This paper experimentally analyzes the effects if signatories to an international environmental agreement (IEA) apply different voting schemes to determine the terms of the agreement. To this end, unanimity, qualified majority voting, and simple majority voting are compared with respect to the resulting pollution abatement level and social welfare. At first sight in line with theoretical predictions, the experiment shows that the change of the voting scheme implemented in an IEA does not significantly change social welfare. However, changing the majority required to determine the terms of an IEA alters the 'depth and breadth' of cooperation. The coalitions under the unanimity rule are relatively large and implement moderate effort levels while the coalitions with majority votes implement very high effort levels but attract only few participants.
international environmental agreements cooperation, voting