Marine Cloud Brightening to Cool the Arctic: An Earth System Model Comparison

Abstract Marine cloud brightening (MCB) via sea‐salt aerosol (SSA) injections is one commonly researched method to cool the Earth either regionally or globally, and potentially reduce impacts of global warming. There is evidence from both high‐resolution climate modeling and natural analogs that the introduction of aerosols in the Arctic atmosphere leads to cloud brightening. This study is the first comparison of Arctic MCB using multiple Earth System Models (ESMs). All three models suggest that SSA injection induces cloud and sky brightening that can substantially cool the Arctic. However, uncertainties in aerosol‐cloud interactions mean that the SSA mass required for cooling varies greatly between models, a feature which was also found for injections at lower latitudes. We evaluate a possible Arctic MCB scenario in which SSA injection is scaled up over time to maintain near present‐day annual‐mean Arctic surface air temperature under a moderate greenhouse gas emissions scenario. The MCB cooling of the Arctic successfully maintains Arctic sea ice and, in contrast to our expectation that cooling one hemisphere leads to the large tropical rainfall shifts, we do not see robust precipitation changes outside of the Arctic. The Atlantic Meridional Overturning Circulation (AMOC) is also shown to be maintained but we caution that not all processes driving the AMOC are represented in these ESMs. Finally, we emphasize that we idealize aspects of the SSA injection in these simulations and we do not consider the technical or governance feasibility of deploying Arctic MCB, nor the impacts on coastal communities, ecosystems, and atmospheric chemistry.