Climate Engineering

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https://hdl.handle.net/1813/69938

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Data from: Transboundary effects from idealized regional geoengineering
MacMartin, Douglas G.; Kravitz, Ben; Goddard, Paul (2023-08-08)
These files contain data supporting results reported in MacMartin et al., "Transboundary effects from idealized regional geoengineering", which looks at albedo modification on small scales over the Gulf of Mexico or Great Barrier Reef to evaluate climatic effects outside of the targeted region.
Data and scripts from: Climate response to off-equatorial stratospheric sulfur injections in three Earth System Models
Visioni, Daniele; Bednarz, Ewa; Lee, Walker R. (2023-01-13)
These files contain data supporting all results reported in Visioni et al. (2023, part 1) and Bednarz et al. (2023, part 2): Climate response to offequatorial stratospheric sulfur injections in three Earth System Models. Here we present the results from the first systematic intercomparison of climate responses in three Earth System Models where the injection of SO$_2$ occurs at different latitudes in the lower stratosphere: CESM2-WACCM6, UKESM1.0 and GISS-E2.1-G. The first two, and a version of the third, use a modal aerosol microphysics scheme, while a second version of GISS-E2.1-G uses a bulk aerosol microphysics approach. Our aim is to determine commonalities and differences between the climate model responses in terms of the distribution of the optically reflective sulfate aerosols produced from the oxidation of SO₂, and in terms of the surface response to the resulting reduction in solar radiation. A focus on understanding the contribution of characteristics of models transport alongside their microphysical and chemical schemes, and on evaluating the resulting stratospheric responses in different models is given in Bednarz et al. (2022). The goal of this exercise is not to evaluate these single point injection simulations as stand-alone proposed strategies to counteract global warming; instead we determine sources and areas of agreement and uncertainty in the simulated responses and, ultimately, the possibility of designing a comprehensive intervention strategy capable of managing multiple simultaneous climate goals through the combination of different injection locations.
Data from: Interactive Stratospheric Aerosol models response to different amount and altitude of SO₂ injections during the 1991 Pinatubo eruption
Quaglia, Ilaria; Timmreck, Claudia; Niemeier, Ulrike; Visioni, Daniele; Pitari, Giovanni; Bruehl, Christoph; Dhomse, Sandip; Franke, Henning; Laakso, Anton; Mann, Graham; Rozanov, Eugene; Sukhodolov, Timofei (2022-11-22)
These files contain data supporting all results reported in Quaglia, et al. (2022), . in Quaglia, et al, we found: Recent model inter-comparison studies highlighted model discrepancies in reproducing the climatic impacts of large explosive volcanic eruptions, calling into question the reliability of global aerosol model simulations for future scenarios. Here, we analyse the simulated evolution of the stratospheric aerosol plume following the well observed June 1991 Mt. Pinatubo eruption by six interactive stratospheric aerosol microphysics models in comparison to a range of observational data sets. Our primary focus is on the uncertainties regarding initial SO2 emission following the Pinatubo eruption in 1991, as prescribed in the Historical Eruptions SO2 Emission Assessment experiments (HErSEA), in the framework of the Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP). Six global models with interactive aerosol microphysics took part in this study: ECHAM6-SALSA, EMAC, CHAM5-HAM, SOCOLAERv2, ULAQ-CCM and UM-UKCA. Model simulations are performed by varying SO2 injection amount (ranging between 5 and 10 Tg-S), and the altitude of injection (between 18-25 km). We find that the common and main weakness among all the models is that they can not reproduce the persistence of the sulfate aerosols in the stratosphere. Most models show a stronger transport towards the extratropics in the northern hemisphere, at the expense of the observed tropical confinement, suggesting a much weaker subtropical barrier in all the models, that results in a shorter e-folding time compared to the observations. Moreover, the simulations in which more than 5 Tg-S of SO2 are injected show a large surface area density a few months after the eruption compared to the values measured in the tropics and the in-situ measurements over Laramie. This results in an overestimation of the number of particles globally during the build-up phase, and an underestimation in the Southern Hemisphere, which draws attention to the importance of including processes as the ash injection and the eruption of Cerro Hudson.
