Marine cloud brightening climate intervention is simulated by CESM2 under a susceptibility-based strategy under SSP2-4.5

The efficiency of marine cloud brightening in cooling Earth's surface temperature is investigated by using a medium ensemble of simulations with the Community Earth System Model version 2 (CESM2). Various cloud seeding schemes based on susceptibility are examined to determine what area extent will be required to induce 1.5 degrees C cooling under SSP2-4.5. The results indicate that cloud seeding over 5% of the ocean area is capable of achieving this goal. Under this seeding scheme, cloud seeding is mainly deployed over lower latitudes where strong surface temperature and precipitation responses are induced. The simulations also reveal that the 5% cloud seeding scheme reduces precipitation over the ocean, but enhances precipitation over land, with an overall reduction in global precipitation. Previous modeling studies indicate that even though marine cloud brightening under a susceptibility-based strategy is effective in reducing the global average surface temperature, it can induce several highly undesirable outcomes. Under such marine cloud brightening intervention, a La Nina-like sea-surface temperature response is triggered with cooling mostly confined within lower latitudes. It is likely to pose a threat to disrupt the El Nino Southern Oscillation. A different cloud seeding strategy is explored to alleviate such undesirable outcomes. It is hypothesized that deployment of marine cloud brightening over broader regions with low susceptibility to cloud seeding might induce cooling more evenly distributed over the globe, and hence exert much weaker regional forcing on the climate system. This hypothesis is tested with the Community Earth System Model, version 2 (CESM2). Our simulations with CESM2 reveal that this new strategy indeed alleviates the highly undesirable outcomes previously found. The CESM2 SSP2-4.5 ensemble simulations can be accessed at https://doi.org/10.26024/j23t-pc83.