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

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025AV001939

Authors: Sarah J. Doherty, Michael S. Diamond, Robert Wood, Haruki Hirasawa

First published: 11 March 2026

https://doi.org/10.1029/2025AV001939

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.

Plain Language Summary

Solar radiation modification (SRM) describes a group of potential approaches for cooling the climate by adding airborne particles (aerosols) to the atmosphere to increase sunlight reflection. Most of what we understand about SRM's potential benefits and harms has come from computer modeling studies with both known and potentially unknown sources of error. Multiple reports have noted that well-designed field studies involving the emission of relatively small quantities of aerosols would provide substantially more robust assessment of these approaches. Here, we describe a framework for defining different scales of field studies based on their spatial extent and duration, and the atmospheric energy perturbation they produce. We apply this framework to the SRM approach of marine cloud brightening (MCB). We describe six scales of study to achieve specific scientific goals, and how they compare in scale to natural analogs, like the effects on clouds of international shipping and volcanoes, as well as to the implementation of MCB to cool climate. Emphasized is the importance of determining what impacts will be detectable at different scales of studies, and the utility of the framework for governance of MCB

Source: AGU