In the IPCC’s AR6, the chapters of each of the three Working Groups are structured with the intention of integrating ‘cross-cutting themes’ and ‘handshakes’ between them. While integration received special emphasis in AR6, it is not new. The IPCC has long considered how to treat issues such as representations of uncertainty and scenario data consistently across WGs. The IPCC’s effort to integrate knowledge across WGs raises important epistemological and ethical questions related to how the humanities, natural sciences, and social sciences shape understandings of climate change. To illustrate the theme of integration as applied within the IPCC, this chapter focuses on how risk is integrated across WGI and WGII in the AR6.

In IPCC reports, calibrated language is used to communicate confidence and/or agreement in claims. This language is highly specialised and has developed over time to account for diverse sources of knowledge and types of agreement. Currently, the IPCC uses two typologies for calibrated language — a qualitative confidence scale that assesses the amount of evidence, and expert agreement about that evidence; and a more quantitative scale that measures and expresses uncertainty. IPCC leadership intends for calibrated language to help make their reports scientifically clearer, although the resulting stylised language raises readability challenges. Calibrated IPCC language is also used, cynically, as a diplomatic tool during the report adoption plenaries of the Panel, as government delegates raise questions about the characterisation of climate facts. Uncertainty language in the IPCC, then, signifies both technical advancement in the characterisation of uncertainty and the challenges of communicating climate science in diverse contexts.

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.

Despite many flaws, including variable quality and a lack of universal standards, peer review – the formal process of critically assessing knowledge claims prior to publication – remains a bedrock norm of science. It therefore also underlies the scientific authority of the IPCC. Most literature used in IPCC assessments has already been peer reviewed by scientific journals. IPCC assessments are themselves reviewed at multiple stages of composition, first by Lead Authors, then by scientific experts and non-governmental organisations outside the IPCC, and finally by government representatives. Over time, assessment review has become increasingly inclusive and transparent: anyone who claims expertise may participate in review, and all comments and responses are published after the assessment cycle concludes. IPCC authors are required to respond to all comments. The IPCC review process is the most extensive, open, and inclusive in the history of science. Challenges include how to manage a huge and ever-increasing number of review comments, and how to deal responsibly with review comments that dispute the fundamental framing of major issues.

Since its creation in 1988, the IPCC has taken increasing care to formalise its procedures. IPCC procedures define the creation and role of the IPCC Bureau, Task Forces and Working Groups, as well as the steps that must be taken by experts when preparing reports, and by administrators for overseeing the institution’s funding. Increasingly detailed over time and now running over several dozen pages, the IPCC procedures are not a boring part of IPCC studies. They are key observation points of the main issues that the IPCC has had to address over time. They reflect the compromises it has made in its efforts to give the greatest political efficiency to its reports, while ensuring that their scientific robustness remains irreproachable. The procedures therefore constitute a site from which many of the issues addressed in this book can be read. However, they should not be taken as descriptions of actual practices: their implementation is open to interpretation and thereby to debate. The drafting and amendment of procedures therefore remains an open process.

This chapter discusses the concept of ‘civic epistemology’ in relation to the IPCC and the governance of climate change. Civic epistemology refers to ’the institutionalised practises by which members of a given society test and deploy knowledge claims used as a basis for making collective choices’ (Jasanoff, 2005: 255). Differences in civic epistemologies seem to be directly related to how scientific climate knowledge – presented in IPCC assessment reports – relates to political decision-making at different scales—national, regional, global. The concept is especially rich because it enables a nuanced understanding of the role of IPCC assessments in national climate governance and in meeting the challenges of building more cosmopolitan climate expertise. Both of these aspects are important if emerging institutional arrangements that seek to govern global environmental change are to be understood. Through a critical review of the civic epistemology literature related to the IPCC, this chapter investigates how the cultural dimensions of the science–policy nexus, in different national and geopolitical contexts, conditions the legitimation and uptake of IPCC knowledge.

