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Stratospheric Aerosol Injection | A Solar Radiation Management (SRM) Geoengineering Approach

What is Stratospheric Aerosol Injection?

Stratospheric aerosol injection is a solar radiation management (srm) geoengineering or climate engineering approach that uses tiny reflective particles or aerosols to reflect sunlight into space in order to cool the planet and reverse or stop Global Warming. The approach involves spraying reflective sulfate aerosol particles into the stratosphere with high altitude airplanes, tethered balloons, high-altitude blimps or artillery.

Stratosphere definition?

The stratosphere (see NOAA image below) is a layer of the Earth’s atmosphere that ranges between 7 to 31 miles above the ground between the Troposphere and the Mesophere. The stratosphere is an ideal target for atmospheric geoengineering because it is relatively isolated from human populations, is accessible by planes (and other transport/delivery methods), and doesn’t have weather such as rain that would cause aerosol spray particles to fall quickly to the ground. 

Image of the Stratosphere where sulfate aerosol particles could be sprayed or injected to counteract Global Warming. Courtesy of NOAA Satellite and Information Service.

Who first proposed Stratospheric Aerosol Injection?

Stratospheric aerosol injection was first proposed by the Russian climatologist Mikhail Ivanovich Budyko in 1974 (Rasch et al., 2008/Keith, 2000). The idea developed out of observations that natural atmospheric sulfate injections by large volcanic eruptions (see Volcano Eruptions Size Comparison YouTube video below) are generally followed by 1 to 2 years of cool weather over large areas of the planet.

Volcano Eruptions Size Comparison. Video courtesy of Taype Studios.

Would Stratospheric Aerosol Injection Cool the Planet?

Stratospheric Aerosol Injection is a very promising geoengineering solution to Global Warming because, based on research conducted on numerous recent and historic volcanic eruptions such as Mount Pinatubo in 1991 and complex climate model simulations, there is strong evidence that it would be very effective in cooling the planet and mitigating the effects of Climate Change.

How long would deployed Stratospheric Aerosol Injection aerosols stay up in the stratosphere?

“Historically, the SO2 from large volcanic eruptions produces an abundance of stratospheric aerosols that cause a temporary decrease in tropospheric temperatures due to the reduction in solar radiation reaching the troposphere (Aurby et al., 2021; Hansen et al., 2002; Marshall et al., 2022; Stenchikov, 2016). Volcano‐sourced sulfuric acid aerosols can persist for years and even self‐loft when the aerosols are mixed with ash (Khaykin, de Laat, et al., 2022; Khaykin, Podglajen, et al., 2022). Robock (2000) and Thomason and Peter (2006) state that volcanic aerosol global lifetimes for large tropical eruptions are about ∼1 year. Yet there is evidence that the Pinatubo eruption’s aerosol mean stratospheric lifetime was closer to 2 years (Toohey et al., 2025, T25T25) (Schoeberl et al., 2025).”

Based on analysis of global stratospheric aerosol observations, Toohey et al., 2025 estimated “that the stratospheric lifetime of stratospheric aerosol from the 1991 Pinatubo eruption was approximately 22 months (Toohey et al., 2025).”

Schoeberl et al., 2025 simulated “the evolution of the water vapor plume from the January 2022 Hunga eruption. The simulation suggests a lag time of 1.4 years and the decay time 2.35 ± 0.05 years, producing a stratospheric lifetime of 3.75 ± 0.05 years. From Microwave Limb Sounder observations, we estimate the Hunga water vapor plume decay time to be 2.6 ± 0.75 years and the lifetime to be 4.0 ± 0.75 years which is in good agreement with our model calculations. Overall, we find that injected material lifetime increases with altitude and decreases with the latitude (Schoeberl et al., 2025).”

The Puyehue Cordon Volcano in Chile expelling a stream of gases. Courtesy of NASA Earth Observatory.
The Volcano Ubinas in Peru expelling aerosols in the atmosphere. Courtesy of NASA Earth Observatory.
The Shiveluch Volcano in northeast Russia expelling aerosols in the atmosphere. Courtesy of NASA Earth Observatory.

Can Stratospheric Aerosol Injection prevent Climate Change Tipping Points?

Multiple studies (see below) have showed that Stratospheric Aerosol Injection can prevent multiple tipping points including:

  • melting of the polar ice caps, permafrost, and methane hydrate
  • the loss of the Amazon rainforest
  • the bleaching of coral reefs around the world
  • the weakening of the Atlantic Meridional Overturning Circulation or Great Ocean Conveyor Belt

Polar ice caps, permafrost, and methane hydrate

Lee et al., 2023 used “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 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 produces the most cooling near the pole, 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. For these reasons, it would be incorrect to consider Arctic-focused SAI as “local” geoengineering, even when compared to a globally focused strategy (Lee et al., 2023).”

Amazon rainforest

“Parry et al., 2022 examined results from seven 6th generation models (CMIP6) which include vegetation dynamics, and in some cases 5 interactive forest fires. Although these models typically project increases in area-mean forest carbon across Amazonia under CO2-induced climate change, five of the seven models also produce abrupt reductions in vegetation carbon which indicate localized dieback events. The Northern South America region, which contains most of the rainforest, is especially vulnerable in the models. These dieback events, some of which are mediated by fire, are preceded by an increase in the amplitude of the seasonal cycle in near surface temperature, which is consistent with more extreme dry seasons. Based on the 10 ensemble mean of the detected dieback events we estimate that 7+/-5% of the Northern South America region will experience abrupt downward shifts in vegetation carbon for every degree of global warming past 1.5°C (Parry et al., 2022).”

