In the past forty years the architecture for global environmental governance (GEG) has been heavily debated. Numerous proposals to improve the GEG system have been developed, many of which call for the establishment of some kind of World Environment Organisation (WEO). Although there is consensus among governments and scholars that the system needs improvement, no substantial decisions on reform have been taken. This paper addresses the issue identified by the Berlin Conference concerning social barriers to effective environmental policies at the international level. Based on a literature study and more than twenty interviews, the paper identifies the main barriers for GEG reform, using three theories of new institutionalism: rational choice, discursive, and historical institutionalism. Rational choice institutionalism suggests that the fundamental differences between national and institutional self-interests is one of the barriers to GEG reform. According to discursive institutionalism, the incentive to maintain the status quo is a key hurdle, mainly caused by the fear of states and international organisations to lose part of their authority. Historical institutionalism shows that power inequalities and trust gaps between nation-states further hamper the debates. While historical institutionalism focuses on the complex nature and the ad-hoc and diffused development of the GEG system, discursive institutionalism shows that the nature of the debates concerning GEG reform thwarts progress towards agreement: debates are fragmented, tend to ‘recycle’ issues, and lack involvement of civil society and academics. The second issue identified by the Berlin Conference that the paper focuses on is the (synergies and conflicts between) theoretical approaches to questions relating to the social dimensions of environmental governance. The paper provides a critical evaluation of the utility of the theories of new institutionalism, showing that despite some fundamental differences the three theories complement rather than contradict one another in their account of the barriers to GEG reform.