Recent literature has underlined the interplay among climate mitigation, adaptation, and finance, as well as between climate action and other development agendas, including sustainable resource use, human development and equity, and environmental pressures. Such an interconnected policy environment requires an integrated ecosystem of disciplines, methods, and tools. Despite the significant evolution of integrated assessment models (IAMs) in the last decade, there remain several criticisms on their design, use, and adequacy to respond to unaddressed and emerging questions in the light of the Paris Agreement and net-zero ambition. These include openness, legitimacy, and ownership, as well as technical feasibility to represent demand-side and broader societal transformations, cross-sectoral interactions, physical impacts and adaptation, climate finance and labour dynamics, and other sustainability goals. DIAMOND will update, upgrade, and fully open six IAMs that are emblematic in scientific and policy processes, improving their sectoral and technological detail, spatiotemporal resolution, and geographic granularity. It will further enhance modelling capacity to assess the feasibility and desirability of Paris-compliant mitigation pathways, their interplay with adaptation, circular economy, and other SDGs, their distributional and equity effects, and their resilience to extremes, as well as robust risk management and investment strategies. This will be done via integration of tools and insights from psychology, finance research, behavioural and labour economics, operational research, and physical science. We will develop a transdisciplinary scientific approach to legitimise the implementation process and co-create research questions that stretch the frontiers of climate science, as well as establish vibrant communities of practice to transparently open model enhancements and to develop capacities, thereby lowering the entrance barriers to the established IAM community.

PARIS REINFORCE aims to underpin climate policymaking with authoritative scientific processes and results, and enhance the science-policy interface, in light of the Paris Agreement and associated challenges. In particular, our aim is to develop a novel, demand-driven, IAM-oriented assessment framework for effectively supporting the design and assessment of climate policies in the EU as well as in other major emitters and selected less emitting/developed countries, in respect to the Paris Agreement objectives. Building on an exhaustive facilitative dialogue and a strong ensemble of complementary—in terms of mathematical structure, geographical, sectoral and focus coverage—integrated assessment, energy system and sectoral models, we will create an open-access and transparent data exchange platform, I2AM PARIS, in order to support the effective implementation of Nationally Determined Contributions, the preparation of future action pledges, the development of 2050 decarbonisation strategies, and the reinforcement of the 2023 Global Stocktake. We also seek to enhance the legitimacy of the scientific processes in support of climate policymaking, by introducing an innovative stakeholder inclusion framework and improving the transparency of the employed models, methods and tools. Beyond effectively communicating respective outputs and fostering wider societal acceptance of climate policy, we actively involve policymakers and other stakeholder groups in all stages: from the formulation of policy questions and the definition of modelling assumptions in a demand-driven approach; to the design of I2AM PARIS interfaces and specifications, and the mobilisation of tacit knowledge embedded in them in the aim of bridging knowledge gaps. Finally, we will introduce innovative integrative processes, in which IAMs are further coupled with well-established methodological frameworks, in order to improve the robustness of modelling outcomes against different types of uncertainties.