The efficiency of marine cloud brightening in cooling Earth's surface temperature is investigated using an ensemble of simulations with the Community Earth System Model version 2 (CESM2). We employ a susceptibility‐based cloud seeding strategy, previously developed under the Community Climate System Model version 3 (CCSM3) to counteract the warming of CO 2 doubling, in which we target the regions of the ocean most easily brightened, to determine what area extent will be required to induce 1°C cooling under SSP2‐4.5. The results indicate that cloud seeding over 5% of the ocean area is capable of achieving this goal in CESM2. Under this seeding scheme, cloud seeding is mainly deployed over lower latitudes which leads to a La Niña‐like pattern of response which is a major unintended consequence. Potential mechanisms behind such side effects are presented and discussed. The simulations also reveal that the 5% cloud seeding scheme induces an overall reduction in global precipitation, with an increase over land and a decrease over the ocean.
