The effectiveness of solar radiation management for marine cloud brightening geoengineering by fine sea spray in worldwide different climatic regions

Abstract. Marine Cloud Brightening (MCB) geoengineering aims to inject aerosols over oceans to brighten clouds and reflect more sunlight to offset the impacts of global warming or to achieve localized climate cooling. There is still controversy about the contributions of direct and indirect effects of aerosols in implementing MCB and the lack of quantitative assessments of both. Here, we conducted experiments with injected sea-salt aerosols in the same framework for five open oceans around the globe. Our results show that a uniform injection strategy that did not depend on wind speed captured the sensitive areas of the regions that produced the largest radiative perturbations during the implementation of MCB. When the injection amounts were low, the sea-salt aerosols dominated the shortwave radiation mainly through the indirect effects of brightening clouds, showing obvious spatial heterogeneity. As the indirect effects of aerosols saturated with increasing injection rates, the direct effects still increased linearly and exceeded the indirect effects, producing a consistent increase in the spatial distributions of top-of-atmosphere upward shortwave radiation. Our research emphasizes that MCB was best implemented in areas with extensive cloud cover, while the aerosol direct scattering effects remained dominant when clouds were scarce.