1 Introduction

For more than three decades, the Intergovernmental Panel on Climate Change (IPCC) has been the central figure in the global debate on climate change. The authoritative assessment reports of the IPCC are the most basic source of scientific information for international political negotiations at the United Nations Framework Convention on Climate Change (UNFCCC). For some, particularly youth climate activists, the IPCC is effectively the science of climate change. At her testimony before the United States (US) Congress in September 2019, Swedish climate activist Greta Thunberg submitted the IPCC’s Special Report on Global Warming of 1.5 °C (known as SR15) (IPCC 2018) and said “I am submitting this report as my testimony because I don’t want you to listen to me. I want you to listen to the scientists. And I want you to unite behind the science” (cf. Jarvis 2019). This episode vividly illustrates the far-reaching impacts that this IPCC report made on real-world politics.

SR15 is one of three special reports that the IPCC produced during the Sixth Assessment Report (AR6) cycle. The other two reports are the Special Report on Climate Change and Land (known as SRCCL) (IPCC 2019a) and the Special Report on the Ocean and Cryosphere in a Changing Climate (known as SROCC) (IPCC 2019b). SR15 is most well-known to the public because the production of the report was in the first place requested by the 21st Conference of the Parties (COP) to the UNFCCC at which the landmark Paris Agreement was adopted. The apparent success of SR15 built a reputation for IPCC special reports as a convenient device for accelerating new scientific research on specific topics and helping resolve urgent policy problems. Since then, there have been mounting calls by scientists, policymakers and activists for new special reports on various topics from climate tipping points to loss and damage, carbon dioxide removal and solar geoengineering in the Seventh Assessment Report (AR7) cycleFootnote 1Footnote 2 (Kemp et al. 2022; Nature 2022; Huq 2023; Reynolds 2021). Although it was decided that no further special reports in addition to a special report on cities will be produced during the AR7 cycle (IISD 2024), these calls indicate a great deal of public interest in IPCC special reports.

Given its prominence as an institutional body for global scientific assessment, the IPCC has been studied extensively from many different aspects, ranging from history to processes, participants, influence and so forth (De Pryck and Hulme 2022; see also Vardy et al. 2017). A significant amount of scholarly attention was also paid to SR15 to analyse why the report came to be produced, how the assessment processes were organised and what kind of impacts were made on science, politics and society (Asayama et al. 2019; Boykoff and Pearman 2019; Hansson et al. 2021; Hermansen et al. 2021; Livingston and Rummukainen 2020; 2023; van Beek et al. 2022; Lidskog and Sundqvist 2022; Cointe and Guillemot 2023; Schenuit 2023). However, to date, there is not much social scientific research done on the history of IPCC special reports (except Provost 2019) and the particular role they play at the interface between science and policy.

This article focuses on how the IPCC uses special reports to provide advice on specific, timely and policy-relevant issues. As the IPCC states its mandate is to provide “policy-relevant and yet policy-neutral, never policy-prescriptive”Footnote 3 scientific information, studying how special reports have been produced and received can shed new light on the IPCC’s struggle over the boundaries between policy relevance, neutrality and prescriptiveness (Mahony 2022)—and more broadly, the process of ‘co-production’ of science and politics (Jasanoff 2004). Tracing the historical evolution of special reports could also offer useful insight for the ongoing discussions about the future work of the IPCC. In new political contexts that emerged in the wake of the Pari Agreement, the IPCC is now being called to adapt its assessment practices, including the conduct of special reports, to stay relevant to policy needs and help catalyse social change (Asayama et al. 2023; Hermansen et al. 2023).

In this article, I address three questions regarding IPCC special reports and organise the structure of the paper accordingly: (1) the history (‘where they come from’); (2) the function (‘what they are doing’); and (3) the future (‘where they are going’). For the history part (Section 2), I trace the origin of each special report and describe how the planning of special reports has evolved over time through each assessment cycle. For the function part (Section 3), I look at the role of special reports at the science-policy interface and argue that they exhibit the dual functionality of politicisation and normalisation. For the future part (Section 4), I discuss how the role of special reports could be redefined in the future and suggest potential reform options for designing the future conduct of special reports beyond the AR7 cycle. Finally, the article is concluded by reflecting on a trade-off entailed in IPCC special reports between provisional science and lasting political impact.

2 The history of IPCC special reports

Since the Second Assessment Report (AR2) cycle, the IPCC has regularly published special reports on various topics as part of each assessment cycle, typically a few years ahead of the release of comprehensive assessment reports (see Table 1). The IPCC has also gradually institutionalised the procedure of deciding the number and topic of special reports produced during the assessment cycle, especially since the Fourth Assessment Report (AR4) cycle. In 2003, the IPCC adopted a decision framework for special reports, amended later in 2008, to define priorities and a set of criteria for special reports (IPCC 2008a).

Table 1 Summary of IPCC special reports published from the Second Assessment Report cycle to the Sixth Assessment Report cycle (No special reports were produced during the First Assessment Report cycle.)
Full size table

In this section, I trace back the history of IPCC special reports and describe how the preparation of special reports has evolved from unplanned improvisation in responding to the request from the UNFCCC to formal proceduralisation for carefully planning the production of special reports at the beginning of the assessment cycle.

