Impact of the Latitude of Stratospheric Aerosol Injection on the Southern Annular Mode

Bednarz, Ewa; Visioni, Daniele; Richter, Jadwiga H.; Butler, Amy H.; MacMartin, Douglas G.

doi:10.1029/2022gl100353

Cited by 16 publications

(40 citation statements)

References 39 publications

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“…While the high-latitude SH atmospheric response to various SAI cases shown in this study is consistent with previous SAI studies (Bednarz et al, 2022;McCusker et al, 2015), the role SAI can play in the Antarctic region has generally not yet been extensively studied and as such remains relatively poorly understood. The detailed evaluation of the Antarctic shelf ocean response to multiple SAI cases (which latitude(s) and amount of cooling) has not, to our knowledge, been performed before and as such our work constitutes a novel contribution to this research field for which direct comparisons to previous SAI research are minimal.…”

Section: Limitations and Future Worksupporting

confidence: 90%

Stratospheric Aerosol Injection Can Reduce Risks to Antarctic Ice Loss Depending on Injection Location and Amount

Goddard,

Kravitz,

MacMartin

et al. 2023

JGR Atmospheres

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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.

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Section: Limitations and Future Worksupporting

confidence: 90%

Stratospheric Aerosol Injection Can Reduce Risks to Antarctic Ice Loss Depending on Injection Location and Amount

Goddard,

Kravitz,

MacMartin

et al. 2023

JGR Atmospheres

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“…This work highlights that SAI studies, by adding a novel dimension to the ability to influence global warming impacts, need even more care when explaining how they are defining a certain simulated impact. Comparisons between different baseline periods can yield different insight onto what constitutes a direct SAI impacts, as opposed to what constitutes an imperfect compensation between GHG‐induced warming and SAI: for instance, a change in tropospheric circulation due to stratospheric heating (Bednarz et al., 2022; Simpson et al., 2019) as opposed to the sea‐land contrast not restored due to different heat capacities resulting in monsoonal circulation changes (Visioni, MacMartin, Kravitz, Richter, et al., 2020). While such comparisons are fundamental for determining some of the physical drivers (Hueholt et al., 2023) (and thereby, might warrant SAI simulations with higher signal‐to‐noise ratio), it is hard to capture the nuance when discussing potential impacts and risks from a policy‐relevant perspective.…”

Section: Discussionmentioning

confidence: 99%

The Choice of Baseline Period Influences the Assessments of the Outcomes of Stratospheric Aerosol Injection

Visioni,

Bednarz,

MacMartin

et al. 2023

Earth's Future

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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.

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“…Here, we introduce four hemispherically-symmetric injection strategies. These four new strategies along with the three existing strategies described in MacMartin et al (2022), Lee et al (2023), and Bednarz et al (2022b) -i.e. a multi-objective strategy, an Arctic-focused strategy and a single-latitude injection case, respectively -collectively span the space of possible surface air temperature and precipitation responses for a global cooling of 1-1.5 • C. Section 2 describes the climate model.…”

Section: Estimated Based On Community Earthmentioning

confidence: 99%

“…In addition to the multi-objective strategy and the four hemispherically-symmetric strategies, a complete set of strategies spanning the space of the seven injection choices described by Zhang et al (2022) would also include two other strategies, such as a spring injection at 60 • N described by Lee et al (2023) and an annually-constant injection at 30 • N described by Bednarz et al (2022b). However, we note that injecting solely at either 60 • N or 30 • N will primarily cool the northern hemisphere, which would result in a significant perturbation of the interhemispheric temperature gradient and the associated location of tropical precipitation.…”

Section: Climate Modelmentioning

confidence: 99%

Introducing a Comprehensive Set of Stratospheric Aerosol Injection Strategies

Zhang

MacMartin

Visioni

et al. 2023

Preprint

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Abstract. Stratospheric aerosol injection (SAI) comes with a wide range of possible design choices, such as the location and timing of the injection. Different injection strategies can yield different climate responses; therefore, making informed future decisions on SAI requires an understanding of the range of possible climate outcomes. Yet to date, there has been no systematic exploration of a comprehensive set of SAI strategies. This limits the ability to determine which effects are robust across different strategies and which depend on specific injection choices, or to determine if there are underlying trade-offs between different climate goals. This study systematically explores how the choice of SAI strategy affects climate responses. Here, we introduce four hemispherically-symmetric injection strategies, all of which are designed to maintain the same global mean surface temperature: an annual injection at the equator (EQ), an annual injection of equal amounts of SO2 at 15° N and 15° S (15N+15S), an annual injection of equal amounts of SO2 at 30° N and 30° S (30N+30S), and a polar injection strategy that injects equal amounts of SO2 at 60° N and 60° S only during spring in each hemisphere (60N+60S). We compare these four hemispherically-symmetric SAI strategies with a more complex injection strategy that injects different quantities of SO2 at 30° N, 15° N, 15° S, and 30° S in order to maintain not only the global mean surface temperature but also its large scale horizontal gradients. We find that the choice of SAI strategy notably affects the spatial distribution of aerosol optical depths, injection efficiency, and various surface climate responses. Among other findings, we show that injecting in subtropics produces more global cooling per unit injection, with the EQ and the 60N+60S cases requiring, respectively, 59 % and 50 % more injection than the 30N+30S case to meet the same global mean temperature target. Injecting at higher latitudes results in larger equator-to-pole temperature gradients. While all five strategies restore September Arctic sea ice, the high-latitude injection one is more effective due to the SAI-induced cooling occurring preferentially at higher latitudes.

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Impact of the Latitude of Stratospheric Aerosol Injection on the Southern Annular Mode

Cited by 16 publications

References 39 publications

Stratospheric Aerosol Injection Can Reduce Risks to Antarctic Ice Loss Depending on Injection Location and Amount

Stratospheric Aerosol Injection Can Reduce Risks to Antarctic Ice Loss Depending on Injection Location and Amount

The Choice of Baseline Period Influences the Assessments of the Outcomes of Stratospheric Aerosol Injection

Introducing a Comprehensive Set of Stratospheric Aerosol Injection Strategies

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