Data from: Impact of the latitude of stratospheric aerosol injection on the Southern Annular Mode
Bednarz, Ewa M.; Visioni, Daniele (2022-09-08)
This data supports the results of "Impact of the latitude of stratospheric aerosol injection on the Southern Annular Mode" (Bednarz et. al., in review), which reported: The impacts of Stratospheric Aerosol Injection strategies on the Southern Annular Mode (SAM) are analysed with the Community Earth System Model (CESM). Using a set of simulations with fixed single-point SO2 injections we demonstrate the first-order dependence of the SAM response on the latitude of injection, with the northern hemispheric and equatorial injections driving a response corresponding to a positive phase of SAM and the southern hemispheric injections driving a negative phase of SAM. We further demonstrate that the results can to first order explain the differences in the SAM responses diagnosed from the two recent large ensembles of geoengineering simulations utilising more complex injection strategies – GLENS and ARISE-SAI – as driven by the differences in the simulated sulfate aerosol distributions. Our results point to the meridional extent of aerosol-induced lower stratospheric heating as an important driver of the sensitivity of the SAM response to the injection location.
Data from: High-latitude stratospheric aerosol injection to preserve the Arctic
Lee, Walker R.; MacMartin, Douglas G.; Visioni, Daniele; Kravitz, Ben; Chen, Yating; Moore, John C.; Leguy, Gunter; Lawrence, David M.; Bailey, David A. (2022-07-23)
This data supports the results of "High-latitude stratospheric aerosol injection to preserve the Arctic" (Lee et. al., 2022), which reported: Stratospheric aerosol injection (SAI) has been shown in climate models to reduce some impacts of global warming in the Arctic, including the loss of sea ice, permafrost thaw, and reduction of Greenland Ice Sheet (GrIS) mass; SAI at high latitudes could preferentially target these impacts. In this study, we use the Community Earth System Model to simulate two Arctic-focused SAI strategies, which inject at 60°N latitude each spring with injection rates adjusted to either maintain September Arctic sea ice at 2030 levels (“Arctic Low”) or restore it to 2010 levels (“Arctic High”). Both simulations maintain or restore September Arctic sea ice to within 10% of their respective targets, reduce permafrost thaw, and increase GrIS surface mass balance by reducing runoff. Arctic High reduces these impacts more effectively than a globally-focused SAI strategy that injects similar quantities of SO2 at lower latitudes. However, Arctic-focused SAI is not merely a “reset button” for the Arctic climate, but brings about a novel climate state, including changes to the seasonal cycles of Northern Hemisphere temperature and sea ice and less high-latitude carbon uptake relative to SSP2-4.5. Additionally, while Arctic-focused SAI predominantly cools the Arctic, its effects are not confined to the Arctic, including detectable cooling throughout most of the northern hemisphere for both simulations, increased mid-latitude sulfur deposition, and a southward shift of the location of the Intertropical Convergence Zone (ITCZ).
Data from: Scenarios for modeling solar radiation modification
Visioni, Daniele (2022-07-07)
Making informed future decisions about solar radiation modification (SRM, also known as solar geoengineering) – approaches such as stratospheric aerosol injection (SAI) that would cool the climate by reflecting sunlight – requires projections of the climate response and associated human and ecosystem impacts. These projections in turn will rely on simulations with global climate models. As with climate change projections, these simulations need to adequately span a range of possible futures, describing different choices such as start date and temperature target as well as risks such as termination or interruptions. SRM modeling simulations to date typically consider only a single scenario, often with some unrealistic or arbitrarily chosen elements (such as starting deployment in 2020), and have often been chosen based on scientific rather than policy-relevant considerations (e.g., choosing quite substantial cooling specifically to achieve a bigger response). This limits the ability to compare risks both between SRM and non-SRM scenarios, as well as between different SRM scenarios. To address this gap, we begin by outlining some general considerations on scenario design for SRM. We then describe a specific set of scenarios to capture a range of possible policy choices and uncertainties and present corresponding SAI simulations intended for broad community use. This dataset includes all data used for the figures in this paper.
Data from: The overlooked role of the stratosphere under a solar constant reduction
Bednarz, Ewa; Visioni, Daniele (2022-05-11)
Modelling experiments reducing surface temperatures via an idealized reduction of the solar constant have often been used as analogues for stratospheric aerosol injection (SAI), thereby implicitly assuming that solar dimming captures the essential physical mechanism through which SAI influences surface climate. While the omission of some important processes that otherwise operate under SAI was identified before, here we demonstrate that the imposed reduction in the incoming solar radiation also induces a different stratospheric dynamical response, manifested through a weakening of the polar vortex, that propagates from the stratosphere down to the troposphere. The coupled stratospheric-tropospheric response exerts a previously overlooked first-order influence on southern hemispheric surface climate in the solar dimming experiments, including on the position of the tropospheric jet and Hadley Circulation and thus, ultimately, precipitation patterns. This perturbation, opposite to that expected under SAI, highlights the need for caution when attributing responses in idealised experiments. In this dataset, we provide the model output used in the paper that demonstrate our findings.
