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Dans les années 1970, quelques chercheurs comme Ignacy Sachs et René Passet ont permis en France l’élaboration de programmes de recherche novateurs pour mieux appréhender les questions de développement (Nord et Sud) et de préservation de l’environnement. Sur la base d’archives et d’entretiens, cette contribution reconstruit et analyse le processus de structuration, tant intellectuelle qu’institutionnelle, de l’expertise combinée environnement-développement en France. Le cas du CIRED, fondé par Sachs en 1973, sert de fil rouge pour mettre en lumière les lignes de force, leviers et obstacles rencontrés dans l’élaboration de ce nouvel agenda. Il ressort de cet examen que le soutien des institutions (nationales et internationales) a joué un rôle déterminant, et que l’expertise, tout en cherchant à s’autonomiser, a dû passer par un processus de normalisation pour s’installer dans le paysage scientifique des années 1980. In the 1970s, in France, a few researchers such as Ignacy Sachs and René Passet elaborated innovative research programmes to have a better understanding of development (North and South) and environmental issues. On the basis of archives and interviews, this article reconstructs and analyses the structuring process, both intellectual and institutional, of the environment-development expertise in France. The case of CIRED, created by Sachs in 1973, helps us illuminate how this new agenda was settled. Our findings are the followings: the support from national and international institutions has been crucial; and while the new expertise tried to become a new, autonomous field, it finally had to go through a normalization process to exist in the academic landscape of the 1980s. An English translation of this article is available at: https://hal.science/halshs-02548876v1.

Greenhouse gas emission scenarios are key in analyses of human interference with the climate system. They are mainly produced by one category of computer models: Integrated Assessment Models (IAMs). We analyse how IAM research organised into a community around the production of socio-economic scenarios during the preparation of the IPCC AR5 (2005-2014). We seek to describe the co-emergence of a research community, its instruments, and its domain of applicability. We highlight the role of the IPCC process in the making of the IAM community, showing how IAMs worked their way to an influent position. We then survey three elements of the repertoire that served to organise collective work on scenarios in interaction with the IPCC and the European Union, and which now frames the community and its epistemic practices. This repertoire needs to articulate epistemic practices with the pursuit of policy relevance, which shows how epistemic communities and patterns of co-production materialise in practical arrangements.

International audience; One year after COP21 in Paris that reached to a global agreement on climate action, it is timely to come back to the scientific expertise that is part of the debates about climate change. The almost symbiotic relationship between scientific expertise and political discussions in this field is well‐documented (e.g. Shackley and Wynne, 1996; Agrawala, 1999; Miller, 2004; Edwards, 2010). This scientific expertise is not limited to climate science, but it is rarely considered in all its diversity, with physical and natural science drawing most of the attention. While the history and the role of climate scenarios/models and the development of expertise on climate change have been extensively analysed (e.g. Edwards, 1996, 2010; Guillemot, 2007; van der Sluijs et al., 1998), the development of socio‐ and techno-economic assessments in this fieldhas not received the same attention. However, these seem to play a crucial role in the elaboration of climate policy, insofar as they contribute to the understanding of the interactions between climate and societies. The rise of climate change on the public agenda since the late 1980s has prompted the need for quantitative assessments of the costs and impacts of mitigation strategies, in particular in view of the IPCC reports. To meet this demand, an increasing number of scenarios have been produced by Energy‐Economy‐Environment (E3) models. These gather different types of models – including the Integrated Assessment Models (IAMs) – which help to reduce the complexity and heterogeneity of relevant processes, inform and to an extent frame international climate negotiations, by producing a large array of numerical projections and scenarios.This paper focuses on Integrated Assessment models (IAMs). It follows the co-evolution of the IAMs institutions and research community, and of their agenda of modelling efforts. We do so by focusing on the preparation of the 5th Intergovernmental Panel on Climate Change (IPCC) Assessment Report (AR5). IAMs are stylized numerical approaches which aim at representing complex socio-physical interactions among energy, agriculture, the economic system … as systems. Based on a set of input assumptions, they produce quantified scenarios (e.g. energy system transitions, land use transitions, economic effects of mitigation, emissions trajectories …) that helps us exploring potential climate policy strategies. They are a heterogeneous category that has gradually emerged from a set of distinct intellectual traditions (Weyant et al., 1996; Crassous, 2009). IAMs can thus be built on rather different assumptions: they can follow distinct logics and represent the same processes with different levels of details. IAMs and the scenarios they produce have grown central to the work of IPCC and seem to play an increasingly important part in climate negotiations and policies. Their influence has become particularly striking in the IPCC Fifth Assessment Report through the work and contribution of “Working Group III” – entitled ‘mitigation of climate change’. During the process of preparing the AR5, Working Group III was chaired by one of the main actors of the current IAM research community. IAMs outcome and perspective were used as a guiding and structuring principle. IAM scenarios were expected to serve as bridging devices between the three IPCC working groups (which involve different scientific disciplines), albeit interviews suggest that the extent to which they succeeded in this respect remains unclear. IAMs influence has built up conjointly with the structuring of IAM research as a distinct field of expertise and that of IAMs researchers network through a series of European Projects