https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL108314
*Authors* Daniele Visioni, Ilaria Quaglia, Isabelle Steinke *First published: 24 May 2024* https://doi.org/10.1029/2024GL108314 *Abstract* There are obstacles in better understanding the climate impacts associated with new materials that could be used for Stratospheric Aerosol Injections (SAI), like the lack of an integrated framework that combines climate modeling across scales, laboratory studies and small-scale field experiments. Vattioni et al. (2023, https://doi.org/10.1029/2023gl105889) explored one aspect of using alternative, non-sulfate materials for SAI. They investigated how uncertain the response of stratospheric ozone would be to alumina injections for SAI. In their study, they quantify chlorine activation rates in the presence of alumina, and then cascade these uncertainties into estimates of ozone depletion, concluding that alumina might have less detrimental impacts on stratospheric chemistry than sulfate, but with large uncertainties. Their results provide a useful basis upon which future research endeavors combining indoor and outdoor experiments and modeling may be structured to produce robust assessments of SAI impacts, benefits and uncertainties, together with clarifying what kind of research needs to be prioritized. *Key Points* •Vattioni et al. (2023, https://doi.org/10.1029/2023gl105889) demonstrated large uncertainties in the projected impacts of alumina particles in the stratosphere •We use the results to discuss more broadly how to better think about the climate impacts and side effects of Stratospheric Aerosol Injection •We propose the idea of a “living assessment” of Stratospheric Aerosol Injections that can constantly integrate useful experimental results with modeling work *Plain Language Summary* We could use tiny particles injected into the higher atmosphere to reflect a small portion of incoming sunlight and thereby cool the planet. But doing so comes with risks and uncertainties: for instance, one might wonder how do we select which kind of particles to use. Sulfate is present in nature, for instance during the aftermath of volcanic eruptions followed by an observable surface cooling. However, we know that mimicking that effect would come with some drawbacks, for example, it heats the upper layer of the atmosphere and affects ozone. Alumina, supposedly, would impact atmospheric chemistry less than sulfate and so might be considered “preferable,” but not being naturally present in the atmosphere, there are lots of things we don't know. For example, Vattioni et al. (2023, https://doi.org/10.1029/2023gl105889) demonstrate that even potential implications for atmospheric chemistry are highly uncertain when looking at alumina particles as a candidate for Stratospheric Aerosol Injections (SAI). Therefore, their study is a good opportunity to think more broadly about intended SAI-associated climate impacts and unwanted side effects, and how to better coordinate research activities in this space. [image: Details are in the caption following the image] <https://agupubs.onlinelibrary.wiley.com/cms/asset/e813d7a8-6719-40cd-9622-61c0a10fad4b/grl67611-fig-0001-m.jpg> Figure 1 (a) A simplified summary of the results in Vattioni et al. (2023 <https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL108314#grl67611-bib-0022>), focusing on tropical ozone changes. For SO2 (red dot), an uncertainty bar derived using multi-model results from Tilmes et al. (2022 <https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL108314#grl67611-bib-0021>) has been added, even if the injection magnitude are higher in that case. (b) Schematic of potential uncertainty ranges that would be associated with sulfate or alumina (or other materials) in the case of SAI for both effectiveness and environmental impacts. Due to the lack of natural analogs, physical and environmental uncertainties might be larger for alumina compared to sulfate, but with the potential for the central value to be lower for a close to ideal material, as shown in panel (a). Some uncertainties can be narrowed down with further observations, or with direct tests. Scenario uncertainty, which depends on factors that might not be related directly to chemistry or physics, such as the underlying emission scenario of ozone depleting substances, or other sources that are not within direct control, and that require more holistic assessments, are also relevant to an overall assessment. *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 on the web visit https://groups.google.com/d/msgid/geoengineering/CAHJsh9-nLYtdhzKcqCV8ZD1ukW7pOmfnUEWXJ0E15nR5jKxfFg%40mail.gmail.com.
