Deployment Strategy Shapes the Polar Climate Response to Marine Cloud Brightening

Abstract Marine cloud brightening (MCB) is a proposed solar climate intervention strategy that increases marine cloud reflectivity to cool Earth's surface. While previous studies have largely examined its global temperature and precipitation effects, little is known about how MCB deployment strategies influence polar climate and sea ice. Here, we use nine MCB simulations with the Community Earth System Model v.2 (CESM2) to evaluate how deployment location and seasonality affect polar surface temperature, sea ice area, and thickness. All experiments target global mean surface temperature restoration to 1.5°C above pre‐industrial levels but differ in MCB deployment location and timing. We find that MCB is more effective at restoring sea ice when deployed in the same hemisphere and during local summer months, whereas opposite‐hemisphere or winter deployments are less effective. When deployed in both hemispheres rather than in a single hemisphere, midlatitude MCB schemes improve polar temperature and sea ice conditions compared with climate change (the control, following SSP2‐4.5), especially in the Antarctic. Of all CESM2 MCB simulations examined in this study, it is essential to deploy MCB over the Southern Ocean to restore Antarctic sea ice. Our results demonstrate that both the location and seasonality of MCB deployment critically determine its efficacy in polar sea ice and temperature restoration as well as broader climate consequences. Designing MCB strategies with hemispheric balance and appropriate timing may enhance the feasibility of sea ice restoration without inducing major climate disruptions, such as disrupting the El Niño Southern Oscillation or shifting the Intertropical Convergence Zone.