Abstract
Abstract. Stratospheric sulfate aerosol geoengineering is a proposed method to temporarily intervene in the climate system to increase the reflectance of shortwave radiation and reduce mean global temperature. In previous climate modeling studies, choosing injection locations for geoengineering aerosols has, thus far, only utilized the average dynamics of stratospheric wind fields instead of accounting for the essential role of time-varying material transport barriers in turbulent atmospheric flows. Here we conduct the first analysis of sulfate aerosol dispersion in the stratosphere, comparing what is now a standard fixed-injection scheme with time-varying injection locations that harness short-term stratospheric diffusion barriers. We show how diffusive transport barriers can quickly be identified, and we provide an automated injection location selection algorithm using short forecast and reanalysis data. Within the first 7 d days of transport, the dynamics-based approach is able to produce particle distributions with greater global coverage than fixed-site methods with fewer injections. Additionally, this enhanced dispersion slows aerosol microphysical growth and can reduce the effective radii of aerosols up to 200–300 d after injection. While the long-term dynamics of aerosol dispersion are accurately predicted with transport barriers calculated from short forecasts, the long-term influence on radiative forcing is more difficult to predict and warrants deeper investigation. Statistically significant changes in radiative forcing at timescales beyond the forecasting window showed mixed results, potentially increasing or decreasing forcing after 1 year when compared to fixed injections. We conclude that future feasibility studies of geoengineering should consider the cooling benefits possible by strategically injecting sulfate aerosols at optimized time-varying locations. Our method of utilizing time-varying attracting and repelling structures shows great promise for identifying optimal dispersion locations, and radiative forcing impacts can be improved by considering additional meteorological variables.
Highlights
Stratospheric sulfate aerosol geoengineering relies on triggering an atmospheric perturbation through deliberate injections of sulfate aerosols or their precursors into the lower stratosphere to mimic the cooling effects seen after large volcanic eruptions (The Royal Society, 2009)
For the infinitesimal neutral tracer advection experiment (Fig. 3; left column), the global coverage of pseudo-aerosols injected at seven dynamically varying diffusion barrier strength (DBS) locations was much greater than coverage from the seven fixed (FI) locations
We found an immediate increase in global coverage for the DI experiments, as predicted from the mathematical definition of large DBSFW values
Summary
Stratospheric sulfate aerosol geoengineering relies on triggering an atmospheric perturbation through deliberate injections of sulfate aerosols or their precursors (often SO2) into the lower stratosphere to mimic the cooling effects seen after large volcanic eruptions (The Royal Society, 2009). There are, many open questions about the effects of radiative forcing from sulfate injections (Kravitz and MacMartin, 2020). The importance of choosing the altitude and latitudes of injection, and the distribution of injection rates across those, has been clearly demonstrated, as well as adjusting injection locations based on the season (Visioni et al, 2020). Even for sulfate aerosols, the method of dispersal will affect aerosol size distribution and, the amount of material that needs to be injected. Many of these uncertainties are based on a climate response from fixed-injection locations (e.g., Robock et al, 2008; Heckendorn et al, 2009; Tilmes et al, 2017), which is a significant limitation for pre-
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