This session focuses on advances in the natural science of climate intervention which seeks to identify or reduce sources of uncertainty related to SRM. This may include climate modeling studies, idealized process investigations, experimental results, or observations of natural analogues. We welcome submissions from across the natural sciences as well as the social sciences, including impacts assessment or governance related to SRM strategies. We are particularly interested in work which focuses on understanding and constraining uncertainty related to regions or communities that are especially vulnerable to climate change, and we encourage early career or new members of the research community to consider applying.
Stratospheric sulfate aerosols, produced by explosive volcanic eruptions or through artificial stratospheric aerosol injection for solar radiation management, can perturb Earth’s radiative budget for several years. However, the understanding of the state dependence of aerosol forcing and its effect on radiative feedback remains incomplete.
We use a one-dimensional radiative–convective equilibrium model of the tropical atmosphere to quantify the clear-sky forcing and feedback contributions from aerosol absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapor.
We show that aerosol forcing exhibits a stronger surface temperature dependence than CO2 forcing. Between 280 and 300 K, aerosol forcing becomes less negative with increasing surface temperature because its longwave component becomes increasingly positive. Additionally, the radiative feedback is less negative in the presence of the aerosol. Both the feedback’s dependence on aerosol concentration and the forcing’s dependence on temperature arise from aerosol absorption in optically thin spectral regions, which masks temperature-dependent surface emission.
This highlights the critical role of the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of stratospheric sulfate forcing and in weakening radiative feedbacks compared to an atmosphere without stratospheric aerosol.
How to cite: Hegde, R., Günther, M., Schmidt, H., and Kroll, C.: Surface temperature dependence of stratospheric sulfate aerosol clear-sky forcing and feedback, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6807, https://doi.org/10.5194/egusphere-egu26-6807, 2026.
While the cooling from stratospheric aerosol injection (SAI) can offset greenhouse gas impacts on rainfall, direct radiative effects on the underlying troposphere can cause unintended rainfall changes. Here we use simulations of tropical climate with prescribed sea-surface temperatures to reveal how stratospheric aerosols directly heat the troposphere and subsequently modify convection, clouds, and precipitation. Our multi-model framework includes convection-resolving small-domain and mock-Walker simulations, alongside global climate model experiments. Across models, SAI produces a reduction in tropical mean rainfall, although this response is moderated – and made less predictable – by a reduction in cloud radiative heating. Regional rainfall anomalies within the tropics can be substantial, even though tropical circulation is found to be insensitive to aerosol direct radiative effects. These results clarify the mechanisms through which SAI can inadvertently alter hydroclimate, while highlighting key uncertainties for SAI risks stemming from poorly constrained cloud processes.
How to cite: McGraw, Z. and Polvani, L. M.: Inadvertent Tropical Rainfall Responses to Stratospheric Aerosol Injection: Disentangling Aerosol-Radiation-Precipitation Coupling in Convection-Resolving and Global Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8264, https://doi.org/10.5194/egusphere-egu26-8264, 2026.
Tropical cyclones can cause extreme weather (wind, rain, storm surges) but also provide beneficial precipitation. Their frequency, trajectories and intensity are expected to shift under global warming and these changes may not all be restored by Stratospheric Aerosol Injection (SAI), even if the same global mean surface temperature is achieved.
Despite their importance to climate risk, the effects of SAI on tropical cyclones has not been much studied, because resolving tropical cyclones requires a model resolution of a quarter degree or higher, whereas SAI simulations so far, including GeoMIP and ARISE, typically work with much lower resolutions.
We studied the effect of SAI on tropical cyclone trajectories and risk potential using three simulations in CESM1 at 0.1º ocean and 0.25º atmosphere resolution: one at constant year-2000 conditions (“present-day”), one in which CO2 increases strongly (“RCP8.5”), and one in which CO2 increases as in RCP8.5, but global mean surface temperature is cooled back to year-2000 conditions from 2050 onwards by means of SAI (“SAI”).
To save computation time, we use the atmosphere component CAM (rather than the several times more expensive WACCM). CAM does not model the evolution of stratospheric aerosol, hence we force the model with stratospheric aerosol fields obtained from CESM-WACCM simulations (Tilmes et al, 2018). The aerosol concentrations are scaled using a feedback procedure in order to achieve the temperature target (de Jong et al, 2025).
In agreement with the literature, we find that under RCP8.5, the number of tropical cyclones decreases, but peak winds and precipitation increase, albeit with regional differences. Sea Surface Temperature (SST) increases in all regions, which is favourable for tropical cyclone development, but vertical windshear also increases in most regions, which is unfavourable. SAI largely compensates the effect on SST, but its effect on shear varies per region. Globally, tropical cyclone counts decrease even further under SAI, while the frequency of strong (windy or wet) cyclones is roughly restored. Therefore, SAI may reduce the risk from tropical-cyclone-related extreme weather, but also decreases cyclone-related precipitation, on which some coastal regions depend.
