The role of climate-society impacts in an Integrated Assessment Model: feedbacks, cascades and interdependencies

Abstract. Conventional Integrated Assessment Models (IAMs), including those used in Shared Socioeconomic Pathway (SSP) projections, often represent climate damages with limited cross-sectoral coupling, potentially missing system–wide and nonlinear risks. Policy approaches that assume gradual, reversible, and predictable change are therefore likely to underestimate both the risks of delayed action and the benefits of early, coordinated intervention. These limitations highlight the need for IAMs to incorporate increasingly comprehensive representations of climate–society feedbacks in order to better characterize climate risks under real-world conditions.

To address this gap, this study investigates how explicit climate–society feedbacks alter long-term projections in a coupled human–Earth system. We use the Feedback-based knowledge Repository for Integrated Assessments version 2.1 (FRIDA v2.1), a global IAM designed to capture bidirectional feedbacks between climate and multiple socio-economic modules—Energy, Finance, Demography, Human Behaviour, Land Use, and Resource Infrastructure—via 19 climate impact channels grouped into 9 broader categories.

We compare a counterfactual simulation ensemble without climate-society impacts (NoImpacts) to a fully coupled experiment with all of the impact channels (AllImpacts), and to experiments where impact channels are activated individually. Across these experiments, we find that explicit climate feedbacks fundamentally alter socioeconomic trajectories, with the AllImpacts case exhibiting substantially lower economic growth than the NoImpacts case due to cascading feedback loops that propagate through financial, energy, demographic, and resource systems. Indirect economic channels—particularly climate-induced changes in investment and bank assets—emerge as the dominant drivers of system-wide outcomes, while other impacts remain largely sector-specific. These cascading mechanisms imply a growth-damage rather than a level-damage representation of climate impacts relative to canonical IAMs (e.g., DICE), resulting in substantially larger economic losses.

The analysis reveals strongly nonlinear climate-society interactions driven by cross-sectoral feedbacks, state-dependent responses, and regime-switching dynamics. Nonlinearities are particularly pronounced in food demand, crop yield, agricultural water use, and surface temperature anomaly, reflecting heterogeneous response mechanisms across coupled biophysical and socio-economic systems. These results demonstrate that tightly coupled human-Earth systems can generate non-linear system-wide changes even in the absence of explicit tipping elements.