Assessing combinations of regional MCB designed to target multiple climate response objectives

Abstract. Marine Cloud Brightening (MCB) is a proposed method of Solar Radiation Modification (SRM). MCB proposes the injection of sea salt aerosols into marine clouds to enhance their reflectivity aiming to counteract greenhouse gas (GHG) driven warming. Modelling suggests that the climate effect of MCB depends on the location of deployments, with some regional MCB resulting in potentially undesirable climate changes. MCB in midlatitude regions was found to cause a relatively homogeneous temperature and precipitation change pattern. Here we seek to quantify the trade-offs associated with different MCB strategies and to design an “optimal” deployment strategy. This study analyses 42 MCB patch simulations in UKESM1.0, spanning fourteen different regions and three different injection rates. These simulations are used to inform deployments with the aim to restore the SSP2-4.5 2040s mean climate to a baseline of 2014–2033. Multiple climate targets, consisting of global mean surface air temperature, precipitation, Arctic September sea ice extent, southern oscillation index, and hemispheric mean temperatures, are used to inform the design of an optimised 14-region deployment and a reduced complexity optimised 6-region deployment, which we compare to the aforementioned 5-region midlatitude MCB deployment. Some improvements to the midlatitude MCB deployment are observed, in sea ice restoration and zonal mean temperature response. These results show it may be possible to design MCB strategies that target several climate responses simultaneously when combining regional MCB deployments. The results highlight the importance of including high latitude MCB to achieve Arctic sea ice restoration in UKESM1.0.