IPCC reports are not produced by scientific experts disconnected from policy. They are produced within a political framework. The governmental endorsement of IPCC reports is a key element of the perceived success of the organisation. In particular, the approval of the Summaries for Policymakers makes the Member States of the IPCC active participants in the assessment process and creates ownership of their content. At first sight, the involvement of governments in the IPCC reveals a genuine exercise of co-production between science and politics. It is expected to make the reports more legitimate and policy relevant. Yet a closer look at the practices through which governmental ownership of IPCC reports is produced shows that governments may in some cases contribute to making them policy irrelevant.

This chapter outlines the process of IPCC report writing and discusses, through specific examples, how these reports are produced within, and shaped by, political and scientific contexts. The IPCC produces Assessment Reports, Special Reports, and Methodological Reports, which are central to the institution’s operations and perceived impact. There are also sub-elements of these reports – Summary for Policymakers and Technical Summaries – which fulfil important standalone roles. The process of writing these reports is well-institutionalised and involves maintaining a balance between scientific credibility and policy relevance. The reports produced are therefore accountable to, and co-produced with, scientific and policy communities. The chapter shows how the framing of IPCC reports has changed over time and continues to evolve. This also raises questions about the future of IPCC reports in relation to IPCC processes and in response to diversifying audiences and new media.

This chapter positions the IPCC in the context of global efforts to understand and combat climate change. Throughout its first three decades, as nations have sought to understand and prioritise climate change in global policy, the IPCC has served as the world’s principal knowledge-making institution. It has created, authorised, and narrated a new kind of global knowledge, profoundly shaped global public imagination of the climate emergency, and provided epistemic support to the call for collective global action to tackle it. Looking forward, however, it is less clear whether the IPCC is well positioned to help support the work of institutions around the world to end fossil fuel use and reduce greenhouse gas emissions. The chapter asks, therefore, whether the IPCC needs to be re-imagined if it is to help advance the transition to a climate-neutral global economy and energy systems.

This chapter discusses the role of NGO observers in the IPCC and the extent to which they have access to and participate in the work of the Panel. Many UN institutions have arrangements for participation by NGOs and the IPCC is no exception. NGO observers include academic institutions, think tanks, civil society, Indigenous Peoples Organisations, and business associations. They take part in IPCC meetings and nominate their representatives to serve as authors and reviewers in the preparation of assessment reports. NGO observers’ participation in the Panel is an important topic in light of the increasing emphasis on inclusiveness and diversity of views in science-policy interfaces and international institutions. The chapter also identifies related knowledge gaps and summarises the challenges and opportunities for enhanced NGO engagement in the IPCC.

The final chapter of the book summarizes its central argument and expands on the policy implications of the study. The preceding chapters, for example, suggest that perceived weaknesses in the nuclear nonproliferation regime could act as a proliferation trigger, pushing states to take that final step toward nuclear pursuit. This raises the stakes for policymakers in maintaining the credibility of the regime, by reassuring allies, committing to punishment of violators, and closing persistent regime loopholes. At the same time, the link between regime membership and latent nuclear capability suggests that confidence in the constraining power of the nonproliferation regime could give us a false sense of security.

The opening chapter gives a general outline of the nuclear nonproliferation regime, summarizes the argument and approach to the subject, explains the book’s contribution to the literature and policy debate, and provides an overview of the remaining chapters.

This chapter reviews the types, use, production, accessibility and efficacy of data visuals contained in IPCC assessments and special reports, drawing upon available published literature. Visuals of different types are key to the communication of IPCC assessments. They have been subject to academic interest among social and cognitive scientists. Furthermore, wider societal interest in the IPCC has increased, especially since the publication of its Fifth Assessment Report. In response, the IPCC has revisited its approach to communication including visuals, which has resulted in a greater professionalisation of its visualisations — involving information designers and cognitive scientists — and in new forms of co-production between authors and users.