2.1 Direct response to meet the UNFCCC requestFootnote 4

In the early history of the IPCC, the preparation of special reports often started at the request of the UNFCCC which needed timely scientific inputs to its intergovernmental political negotiations. As shown in Table 1, the origin of most special reports produced during the period from AR2 to AR4 was the request from the UNFCCC, except in two cases: the Special Report on Aviation and the Global Atmosphere (IPCC 1999) was prepared following a request from the International Civil Aviation Organization (ICAO) and the Special Report on Emissions Scenarios (known as SRES) (IPCC 2000a) was the IPCC’s own initiative to develop a new set of emissions scenarios which aimed to be used for the Third Assessment Report (AR3). While the IPCC had its own set schedule for producing comprehensive assessment reports, the production of special reports was often driven by immediate political needs and therefore their schedule was determined largely by the rhythms of international negotiations at the UNFCCC.

This was particularly evident in the undertaking of the IPCC’s first special report—the Special Report to the UNFCCC COP1 (IPCC 1994a; 1994b). Unlike any other special report, this first special report is not a single document but consists of two separate reports and contains three different parts, each of which was prepared and approved independently by the three Working Groups (WGs).Footnote 5 The story behind the birth of this first special report was that fast-evolving politics in the early 1990s necessitated the readjustment of the work schedule of IPCC assessment (Bolin 2007; Provost 2019).

After the adoption in 1992, the ratification of the UNFCCC proceeded earlier than expected and soon it became clear that the Convention came into force in early 1994 and COP1 would take place before the completion of AR2, which was already scheduled for late 1995. Because of this mismatch of timetable between COP1 and AR2, the chair of the Intergovernmental Negotiating Committee (INC) for the UNFCCC strongly urged the IPCC to produce a special report covering key issues relevant to the discussions at COP1. Because it was significant for the IPCC to have close cooperation with the INC in fulfilling its mandate, the IPCC decided to undertake a special report for COP1 at the 9th session in June 1993 and completed its production within less than 18 months by late 1994 (IPCC 1993; 1994c).

Similarly, the political dynamics of UNFCCC negotiations led to the production of the Special Report on Land Use, Land-Use Change and Forestry (known as SRLULUCF) (IPCC 2000b). In the wake of the adoption of the Kyoto Protocol in 1997, whilst land use, land-use change and forestry (LULUCF) activities were included in the provisions of the Kyoto Protocol, the definition and accounting rule of LULUCF activities were left open for future negotiations. Because the definitional problems of LULUCF activities needed to be resolved to implement the Kyoto Protocol, the UNFCCC Subsidiary Body for Scientific and Technological Advice (SBSTA) requested the IPCC to prepare a special report that would provide the scientific and technical information on the issues. In short, SRLULUCF was designed particularly to help the implementation of specific provisions of the Kyoto Protocol, and it was delivered in May 2000, less than 2 years since the SBSTA request in June 1998 (IPCC 1998; 2000b).

From the AR3 cycle, recognising a trade-off between the importance of a quick response to the UNFCCC request and the heavy workload required to prepare special reports, the IPCC introduced a new category of ‘technical papers’ that are based on materials already in assessment reports and special reportsFootnote 6 (IPCC 1995). During this period, the IPCC released four technical papers, all at the request of the UNFCCC. But in some cases, while the UNFCCC originally requested to prepare technical papers, the IPCC decided to rewrite these as special reports instead, mainly because new literature was available for more up-to-date assessment or there was no sufficient information in previous reports. This was the case for the Special Report on The Regional Impacts of Climate Change: An Assessment of Vulnerability (IPCC 1997) and the Special Report on Methodological and Technological Issues in Technology Transfer (known as SRTT) (IPCC 2000c).

Despite the creation of technical papers as a way to provide scientific information in a timely manner while avoiding the increase in additional workload, they thus far have not been fully exploited in the IPCC work. After the AR3 cycle, only two technical papers were produced,Footnote 7 the latest one being the IPCC Technical Paper on Climate Change and Water (IPCC 2008b) published in 2008. This underutilisation of technical papers might be partly because of their restriction that allows using only materials already in previous reports. This restriction is making technical papers less useful for communicating the latest science on specific topics, especially in today’s rapidly changing landscape of scientific publishing (cf. Callaghan et al 2020). Interestingly, a technical paper on water was initially proposed as a possible special report during the AR4 cycle (IPCC 2002). However, following an expert meeting in November 2002, it was decided to treat water as a cross-cutting theme in AR4 and prepare a technical paper thereafter (IPCC 2003a; 2003b).

During the AR4 cycle, the IPCC produced two special reports, both published in 2005—the Special Report on Carbon Dioxide Capture and Storage (known as SRCCS) (IPCC 2005) and the Special Report on Safeguarding the Ozone Layer and the Global Climate System (known as SROC) (IPCC/TEAP 2005). Both reports were also prepared as a response to the invitation by a decision taken at the UNFCCC COP. For SRCCS, the IPCC was at first invited to prepare a technical paper by COP7; however, as a technical paper was deemed of limited value, it instead decided to undertake a special report (IPCC 2002; 2003a; 2003c). On the other hand, SROC was prepared jointly with the Montreal Protocol’s Technology and Economic Assessment Panel (TEAP) following the invitation by COP8 to the UNFCCC and by the 14th Meeting of the Parties (MOP) to the Montreal Protocol (IPCC 2003a; 2003d). The preparation of the report was supervised by a joint IPCC/TEAP steering committee which was comprised of representatives from each organisation.

Thus, up until the AR4 cycle, special reports remained largely a direct channel to serve the political needs of the UNFCCC. No special reports (except SRES) were prepared by the IPCC’s own initiative; they were all requested by the UNFCCC or other UN conventions/organisations. At the time of the scoping of AR4, however, the IPCC made an important step towards institutionalising the preparation of special reports within the assessment cycle.