References:
Tilmes et al., 2018: https://journals.ametsoc.org/view/journals/bams/99/11/bams-d-17-0267.1.xml
De Jong et al., 2025: https://gmd.copernicus.org/articles/18/8679/2025/
How to cite: Wieners, C., de Jong, J., and Baatsen, M.: Impact of SAI on tropical cyclones in a high-resolution simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8382, https://doi.org/10.5194/egusphere-egu26-8382, 2026.
Assessments of Amazon rainforest dieback have primarily focused on the magnitude of forest loss under transient climate change, while less attention has been paid to the rate, variability, and commitment of ecosystem decline under alternative climate intervention pathways. The concept of realized and committed ecosystem change has shown that Amazon forest loss can be effectively locked in long before it becomes observable (Jones, C. et al., 2009), while recent policy-oriented assessments demonstrate that such commitments remain a substantial risk even under 1.5 °C stabilization and overshoot pathways (Munday, G. et al., 2025). This study explores whether solar geoengineering modifies long-term Amazon forest commitment or primarily alters the timing and variability of dieback.
Here, we propose to extend the concept of committed ecosystem change to quantify the speed and temporal variability of Amazon forest dieback under scenarios with and without stratospheric aerosol injection (SAI). Using the Met Office Hadley Centre climate carbon cycle model HadCM3, we will analyse transient and equilibrium forest responses to stabilized forcing states derived from high emission baseline scenarios.
The analysis follows the realized and committed ecosystem framework developed in earlier coupled climate vegetation studies using HadCM3 (Jones, C. et al., 2009) without solar geoengineering. We first reproduce this analysis under a non-SAI baseline and subsequently apply the same diagnostics to simulations from the UK Earth System Model (UKESM) incorporating stratospheric aerosol injection, enabling a consistent comparison of Amazon dieback speed and variability across scenarios.
For each scenario, we distinguish between realized (time evolving) and committed (equilibrium) states of Amazon forest cover, using equilibrium diagnostics to estimate the long-term ecosystem response to fixed climate conditions. Dieback speed will be defined as the rate of fractional forest loss per degree of global mean temperature change, while variability will be assessed through interannual and decadal fluctuations in forest cover and associated hydroclimatic drivers. This analysis is expected to provide preliminary insights into whether SAI delays or modifies the rate and variability of Amazon forest dieback, while potentially leaving committed long-term losses largely unchanged once critical climatic thresholds are exceeded. As this study is at an early stage, the results will be exploratory in nature and intended to provide a first-order assessment of potential ecosystem risks associated with solar geoengineering rather than definitive projections.
Reference
- Jones, C., Lowe, J., Liddicoat, S. et al. Committed terrestrial ecosystem changes due to climate change. Nature Geosci 2, 484–487 (2009). https://doi.org/10.1038/ngeo555
- Munday, G., Jones, C.D., Steinert, N.J. et al. Risks of unavoidable impacts on forests at 1.5 °C with and without overshoot. Nat. Clim. Chang. 15, 650–655 (2025). https://doi.org/10.1038/s41558-025-02327-9
How to cite: K Xavier, A. and Jones, C.: Does Solar Geoengineering Delay Amazon Dieback? , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12794, https://doi.org/10.5194/egusphere-egu26-12794, 2026.
Stratospheric aerosol injection (SAI) is one of the most researched Solar Radiation Modification strategies to counteract greenhouse-gas-induced warming. However, conventional approaches involve the injection of gaseous SO2 (S-based SAI). Due to the substantial lower-stratospheric heating they lead, S-based SAI alter precipitation and circulation patterns and potentially also ocean circulation. Our work explores the risks and benefits of alternative materials—alumina, calcite, and diamond dust—with markedly lower infrared absorptivity but similar shortwave scattering properties to sulfate. We consistently show that these less absorptive particles reduce lower-stratospheric warming, resulting in reduced hydrological and dynamical responses. These materials can potentially reduce disruptions in key circulation metrics such as Hadley Cell strength, ITCZ position, the North Atlantic Oscillation, and the Southern Annular Mode compared to conventional S-based SAI. Reduced changes in atmospheric circulation also translate to smaller perturbations in surface wind stress, ocean heat fluxes, and the Atlantic Meridional Overturning Circulation. Taken together, these findings highlight the potential of alternative materials for optimizing radiative efficacy of SAI, while minimizing atmospheric and oceanic side effects. This work will discuss the physical, chemical, and climatic implications of alternative SAI materials, bridging insights from microphysics to Earth system responses, as well as the underlying uncertainties.
How to cite: Chiodo, G., Geurts, M., Sukhodolov, T., Vattioni, S., Sedlacek, J., Ayantika, D., and Schuring, I.: Chemical and climatic impacts of stratospheric aerosol injections: can aerosols with smaller infrared absorptivity reduce undesired side-effects?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22180, https://doi.org/10.5194/egusphere-egu26-22180, 2026.
