Over three decades, the IPCC has been no stranger to controversies. Given its institutional character as a boundary organisation working between science and policy, it is no surprise that IPCC reports often reflect wider controversies in the scientific and political life of climate change, especially those concerning its consequences and potential solutions. In this chapter, we explain why controversies about the IPCC’s knowledge assessment are inevitable and point out how the IPCC could use controversies for adapting and developing its assessment processes in constructive ways. That is, we show how controversies serve as ‘generative political events’ for the IPCC’s own learning process. To do so, we classify IPCC knowledge controversies into four types (factual, procedural, epistemic and ontological) and, using two illustrative cases, distinguish between controversies which the IPCC triggers and those which the IPCC absorbs into its knowledge assessment.

This chapter introduces the aims, scope, framing, intended readership, and organisation of the book. We explain why a book offering a critical assessment of the IPCC is necessary and we situate this justification in the context of other global environmental assessments. We point out the intended readership of the book and why it is of importance and relevance for these readers. We conclude by explaining how the book is structured around five parts.

A widely shared expectation of science is that it speaks authoritatively about how the physical world works and therefore about what the consequences of different human actions and policy interventions are likely to be in that world. Science, and therefore the scientist, is believed to offer public life something different – something more truthful and hence more authoritative – than offered by politicians, journalists, lawyers, priests, or celebrities. Scientists ‘reaching a consensus’ and ‘speaking with one voice’ are integral to science’s projection of epistemic authority. This is especially the case with the IPCC, where its authority is perceived to rest on its communication of a scientific consensus. This chapter first summarises the nature of consensus-making in science in general, before examining the IPCC’s consensus-seeking practices. It then evaluates some of the arguments for and against the pursuit of consensus by the IPCC and concludes by highlighting some future challenges for the IPCC with respect to its pursuit of consensus.

In this chapter we offer concluding remarks based on issues raised in the book and informed by discussions between its contributors at a workshop held in December 2021. We emphasise the need to understand the IPCC as a complex epistemic, social, political and human institution and we evaluate its activities, achievements and challenges using three metaphors. First, we suggest opening the ‘black box’ of the IPCC to examine its internal workings, to understand how it functions and where its authority comes from. Second, we call for thinking of the IPCC as a ‘ship on the ocean’ to help situate its work within the scientific and (geo)political context in which it evolves. Finally, we caution against thinking of the IPCC as a ‘Swiss army knife’ that can successfully be all things for all people. These reflections on the design, function and future of the IPCC have implications for the study of other expert institutions.