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

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025EF006508

Authors: Matthew Henry, Haruki Hirasawa, Jim Haywood, Philip J. Rasch

First published: 11 December 2025

https://doi.org/10.1029/2025EF006508

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.

Plain Language Summary

Marine cloud brightening (MCB) is one of several proposed sunlight reflection methods which could potentially be used to cool the planet on a relatively short timescale. In this work, we use complex models of the Earth system to simulate what would happen if small sea-salt particles were emitted near the surface to brighten the clouds in the Arctic. There is evidence from both high-latitude effusive volcanoes and higher resolution models that the addition of small particles in the Arctic atmosphere does brighten clouds. We run simulations using a middle-of-the-road greenhouse gas emissions scenario, which would lead to around 3 degrees of global warming by 2100, and we aim to maintain the Arctic temperature to near present-day levels. These simulations show that the introduction of sea-salt particles brightens the clouds in the Arctic and leads to substantial Arctic cooling, which also restores Arctic sea ice. Additionally, we find limited evidence for impacts outside of the Arctic. Finally, we emphasize that this is a very idealized modeling exercise where the technical and governance feasibility, as well as the impacts on coastal communities, ecosystems, and atmospheric chemistry are not considered. Thus, results should be interpreted with caution.

Key Points

Marine cloud brightening via sea-salt aerosol injection is able to substantially cool the Arctic in three Earth System Models

The cooling of the Arctic successfully maintains Arctic sea ice and we do not see robust precipitation changes outside the Arctic

We caution that we do not consider the technical aspects of aerosol injection, nor the impacts on coastal communities, ecosystems, and atmospheric chemistry

Source: AGU