2.2 Institutionalised procedure within the assessment cycle

At the 18th session in September 2001, when concluding the AR3 cycle, the Panel had a discussion about several key issues regarding the future work of the IPCC such as the timing and characteristics of AR4, the structure of WGs and the role of special reports (IPCC 2001). In this discussion, it was decided that the IPCC would continue to consider a request for special reports from the UNFCCC or other organisations on a case-by-case basis, but it was also agreed to develop a framework and set of criteria for establishing priorities for special reports during the AR4 cycle. Following this decision, a decision framework for special reports was adopted at the 20th session in February 2003 (IPCC 2003a).

In this framework, three key priorities were established for special reports: (1) priority should be given to comprehensive assessment report; (2) requests from the UNFCCC should be accorded higher priority than requests from other UN conventions and organisations; and (3) where appropriate, the IPCC’s own initiative to serve the policy community in a proactive fashion is a key element in choosing special reports (IPCC 2003e). In addition, a set of criteria was defined to guide decisions on whether to prepare special reports (e.g., the availability of sufficient scientific literature, the origin of the request, the availability of experts, the timeliness of the report, financial and human resources, etc.). It was also noted that the framework was to “guide, but not prescribe, future decisions by the Panel” and decisions regarding the conduct of special reports would be considered on a case-by-case basis (IPCC 2003a). Basically, the framework was devised to help balance two competing demands between serving the needs of the policy community (particularly the UNFCCC) and managing the IPCC’s overall human resources.

This decision framework was applied again for preparation in the Fifth Assessment Report (AR5) cycle, but it was amended to add a new criterion to consider issues that require input from more than one WG (IPCC 2008a; 2008c). With this amendment, special reports have become seen as a means to address cross-cutting issues in more integrative and comprehensive ways across three WGs. In the AR5 cycle, the Panel further discussed two options for the planning of special reports: (1) seek proposals on possible topics and consider a slate of special reports at the beginning of the cycle; or (2) consider proposals for special reports (e.g., requests from the UNFCCC) on an ad-hoc basis (IPCC 2009a). While the first option was better suited to set priorities on the topics of special reports in the overall context of the entire assessment, the second option allowed responding to unforeseen requests for special reports that might come up at a later stage of the cycle. The Panel eventually decided to go with the second option (IPCC 2009b).

Interestingly, the origin of two special reports produced during the AR5 cycle—the Special Report on Renewable Energy Sources and Climate Change Mitigation (known as SRREN) (IPCC 2011) and the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (known as SREX) (IPCC 2012)—was not the request from the UNFCCC but was the IPCC’s own initiative based on the proposals by its member governments. Both SRREN and SREX were proposed respectively by Germany and Norway,Footnote 8 referring to the third priority (‘serve the policy community in a proactive fashion’) of a decision framework mentioned above as a rationale for the conduct of these reports (IPCC 2006; 2008d). This indicates the changing nature of special reports from the AR5 cycle, not merely as a direct channel for quickly responding to the UNFCCC request but more broadly as a vehicle for shaping the public discourse on certain specific issues deemed of interest to a wider range of policymakers and social stakeholders.

The production of special reports was further institutionalised for the AR6 cycle. In contrast to the previous cycles, the Panel at this time decided to identify the topics of special reports at the beginning of the cycle within the context of the overall scoping of the entire assessment, and hence it decided at the 41st session in February 2015 to invite member states and observer organisations to submit their proposals on possible themes for special reports (IPCC 2015). This decision was made before COP21 in December 2015 which invited the IPCC to provide a special report on the impacts of global warming of 1.5 °C in 2018. The invitation by COP21 was treated as one among many other proposals and the Bureau was tasked with reviewing a total of 31 proposals received from 27 sources (IPCC 2016a). The co-chairs of the three WGs consolidated those proposals into nine clusters by themes and then considered them against five criteria formulated using the above-mentioned decision framework, that special reports: (1) must be relevant for at least two WGs; (2) should complement the AR6 and be scientifically focused; (3) should cover timely topics not recently adequately covered by earlier special reports; (4) can only be implemented late in the cycle if they would strongly depend on new climate simulations from CMIP6 (Coupled Model Intercomparison Project Phase 6); and (5) may integrate different individual proposals in a coherent framework (IPCC 2016b; 2016c; 2016d). Based on their review, the WG co-chairs identified four clusters as priority themes: Cluster A (land use, land degradation and agriculture); Cluster B (oceans and cryosphere); Cluster F (emissions pathways, including the 1.5 °C proposal); and Cluster I (cities). The Bureau then came to a conclusion that it would recommend the Panel to accept the invitation by COP21 to prepare a special report on 1.5 °C as well as undertake one or more additional themes for a special report among the four clusters (IPCC 2016e).

At the 43rd session in April 2016, there was an intense exchange of opinions among government delegates about the number and topics of special reports (IISD 2016; IPCC 2016f). While there was a broad consensus on accepting the invitation by COP21, government delegates were split on whether to produce two or three reports during the AR6 cycle. Some delegates and WG co-chairs expressed their concern over the heavy workload required for completing three reports. Regarding the topics, all the other three clusters of themes (land use, oceans and cryosphere, cities) were met with strong support from many governments. Eventually, it was decided to undertake three special reports on 1.5 °C, land use, and ocean and cryosphere during the AR6 cycle and it was also agreed that a special report on cities would be included in the AR7 cycle.

In sum, the conduct of special reports has been gradually institutionalised over time and now is firmly embedded in the strategic planning on the scoping of the entire assessment cycle. While special reports remain a primary channel to respond to requests from the UNFCCC, they also serve as a practical device for the IPCC to prove its policy relevance by filling the knowledge gap of specific issues that need timely and cross-cutting scientific perspectives.

