(Un)Trustworthy pledges and cooperation in social dilemmas.

The 2015 Paris Agreement on climate change introduced Intended Nationally Determined Contributions (INDCs) into the process. INDCs share many features of pledges, i.e. public statements by parties in which they announce how they will behave in the social dilemma in the future. Prior evidence on how pledges enhance cooperation is inconclusive, however. We explore how differences in the information about pledgers' trustworthiness affect outcomes in a social dilemma that parallels climate change. In an online experiment, two participants interact with a randomly matched third player in a repeat maintenance game with a pledge stage. Treatments manipulate whether the third player is more or less trustworthy; and whether trustworthiness is observable. Disentangling composition and information effects, we find that only trustworthy pledgers can leverage the pledge stage for cooperation. This can explain evidence from social dilemmas such as international climate policy that reputational mechanisms in International Environmental Agreements are only effective when high-reputation countries are involved. • Prior evidence on how pledges enhance cooperation is inconclusive. • An experiment manipulates a pledger's trustworthiness and others' awareness thereof. • We find that only trustworthy pledgers can leverage the pledge stage for cooperation. • This can explain evidence from social dilemmas such as international climate policy. [ABSTRACT FROM AUTHOR]