and regular meetings. All of this contributed to the consolidation of IAM as a category of models with common – or at least comparable – characteristics. How did ‘IAM’ emerge as a relatively unified – though diverse – category and research field? How and where did the IAM community organise as such, and what is it made of? How have integrated assessment modellers organised the heterogeneity of their models so as to establish them as credible and reliable sources of policy-relevant expertise? How do they manage uncertainties, considering both the scope and complexity of the systems they study, and the many conceptual repertoires they draw from (physics, economics, systems dynamics, environmental sciences…)?In order to answer such questions, we conducted a first series of interviews with modellers and key players in the IAMs community. These were undertaken on different occasions such as: the conference Our Common Future Under Climate Change (OCFCC) (Paris, July 2015), the venue to France of the head of the Energy Modelling Forum (October 2016), two visits to major research institutes in this field (PIK and PBL/University of Utrecht). These interviews have been completed by observations during two conference sessions focused on IAMs: a side event entitled « New frontiers of integrated assessment of climate change and policies » during the OCFCC Conference, and the 8th meeting of the Integrated Assessment Modelling Consortium (IAMC) (Postdam, November 2015). Attending and observing these sessions gave us an overview of the debates among modellers, the diversity of their approaches, the key challenges that are discussed in the community, the potential tensions within the community, and the way in which this research field is structuring itself. Last, we analysed the main inter-comparison modelling programs that were developed between the publications of the 4th and 5th IPCC reports and the material that was produced on these occasions (reports, articles…). In gathering and studying this empirical material, we tried to combine two approaches: a sociological perspective on the communities, networks, practices and discourses relevant to IAMs, and an historical perspective on the emergence and evolution of IAM research in terms of content, objectives and communities.In our contribution, we will emphasize the role of the research programs that have been conducted in specific forums – such as: the Energy Modeling Forum coordinated by Stanford University, the EU FP7 projects…- looking at the way in which they contributed in setting the agenda of the modelling research community and in steering the production of scenarios. We will also analyse the mutual relationship between these program, their outcomes and the contribution of WG III to the IPCC process and outcome, in particular within the 5th Assessment report. Model inter-comparison is a crucial part of these programs which have multiplied since the early 2000’s. It consists in comparing the outputs of a range of models under similar hypotheses, usually focusing on one specific modelling and/or policy issue (e.g. technological innovation, land-use changes, etc.). Though it draws from similar practices in climate change research, the reliance on model inter-comparisons appears as a defining feature of IAM research, and it has played a role in the cohesion of IAM as a category of expertise relevant to climate policy.For instance, since the 4th IPCC report published in 2007, the feasibility of low carbon trajectories consistent with the 2°C target that was institutionalized in 2009 at the Copenhagen conference has been a key question. It was the subject of the main modelling exercises conducted by the Energy Modeling Forum (EMF) headed by Stanford University and European research programs, mostly funded by the Commission. From 1991 onwards, the EMF organized a series of workshops dedicated to climate issues. In view of the IPCC 5th Assessment Report, EM 22, 24, 27 and 28 provided a global inter-comparison modeling exercise around the 2°C objective target, at different scales (world, US and EU level). Each of these sessions gathered researchers with an expertise of the question under consideration and followed the same protocol: a first stage was dedicated to the elaboration of a set of common scenarios based on harmonized assumptions that were then assessed by models. Since 2007, another large part of the scenarios produced for the IPCC 5th Assessment Report has come from similar inter-comparison modeling projects funded by the 7th European Framework Program. This highlights EU’s growing political and scientific interest in climate policies over this period. The main findings of these research programs were synthetized in consolidated reports. They were published in international peer‐reviewed journals in the energy and climate fields. The results from these projects represent a significant part of the scenario database included in the IPCC 5th Assessment Report , which included over 1000 scenarios. The Integrated Assessment Modeling Consortium (IAMC), another and newer forum for discussing IAM research, also is a key arena for comparing IAMs and organizing priorities for future research. It was created in 2007 and was instrumental in the preparation of the contribution of Working Group III to the IPCC 5th Assessment Report. Besides providing resources and a setting for regular meetings of IAM researchers, IAMC puts a lot of efforts into the mapping and systematization of IAM models and scenarios, thereby contributing to their unification as a category of models.Last but not least, we will also investigate how, by fostering common problem definitions and methodological approaches within the research programs or the creation of the IAMC, these inter-comparison modeling have contributed to delineate an IAM community. Our paper will wonder to what extent the IAM community can be described as an epistemic community (Haas, 1992) which participates, through the production of socio-economic scenarios, to the framing of the assessment of climate policies in IPCC Working Group III. It will also reflect on current evolutions, in particular those related to the Paris agreement on climate change and to the emergence of potential competing approaches and forums focused on national assessment and practical solutions in its wake (e.g Deep Decarbonization Pathway Project). In doing so, it will shed light on the epistemic, institutional and social dynamics involved in the production, framing and diffusion of a very specific type of expertise about the future.