3 The function of IPCC special reports

In this section, I now turn to a central question of the article: What role do IPCC special reports play at the interface between science and policy? What sort of political impact does the release of special reports have on the public discourse? On the other hand, how do political interests or agendas influence the preparation of special reports? Given that the main purpose of special reports is to serve the needs of the policy community by addressing specific timely issues of policy relevance, the scientific assessment in special reports is inextricably tied to and hence embroiled in the wider political dispute and controversy around climate change.

Here I argue that IPCC special reports play a dual political role at the science-policy interface—the politicisation of scientific assessment and the normalisation of politically contested ideas. This dual function of politicisation and normalisation is somewhat like two sides of the same coin, the different roles that the IPCC takes when it is confronted with political controversy. Whilst politicisation is the process that the IPCC gets caught up in and then becomes the central focus of political controversy, normalisation is the process in which the IPCC is being employed as a means to tame political controversy and thereby justify certain policy options. As discussed below, the two functions can play out at the same time in the conduct of special reports (e.g., SRLULUCF and SR15), but this may not always be the case.

It must be also noted that the two functions of politicisation and normalisation are not peculiar to special reports. They can be rather understood as general organisational characters inherent in the IPCC as a ‘boundary organisation’ that aims to establish close cooperation—while at the same time stabilise a demarcation—between science and policy (Hoppe et al. 2013; Beck and Mahony 2018a; Gustafsson and Lidskog 2018). The IPCC embeds “a paradoxical desire” (Lahn and Sundqvist 2017) for the integration and separation of science and policy into its institutional arrangement. As a consequence, IPCC assessment practices necessarily entail some degree of politicisation and normalisation. The point of my argument is that these functions become more salient in the conduct of special reports that focus on timely policy-relevant topics.

Below I describe how this double role of politicisation and normalisation played out in the conduct of previous special reports with particular attention to the cases of SRLULUCF in 2000, SRCCS in 2005, SRREN in 2011 and SR15 in 2018.

3.1 Politicisation of scientific assessment

Before delving into the details of specific cases, what does ‘politicisation’ mean? While the meaning of politicisation can be defined in many ways, in this article, I follow the definition by Brown (2015) who argues that politicisation is “a process whereby people persistently and effectively challenge established practices and institutions, thus transforming them into sites or objects of politics”. By conceiving politics not as a particular sphere but as a certain kind of activity, Brown (2015) also defines politics as “purposeful activities that aim for collectively binding decisions in a context of power and conflict”. From this view of politics, politicising science amounts to a deliberate act by someone of introducing conflict into established scientific practices or institutions and requiring collective decision-making to resolve conflict. A contentious negotiation on the approval of the Summary for Policymakers (SPM) of IPCC reports is a clear example of such politicisation of science (De Pryck 2021; see also Hughes and Vadrot 2019).

Crucially, politicisation is not bad per se. Given its intergovernmental nature, government interference in scientific assessment is not only unavoidable but also somewhat required to secure the political legitimacy of the IPCC (Hughes 2015; 2022). Politicisation is a necessary part of IPCC assessment that aims at producing politically-negotiated scientific reports. But politics can become dysfunctional when no agreement can be reached to resolve conflict. A problem is excessive politicisation whereby conflict is too deep to be resolved within a given time and any related activities are suspended until reaching an agreement. In Brown’s definition, politics is also understood as a certain kind of political activity that takes place in many different venues. This means that the politicisation of IPCC science can happen both inside (during the preparation of reports) and outside (after the release of reports) of the IPCC.

Politicisation inside the IPCC

The controversy over SRLULUCF is a case in which the IPCC’s assessment process itself became the site of politics. As briefly discussed above, the preparation of SRLULUCF originated from the request by the UNFCCC SBSTA which expected the IPCC to set the scientific and technical context for political negotiations over the interpretation of the provisions related to LULUCF activities in the Kyoto Protocol (Fry 2002; Fogel 2005; Lövbrand 2009). These provisions allowed developed countries to include the removal of greenhouse gases by biological sinks in the LULUCF sector to meet their emission reduction commitments in the Kyoto Protocol. However, many key terms of the provisions remained undefined and were poorly understood at COP3 in Kyoto. Because the interpretation of these sink provisions had profound implications for the obligations of emission reduction by developed countries, it was subject to an intense political struggle and bargaining among negotiating parties (Fry 2002; Lövbrand 2009). Whereas the US and several other industrial countries were in favour of a flexible definition of afforestation/reforestation and a comprehensive approach to the accounting of LULUCF activities, the European Union (EU) and many developing countries were proposing a stringent definition and a restrictive accounting rule. Given the high political stakes involved in determining these terms, the planning and writing of SRLULUCF within the IPCC immediately became the site of politicised debates about forest science and the concept of biological sink (Fogel 2005; Lövbrand 2009).

The politically sensitive nature of SRLULUCF was reflected in the fact that the then IPCC chair Robert Watson himself assumed the position of chair to oversee the whole process and established a steering committee comprised of the Bureau members from all the three WGs and the Task Force on National Greenhouse Gas Inventories (TFI) (IPCC 1998). According to Fogel (2005), at every stage of the process, government delegates tried to manoeuvre the report’s terms of reference or findings into their preferred policy positions. Due to diametrically opposing policy preferences among negotiating parties, IPCC authors were accused from all sides of stepping into the realm of ‘policy prescriptiveness’. The controversy was so intense that the IPCC plenary discussions on the SPM approval were nearly as tumultuous as the negotiations at the UNFCCC COP. In this sense, SRLULUCF served as an additional place for the politics of definitions and accounting methods regarding LULUCF activities in the run-up to COP negotiations.