Cirrus cloud modification (CCM) is a proposed solar radiation modification approach that could reduce the net warming from high-level ice clouds by altering how ice forms and how long cirrus persists. Under some conditions, changing the availability and properties of ice nucleating particles
(INPs) may shift ice formation towards fewer, larger crystals that sediment and sublimate quicker. Although the potential global benefit has been estimated at 2-3 W m^-2, published modelling studies remain inconsistent, and in several cases suggest limited or no benefit. A major reason is
uncertainty in background INP concentrations and aerosol-ice microphysics at cirrus temperatures, which makes it difficult to identify when and where CCM is feasible.
This talk will present the plan and preliminary results from an observation-led programme to de-risk these uncertainties, using aviation as a relevant, existing perturbation and preparing for an observational campaign to assess the effects of aviation soot on cirrus. Phase 1 focuses on “data mining” of historical cases. We will identify events where aircraft traverse clear air that is predicted to become ice supersaturated shortly afterwards and then track the affected air mass downwind using Lagrangian trajectories and coincident satellite observations. Geostationary thermal infrared imagery will be used to assess whether detectable cirrus changes emerge within several hours after passage. Where available, CALIPSO and CloudSat will be used to constrain
cloud vertical structure, and DARDAR-Nice and CALIOP-IIR retrievals will help evaluate changes in ice crystal number concentration. These analyses will quantify detectability limits and prioritise meteorological regimes and target regions for phase 2.
Phase 2 is a UK observational campaign using the FAAM research aircraft, where the only “intervention” is normal engine exhaust, mirroring what occurs globally every day but with dedicated measurement and attribution. We plan approximately 50 flight hours across 10 sorties, timed to occur in forecast ice-supersaturated layers with relatively simple advection and clear satellite viewing. The flight pattern will be designed to create a controlled perturbation region alongside nearby unperturbed control regions, allowing matched comparisons downwind. We will coordinate in situ sampling with new INP measurements using PINEair (targeting cirrus-relevant temperatures) to constrain background INP levels, complemented with laboratory studies of aviation soot ice nucleation under cirrus conditions, including the role of plausible impurities such as fuel additives and engine metal oxides.
A dedicated high-resolution forecast capability, informed by in situ and satellite observations, via RIKEN/Fugaku, will support go/no-go decisions and flight targeting. Finally, we will translate observed signals into an efficacy estimate using an observation system simulation experiment with km-scale and regional modelling (including ICON). The primary outcome metric is trajectory-integrated outgoing longwave radiation from initial cirrus development to 24 hours afterwards, compared to matched control air masses.
How to cite: Leong, G., Stettler, M., Gryspeerdt, E., Daily, M., Murray, B., Taylor, J., Miyoshi, T., Gasparini, B., and Eastham, S.: De-risking cirrus management, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14215, https://doi.org/10.5194/egusphere-egu26-14215, 2026.
Our study assesses the differences in intensity and frequency of Atmospheric Rivers (ARs) between Solar Radiation Modification (SRM) scenarios and greenhouse gas emission pathways. ARs are among the most important freshwater sources in the midlatitudes. This tropical humidity, transported horizontally to extratropical regions as plumes of water vapor, is associated with extreme precipitation at landfall, which usually triggers natural hazards, such as landslides and floods, especially in arid, semi-arid, and Mediterranean regions. While Earth System Models project more intense AR events and poleward displacement of landfall locations as warming deepens during the 21st century, driven by changes of atmospheric dynamics such as the position of the descending branch of the Hadley Cell, little is known about how SRM’s global warming mitigation goals may alter atmospheric circulation patterns and hence AR characteristics, especially in the Southern Hemisphere. We compare two SRM scenarios, G6Solar (reduction of the solar constant) and G6Sulfur (Stratospheric Aerosol Injection), and two CMIP6 model outputs under greenhouse gas emission pathways SSP2-4.5 and SSP5-8.5. Results reveal an overall decrease in AR frequency in extratropical regions by the end of the century. Conversely, the mid-latitudes experience increases in AR frequency. Under G6solar, frequency change is of similar magnitude as for the SSP2-4.5 scenario, whereas the G6sulfur scenario matches SSP5-8.5’s closest. Regarding ARs’ intensity, we detect worldwide increases in transported moisture content, irrespective of scenarios, with a small decrease near the west coast of South America. The role of SRM on projected changes in the dynamics and thermodynamics of the processes is discussed. These results signal that the Southern Hemisphere’s atmospheric dynamics are not neutral to the SRM technique, as they may deliver a significantly different AR scenario by the end of the century, even if the intended global cooling goals are met.
How to cite: Torrez Rodriguez, L., Manquehual-Cheuque, F., Somos-Valenzuela, M., and Fernandez, A.: Trajectories of Atmospheric Rivers in the Southern Hemisphere under CMIP6 and Solar Radiation Modification, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14171, https://doi.org/10.5194/egusphere-egu26-14171, 2026.
