Under what conditions does science influence environmental policy? International Relations (IR) scholars, such as Peter M Haas, have argued that to gain political influence, science should not connect to policy before scientific consensus has been reached. We take this suggestion as a point of departure for investigating how science is and should be connected to policy in international environmental governance. Using insights from the field of Science and Technology Studies (STS), the contribution of IR is critically discussed, both to present its limitations and, primarily, to further develop the understanding of scientific consensus within IR and the need for separation and connections between science and policy. The organization and performance of the Intergovernmental Panel on Climate Change (IPCC), including the various assessments made by scholars from IR and STS, is used as an illustrative case. From the discussion of IR and STS and the role of the IPCC in climate policy, we conclude that the focus within STS on contextual and informal factors could shed light on how science and technology are understood by IR scholars, who focus more on the formal organizational design of the interplay between science and policy.