Commitment ambiguity and ambition in climate pledges

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.