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Cet article1 examine les enjeux sous-jacents à l’évaluation des cobénéfices des politiques climatiques dans le cadre de la mise en œuvre de politiques multi-objectifs, au sein lesquelles des synergies sont recherchées entre la lutte contre le changement climatique et des objectifs de développement (emploi, santé, sortie de la pauvreté, etc.). L’analyse du cinquième rapport du groupe III du GIEC montre en effet un intérêt grandissant dans la littérature pour les évaluations quantifiées des cobénéfices, en particulier à l’aide de modèles numériques intégrés. Néanmoins, l’évaluation quantifiée à une échelle globale des cobénéfices est confrontée à des difficultés d’ordre méthodologique qui expliquent l’écart entre les pratiques des modélisateurs et la vision théorique des économistes qui repose sur l’analyse coûts-bénéfices. L’article revient enfin sur la nécessité d’élargir le champ d’investigation de l’évaluation des cobénéfices aux politiques non climatiques qui déterminent une part importante des émissions de GES, et constituent un des enjeux majeurs des approches intégrées climat-développement qui montent en puissance dans les négociations climat en cours.

From the World2 and World3 models to contemporary Integrated Assessment Models (IAMs) that model carbon neutral emission pathways, global computer models have served as virtual laboratories for addressing economic, environmental and technological concerns together. Representing technological change has been a controversial element of global modelling efforts because, to a great extent, it sets the parameters on conceivable futures. To retrace this history, this article analyses four moments when modellers debated technological change: the controversy spurred by The Limits to Growth in the 1970s; subsequent global future studies during that decade; the IIASA Energy in a Finite World study in the 1980s; and the shift to endogenous technological change in IAMs in the 2000s. It shows that the notion of technological change as a predictable parameter affecting the future of society was not a given. Technological change progressively became a parameter in models as more elaborate methodologies were developed to simulate it. When modellers began to focus on climate action in the 1990s and 2000s, their interest in the relationship between technological change and social change dwindled. The increasing skill with which modellers formally represented technological dynamics was commensurate to the decline of heated discussions over how conflicting worldviews shaped simulations. [ABSTRACT FROM AUTHOR]

An increasing number of countries issue Deep Decarbonization Strategies (DDS). While DDS contents are well analysed, the processes by which they are developed attract less attention. This paper investigates what numerical model(s) are used in these processes, how they are used, and how models, modellers and stakeholders jointly contribute to the production of DDS. It draws lessons from an in-depth analysis of the second French national low-carbon strategy, complemented with insights from the US, Swedish and Brazilian DDS production processes. While configurations differ, DDS processes typically rely on multiple, sometimes overlapping models and involve a broad range of stakeholders. Articulating models together, and through stakeholder consultations, produces both numbers and collectives that share visions of the future – and both are equally important. Setting up and coordinating such assemblages of models and stakeholders requires effort, time, anticipation and resources. The cases presented here highlight the importance of technical, institutional and relational legacies (e.g. prior experience of joint work, hybrid communities), and of political support. We conclude on the importance for policymakers to account for these dimensions when setting up DDS processes and layout avenues for further research. Key policy insights The production of Deep Decarbonization Strategies (DDS) relies on multi-model, multi-stakeholder processes and requires developing models in consultation with stakeholders. These modelling assemblages produce numbers, shared visions and also relationships – all of which are equally important when it comes to elaborating DDS. Such assemblages require time, resources, trial and error, which in turn points to the importance of institutional, relational and technical legacies (e.g. prior experience with and around modelling tools, hybrid communities), as well as of political support, in facilitating this work. DDS elaboration processes constitute a learning experiment and present opportunities for technical and institutional innovation. Policymakers should anticipate and plan for these dimensions when deciding to produce DDS. [ABSTRACT FROM AUTHOR]

Greenhouse gas emission scenarios are key to analyse 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. [ABSTRACT FROM AUTHOR]

This paper focuses on transformational processes in a post Paris agreement context. It uses IMACLIM-R, an E3 (Environment--Energy--Economy) model allowing for the integration of urban forms, transport dynamics, environmental policies and behaviors. Building upon the study of a set of local low carbon experiments throughout the European Union (EU), the paper explores two contrasted stylized scenarios of the low carbon transition in Europe. It highlights that carbon pricing policies are useful guides for transition but cannot achieve the ambitious objective without significant transition costs. It shows that low carbon experiments in the transport and energy sectors are critical dimensions of complementary measures in favor of green infrastructures. Broadening and upscaling low carbon experiments helps overcome the inertias of the transport sector by fostering radical changes in infrastructures, thereby introducing deep transformations in mobility behavior. This can then generate positive macroeconomic outcomes, even though they are also dependent on specific financial support, calling for a renegotiation of the social contract based on specific fiscal reforms and measures to secure funding for these initiatives. The paper concludes with some research avenues for improving this preliminary work and calls for a better understanding of the complexity of the socio-economic patterns of both the transition and the conditions for an effective implementation. [ABSTRACT FROM AUTHOR]