Scenarios are among the most visible and widely used products of the IPCC. Many kinds of scenarios are used in climate research, but emissions scenarios and the socio-economic assumptions that underpin them have a distinct status because the IPCC orchestrated their development. They have evolved from assessment cycle to assessment cycle and serve as ‘boundary objects’ across Working Groups and as instruments of policy relevance. The field of Integrated Assessment Modelling has emerged to produce these scenarios, thereby taking centre stage within the IPCC assessment process. Because these scenarios harmonise assumptions about the future across disciplines, they are essential tools for the IPCC’s production of a shared assessment of climate research and for ensuring the policy relevance of this assessment. Yet, the reliance on a relatively small set of complex models to generate scenarios spurs concerns about transparency, black-boxed assumptions, and the power of IAMs to define the ‘possibility space’.

By highlighting the importance of venues and meetings for the work of the IPCC, this chapter offers a novel angle from which to study the institution. Thinking of the IPCC as a ’travelling village’ and a ’system of meetings’, we discuss the various functions of venues and meetings in organising and maintaining the IPCC’s assessment process. We argue that because of the global and networked nature of its activities and institutional arrangements, participating in the IPCC means making the world one’s workplace. The chapter also shows how established IPCC meeting practices have been tested by the COVID-19 pandemic and we shed light on some of the implications of the shift from in-person to virtual meetings.

The nuclear nonproliferation regime lacks formal enforcement mechanisms, but this does not mean that violations of nonproliferation commitments always go unpunished. States that violate the NPT routinely face pressure from others to change their behavior, including through economic sanctions. But the lack of formal enforcement measures does contribute to significant variation in the states that are targeted for punishment – enforcement is always at the discretion of the punishing state. Why do some states face punishment while the transgressions of others are overlooked? This chapter argues that enforcing states look to the policy preferences of violators for signals about the likelihood that enforcement will change state behavior and about the cost to the international community of allowing the violation to continue. Patterns of institutional membership within the larger regime help to credibly reveal the preferences of state parties. Using data on membership in the various agreements that make up the nuclear nonproliferation regime, this chapter shows that violating states are less likely to face costly enforcement action the more embedded they are within the regime.

The knowledge that is used in IPCC assessments predominantly stems from a wide variety of academic disciplines. Given the high scientific and political profile of the IPCC, the production of knowledge in disciplines is impacted by the existence and dynamics of the IPCC assessment process. In some cases, the dynamics between academic disciplines and the IPCC is characterised by the presence of positive feedback loops, where the production of knowledge is structured and programmed by the IPCC. The subsequent findings then receive a preeminent role in later IPCC assessments, and so the cycle continues. It is important to critically reflect on these dynamics, in order to determine whether visions of climate change’s past, present, and future – for example, pathways for the climate-change problem and its potential solutions, as far as they exist – have not been unduly constrained by the IPCC process. The IPCC runs the risk of unreflexively foregrounding some scientific and policy approaches at the expense of other approaches.

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.

The IPCC has begun to acknowledge, albeit slowly, the importance of Indigenous knowledge (IK) systems in contributing to understandings of climate change and effective climate action. Yet Indigenous Peoples (IPs) and IK systems remain largely excluded and marginalised from the IPCC global assessment reports. IPCC scientists and leaders have a unique and specific obligation to IK systems that does not extend to other knowledge systems. IK is the knowledge of rights holders and therefore acknowledging and respecting the self-determination of IPs over their knowledge – including how it is used, interpreted, and synthesised – is imperative. There are examples of IPs organising themselves in other international spaces that could inform how the IPCC can approach a stronger, more durable engagement with IPs. Perhaps the ultimate challenge for the IPCC is that when bringing IK systems together with other knowledge systems, the framing of evidence must reflect the diversity of these distinct and discrete ways of knowing. Examples from the lived experience of the Inuit Circumpolar Council in engaging with the IPCC demonstrate diverse channels for engagement, yet significant limitations persist.

A core promise of the nuclear nonproliferation regime is that it will provide nonnuclear weapons states with access to civilian nuclear technology. At the same time, nonproliferation advocates see the regime as a major tool in limiting the development of this dual-use technology and the spread of nuclear weapons. This chapter examines the effect of membership in the nonproliferation regime on the provision of nuclear latency – the underlying capability to quickly acquire a nuclear weapon. Using data and findings from the previous chapters, it shows that regime membership, for all its positive effects, comes at the cost of contributing to members’ latent nuclear capability.

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.

Climate computer models are irreplaceable scientific tools to study the climate system and to allow projections of future climate change. They play a major role in IPCC reports, underpinning paleoclimate reconstructions, attribution studies, scenarios of future climate change, and concepts such as climate sensitivity and carbon budgets. While models have greatly contributed to the construction of climate change as a global problem, they are also influenced by political expectations. Models have their limits, they never escape uncertainties, and they receive criticisms, in particular for their hegemonic role in climate science. And yet climate models and their simulations of past, present and future climates, coordinated via an efficient model intercomparison project, have greatly contributed to the IPCC’s epistemic credibility and authority.

This chapter explores the role of governments in the IPCC, how this is theorised, and how government participation in the organisation has changed over time. One of the most distinctive features of the IPCC is its intergovernmental character. While some scholars criticise government membership of the IPCC, many IPCC actors see this as key to ensuring the political relevance of the assessment. But what does government membership mean? What do member governments do in the organisation? And who are IPCC delegates and focal points? This chapter addresses these questions and identifies how member governments have deepened their involvement in the IPCC over time as their knowledge has grown and as the stakes in climate politics have risen. However, participation between countries remains uneven and the chapter explores how concerns about developing countries’ capacity to contribute has shaped the IPCC and assessments of climate change.