As the global community struggles to limit global warming, interest is growing in interventions to lower global temperatures. Stratospheric Aerosol Injection (SAI), a method of stabilizing temperatures by releasing reflective particles into the upper atmosphere, appears to offer a practical means of doing so. The IPCC Sixth Assessment Report (AR6) acknowledged that Stratospheric Aerosol Injection (SAI) could offset some of the effects of increasing greenhouse gases (GHGs), yet this conclusion lacked a standardized, quantitative framework to measure performance across a diverse range of climate hazards. To address this for the upcoming Seventh Assessment Report (AR7), we introduce a systematic methodology designed to quantify SAI efficacy through the lens of the IPCC Climate Impact-Drivers (CIDs). This research transitions away from descriptive, qualitative summaries toward a data-driven performance analysis, assessing how effectively SAI counteracts the specific "effects of climate change" defined by the IPCC.
Our analytical approach utilizes multi-model ensembles, specifically incorporating G6sulfur simulations from GeoMIP and ARISE-SAI simulations. To ensure a fair comparison across various deployment strategies and scenarios, we apply a normalization framework based on linear scaling. This allows us to evaluate climate feedback on a per-degree basis of warming versus cooling, isolating "first-order" physical responses that remain consistent across different SAI implementations. By synthesizing these results across global regions and diverse physical metrics, this work builds a rigorous foundation for determining the efficacy of SAI to minimize climate risks. The ultimate goal is to identify for which indicator and in which regions SAI could work well and where it could worsen the impacts of climate change. This work will help provide a vital, evidence-based foundation for an informed discussion of SAI as a climate policy option.
How to cite: Singh, R. and Irvine, P.: From Qualitative to Quantitative: A Systematic Framework for Measuring SAI Efficacy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11499, https://doi.org/10.5194/egusphere-egu26-11499, 2026.
Earth System models are increasingly used to explore physical uncertainties to possible Solar Radiation Modification. However, the primary risks of SRM lie in potential human ability to maintain long-term deployment without interruption, conflict or reduction in carbon mitigation ambtion. As such, physical and societal SRM risks could be significantly increased in an era of geopolitical fragmentation and institutional volatility
Mitigation scenarios are generally constructed by optimising mitigation costs over decades to limit temperature increase on a century timescale - ignoring political processes like conflicts, or policy reversals. However, for SRM, these 'fast' human processes can change the climate on a timescale of months, allowing a direct coupling of climate responses and political dynamics. This makes governance instability a first-order driver of risk.
We present the Solar Radiation Modification Pathway (SRMP) framework, which defines parameters for SRM deployment, including interruption probability, detecability and efficacy of action, regional heterogeneity, and mitigation coupling (moral hazard). This enables a structured exploration of non-ideal futures, including governance failure, geopolitical conflict, and coalition-driven deployments creating unequal outcomes for vulnerable regions.
We illustrate these dynamics with the FaIR simple climate model, coupled to a stochastic SRM algorithm with SRMP-defined failures and feedbacks. Results show SRM deployment under non-optimal conditions can increase climate damages relative to a non-SRM baseline: termination shocks produce warming rates far exceeding conventional scenarios, while high moral hazard parameters can increase long-term damages and overshoot commitment.
These results demonstrate that 'peak shaving' experiments imply optimistic assumptions of high international cooperation with robust mitigation ambition. The SRMP framework provides a common structure to encourage diverse modeling approaches toward assessment that confronts the full risk space of deployment in both cooperative and uncooperative futures.
How to cite: Sanderson, B., Baur, S., Schleussner, C.-F., Peters, G., Mittal, S., Sandstad, M., Kallbekken, S., Smith, C., Fuss, S., Van Ruijven, B., Fisher, R., Rogelj, J., Seferian, R., Samset, B., Steinert, N., Terray, L., and Fuglestvedt, J.: Beyond best-case SRM: Scenarios for a messy reality, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6004, https://doi.org/10.5194/egusphere-egu26-6004, 2026.
In this work, we propose to separate the concept of uncertainty for the purpose of SRM evaluation into the following two macro-categories: the first is storyline uncertainty, which includes the sub-categories of scenario uncertainty (related to emissions and societal response); target uncertainty (what is the specific target that SRM tries to achieve) and strategy uncertainty (how is the SRM deployed to achieve the target). The second is physical uncertainty, which can be investigated through the exploration of both inter-model SRM uncertainty (related to the Earth system processes specific to SRM) and inter-model climate uncertainty (related to underlying uncertainty in the representation of climatic processes). Finally, there is a component of internal variability that can be treated similarly to climate change.