Politicisation outside the IPCC

The controversy over the reception of SR15 points to a case in which the IPCC’s scientific assessment became the object of politics at venues outside the IPCC. Although SR15 is generally considered a remarkable success by attracting praise from a wide range of social stakeholders and high-profile media coverage (Boykoff and Pearman 2019; Cointe and Guillemot 2023), the reception of SR15 at the formal UNFCCC negotiations was actually quite controversial (Provost 2019; Hermansen et al. 2021; Schenuit 2023). At COP21, the UNFCCC invited the IPCC to provide SR15 in 2018 so that the report could feed into the 2018 facilitative dialogue (later known as the Talanoa Dialogue), a year-long process that aimed to help countries increase the ambition of their Nationally Determined Contributions (NDCs). The Talanoa Dialogue was a precursor of the Paris Agreement’s Global Stocktake; it was launched at COP23 under the Presidency of Fiji and concluded at COP24 in Katowice, Poland. When SR15 was sent to the floor at COP24, however, the report was met with a strong objection from a handful of countries and became the politicised issue at hand. The US, Russia, Kuwait and Saudi Arabia refused to “welcome” the report and insisted instead that the COP would only “take note” of it (Provost 2019; Hermansen et al. 2021). In particular, Saudi Arabia was the most visible opponent throughout the production of SR15. From the very beginning, Saudi Arabia was against the decision to invite the IPCC to produce SR15; during the approval of SR15, it strongly contested direct reference to NDCs in the text as it claimed that this would contradict the IPCC’s principle of policy neutrality (Schenuit 2023; see also Hermansen et al. 2021).

Thus, the controversy over the reception of SR15 could be seen as a further attempt by Saudi Arabia (and a few other countries) to politicise the IPCC science outside the purview of IPCC assessment. The approval of SR15 at the IPCC plenary might cease—but not end—the conflict temporarily but unresolved issues spilled over into the UNFCCC negotiations. Eventually, parties failed to reach an agreement on how to receive SR15 at COP24. Later this controversy was ‘closed’ with a decision in which parties expressed only their “appreciation and gratitude” to the IPCC for responding to the invitation by COP21 to provide SR15 but without taking further action (Farand 2019).

The politicisation of IPCC science after the release of a special report could be provoked in other venues than COP negotiations. For example, when the IPCC released SRREN in 2011, it was immediately embroiled in a political controversy about alleged conflicts of interest (Pearce 2011; Nature Climate Change 2011). The allegation against SRREN was made by critics that a lead author of the report—who was also at that time affiliated with Greenpeace—might have had unfair influence over the content of the report, giving more prominence to the scenario with an optimistic prospect of renewable energy supply (Lynas 2011). While the IPCC categorically denied this allegation and defended that SRREN was balanced and scientifically sound, it nonetheless raised a question about who should be—or should not be—authors of IPCC reports (Edenhofer 2011). This controversy over SRREN didn't lead to any change in assessment practices but it suggests that the IPCC might be inadvertently drawn into political contentions that cannot be anticipated before the release of the report. In short, political controversy is an unavoidable fact of life for the IPCC (Asayama et al. 2022).

3.2 Normalisation of politically contested ideas

In addition to politicising scientific assessment, IPCC special reports could also have the effect of normalising politically contested ideas. Gupta and Möller (2019) argue that authoritative assessments conducted by eminent scientific bodies such as the IPCC are a key source of what they call ‘de facto governance’—i.e., a form of governance that entails ‘unacknowledged steering’ that is not explicitly recognised as an act of governing and yet generates the governance effects of ordering a nascent and highly contested field of inquiry in specific directions, thereby shaping the context for de jure governance. Gupta and Möller (2019) also point out that such an ordering occurs through two sequential processes: the normalisation and institutionalisation of research directions (e.g., the establishment of research programs, the delineation of research communities, the creation of funding streams). As such, authoritative assessments may well contribute to legitimising unconventional, politically contested ideas and hence shifting the focus of governance debates from ‘what, if, and whether’ questions of desirability to ‘how, when, and who’ questions of (technical) design.

The function of normalisation can be understood as an effect of what Beck and Mahony (2018b) called the ‘policy performativity’ of scientific assessment—that is, an intangible political effect of IPCC assessment on defining the possibility space within which particular descriptions of the future are brought into being more thinkable and actionable in policy. As Lahn (2021) showed, the IPCC provides the institutional setting (or a ‘common infrastructure’) that enables scientists to develop a new scientific concept (e.g., the carbon budget) and present it to policymakers with prominence and credibility (see also Asayama 2021; Lahn 2022). Despite the principle of policy neutrality, the IPCC thus exercises the symbolic power to authorise certain forms of scientific knowledge and thereby legitimise particular courses of policy action (Hughes 2015).

The normalising effect of IPCC special reports on politically contested ideas is evident in the production of SRCCS which rendered carbon capture and storage (CCS) technology accepted as a key mitigation option among the expert and policy community and helped accelerate the technology development (Meadowcroft and Langhelle 2009; Bäckstrand et al. 2011; Kheshgi et al. 2012; de Coninck and Benson 2014; Gale et al. 2015). During the 1990s, the IPCC was at first hesitant to recognise CCS as an appropriate mitigation option and therefore gave little attention to CCS in AR2 and AR3 (Meadowcroft and Langhelle 2009). This relative ignorance of CCS in the IPCC came to change in the 2000s as the UNFCCC COP7 in 2001 invited the IPCC to prepare a technical paper on CCS. In response to this UNFCCC request, the IPCC held an expert workshop in Regina, Canada in late 2002 and then decided to prepare a special report instead of a technical paper in order to assess more comprehensively the scientific, technical, environmental, economic and social aspects of CCS (IPCC 2003a; 2003c).

