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The Paris COP-21 reached a climate agreement on 2-degree global emissions stabilisation target. However, the likelihood of successfully implementing a legally binding global climate treaty will depend to a large degree on the macroeconomic impacts of different policy options on developing and emerging economies. It is thus crucial to evaluate the transition costs of implementing different climate policy architectures under socioeconomic and technological uncertainties from a multiregional perspective. Here we use a hybrid computable general equilibrium model, in which sub-optimalities, infrastructural inertia and technological uncertainties are explicitly introduced, to quantify the trajectories of variation in transitions costs under a range of climate policy scenarios in both Annex I and developing nations. The policy architectures are based around the implementation of the ‘streamlined Paris Pledges’ (SPP) in developing countries with a particular focus on China and India. Our results indicate that the distributional effects should be taken into account by policymakers through extension of SPP to 2050 as global climate policies may have asymmetrical economic impacts between Annex I and developing countries. A first-best policy of global cap-and-trade scheme alone could be welfare-deteriorating for some parties, reflected by a significant reduction in macroeconomic growth rate over the course of the next decades. Modelling results also suggest that articulating both global and national policies in a multiregional climate deal can provide a palatable solution for countries like China as this would allow for significant reduction in the economic losses associated with a unique-carbon-price global climate policy. This hybrid approach is also aligned with specific development priorities in developing and emerging countries by providing flexibility to their domestic policy framework, which expects to facilitate the transition to low carbon growth trajectory by encouraging intersectoral coordination. Last, procrastination of technical change and delayed structural reform for decarbonising economy would entail significantly higher transition costs for developing countries in case of stringent climate policy due to the economic competitiveness forgone as a result of exorbitant carbon prices in the longer term. Relevant policy options and research perspectives are discussed accordingly. [ABSTRACT FROM AUTHOR]

The aim underlying the notion of a Net zero 2050 future (NZ 2050) is the achievement of a balance between anthropogenic emissions of greenhouse gases by sources, and their removals by carbon sinks, by the mid-point of the current century. This paper delves into the relation between numerical modelling and political decisionmaking in the construction of a NZ future, by examining the recent development of the French national low-carbon strategy (SNBC-2) (2016-2018) and related processes. SNBC-2 was the first attempt to put a NZ2050 France, and the path towards it, into a numerical, calculative form. We show that, aside from yielding a collective capacity to quantify farther into the future, one major lesson of the French attempt at representing NZ2050 was that available models for doing so were of limited relevance. The analysis discusses these shortcomings and their implications with regard to the performativity of numerical models in making NZ2050 a doable horizon. Performativity refers to a circular and dynamic relation between modelling and the realm that they aim to represent (here, NZ2050 future). Modelling a future is thus conceived as an algorithmic and relational process, which contributes to the assembly of all the elements that might compose this future, or to bringing about their emergence. Based on the notion, drawn from science and technology studies, of 'qualculation' – which understands calculation as a process that is at once qualitative and quantitative, relational and algorithmic – we underline the crucial, but ambiguous role of non-calculative adjustments used to compensate for the calculative limitations of models. We show that these adjustments can potentially lead to both gain and loss in performativity, depending on whether or not the qualculation process makes them explicit and allows them to be collectively remembered and critically discussed. We also argue that calculative limitations and the resulting adjustments show that the relationship between models and policymaking is somewhat more reciprocal than what has been argued in the literature: models do encapsulate a form of politics which they enact, but they also can be challenged and reshaped by the emergence of new political objectives. • considers the recent devising of the French national low-carbon strategy (SNBC-2) (2016-2018) and related processes • delves into the relation between numerical modelling, the construction of a NZ future and its performativity • shows limited relevance of available French models to represent French 2050 NZ and discusses these shortcomings • underlines key and ambiguous role of non-calculative adjustments implemented to offset the calculative limitation of models • shows that non-calculative adjustments are potentially a source of both gain and loss in performativity • shows that 2050 NZ performativity is tightly related to a qualitative understanding of models quantitative outcomes • shows a reciprocal relationship between models and policymaking: models encapsulate a form of politics which they enact, but they also can be challenged and reshaped by the emergence of new political objectives. [ABSTRACT FROM AUTHOR]

• Integrated Assessment Models are key in exploring future climate action. • Their key role can be explained from historic science-policy interactions. • From 1970 to 2015, this role differed from agenda-setting to monitoring ambition. • Explanatory factors include the model structure and the pro-active model community. Integrated Assessment Models (IAMs) have gained a prominent role in the climate science-policy interface. The article reconstructs the evolution of IAMs and their changing role in this interface, investigating how and why IAMs have become so prominent. Based on literature analysis, quantitative document analysis and semi-structured interviews, we describe the historic evolution of the interactions between IAMs and policy-making between 1970 and 2015. We identify five historic phases in which IAMs played distinct mediating roles between science and policy, succeeding to adjust their scenario efforts to the continuously changing demands for knowledge from the policy community. In explaining the prominent role of IAMs, we differentiate between background conditions (material and sociological) and more contextual factors, most notably the flexible, hybrid and broad nature of IAMs as well as the pro-active character of the IAM community to enhance their policy relevance. We draw on the notion of institutional work to explain this success. In light of the urgency of responding to the climate crisis, we suggest that the IAM community may expand their scope of anticipated futures and consider engaging a wider range of publics and societal stakeholders beyond the science-policy interface. [ABSTRACT FROM AUTHOR]