Seeking to contribute to the governance stream of this year’s Berlin Conference, the paper addresses an emerging phenomenon of global environmental governance: the increasing overlap and interplay among institutions that touch upon related subject matters. Presenting one of the first outcomes of the Earth System Governance project, the paper focuses on one specific case of institutional interplay, namely the overlap between the United Nations climate regime and the World Trade Organization (WTO). While parties of the UN climate regime discuss trade-related measures for a post-2012 agreement, WTO parties debate climate-related trade measures. This duplication of debates entails a lack of legal clarity, which may have detrimental implications for the further negotiation and implementation of both regimes. Drawing on neoliberal institutionalism and cognitivism, we identify two reasons for these interplay effects: the constellation of preferences and the lack of consensual knowledge on overlapping issues. Based on a workshop organized jointly with the UN Environment Programme, we developed suggestions to tackle these reasons. Policies could accommodate the lack of knowledge by means of flexible approaches, e.g. default values for border cost adjustments and ‘living lists’ of sustainability criteria for lifting trade barriers. With regard to the constellation of country preferences, a careful linkage of debates across arenas can produce additional trade-offs and break some of the deadlocks in which these discussions have ended up. On the other hand, the paper attends to the caveats and limits of such linkages.