An endogenous modelling framework of dietary behavioural change in the fully coupled human-climate FRIDA v2.1 model

Abstract. Integrated assessment models (IAMs) occupy a central role in understanding and assessing the intricate interlinkages within the human-climate system for informing climate mitigation and adaptation strategies. However, there has been limited work on explicitly representing the internal social system dynamics that underlie human behavioural responses to climate change within IAMs. Instead, behavioural change and demand-side strategies are assessed with external, non-probabilistic narrative-based scenario analyses. In this paper, we introduce an alternative fully endogenous behavioural change modelling framework within the FRIDA v2.1 model, operationalized with the system dynamics method. Applied to the context of dietary behaviour, the framework models behavioural change as a function of perceived accessibility, descriptive norm, and personal norms, constrained by accessibility and past behaviour. By doing so, it captures the complex social-economic-cultural-environmental feedback processes within the human-climate system that dynamically determine per capita food demand and consumption. Our simulation results show that endogenizing human behaviour leads to lower future demand projections compared to the more prevalent GDP-driven modelling approach. This demonstrates the significant impact of behavioural feedbacks on emission behaviours and thus climate outcomes. Importantly, using an uncertainty approach, our results account for a range of plausible behaviours within the 95 % confidence bounds, which includes scenarios where we observe reversals of sustainable behavioural change in the future. We contribute to the limited work on human behaviour in IAMs, extending the complexity of current representations. Future work will extend this framework to other domains of high-impact behaviours, enhancing the robustness of IAMs for assessing demand-side mitigation.