The Geoengineering Model Intercomparison Project (GeoMIP) contribution to CMIP7-description of new experimental protocols and preliminary results

The Geoengineering Model Intercomparison Project (GeoMIP) is a coordinated international model intercomparison effort with the aim of providing robust experimental protocols for simulations of various Solar Radiation Modification (SRM) methods. Through many iterations and discussions within the GeoMIP community, it has become clear that balancing simplicity, scientific realism, policy relevance and associated complexities is fundamental when designing modeling experiments. Such experiments must both diagnose areas of model agreement and disagreement through the lens of climate science and provide results useful for understanding the potential downstream impacts of SRM across different sectors. Here we present a suite of new climate model experiments designed for the Coupled Model Intercomparison Project Phase 7 (CMIP7), building on lessons learned from previous GeoMIP experiments, recent SRM research, and new simulations developed for CMIP7. We provide detailed experimental designs and their underlying rationale, including preliminary results from sensitivity analyses performed with CMIP6 models. Compared to previous GeoMIP iterations, we organize experiments into three categories: (i) Preparatory Experiments, designed to diagnose model responses and inform more complex experimental designs; (ii) Tier 1 experiments, the core simulations that all participating models should run; and (iii) Tier 2 experiments, which provide a flexible framework for exploring structural and scenario uncertainties under SRM, including the potential interaction with temporary overshoot scenarios and tipping elements dynamics. This framework encourages modeling groups to propose their own experiments building upon the Tier 1 backbone, enabling more targeted exploration while ensuring cross-model compatibility.