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Sulfur‐rich volcanic eruptions happen sporadically. If Stratospheric Aerosol Injection (SAI) were to be deployed, it is likely that explosive volcanic eruptions would happen during such a deployment. Here we use an ensemble of Earth System Model simulations to show how changing the injection strategy post‐eruption could be used to reduce the climate risks of a large volcanic eruption; the risks are also modified even without any change to the strategy. For a medium‐size eruption (10 Tg‐SO2) comparable to the SAI injection rate, the volcanic‐induced cooling would be reduced if it occurs under SAI, especially if artificial sulfur dioxide injections were immediately suspended. Alternatively, suspending injection only in the eruption hemisphere and continuing injection in the opposite would reduce shifts in precipitation in the tropical belt and thus mitigate eruption‐induced drought. Finally, we show that for eruptions much larger than the SAI deployment, changes in SAI strategy would have minimal effect. Plain Language Summary: The artificial injection of aerosols in the stratosphere (SAI) may help mitigate risks from increasing surface temperatures by reflecting some of the incoming sunlight. Such injections would need to be continued for decades, meaning that the chance is high for a sulfur‐rich volcanic eruption to happen during that time. When such an eruption happens, temperatures are reduced abruptly, and there might be changes in precipitation patterns if most of the aerosols are in only one hemisphere. We show that one could envision mitigation strategy during SAI that reduce the risks arising from the abrupt changes produced by volcanic eruption, by shifting where the artificial injections happen and their amount. However, this depends on the magnitude of the eruptions, as for those too large (5 times as big as the largest eruption of the 20th century) such mitigation strategies would simply not be enough. Key Points: It is likely that a large volcanic eruption would happen during an eventual Stratospheric Aerosol Injection (SAI) deploymentThe disruption to the stratospheric aerosol layer would require a modification of the SAI injection strategyWe show that the hydrological impacts of a large volcanic eruption could be mitigated by such a change in strategy [ABSTRACT FROM AUTHOR]

The specifics of the simulated injection choices in the case of stratospheric aerosol injections (SAI) are part of the crucial context necessary for meaningfully discussing the impacts that a deployment of SAI would have on the planet. One of the main choices is the desired amount of cooling that the injections are aiming to achieve. Previous SAI simulations have usually either simulated a fixed amount of injection, resulting in a fixed amount of warming being offset, or have specified one target temperature, so that the amount of cooling is only dependent on the underlying trajectory of greenhouse gases. Here, we use three sets of SAI simulations achieving different amounts of global mean surface cooling while following a middle‐of‐the‐road greenhouse gas emission trajectory: one SAI scenario maintains temperatures at 1.5°C above preindustrial levels (PI), and two other scenarios which achieve additional cooling to 1.0°C and 0.5°C above PI. We demonstrate that various surface impacts scale proportionally with respect to the amount of cooling, such as global mean precipitation changes, changes to the Atlantic Meridional Overturning Circulation and to the Walker Cell. We also highlight the importance of the choice of the baseline period when comparing the SAI responses to one another and to the greenhouse gas emission pathway. This analysis leads to policy‐relevant discussions around the concept of a reference period altogether, and to what constitutes a relevant, or significant, change produced by SAI. Plain Language Summary: By adding CO2 to the atmosphere, the planet warms. As the primary energy input to the system is the Sun, you can try to balance this warming by slightly reducing the incoming sunlight, for example, by adding tiny reflecting particles to the atmosphere (aerosols). This cooling will not perfectly cancel the warming from CO2 due to different physical mechanisms. Understanding how the resulting climate from both effects changes requires a comparison with a "base" state: but there isn't one single choice, something which is made even more clear once one considers multiple amounts of cooling one could do. There isn't only one option as one could decide to just prevent future warming (or some of it), or also try to cancel warming that already happened. Here we explore how the projected outcomes can depend on the base state one selects and which change are linear with the amount of cooling achieved. Key Points: We analyze results from a set of simulations considering various amounts of cooling using stratospheric aerosolsMany of the climatic responses at the surface can be considered linearly related to the amount of coolingThe choice of the specific baseline period influences the analyses of these results [ABSTRACT FROM AUTHOR]

Methane emissions by global wetlands are anticipated to increase due to climate warming. The increase in methane represents a sizable emissions source (32-68 Tg CH 4 year -1 greater in 2099 than 2010, for RCP2.6-4.5) that threatens long-term climate stability and poses a significant positive feedback that magnifies climate warming. However, management of this feedback, which is ultimately driven by human-caused warming and thus "indirectly" anthropogenic, has been largely unexplored. Here, we review the known range of options for direct management of rising wetland methane emissions, outline contexts for their application, and explore a global scale thought experiment to gauge their potential impact. Among potential management options for methane emissions from wetlands, substrate amendments, particularly sulfate, are the most well studied, although the majority have only been tested in laboratory settings and without considering potential environmental externalities. Using published models, we find that the bulk (64%-80%) of additional wetland methane will arise from hotspots making up only about 8% of global wetland extent, primarily occurring in the tropics and subtropics. If applied to these hotspots, sulfate might suppress 10%-21% of the total additional wetland methane emissions, but this treatment comes with considerable negative consequences for the environment. This thought experiment leverages results from experimental simulations of sulfate from acid rain, as there is essentially no research on the use of sulfate for intentional suppression of additional wetland methane emissions. Given the magnitude of the potential climate forcing feedback of methane from wetlands, it is critical to explore management options and their impacts to ensure that decisions made to directly manage-or not manage-this process be made with the best available science., (© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

Stratospheric aerosol intervention (SAI) is a proposed strategy to reduce the effects of anthropogenic climate change. There are many temperature targets that could be chosen for a SAI implementation, which would regionally modify climatically relevant variables such as surface temperature, precipitation, humidity, total solar radiation and diffuse radiation. In this work, we analyse impacts on national maize, rice, soybean and wheat production by looking at output from 11 different SAI scenarios carried out with a fully coupled Earth system model coupled to a crop model. Higher-latitude nations tend to produce the most calories under unabated climate change, while midlatitude nations maximize calories under moderate SAI implementation and equatorial nations produce the most calories from crops under high levels of SAI. Our results highlight the challenges in defining 'globally optimal' SAI strategies, even if such definitions are based on just one metric., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)