模型，将承诺模糊性解开为两种不同的形式：结构性和战略性。我们认为，结构性模糊是由于政府准确评估其承诺潜力所需的信息受到限制而引起的，这削弱了承诺的雄心水平。这种审慎效应是由合规性问题驱动的：在不合规的情况下对受众成本的预期促使政策制定者下调雄心。我们对各国国家自主贡献的实证分析表明，模棱两可的承诺比精确的承诺表现出更低的雄心。根据我们的理论，这种模糊性的审慎效应主要在民主国家中很明显，如果不遵守承诺，它们面临的国内观众成本高于独裁国家。本文提出了一个关于国际机构中歧义和雄心壮志的新理论，它展示了基于受众的合规性问题如何约束廉价的谈话。 此外，本文的实证研究结果为各国在《巴黎协定》下的气候承诺的可信度提供了见解，并对条约的整体有效性前景产生了影响。