We apply our framework to a large and diverse set of climate model simulations of stratospheric aerosol injections (SAI) and find four important results using our framework analyzing surface temperature and precipitation data: 1) in the same set of models, inter-model uncertainties due to climate change are larger than inter-model SRM uncertainties independently of spatial aggregation considered, (68% larger for surface temperatures, 23% larger for annual precipitation); 2) inter-model SRM uncertainties in SAI simulations are strongly driven by uncertainties in the representation of aerosols, including their impacts on composition, transport and secondary effects, leading us to conclude that resolving such uncertainties across models has the potential to reduce overall uncertainties by 33% and 39%, respectively, for surface temperatures and precipitation; 3) uncertainties related to the deployment of different kind of aerosols in a single model are small compared to inter-model SRM uncertainties, constituting only a 10% and 16% fraction of overall uncertainties, respectively, for surface temperatures and precipitation, with some important regional differences for the latter; 4) by looking at results of different strategies and scenarios with one single model, we conclude that, while at the global level temperature and precipitation are overwhelmingly driven by target uncertainty, at the regional level the strategy uncertainty can be a relevant portion of the overall uncertainty.
How to cite: Visioni, D.: A framework for understanding and narrowing modeling uncertainties for Stratospheric Aerosol Injection (SAI), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20764, https://doi.org/10.5194/egusphere-egu26-20764, 2026.
The stratospheric circulation is driven by complex wave-mean flow interactions, and models and even reanalysis products have significant differences in their representation of the stratospheric circulation. Nevertheless, these models have been used to predict climate change due to Solar Radiation Management (SRM) strategies. The introduction of aerosol or aerosol precursors to create an artificial reflective stratospheric aerosol layer, known as stratospheric aerosol injection (SAI), leads to two major radiative effects: (1) a reduction in short wave forcing, and (2) an increase in lower stratospheric heating.
To date, very little work has been done to specifically examine the effects and uncertainties related to this lower stratospheric heating. To fill this gap, we analyze the outputs of a model intercomparison project in which a persistent, idealized heating rate is applied in the equatorial lower stratosphere of five GCMs. Despite an identical forcing, each model exhibits unique stratospheric and surface adjustments. We quantify inter-model differences in the stratospheric dynamical response to heating, providing a basis for understanding discrepancies in the corresponding tropospheric responses. In particular, we assess which features of the mean state stratosphere are most influential in controlling the response to heating, and leverage idealized modeling to explore test the state dependence of the stratospheric response to aerosol induced stratospheric heating. We hope to extend this work to provide a useful basis for future work employing emergent constraints to limit uncertainty across the response.
How to cite: Golja, C.: Understanding the role of mean state biases in the stratospheric response to SAI , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22164, https://doi.org/10.5194/egusphere-egu26-22164, 2026.
How to cite: von Salzen, K., Hirasawa, H., Rasch, P., Wood, R., McMichael, L., and Doherty, S.: The Impact of Aerosol Size on the Efficacy of Marine Cloud Brightening, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3591, https://doi.org/10.5194/egusphere-egu26-3591, 2026.
As global warming accelerates, Solar Radiation Management (SRM), including stratospheric aerosol injection (SAI) and marine cloud brightening (MCB), are increasingly viewed as a potential tool to circumvent near-term climate risks. However, the complex interplay between chemistry, radiation, and dynamics creates deep uncertainties regarding regional climate disruptions and unintended feedback. Traditional evaluation relies on computationally intensive Earth System Models (ESMs), which often limit the scalability, spatial resolutions and temporal scales required for adaptive governance.
To bridge this gap, we propose a framework that leverages deep learning and explainable artificial intelligence (XAI) to accelerate the assessment of SRM impacts. A core component of our work involves adapting NeuralGCM, a hybrid atmospheric model that combines differentiable physics with machine learning, to SRM-specific scenarios. By training on diverse climate model simulations and historical analogs, we aim to assess lower temporal and spatial resolution, providing high-fidelity results of traditional models at a fraction of the computational cost.
To ensure these "black-box" models are reliable for policy-relevant science, we adapt XAI methods specifically for the climate context. These tools allow domain experts to interpret model behavior across multiple timescales, detect incorrectly learned physical mechanisms or spurious correlations, and assess risk propagation and regional uncertainties, particularly in vulnerable areas. By improving the speed, transparency, and reliability of climate intervention modeling, this approach contributes to a safer, more informed exploration of SRM as a component of global climate strategy.
How to cite: Roesch, C., Bommer, P., Golja, C., and Hegerl, G.: AI for Safe Climate Cooling: Deep Learning and XAI for Rapid SRM Risk Assessment , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8144, https://doi.org/10.5194/egusphere-egu26-8144, 2026.
