Transitioning towards Harmonious Living: A Society-Economy-Nature model with heterogeneous agents, finite resources and politics (SEN-HARP) for Europe-27

The urgent need to mitigate climate change demands rapid and extensive de-carbonization of global economies. Transition to net-zero carbon is not merely technical but a complex socio-political endeavour with significant trade-offs involving inequality, well-being, sustainability, and political acceptability. If perceived as unfair, the transition risks rejection and political backlash. Still, a just and inclusive transition can also enhance social cohesion and accelerate sustainable policy adoption. In this paper, we introduce a new Agent-Based Model (ABM) called SEN-HARP which integrates biophysical and socio-political modules through original feedback loops to study how these interactions might shape the feasibility and effectiveness of different scenarios of European Union's Green Deal: market-based and innovation, augmented Green Deal, and a disruptive post-growth called "harmonious living". SEN-HARP articulates the micro and macro levels for simulating the joint dynamics of resource use, warming impacts, livelihood dynamics and voting behaviour the latter being based on perceived gains or losses from transition policies. By combining an Agent-Based Stock-Flow Consistent (AB-SFC) approach with an environmental biophysical module, SEN-HARP can also explore how sustainability goals interact with inequality and political acceptability within fiscal and physical boundaries. While significant progress has been made in understanding the biophysical dimensions of climate change, the socio-political aspects remain largely under-explored by assessment models. This paper therefore provides a useful tool for analysing more comprehensively the trade-offs between effectiveness, fairness and political feasibility brought by the net-zero carbon transition.