Importantly, a political motivation behind this decision to produce SRCCS was to provide a common scientific ground for future policy debates on CCS, a controversial emerging technology that was already becoming a divisive issue between different stakeholder groups (Narita 2012). As documented by Narita (2012), Bert Metz, the WGIII co-chair at the time, saw this opportunity and seized it to bring both advocates and critics of CCS together to make a special report on the topic. In the writing of SRCCS, the authors of the underground geological storage chapter were repeatedly asked by the IPCC leadership to produce clear statements on quantitative estimates of the safety and security and the potential capacity of geological CO2 storage (Narita 2012). It was deemed essential for the IPCC to provide scientifically credible numerical estimates on storage security and capacity to be useful for policymaking.Footnote 9 Later these quantitative estimates became a symbolic figure of SRCCS to represent the technical promise of CCS, widely circulated in media coverage (Asayama and Ishii 2017). As such, SRCCS played a pivotal role in mainstreaming CCS as a key mitigation option. The IPCC ‘imprimatur’ lent substantial legitimacy to CCS (cf. Meadowcroft and Langhelle 2009).

The normalisation effect is also partly observed in the role that SRLULUCF played in the biological sink controversy. Whilst the preparation of SRLULUCF became the site of politicised debate, the IPCC’s engagement nevertheless contributed to validating the abstract sink concept as a scientifically sound mitigation option (Lövbrand 2009). Notably, though, SRLULUCF might help the recess or closure of political controversy over the sink provisions in the Kyoto ProtocolFootnote 10 but there remained the lingering ethical concern over using terrestrial carbon sinks as a substitute for reducing emissions from fossil fuels. This ethical issue resurfaced again when political interests in land-based carbon removal increased since the adoption of the Paris Agreement (see Carton et al. 2020).

Furthermore, SR15 also played a significant role in giving scientific legitimacy to the 1.5 °C target and normalising it as the new guardrail for climate action (Cointe and Guillemot 2023; Livingston and Rummukainen 2020; van Beek et al. 2022). In contrast to the long history of the 2 °C target that could date back to the adoption of the UNFCCC in 1992, the 1.5 °C target emerged in a relatively short period of time and its origin is clearly rooted in the diplomatic negotiations within the UNFCCC (Cointe and Guillemot 2023). At COP21, the Alliance of Small Island States (AOSIS) and the Least Developing Countries (LDCs) group pushed for the inclusion of the 1.5 °C target in the Paris Agreement, whereas other countries strongly opposed it. Eventually, a political compromise was reached to adopt 1.5 °C as an aspirational target and at the same time invite the IPCC to provide a special report in 2018, thereby avoiding further consideration at the time (Schenuit 2023; Hermansen et al. 2021). The invitation for SR15 can thus be understood as an attempt to pass on a politically difficult subject to the IPCC and expect it to resolve the conflict.

The initial reactions to the request for SR15 from the scientific community were mostly surprise, concern or scepticism as many scientists considered the 1.5 °C target unrealistic and so they viewed this research as a waste of time and resources (Livingston and Rummukainen 2020; Cointe and Guillemot 2023). Before the Paris Agreement, there were virtually no emissions scenarios consistent with the 1.5 °C pathway. Despite that, SR15 immediately became an institutional mechanism to mobilise a range of scientific research on studying the impacts and feasibility of 1.5 °C. In the undertaking of SR15, the integrated assessment model (IAM) community played a crucial role in rendering the 1.5 °C target ‘achievable’ by including an acceptable level of overshoot and the use of carbon removal technologies (van Beek et al. 2022). Being well aware of the needs of policymakers, IAM modellers produced a variety of quantitative projections for 1.5 °C pathways and thereby helped to create the perceived feasibility of the 1.5 °C target.

As Livingston and Rummukainen (2020) pointed out, without the UNFCCC request to produce SR15, there would likely not have been such a collective scientific focus on 1.5 °C. But by the same token, through the publication of SR15, the IPCC gave scientific legitimacy to the 1.5 °C target and made it a moral necessity to achieve this political target. SR15 thus functioned as de facto governance to normalise and institutionalise 1.5 °C in both scientific research and policy debate.

4 The future of IPCC special reports

As shown in Section 2, the IPCC has institutionalised the conduct of special reports over time and now firmly embeds it within the overall scoping of the entire assessment cycle. In the AR6 cycle, the planning of special reports was done by identifying the number and topics of special reports at the beginning of the cycle. The AR7 cycle followed suit. Member governments were solicited to submit their proposals on topics for special reports and the most favoured topics were ‘tipping points’, ‘adaptation’ and ‘loss and damage’ (IPCC 2024b). For further consideration at the plenary session, these proposed topics were grouped into four “umbrella, cross-cutting topics”Footnote 11 that could be deemed to provide relevant and timely information for the second Global Stocktake in 2028 (IPCC 2024a). At the 60th session in January 2024, the Panel discussed the work programme in the AR7 cycle and decided to produce no additional special reports other than the Special Report on Climate Change and Cities, the production of which was already agreed upon in the AR6 cycle. This decision was due to a lack of consensus on having a second special report—many countries supported the idea but some were against it with concerns over heavy workload (IISD 2024).