Solar radiation modification (SRM) techniques such as mixed-phase cloud thinning (MCT), cirrus cloud thinning (CCT), and stratospheric aerosol injection (SAI) all include introducing foreign material into the troposphere and stratosphere, and can have unexpected effects on clouds spatially removed from the intended targets. It has been shown that mixed-phase clouds affect precipitation patterns over land, which in turn has tangible effects on agriculture. Mixed-phase clouds are generated at the Pi Chamber facility at Michigan Technological University by setting a temperature difference between the top and bottom plate of the chamber to create a convective cell, and then injecting aerosols or ice nucleating particles (INP). Using our own water isotope instruments and the cloud probes at the chamber, we will study the isotopic response of water vapor and condensate (H2O, HDO, H218O) in these mixed-phase clouds at varying glaciation fractions. We aim to better understand the growth and evolution of mixed-phase clouds in the presence of SRM material, in particular: the glaciation altitude of mixed-phase clouds, how processed SAI aerosols transported to the poles might affect mixed-phase clouds in that region, and the secondary effects of sedimenting particles used in CCT on mixed-phase clouds. We will also vary the amount and type of INP to study at what point precipitation might become suppressed. Ice deposition growth via the Wegner-Bergeron-Findeisen (WBF) process, which encourages the rapid growth and then sedimentation of ice crystals at the expense of liquid droplets, produces a strong isotopic signal that we will use to probe cloud microphysics and provide constraints on models. Early results from a bin-resolved microphysics model (BRIMM) show that our instruments are sensitive enough to see the expected isotopic signature from the WBF process. While only small modifications are needed to our previously field-tested flight and lab spectrometers to allow integration into the chamber (ChiWIS-airborne used in StratoClim and ACCLIP, and ChiWIS-lab used in IsoCloud), a method to best discriminate particles from vapor, without disturbing the cloud to be studied, is required. We explain design constraints and present early engineering test results.
How to cite: KleinStern, C., Desmoulin, A., Clouser, B., Anderson, J., Shaw, R., Cantrell, W., and Moyer, E.: Water isotopologues as tracers of mixed-phase cloud processes at the Pi Chamber laboratory, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20438, https://doi.org/10.5194/egusphere-egu26-20438, 2026.
Stratospheric Aerosol Geoengineering (SAG), which involves injecting sulfur dioxide (SO2) into the stratosphere, has been proposed as a potential climate intervention strategy to mitigate global warming. In this study, we assess how SAG could affect chlorophyll concentrations in the Congolese Upwelling System (CUS), and identify the key processes responsible for these changes, using data from the Community Earth System Model version 2, specifically the SSP5-8.5 and Geo SSP5-8.5 datasets. The model reproduces chlorophyll concentrations at both the surface and subsurface, although it tends to underestimate their magnitude compared to observations. Under climate change (RCP8.5), compared to current climate, chlorophyll concentrations are projected to decrease throughout the year, mainly due to a reduction in diatoms, the dominant chlorophyll phytoplankton group in the region. Under SAG, a net increase in chlorophyll concentration is observed all year-round, except in September-October, largely driven by an increase in diatoms. The results reveal that, under global warming, the decrease in chlorophyll concentration is mainly linked to strong stratification observed below 20 m of the mixed layer, which prevents nitrate supply to the euphotic layer and consequently reduces biological activity that should increase chlorophyll. It should be noted that changes in meridional advection driven by changes in the meridional chlorophyll gradient also contribute to this decrease in chlorophyll in March-April and June. Under SAG, the increase in chlorophyll concentration seen is mainly associated with a decrease in stratification, which permits an increase in the supply of nutrients (nitrate) to the euphotic layer and thus high biological activity. Finally, the decrease in chlorophyll noted in August-October is caused by changes in meridional advection resulting from changes in the meridional current.
How to cite: Da-Allada, Y. C., Mekonou Tamko, L. G., Ngakala, R. D., and Baloitcha, E.: Influence of Stratospheric Aerosol Geoengineering on Chlorophyll Concentration in the Congolese Upwelling System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8458, https://doi.org/10.5194/egusphere-egu26-8458, 2026.
The emerging regional climate discrepancies in global climate models raise questions about our ability to predict regional impacts of solar geoengineering scenarios. Our mechanistic understanding of regional impacts of solar geoengineering is also not as advanced as for climate change due to greenhouse gases and tropospheric aerosols. Therefore, we have recently started creating a perturbed parameter ensemble (PPE) to quantify structural uncertainties and thereby address the knowledge gaps that have emerged as regional climate discrepancies have accumulated. The PPE is based on a Geoengineering Model Intercomparison Project (GeoMIP) scenario involving stratospheric aerosol injection (SAI), which uses a prescribed artificial layer of sulfate aerosol to reduce the global temperature.
This project uses the new MPI-M CMIP7 ICON XPP model (Müller et al, 2025), an Earth system model with a horizontal resolution of 80 km for the atmosphere and 20 km for the ocean. The optical properties of the stratospheric aerosol layer for SAI are prescribed in ICON. These properties were previously simulated using the ECHAM-HAM aerosol microphysical model. Sulfur was injected into the stratosphere at two points: 30° N and 30° S.
