Assessing Outcomes in Stratospheric Aerosol Injection Scenarios Shortly After Deployment

Hueholt, Daniel M.; Barnes, Elizabeth A.; Hurrell, James W.; Richter, Jadwiga H.; Sun, Lantao

doi:10.1029/2023ef003488

Cited by 9 publications

(4 citation statements)

References 125 publications

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“…Finally, instead of selecting just one "baseline" with a strict comparison of periods with the same global mean temperature, one can compare against a larger portion of the historical period, focusing on understanding when the compensation of GHG warming with SAI cooling results in a state that lies in a certain range of historical variability. A similar comparison framework as the one detailed above has been independently proposed recently also in Hueholt et al (2023), with a framing closely tied to ours in the comparison periods 1 and 2; in this work, the presence of multiple temperature target simulations allows us to expand this conceptually also to the kind of comparison period we describe in point 3.…”

Section: Temperature Responsementioning

confidence: 74%

“…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 . 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. The choice of reference period is also relevant because people will interpret such comparison plots to infer influences on climate impacts, for example, noting that some precipitation or temperature feature is over-or under-compensated relative to the compensation of global mean temperature; that SAI creates a "novel" climate state.…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Temperature Responsementioning

confidence: 74%

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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“…Our work highlights the need to further research the impacts of possible climate intervention approaches (see also Cheng et al, 2019Cheng et al, , 2022Simpson et al, 2019;Tye et al, 2022;Xu et al, 2020), including the ARISE-SAI simulations (Hueholt et al, 2023;Keys et al, 2022;Labe et al, 2023). In doing so, the notion of "quantifiable climate distinguishability" will be a relevant and informative metric that can be used to assess impacts and expand the design space of possible interventions (W. Lee et al, 2020).…”

Section: Discussionmentioning

confidence: 97%

Using Explainable Artificial Intelligence to Quantify “Climate Distinguishability” After Stratospheric Aerosol Injection

Mamalakis,

Barnes,

Hurrell

2023

Geophysical Research Letters

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Stratospheric aerosol injection (SAI) has been proposed as a possible response option to limit global warming and its societal consequences. However, the climate impacts of such intervention are unclear. Here, an explainable artificial intelligence (XAI) framework is introduced to quantify how distinguishable an SAI climate might be from a pre‐deployment climate. A suite of neural networks is trained on Earth system model data to learn to distinguish between pre‐ and post‐deployment periods across a variety of climate variables. The network accuracy is analogous to the “climate distinguishability” between the periods, and the corresponding distinctive patterns are identified using XAI methods. For many variables, the two periods are less distinguishable under SAI than under a no‐SAI scenario, suggesting that the specific intervention modeled decelerates future climatic changes and leads to a less novel climate than the no‐SAI scenario. Other climate variables for which the intervention has negligible effect are also highlighted.

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“…Whilst there are some differences between a single pulse injection of SO 2 from a volcanic eruption and the continual injection needed to consistently cool the planet (MacMartin et al., 2016; Robock et al., 2013), volcanic eruptions act as natural analogs for assessing the capability of global climate models to model SAI (e.g., Trenberth & Dai, 2007). Model uncertainties (Bednarz et al., 2023c; Henry et al., 2023; Niemeier & Timmreck, 2015; Visioni et al., 2021, 2023a) and different SAI scenario choices, including the choice of baseline emissions scenario (Fasullo & Richter, 2023), injection location or strategy (Bednarz et al., 2023a; Franke et al., 2021; Heckendorn et al., 2009; Kravitz et al., 2019; Zhang et al., 2024), temperature target (Bednarz et al., 2023b; Hueholt et al., 2023; MacMartin et al., 2022; Visioni et al., 2023b) and timing of SAI deployment (Brody et al., 2024) can result in different large‐scale climate responses and the associated regional impacts.…”

Section: Introductionmentioning

confidence: 99%

Identifying Climate Impacts From Different Stratospheric Aerosol Injection Strategies in UKESM1

Wells,

Henry,

Bednarz

et al. 2024

Earth's Future

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Stratospheric Aerosol Injection (SAI) is a proposed method of climate intervention aiming to reduce the impacts of human‐induced global warming by reflecting a portion of incoming solar radiation. Many studies have demonstrated that SAI would successfully reduce global‐mean surface air temperatures; however the vast array of model scenarios and strategies result in a diverse range of climate impacts. Here we compare two SAI strategies—a quasi‐ equatorial injection and a multi‐latitude off‐equatorial injection—simulated with the UK Earth System Model (UKESM1), both aiming to reduce the global‐mean surface temperature from that of a high‐end emissions scenario to that of a moderate emissions scenario. We compare changes in the surface and stratospheric climate under each strategy to determine how the climate response depends on the injection location. In agreement with previous studies, an equatorial injection results in a tropospheric overcooling in the tropics and a residual warming in the polar regions, with substantial changes to stratospheric temperatures, water vapor and circulation. Previous comparisons of equatorial versus off‐equatorial injection strategies are limited to two studies using different versions of the Community Earth System Model. Our study evaluates how the climate responds in UKESM1 under these injection strategies. Our results are broadly consistent with previous findings, concluding that an off‐equatorial injection strategy can minimize regional surface temperature and precipitation changes relative to the target. We also present more in‐depth analysis of the associated changes in Hadley Circulation and regional temperature changes, and call for a new series of inter‐model SAI comparisons using an off‐equatorial strategy.

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Assessing Outcomes in Stratospheric Aerosol Injection Scenarios Shortly After Deployment

Cited by 9 publications

References 125 publications

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

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

Using Explainable Artificial Intelligence to Quantify “Climate Distinguishability” After Stratospheric Aerosol Injection

Identifying Climate Impacts From Different Stratospheric Aerosol Injection Strategies in UKESM1

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