Scholars often point to pressure from the United States as a key factor in driving membership in the nuclear nonproliferation regime, but this explanation has trouble explaining the changes we see in patterns of membership over time. This chapter shows that variation in the perceived effectiveness of the regime – as indicated by overall membership, the strength of verification measures, the effectiveness of enforcement, and a history of cooperation – better explains why states join. Member states are reluctant to forgo nuclear weapons without assurances that others will comply as well, and signals of regime effectiveness reassure states that their commitments will be reciprocated. This argument runs counter to the conventional wisdom among international organizations scholars, that there is a “depth versus breadth” tradeoff in institutional design. Drawing from archival documents, this chapter discusses the illustrative cases of the NPT ratification decision in Australia and Switzerland. It then tests its theory using data on state membership in the NPT.

The NPT was met with skepticism when the treaty first went into force, and 50 years later analysts are still predicting its imminent demise. This chapter highlights the central puzzle of the book: why does the nuclear nonproliferation regime – which most expected to have limited effectiveness – appear to have been so successful? Tracing the history of the regime, it draws from declassified documents and diplomatic records to examine how events have shaped perceptions of the regime’s effectiveness. It describes the parallel expectations of international organizations and international security theory and contrasts the widespread pessimism about the regime with evidence of its success.

This chapter analyses the development of IPCC policy for the communication of its reports, the content and style of IPCC communication, and how IPCC knowledge becomes reappropriated for alternative, often political, purposes. In doing so, we review IPCC policy documents, key literature on the IPCC and climate science communication, as well as providing a case study of a recent controversy in IPCC communication: the reappropriation of a paragraph from the IPCC 1.5 ºC special report to headline a political campaign that there were only 12 years to prevent dangerous climate change. This controversy highlights the huge transformations in the political and media landscapes since the IPCC’s formation in 1988 and opens up the question of whether its communication approach remains fit for purpose. We highlight how the IPCC’s communication dilemma stems from the historic decision to design it to be an authoritative voice rather than a deliberative space.

This chapter argues that Early Career Researchers (ECRs) can contribute to the IPCC in two major ways. First, ECRs can contribute unique skills and competences to the assessment process. Second, ECRs can share the workload with senior researchers and thus enhance the quality of the assessment. By reviewing the IPCC’s Scholarship Programme and the role of Chapter Scientists, this chapter explores the potentials and challenges of introducing ECRs into the IPCC, and for the Panel to engage in capacity building to enhance the quality of the assessment. The review shows how the organisational setup of the Scholarship Programme and the Chapter Scientist role allows the IPCC to informally engage in capacity building without diverting from its mandate that does not include capacity building. Even so, ECRs remains an untapped source of expertise that, through active and strategic work, can contribute to the future development of the IPCC.

This chapter discusses the IPCC’s performance as a ‘learning’ organisation. The Panel has responded to novel challenges by adjusting its governance structure and its underlying objectives and principles. Building on a heuristic of organisational learning, we reconstruct and map these past learning processes. We find that most of these challenges resulted in the IPCC adopting an adaptive mode of learning by incrementally adjusting procedures. There were only a few moments of reflexive learning. Against this backdrop, the chapter discusses future challenges for the IPCC emerging from the Paris Agreement and the call for a ‘solution-oriented assessment’. The IPCC has faced demands in the past for greater political relevance, geopolitical representation, scientific integrity, transparency, and accountability. In the post-Paris world, the Panel has to cope with its role in the polycentric architecture of the climate regime and its role as ‘mapmaker’ in the assessment of pathways to achieve the Paris ambition. We conclude by discussing how the IPCC can best use its learning capacities in responding to these challenges.

Diversity has become increasingly important as an analytic concept and organising principle in the general scientific community. Advancing diversity is seen to be even more essential in a global science-policy interface such as the IPCC. Being able to claim to speak from a broad perspective of geographies, genders and experiences is considered to be important if the IPCC is to produce legitimate and authoritative climate knowledge for policy. This chapter applies a critical lens to examine the IPCC’s procedures and practices in selecting its authors with respect to securing a diverse base of expertise across gender, geography and experience. It then considers how diversity is important, identifying different logics – substantive and instrumental – that have guided the IPCC’s efforts to date. The chapter concludes by considering why diversity should matter and what possibilities are opened for global climate knowledge-making through enhanced capacity building.

The explicit aim of the IPCC is to influence policymaking. By synthesising research on climate change and presenting it to policymakers, the IPCC tries to meet its self-imposed goal of being policy-relevant and policy-neutral, but not policy-prescriptive. The hallmark of the IPCC has been to offer a strong scientific voice demonstrating the necessity of climate policy and action, but without giving firm political advice. Yet scholars have contested the idea of maintaining such a strong boundary between science and policy in the IPCC, questioning whether upholding this boundary has been successful and whether continuing to do so offers a viable way forward. The Paris Agreement provides a new political context for the IPCC, implying a need for solution-oriented assessments. The IPCC itself has also argued that large-scale transformations of society are needed to meet the targets set by the Agreement. To be relevant and influence policymaking in this new political context, the IPCC needs to provide policy advice.

Research on the interaction between climate science and policy has pointed to the production of so-called ‘boundary objects’ as one way in which the IPCC has influenced climate policymaking and broader climate discourses. By providing a common framework that enables interaction across social worlds, while still allowing more localised use by different groups of actors, such objects have been key in bringing together climate science and policy, in turn shaping the trajectory of both. This chapter reviews several concepts that have been analysed as boundary objects — such as the concept of climate sensitivity and the 2 °C and 1.5 °C targets — and explains how they have been productive of new science/policy relations. It also points to new challenges for the IPCC as climate policy development moves towards implementation and increases demand for more ‘solution-oriented’ knowledge.

This chapter discusses the precursors and origin of the IPCC, with a particular focus on the developments that led to the panel’s intergovernmental design. When the IPCC was established in 1988 as an intergovernmental body, the design choice was both novel and risky and came to have significant consequences for the panel’s subsequent operation and impact. The chapter summarises some prominent events from the early scientific discovery of a possible human influence on global climate to the various international science–policy initiatives of the 1970s and 1980s that preceded the IPCC’s establishment. It then draws attention to a set of factors that can explain the decision to deliberately establish the IPCC as an intergovernmental body.

This chapter reviews the history of the IPCC’s efforts to achieve and maintain policy relevance while remaining policy-neutral and staying far away from ‘policy prescriptiveness’. The chapter argues that the boundaries between policy relevance, neutrality and prescriptiveness are a practical achievement – they must be constantly negotiated as the science and politics of climate change evolve. The chapter uses historical case studies to illustrate this point, such as the controversy over the so-called ‘burning embers’ diagram. It ends by discussing recent debates about the IPCC’s new role in the post-Paris Agreement policy landscape. While IPCC actors call for greater policy relevance, observers and critics contend that the IPCC will always and inevitably be policy-prescriptive, even if on a tacit and unintentional level. Achieving even greater policy relevance may therefore mean jettisoning or modifying the aspiration to be policy-neutral.