Beyond the prospect of the AR7 cycle, however, what could or should be the role of special reports in the future work of the IPCC? To answer this question is not simple because the answer can differ considerably, depending on expectations for what kind of role the IPCC should play in connecting science to policy and how the institutional structure should be reformed (or not) to fulfil its mission (Asayama et al. 2023). Here, three specific questions can be raised to think about the future role of IPCC special reports:

  • Should the IPCC prioritise special reports over comprehensive assessment reports?

  • Should the IPCC continue to respond to the UNFCCC request for special reports?

  • How should the IPCC select and define the scope of timely topics for special reports?

Below I delve into each question with discussions about potential reform in designing the future conduct of special reports and the challenges with that the IPCC could face, especially in light of the dual role of politicisation and normalisation.

Priority over comprehensive assessment

Previous IPCC assessments have always given first priority to comprehensive assessment reports prepared by three WGs and given only a complementary role to special reports. This prioritisation is clearly reflected in the latest decision by the Panel that nearly all countries supported continuing the current approach of three WG reports and a synthesis report in the AR7 cycle (IPCC 2024a; IISD 2024). Since the AR5 cycle, however, there have been criticisms from scientists over the slow pace of large comprehensive assessment and calls for shorter, quicker and more targeted assessment through special reports or similar products (Nature 2013; Griggs 2014; Stocker and Plattner 2014; Petersen et al. 2015). The document of lessons learned from the AR6 cycle also pointed out that for the future work of the IPCC, the focus should be on “more concise and targeted reports that address emerging science and policy concerns” (IPCC 2024c).

Thus, there is a common concern among scientists and policymakers that the current model of ‘comprehensive assessment’ is out of date and of little use to inform the most pressing issues at hand. If the IPCC were to strive for policy relevance, it might have to find a new model of assessment alternative to the comprehensive model. As one potential option for the AR7 work programme, the Bureau actually suggested the option called a ‘special report gallery’ that replaces the line-up of three WG assessment reports with a series of topical special reports (IPCC 2024a). As special reports are a tool for interdisciplinary collaborations across the WGs, such a suite of special reports can facilitate more integrative scientific understandings of urgent policy issues from cross-cutting perspectives. However, this option received little support from governments whereas the overwhelming majority opted for the ‘classic’ option with minimum change from past practices (IISD 2024). A challenge lying ahead is therefore how to win political support for change from those governments in strong favour of keeping the status quo.

Responsiveness to the UNFCCC request

Given its historical origin as an intergovernmental body within the UN system (Bolin 2007; Skodvin 2022), the IPCC has had a close—and somewhat inseparable—relationship with the UNFCCC since its inception. Serving the political needs of the UNFCCC has been considered by and large an organisational priority, so it seems self-evident that the IPCC will continue to be responsive to the request from the UNFCCC to provide special reports, if necessary and possible. However, as seen in cases like SRLULUCF and SR15, being faced with an unresolvable conflict in government negotiations, the UNFCCC repeatedly made recourse to the IPCC to provide special reports in expectation of IPCC science taking the heat out of political controversy. Such political resort to the IPCC can be found in a recent call for a special report on loss and damage (Nature 2022; see also Huq 2023). But it is a misplaced hope to expect that new science of IPCC reports could simply resolve the clashes of political interests in COP negotiations. Of course, it is tempting for governments who are struggling to reach an agreement at COP negotiations to request IPCC special reports because this allows them to shift—at least temporarily—the responsibility for handling politically intractable problems onto the IPCC. For the IPCC, however, this is just being used for ‘political venue shopping’ (Schenuit 2023) to cover up conflicts in political negotiations with the potential risk of becoming the site of overly politicised debate that paralyses its assessment activities.

There is thus a reason not to respond—or give high priority—to the UNFCCC request for special reports. The IPCC instead can distance itself from the UNFCCC and focus more on serving the diverse needs of social stakeholders. In other words, the ‘policy relevance’ of special reports needs not be defined narrowly by a direct channel with the UNFCCC. This has been already done at the IPCC’s own initiative through the production of SRREN, SREX, SRCCL and SROCC, most of which are generally well-received by the scientific and policy community. The IPCC could build on these past successes and extend the range of possible topics for special reports. At the same time, the IPCC may as well consider rebranding ‘technical papers’ to meet the needs of the UNFCCC since they are supposed to be “prepared on topics for which an objective, international scientific/technical perspective is deemed essential” (IPCC 2013) for the UNFCCC negotiations. For instance, by relaxing the restrictions to allow technical papers to be based on the methods used—not on the material already—in previous reports (cf. Forster et al. 2023), the IPCC might be able to make the best use of their resources to provide more up-to-date scientific information while not overburdening the authors.Footnote 12

Selection and scope definition of timely topics

Insomuch that the IPCC has become the most authoritative scientific source of climate change knowledge, a political stake in special reports, irrespective of topics, has also increased accordingly. Due to expected social and political impacts, the release of IPCC reports is now regarded as a high-profile political event that could draw global attention from the international media and political leaders in the world. This is particularly true of special reports because they focus on specific timely issues of policy relevance. Given this nature of timeliness, the conduct of special reports could become not only the object of intense political discussions (politicisation) but also the moment of shifting the policy discourse in certain directions (normalisation). The IPCC therefore has to use great caution in the selection of topics for special reports to avoid being the subject of excessively politicised debates or prematurely normalising politically contested ideas.