For the PPE, we will vary the tuning variables for cloud physics, turbulence, and radiation. We will use a Latin hypercube to calculate the perturbation of these variables. This will result in approximately 100 simulations. Additionally, we plan to perform a perturbation of the initial state for each PPE member. The PPE is currently in an early stage of development. Therefore, we plan to present our project and preliminary results. We would like to discuss various focal points of PPE evaluation with interested colleagues at the EGU.
How to cite: Niemeier, U., Kang, S., and Shaw, T.: Quantifying and understanding uncertainties in regional impacts of solar geoengineering , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9663, https://doi.org/10.5194/egusphere-egu26-9663, 2026.
Extratropical cyclones (ETCs) are associated with extreme winds, heavy rainfall, and storm surges, but also provide beneficial precipitation. Their trajectories and intensity are expected to shift under global warming, and these changes may not be fully restored by Stratospheric Aerosol Injection (SAI).
We studied the effect of SAI on extratropical cyclone trajectories, properties, and analysed their risk potential using a set of 3 CESM1 simulations, one at constant year-2000 conditions (“present-day”), a high-emissions scenario with strongly increasing CO₂ concentrations (“RCP8.5”), and one in which CO₂ follows RCP8.5, but global mean surface temperature is cooled back to year-2000 conditions from 2050 onwards by means of SAI (“SAI”).
To save computation time, we use the atmosphere component CAM (rather than the several times more expensive WACCM). CAM does not model the evolution of stratospheric aerosol, hence we force the model with stratospheric aerosol fields obtained from CESM-WACCM simulations (Tilmes et al, 2018). The aerosol concentrations are scaled using a feedback procedure in order to achieve the temperature target (de Jong et al, 2025).
We find that the number of extratropical cyclone tracks decreases under RCP8.5, especially in the Southern Hemisphere, while the precipitation per cyclone increases. SAI roughly reverts these changes. The wind and pressure distributions are not strongly affected by either SAI or RCP8.5. However, the location of the North Atlantic and North Pacific storm tracks is found to shift northwards and southwards, respectively, under SAI.
Additionally, we find that under RCP8.5, ETC-related extreme precipitation events increase. Under SAI, these events decrease below present-day levels, suggesting an overcompensation. ETC-related extreme wind events decrease under RCP8.5 and decline further under SAI.
References:
Tilmes et al., 2018: https://journals.ametsoc.org/view/journals/bams/99/11/bams-d-17-0267.1.xml
De Jong et al., 2025: https://gmd.copernicus.org/articles/18/8679/2025/
How to cite: de Nooij, M., de Jong, J., Wieners, C., and Baatsen, M.: Impact of SAI on extra-tropical cyclones in a high-resolution simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13659, https://doi.org/10.5194/egusphere-egu26-13659, 2026.
Stratospheric aerosol injections have been proposed to mitigate the effects of global warming. The injection of sulphur dioxide into the stratosphere is one possible idea. However, depending on the latitude, high emission rates can lead to very low transmissions from the perspective of a typical satellite solar occultation instrument, leading to the so-called zero transmission problem. Consequently, it is highly unlikely that a physically meaningful retrieval of the stratospheric aerosol extinction profiles is possible, depending on the latitude and wavelength. The current study analyses, using MAECHAM5-HAM and SCIATRAN, continuous injections of 30 Tg S/y as a hypothetical large-scale stratospheric aerosol injection scenario. For this purpose, sulphur dioxide was continuously injected at an altitude of 60 hPa (about 19 km) into one grid box (2.8°x 2.8°) centred on the Equator at 121°E. Specifically, it is investigated which wavelengths, depending on the latitude, are necessary for plausible aerosol extinction profile retrievals. While a wavelength of 520 nm is insufficient for the retrieval for 5°N, the opposite can be concluded for 75°N and 75°S. For the latitudes 45°N and 45°S, a wavelength of at least 1543 nm is necessary. In contrast, 1900 nm is sufficient for 15°N and 15°S, as well as 5°N. Simulation results for an emission rate of 10 Tg S/y show that a minimum wavelength of 1543 nm is already sufficient for 5°N. The results emphasize that the zero transmission problem does not mean that solar occultation measurements are entirely useless.
How to cite: Lange, A., Niemeier, U., Rozanov, A., and von Savigny, C.: Investigating the zero transmission problem in satellite solar occultation measurements in the context of possible stratospheric aerosol injections, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-118, https://doi.org/10.5194/egusphere-egu26-118, 2026.
