Defining Scales of Field Studies and Experiments to Assess Marine Cloud Brightening

Abstract Solar radiation modification (SRM) is being discussed as a potential option for addressing climate risks while atmospheric greenhouse gas concentrations are reduced to lower levels. However, understanding of the potential efficacy, impacts, benefits and harms of different SRM approaches remains limited. Current knowledge almost exclusively stems from observation of natural analogs and from model simulations, with the former of limited direct applicability to SRM and the accuracy of the latter difficult to assess without testing against real‐world observations. Well‐designed field studies with controlled aerosol emissions would provide more robust assessment of SRM approaches. Herein we propose a framework for defining SRM field experiments aimed at improving the ability to understand and predict the efficacy impacts of SRM approaches, specifically applying it to marine cloud brightening (MCB). Within this framework an experiment's scale is based on its spatial extent and duration and the atmospheric energy perturbation produced. Integral to the framework is a set of stage‐gates, whereby physical and social metrics inform decisions around progressing to larger scales of studies. Critical to informed decision‐making is that each study be mapped to scientific goals, metrics for determining scientific success, quantification of the detectability of different parameters of interest, and metrics for determining study impacts. While we focus primarily on this framing within the context of the physical sciences we point out how essential the above information is in the context of the governance of both scientific studies and decisions around the eventual use of SRM.