In response to global climate change,the large-scale assessment led by the Intergovernmental Panel on Climate Change(IPCC) represents the collective efforts of the international scientific community and continues to interact with the international negotiation under the UN framework convention on climate change.The relationship between the two is reflected in various historical stages of global climate governance.By embedding into international institutions,science plays an important role in alerting the public,influencing state actors,reaching international agreements,urging transnational corporations to change behaviors,and facilitating the academic exchanges among research institutions.At the same time,the intergovernmental panel participates in international climate diplomacy through the form of assessment reports.Because of its openness,climate assessments are also often used as a policy tool for nations and non-state actors to exert their influence.From the positive side of the interplays between science and politics,first,IPCC as scientific assessment body has always played the role of promoting the international climate process,and by virtue of its authority,it has continuously strengthened the diffusion of scientific information to policies.Second,the 1.5 ℃ special report in 2018 and the follow-up AR6 are concerned about the impact of the Paris Agreement for the effectiveness of compliance.However,the drawbacks of the current assessment mechanism have been identified by various research and organizational arrangements are highly path-dependent.Also,the dissemination of report conclusions has become increasingly difficult,and issues such as the disconnection from international negotiations have become the main issue.In this regard,this paper argues that these problems are in essence the contradictions between mechanisms of the scientific institution to reach consensus and the rules for science to form consensus.On the one hand,due to the differences between disciplines and large volume of seientific litevature,it is increasingly difficult to form a consensus.On the other hand,IPCC as an epistemic authority has international political preferences that promote consensus in the political process and enhance their international prestige.There has been an increasing tension between the two around the issue of so called scientific consensus.However,climate assessment has already proved its value as an inter-governmental scientific cooperation.Its future evolution and reform will also profoundly affect global climate governance after 2020.Therefore,redefining the role of intergovernmental climate assessment in the formulation of global policies has become an urgent issue in climate governance.