The continued failure to achieve emission reductions consistent with the Paris Agreement has intensified interest in Solar Radiation Modification (SRM), particularly stratospheric aerosol injection (SAI), as a potential component of the climate response portfolio. Current debates largely rely on a “risk–risk” framing that contrasts the risks of SAI deployment with those of unmitigated or insufficiently mitigated warming. This framing obscures a critical comparison: how different pathways to the same global temperature target may lead to fundamentally different climate outcomes. We therefore propose a complementary “world–world” framing that compares two distinct 1.5°C worlds: one achieved through greenhouse gas (GHG) mitigation and one through SAI. Using CESM2-WACCM simulations from the ARISE-SAI protocol, we assess differences in climate impacts between these pathways. In the absence of simulations that stabilize at 1.5°C through GHG mitigation, we apply a correction to the transient 1.5°C baseline of the SSP2-4.5 scenario to account for the influence of warming rates on impact indicators.
We focus in particular on four socio-economically vulnerable regions: South Asia, East Asia, South-Central America, and East Africa. While SAI effectively limits global mean temperature, it introduces substantial regional and seasonal imbalances, especially in hydrological variables. In several regions, nighttime extreme heat is exacerbated under the SAI pathway. As a complementary line of evidence, we apply machine-learning classifiers to distinguish between mitigation-driven and SAI-driven 1.5°C climates, supported by explainability analyses identifying the regions and variables driving this separation. Together, these results provide quantitative insight into the “moral hazard” dimension of SRM, highlighting how reliance on SAI may mask—but not resolve—important regional climate risks.
How to cite: Hwong, Y. L., Shmuel, A., Nauels, A., and Schleussner, C.-F.: Not All 1.5°C Worlds Are Equal: Mitigation versus Solar Radiation Modification, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3837, https://doi.org/10.5194/egusphere-egu26-3837, 2026.
Over land, the freezing level height (FLH) is a critical free-atmosphere parameter that controls ice and snow extents and shapes mountain hydroclimates, including streamflow and surface albedo. We assess future FLH trajectories under two Solar Radiation Modification (SRM) scenarios from the Geoengineering Model Intercomparison Project, phase 6 (GeoMIP6’s G6solar and G6sulfur) and two greenhouse gas emission pathways (SSP2-4.5, SSP5-8.5) to evaluate potential hydroclimatic impacts. We use output fields from models CNRM-ESM2-1 and IPSL-CM6A-LR. To improve accuracy in FLH projections, we applied a Quantile Delta Mapping (QDM) technique to mitigate inherent biases in climate simulations, using ERA5 reanalysis data as a reference. Results thus far show higher FLH values in tropical regions and lower values near the poles. However, the FLH meridional gradient is stronger in the southern hemisphere than in the northern hemisphere for the historical simulations—consistent with ERA5. Globally, the annual maximum FLH increases ~6 m/year for the GeoMIP6 and SSP2-4.5 scenarios between 2020 and 2100, whereas SSP5-8.5 nearly doubles this rate. For most of the world, this increase is strongly correlated with near-surface air temperature rise, suggesting a strong coupling between surface warming and free-atmosphere conditions along high-elevation regions in the future, irrespective of the climate scenario. Although annual and maximum FLHs show linear relationships with near-surface air temperature, the regression slope of the former is, on average, about 100 m/°C smaller than the latter, suggesting a stronger change during the melt season and hence a possible large impact on the high mountain cryosphere. In this presentation, we will showcase these findings together with ongoing analyses using other SRM simulations, and discuss their potential implications for mountain hydroclimates worldwide.
How to cite: Fernandez, A., Torrez- Rodríguez, L., Manquehual-Cheuque, F., and Somos-Valenzuela, M.: Effect of Solar Radiation Modification on Freezing Level Heights across the world , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8392, https://doi.org/10.5194/egusphere-egu26-8392, 2026.
Despite significant advances in low emissions and renewable technologies, global warming is expected to exceed 2 degree and breach the Paris Agreement. Here we applied an Earth system model to simulate stratospheric aerosol injection (SAI) in idealized overshoot scenarios. The objective is to evaluate the impacts of avoiding temperature overshoot using SAI under optimal conditions. Three injection locations were tested: the tropics, and the northern and southern hemispheres’ mid-latitude. While the global mean temperature overshoot can be avoided, regional climatic responses vary considerably depending on the injection location. For example, in the subpolar northern hemisphere, the long-term temperature evolution over the next centuries following SAI cessation is highly sensitive to the SAI-induced changes in the Atlantic Meridional Overturning Circulation (AMOC) evolution. This, in turn, alters long-term projections of Arctic sea-ice and permafrost dynamics. The global warming-induced shift in the Intertropical Convergence Zone (ITCZ) can either be amplified or offset depending on the location of SAI implementation. These results re-emphasize the challenge of avoiding regional disparity introduced by SAI. Our experiments suggest that SAI application would affect both the short- and long-term feedback processes in the Earth system with legacies lasting long after its termination.
How to cite: Tjiputra, J., Olivié, D., Schwinger, J., Fisher, R., Goris, N., and Steinert, N.: Legacy of stratospheric aerosol injection for limiting global warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9275, https://doi.org/10.5194/egusphere-egu26-9275, 2026.
