Abstract
Analyses of stratospheric solar geoengineering have focused on sulfate aerosol, and almost all climate model experiments on sulfate aerosol have assumed injection of SO2. Yet continuous injection of SO2 may produce overly large aerosols. Injection of SO3 or H2SO4 from an aircraft in stratospheric flight is expected to produce new accumulation-mode particles (AM-H2SO4), and such injection may allow the sulfate aerosol size distribution to be nudged towards higher radiative efficacy. We report the first multi-model intercomparison of AM-H2SO4 injection. We compare three models: CESM2(WACCM), MAECHAM5-HAM, and SOCOL-AER coordinated as a testbed experiment within the Geoengineering Model Intercomparison Project (GeoMIP). The intercomparison explores how the injection of new accumulation-mode particles changes the large-scale particle size distribution and thus the overall radiative and dynamical response to sulfate aerosol injection. Each model used the same injection scenarios testing AM-H2SO4 and SO2 injections at 5 and 25 Tg(S) yr−1 to test linearity and climate response sensitivity. All three models find that AM-H2SO4 injection increases the radiative efficacy, defined as the radiative forcing per unit of sulfur injection, relative to SO2 injection. Increased radiative efficacy means that when compared to the use of SO2 to produce the same radiative forcing, AM-H2SO4 emissions could reduce some side-effects of sulfate aerosol geoengineering such as stratospheric heating. We explore the sensitivity to injection pattern by comparing injection at two points at 30° N and 30° S to injection in a belt along the equator between 30° S and 30° N, and find opposite impacts on radiative efficacy for AM-H2SO4 and SO2, suggesting that prior model results for concentrated injection of SO2 may be strongly dependent on model resolution. Model differences arise from differences in aerosol formulation and differences in model transport and resolution, factors whose interplay cannot be easily untangled by this intercomparison.
Highlights
Deliberate modification of Earth’s albedo has been proposed to counteract some of the radiative forcing from the rise in CO2 and other greenhouse gases (GHG) caused by human emissions (Budyko 1974; Crutzen 2006)
Can this be attributed to increased stratospheric lifetime of the aerosols, improved scattering efficacy, or some other factor? What contributes to inter-model differences, and what can these differences tell us about uncertainty in the response to the aerosol injections? we examine some of the side effects of increasing stratospheric aerosol and explore how they differ with
The intermodel differences in radiative forcing and Reff are consistent with the intermodel differences in aerosol burden as diagnosed by the compact relationships among these quantities
Summary
Deliberate modification of Earth’s albedo has been proposed to counteract some of the radiative forcing from the rise in CO2 and other greenhouse gases (GHG) caused by human emissions (Budyko 1974; Crutzen 2006). For the temporal and spatial scale beyond plume models, global GCMs such as the GeoMIP models can be used to simulate injections of the given size distribution of sulfate aerosols into their grid cells These GCMs can effectively simulate changes in global aerosol burden, radiative forcing, ozone, and stratospheric temperature and circulation. As input, they take the particle size distributions from aircraft plume model studies. The CESM2 and MAECHAM5-HAM models employ a modal scheme to prescribe the aerosol size distributions, while the SOCOL-AER model uses a sectional scheme. Region: 30° S-30° N, 19-21 km, all longitudes 5 Tg(S) yr-1 10 Tg(S) yr-1 (optional) 25 Tg(S) yr-1
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
