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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]

Owing to increasing greenhouse gas emissions, the Antarctic Ice Sheet is vulnerable to rapid ice loss in the upcoming decades and centuries. This study examines the effectiveness of using stratospheric aerosol injection (SAI) that minimizes global mean temperature (GMT) change to slow projected 21st century Antarctic ice loss. We simulate 11 different SAI cases which vary by the latitudinal location(s) and the amount(s) of the injection(s) to examine the climatic response near Antarctica in each case as compared to the reference climate at the turn of the last century. We demonstrate that injecting at a single latitude in the northern hemisphere or at the Equator increases Antarctic shelf ocean temperatures pertinent to ice shelf basal melt, while injecting only in the southern hemisphere minimizes this temperature change. We use these results to analyze the results of more complex multi‐latitude injection strategies that maintain GMT at or below 1.5°C above the pre‐industrial. All these multi‐latitude cases will slow Antarctic ice loss relative to the mid‐to‐late 21st century SSP2‐4.5 emissions pathway. Yet, to avoid a GMT threshold estimated by previous studies pertaining to rapid West Antarctic ice loss (1.5°C above the pre‐industrial GMT, though large uncertainty), our study suggests SAI would need to cool about 1.0°C below this threshold and predominately inject at low southern hemisphere latitudes (∼15°S ‐ 30°S). These results highlight the complexity of factors impacting the Antarctic response to SAI and the critical role of the injection strategy in preventing future ice loss. Plain Language Summary: Large portions of the Antarctic ice sheet are imminently vulnerable to melting as global temperatures rise over the 21st century. This melt would lead to consequential sea level rise intensifying coastal flooding and causing large economic and ecological costs. One idea to slow global warming and limit such climate risks, is to deliberately cool the planet by placing reflective particles in the atmosphere to deflect sunlight before it warms the Earth's surface. This idea is called stratospheric aerosol injection (SAI). Here, our computer simulations show that Antarctic ice loss can be slowed by using SAI, however, the results depend on the location of the aerosol injection (Equator, tropics, or high latitudes). We show that putting the particles between 30°N and 30°S with the majority placed in the southern hemisphere has the best potential to slow 21st century Antarctic ice loss in our computer simulations. This study is an example of how various SAI strategies (such as, where to put these particles) can lead to very different regional climate impacts—a result that decision makers must thoroughly consider. Key Points: Antarctic atmospheric circulation responds differently to stratospheric aerosol injections that vary by amount and injection latitude(s)Changes to the coastal winds impacts surface ice accumulation and shelf ocean temperatures near ice shelvesSpecific injection strategies can slow 21st century ice loss and avoid identified thresholds pertaining to Antarctic tipping points [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]