https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL113914
*Authors* Jake J. Gristey, Graham Feingold First published: *21 March 2025* https://doi.org/10.1029/2024GL113914 *Abstract* Intentional modification of the sunlight reflected back to space by Earth has received increasing attention as a potential tool to combat the current climate crisis. Two approaches have emerged as most viable: Stratospheric Aerosol Injection (SAI) and Marine Cloud Brightening. This study identifies a substantial but unrecognized source of cloud brightening caused by SAI, which we call “diffusion-brightening”; essentially, diffusion of the radiation field that would accompany SAI can result in sunlight entering clouds at steeper angles, which increases cloud albedo without actively injecting aerosols into clouds. We present idealized calculations that suggest the diffusion-brightening effect can lead to clouds reflecting about 10% more of the incoming sunlight depending on stratospheric aerosol, cloud, and Sun conditions. We show that the radiative effect of diffusion-brightening could exceed that of stratospheric aerosol reflection in many cloudy scenes, which has global relevance given that clouds cover around two-thirds of the planet. *Key Points* Diffusion of sunlight by stratospheric aerosols can substantially increase cloud albedo The radiative effect of stratospheric aerosol injection would be dominated by inadvertent cloud brightening at many locations and times This diffusion-brightening effect has important implications for solar radiation management *Plain Language Summary* The deliberate release of particles in the stratosphere—to reflect a small amount of sunlight back to space and thereby cool the surface—is a controversial but increasingly common topic of debate in the face of ongoing global warming. One known side-effect is that the sunlight below these particles would be spread out into different directions. We demonstrate that this spreading of sunlight into different directions can make low-level marine clouds substantially brighter. The importance of this cloud brightening does not appear to have been appreciated in previous studies on the topic. Yet, this cloud brightening is crucial to understand the overall amount of sunlight that would be reflected and has profound implications for potential implementation of any such approach in the future. *Source: AGU* -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/geoengineering/CAHJsh9_48izdYbBJ8CKzpfgVFq%3DGr4dByM%3D4cefCuDZ_hYZPrQ%40mail.gmail.com.
