Abstract for: FRIDA v2.1: Modeling the two-way coupling of the climate and humans.

Current climate models used by the IPCC lack full two-way coupling between climate and human processes. Earth System Models (ESMs) and Integrated Assessment Models (IAMs) are typically separate, with assumptions coordinated through RCPs and SSPs. This divide limits understanding of climate-human feedback. An alternative approach, such as FRIDA v2.1, integrates these systems into a unified model, prioritizing feedback dynamics while maintaining precision and interpretability. FRIDA v2.1 is a global model integrating climate and human systems through feedback processes. It represents the carbon, energy, and water cycles alongside human demographics, economics, agriculture, and energy use. Built using the System Dynamics method, it contains 3,618 equations and seven interlinked modules. Each subsystem is calibrated to data and validated by experts to ensure accurate behavior representation. FRIDA v2.1 demonstrates that a feedback-driven modeling approach can maintain precision while capturing climate-human interconnections. It challenges conventional IAMs by highlighting missing feedback structures that affect economic projections. FRIDA suggests SSP5-85 is implausible and SSP2-45 may be overly optimistic, while SSP3-70 and SSP4-60 align more closely with realistic adaptation challenges. Future work will refine climate impact representation, energy modeling, and stakeholder engagement for informed policy-making.