Data from: An approach to sulfate geoengineering with surface emissions of carbonyl sulfide
Quaglia, Ilaria; Visioni, Daniele (2022-04-01)
These files contain data along supporting all results reported in Quaglia et al, "An approach to sulfate geoengineering with surface emissions of carbonyl sulfide". In Quaglia et al. we found: Sulfate geoengineering (SG) methods based on lower stratospheric tropical injection of sulfur dioxide have been widely discussed in recent years, focusing on the direct and indirect effects they would have on the climate system. Here a potential alternative method is discussed, where sulfur emissions are located at the surface or in the troposphere in the form of carbonyl sulfide (COS) gas. Two time-dependent chemistry-climate model experiments are designed from year 2021 to 2055, assuming a 40 Tg-S/yr artificial global flux of COS, geographically distributed following the present day anthropogenic COS surface emissions (SG-COS-SRF), or a 6 Tg-S/yr injection of COS in the tropical upper troposphere (SG-COS-TTL). The budget of COS and sulfur species is discussed, as well as the effects of both SG-COS strategies on the stratospheric sulfate aerosol optical depth, aerosol effective radius, surface SOx deposition and tropopause radiative forcing (RF). Indirect effects on ozone, methane and stratospheric water vapor are also considered, along with the COS direct contribution. According to the model results, the resulting UVB perturbation at the surface accounts for -4.3% as a global-annual average (versus -2.4% in the SG-SO2 case), with a springtime Antarctic decrease of -2.7% (versus a +5.8% increase in the SG-SO2 experiment). Overall, we find that an increase in COS emissions may be feasible, and produce a more latitudinally-uniform forcing without the need for the deployment of stratospheric aircrafts. However, our assumption that the rate of COS uptake by soils and plants does not vary with increasing COS concentrations will need to be investigated in future works, and more studies are needed on the prolonged exposure effects to higher COS values in humans and ecosystems.
Data from: How large is the design space for stratospheric aerosol geoengineering?
Zhang, Yan; MacMartin, Douglas G.; Visioni, Daniele; Kravitz, Ben (2021-08-23)
Data in support of research: Stratospheric aerosol injection (SAI), as a possible supplement to emission reduction, has the potential to reduce some of the risks associated with climate change. Adding aerosols to the lower stratosphere results in global cooling. However, different choices for the aerosol injection latitude(s) and season(s) have been shown to lead to significant differences in regional surface climate, introducing a design aspect to SAI. Past research has shown that there are at least three independent degrees of freedom (DOF) that can be used to simultaneously manage three different climate goals. Knowing how many more DOFs there are, and thus how many independent climate goals can be simultaneously managed, is essential to understanding fundamental limits of how well SAI might compensate for anthropogenic climate change, and evaluating any underlying trade-offs between different climate goals. Here we quantify the number of meaningfully-independent DOFs of the SAI design space. This number of meaningfully-independent DOFs depends on both the amount of cooling and the climate variables used for quantifying the changes in surface climate. At low levels of global cooling, only a small set of injection choices yield detectably different surface climate responses. For a cooling level of 1-1.5℃, we find that there are likely between 6 and 8 meaningfully-independent DOFs. This narrows down the range of available DOF and also reveals new opportunities for exploring alternate SAI designs with different distributions of climate impacts.
Data from: High-latitude stratospheric aerosol geoengineering may be more effective if injection is limited to spring
Lee, Walker Raymond; MacMartin, Douglas G.; Visioni, Daniele; Kravitz, Ben (2021-05-05)
Stratospheric aerosol geoengineering focused on the Arctic could substantially reduce local and worldwide impacts of anthropogenic global warming. Because the Arctic receives little sunlight during the winter, stratospheric aerosols present in the winter at high latitudes have little impact on the climate, whereas stratospheric aerosols present during the summer achieve larger changes in radiative forcing. Injecting SO2 in the spring leads to peak aerosol optical depth (AOD) in the summer. The data presented here contains the results of our simulations, in which we demonstrate that spring injection produces approximately twice as much summer AOD as year-round injection and restores approximately twice as much September sea ice, resulting in less increase in stratospheric sulfur burden, stratospheric heating, and stratospheric ozone depletion per unit of sea ice restored. We also find that differences in AOD between different seasonal injection strategies are small compared to the difference between annual and spring injection.

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