The talk aims to explore the epistemic and political authority of expert bodies and their democratic challenges posed by these forms of global environmental expertise. In particular, I will analyze the role of the Intergovernmental Panel on Climate Change (IPCC) in climate governance. Even if the Panel claims to be neutral and non-prescriptive and it is not granted any formal or de jure authority, it acts as a politically powerful ‘non-state’ player in climate governance. Focusing on the constitutive and performative power of expertise, I will demonstrate that global environmental assessments such as the IPCC are important sites of co-production, where knowledge about the natural world is made within, and reinforces, visions of social needs and responses. The events surrounding ‘climategate’ underlined the authoritative status of scientific knowledge in policy decision-making that paradoxically lead to the intense public attention and scrutiny to which the IPCC is exposed in part by the blogosphere and by heightened media attention. The final section argues that it is time to rethink the future role of IPCC and to discover novel forms of epistemic subsidiarity in time when UN climate multilateralism has lost momentum.