We analyse bargaining over international climate agreements in a setting with incomplete information about abatement costs. Incomplete information is known as one of the key reasons why negotiations may fail more generally, and why efficiency gains cannot be exploited. We ask whether unilateral commitment to high abatement reduces or increases the likelihood for an efficient negotiation outcome. We find that such commitment behaviour reduces the gains from global cooperation and that, in turn, this reduces the probability of reaching efficient international environmental agreements.