The increasingly dismal prospects for rapid and effective mitigation of climate change via swift reductions in the anthropogenic emissions of greenhouse gases has propelled research into climate interventions via methods such as Solar Radiation Management (SRM). SRM is a contentious topic, which has nevertheless gained wide-spread media and scientific attention in the last few years. The most widely studied SRM strategy involves Stratospheric Aerosol Injections (SAI) using sulfur dioxide, mimicking the effects of volcanic eruptions. Sulfur-based SAI would be efficient and relatively cheap to implement. However, stratospheric warming is an undesired side effect of climate intervention via sulfur-based SAI. Recent studies have shown that stratospheric warming could be reduced when injecting solid particles instead of gaseous sulfur dioxide. However, most of these studies looked at the stratospheric particle mass required for a given radiative forcing (RF), without accounting for gravitational settling of particles or the effect of particles sticking together after mutual collision (a process commonly known in aerosol science as «coagulation»).

This study, which was co-authored by IGEO scientist Dr. Gabriel Chiodo, provides the very first comprehensive 3-D modeling effort, simulating the effects of solid particles on global climate. In particular, this paper shows, for the first time, that accounting for microphysical interactions among solid particles significantly reduces the amount of reflected solar radiation per unit of stratospheric particle mass, decreasing the radiative efficiency of the injected material. This is due to the combined effect of faster gravitational settling and the larger fraction of forward reflected radiation over backward reflected radiation with increasing agglomerate size. Most importantly, this study shows that injection of diamond particles at a radius of 150 nm instead of sulfur dioxide significantly reduces required stratospheric injection rates, as well as many of the common unintended side-effects of S-based SAI, such as perturbation of stratospheric winds, age of stratospheric air and stratospheric water vapor concentrations. However, large uncertainties remain as to whether it will be feasible to inject solid particles into the stratosphere at concentrations low enough to prohibit that the particles stick together, thus decreasing their efficiency in cooling global climate.

Vattioni, S., Käslin, S. K., Dykema, J. A., Beiping, L., Sukhodolov, T., Sedlacek, J.,Keutsch, F. N., Peter, T., Chiodo, G. (2024). Microphysical interactions determine the effectiveness of solar radiation modification via stratospheric solid particle injection. Geophysical Research Letters, 51, e2024GL110575. https://doi.org/10.1029/2024GL110575

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