Take for example the proposal by some of a special report on solar geoengineeringFootnote 13 (Rahman et al. 2018; Jinnah and Nicholson 2019; Reynolds 2021). Although gaining prominence as a potential policy option, solar geoengineering is one of the most politically contentious and divisive topics among scientists and policymakers. Despite the relative ignorance of solar geoengineering in its previous reports (Parker and Geden 2016; Reynolds 2021), the IPCC is already being caught up in the middle of the controversy. Whereas there is a call for ‘balanced research’ including thorough and impartial assessment by the IPCC (Wieners et al. 2023), there is a group of people who are adamantly against the normalisation of solar geoengineering through IPCC assessment (Biermann et al. 2022; see also Stephens et al. 2023). Under this circumstance, the undertaking of a special report on solar geoengineering may well exacerbate the conflict and erupt into far more intense political controversy that could possibly cause the dysfunction of IPCC assessment processes themselves.

An intractable conflict on solar geoengineering does not necessarily mean that the IPCC should never be engaged with such controversial topics for special reports. Like SRLULUCF and SR15, even if it wanted to avoid that, the IPCC could be forcibly dragged into the debate through an invitation by the UNFCCC. Here, how to define the scope of the report becomes a crucial step to the successful conduct of special reports on controversial topics. For example, instead of solely focusing on solar geoengineering as a single issue, the overall scope of the report can be broadened to cover a range of relevant cross-cutting issues (e.g., tipping points, overshoot, managed retreat) and address it as just one topic among many others. The topic scope for SRCCL and SROCC was determined in this way by grouping several relevant individual proposals into a coherent ‘umbrella topic’. Broader framing of the timely topic might be able to avoid—to some extent—the situation in which the conduct of special reports causes excessive politicisation that paralyses scientific assessment processes or premature normalisation of controversial ideas like solar geoengineering as a ‘real’ policy option.

5 Conclusion

The history of IPCC special reports is part of a wider story about science and politics of climate change. Since its establishment in 1988, the IPCC itself has undergone significant institutional changes to adapt to changing political contexts and sometimes survive a crisis of its own (De Pryck and Hulme 2022). As the IPCC has grown as the global authority of climate science and the UNFCCC negotiations have culminated in the Paris Agreement, the conduct of IPCC special reports has also evolved over time into formal proceduralisation that firmly embeds its planning in the overall scoping of each assessment cycle. This historical evolution of special reports can be understood as the result of the IPCC’s continuous striving for ever greater policy relevance.

In earlier cycles, special reports were characterised mostly as a direct channel for quickly responding to requests from the UNFCCC. More recently, special reports have also become a vehicle to consolidate cross-cutting scientific perspectives and fill the knowledge gap of specific topics deemed relevant to a diverse group of policymakers and social stakeholders. Special reports remain a primary tool to address specific timely issues of policy relevance, but the notion of ‘policy relevance’ has been extended to serve the broader policy needs of the international community, not only the UNFCCC. In addition, special reports lead IPCC assessment to play a dual political role at the interface between science and policy. Namely, through the production of special reports, the IPCC could turn into the site or object of politicised debates on science (politicisation), but it may also serve as de facto governance with the effect of normalising politically contested ideas (normalisation). This dual function of politicisation and normalisation is two different faces emerging from the process into which the IPCC is brought to deal with political controversy.

Furthermore, the duality of the two functions manifests inherent difficulty in reconciling tensions that lie behind the IPCC’s oft-quoted mantra of being ‘policy-relevant but policy-neutral, never policy-prescriptive’ (Mahony 2022). The pursuit of policy relevance could lead the IPCC to engage more with politically controversial topics in the hope of resolving conflict; as a result, IPCC science could normalise (and legitimise) controversial policy options but also this might turn the IPCC itself into the object of politicised debates by being accused of entering the realm of policy prescriptiveness. In other words, the principle of policy neutrality seems aspirational, but it is actually a façade—or a convenient fiction—to conceal the constant struggles over maintaining the boundary between policy relevance and policy prescriptiveness. The conduct of special reports could make these tensions so acute and salient that it becomes at some point untenable for the IPCC to keep a pretence of being policy-neutral. Rather than blindly adhering to the neutrality principle, the IPCC may have to recognise the ‘policy performativity’ of its scientific assessment and critically reflect on its political clout to shape the public discourse on climate change (Beck and Mahony 2018b).

Finally, the nature of the timeliness of IPCC special reports has two different implications for science and policy. On the one hand, the timeliness of special reports is a clear embodiment of policy relevance. By focusing on specific timely topics of immediate interest to the policy community, special reports could have more direct impacts on policy implementation in the real world than comprehensive assessment reports. This is a reason why the IPCC has been placing higher priority on the request from the UNFCCC. On the other hand, a timely response to the policy needs means that the science of special reports is always provisional. Precisely because the IPCC is tasked with assessing the latest scientific information within a limited time frame scheduled into a political calendar, the ‘best available science’ in special reports is inevitably incomplete for lack of sufficient evidence. This is true of all the special reports but it was especially visible in the cases of SRLULUCF and SR15.

Of course, the provisional science of IPCC special reports is not necessarily a bad thing. It just means that the shelf life of scientific evidence in special reports is rather short, going obsolete fast. In this regard, a cyclical assessment process is an effective mechanism to update regularly—though, too slowly—the content of IPCC reports with the latest science. Nonetheless, the legacy of special reports could have a lasting political impact on shaping the discourse on emerging policy areas in a certain direction. In other words, special reports might create a ‘discursive lock-in’ that fixates the public recognition of the issues to a specific viewpoint. This is a trade-off inherent in IPCC special reports. Recognising such a trade-off is crucial for the future undertaking of special reports on any topic.