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Abstract

One proposed climate intervention scheme would produce a sulfate aerosol layer in the stratosphere, which would not only reduce total insolation at the surface, but also increase the diffuse fraction of sunlight. An increase in diffuse radiation leads to the diffuse radiation fertilization effect, which could boost plant productivity, influence atmosphere-biosphere interactions, and modify the terrestrial carbon, energy, and water budgets. To effectively simulate stratospheric aerosol intervention and to understand its impact, it is critical to also accurately represent potential changes in diffuse radiation. However, current climate models have significant discrepancies when simulating diffuse radiation compared to observations. Here we analyze diffuse radiation from various stratospheric aerosol intervention scenarios (G3, G4, G6sulfur, and ARISE-SAI) simulated by multiple earth system models. Despite having the same radiative forcing or temperature targets, these earth system models show different changes in diffuse radiation. Under G6sulfur scenario, CESM2 and UKESM1-0-LL show similar increases in diffuse radiation, while CNRM-ESM2-1 simulates decreasing diffuse radiation. Moreover, in CNRM-ESM2-1, there is no scattering effect from injected aerosols, which is difficult to justify conceptually. We further quantify the impacts of these differences on surface climate change under the stratospheric aerosol climate intervention. Our results suggest that more work is needed to better understand this understudied consequence of stratospheric aerosol intervention.