“Based on results from five Earth System Models, Parry et al., 2026 found that Stratospheric Aerosol Injection (SAI) 370 geoengineering would likely increase global NPP and land carbon storage relative to both unmitigated climate change (under 27 the SSP585 scenario) and conventional mitigation (as represented by SSP245 relative to SSP585), with NPP and land carbon storage increasing by 15.6% and 5.9% respectively compared to SSP245. The modelled positive impacts of SAI are most marked in Amazonia, where SAI is projected to lead to significant increases in both NPP and land carbon storage. We observe increases in land carbon storage on the order of 8.6% and 10.8% in G6sulfur compared to SSP245 and SSP585, respectively. We note, however, that these observed 375 increases in NPP and land carbon storage are not universal, with regions such as eastern Africa, the northern high latitudes, and Indonesia showing decreases for some models. The best protection for the Amazon rainforest is a combination of reduced rates of both deforestation and anthropognenic climate change. However, this study suggests that SAI geoengineering might provide some emergency protection against climate-change induced Amazon carbon loss, if CO2 induced climate change is not brought under control (Parry et al., 2026).”

Coral reef bleaching

The ocean has absorbed over 90% of the excess heat produced by greenhouse gas emissions (Li et al 2023b). Consequently, marine environments are experiencing more intense and frequent anomalous high-temperature events known as marine heatwaves (MHWs). MHWs are defined as discrete, prolonged events during which the sea surface temperature (SST) deviates significantly from its seasonal norms based on the daily mean (Hobday et al 2016). MHWs have severe impacts on marine life, including massive marine organism dieoffs (Brodeur et al 2019, Leggat et al 2019) and declines in fishery productivity and tourism (McKibben et al 2017, Smith et al 2021). The increased frequency of MHWs across the ocean has induced numerous ecological disruptions and socio-economic losses (Smith et al 2021), including harmful algal blooms (McKibben et al 2017), mass stranding events of marine mammals and seabirds (Cavole et al 2016), and unprecedented mass bleaching events of coral reefs, which increase coral mortality (Hughes et al 2018a, Holbrook et al 2020, Yao et al 2022).

Global warming has increased the duration and intensity of MHWs over the last century, and permanent MHWs have been predicted in many areas of the ocean by the end of the 21st century. Climate interventions, such as stratospheric aerosol injection (SAI), have been proposed to reduce the mean global temperature; however, their potential impact on MHWs is unclear. In this study, we used the output from the Community Earth System Model to quantify MHWs under multiple timeframes and climate change scenarios. We evaluated global MHW properties, including duration and maximum intensity—the maximum exceedance above the climatology—over historical (1990–2009), present (2015–2034), and future (2050–2069) periods. We analyzed output from two SAI scenarios aimed to maintain global mean surface temperatures at ∼1.5 ◦C and ∼1.0 ◦C above pre-industrial levels (ARISE-SAI-1.5 and ARISE-SAI- 1.0) and one non-SAI scenario (SSP2-4.5). Our results show that despite the SAI reducing the global average maximum intensity and duration of MHWs relative to SSP2-4.5, the magnitude of the effects varies spatially. Compared with the present climate, SAI scenarios would reduce MHW intensity in 25%–76% of the ocean and MHW duration in 21%–80% of the ocean. The largest future reductions in maximum intensity and duration occurred in the coastal regions of the Tropical Atlantic, Indian, Arctic, and South Atlantic oceans. Even with a more aggressive SAI scenario (ARISE-SAI-1.0), nearly 25% of the ocean would remain unaffected, with areas like the North Atlantic, Tropical Pacific, and parts of the Southern Oceans still experiencing more intense and longer MHWs, meaning that SAI could be perceived locally as ineffective at mitigating MHW even while the global mean temperature target is being met.

Atlantic Meridional Overturning Circulation or Great Ocean Conveyor Belt

The Atlantic Meridional Overturning Circulation (AMOC) plays a crucial role in the global climate system. The AMOC is the system of ocean currents that act as a planetary conveyor belt that distributes heat around the world. “Various studies report both ongoing and projected reductions in the strength of the AMOC with Global Warming. Bednarz et al., 2025 found that Stratospheric Aerosol Injection with SO2 injections in the Northern Hemisphere would cool North Atlantic surface temperatures, increase surface density, and strengthen the Atlantic Meridional Overturning Circulation (Bednarz et al., 2020).”

A simulation of the Atlantic Meridional Overturning Circulation or Great Ocean Conveyor Belt. Red dotted lines represent surface currents. Blue dotted lines represent deep currents. The background displays the sea-surface density. Credit: NASA  

Can Stratospheric Aerosol Injection prevent severe global droughts and forest fires?

Extreme heat events have increased in frequency, intensity and duration over the last several decades as a result of anthropogenic climate change. Warm spells are prolonged periods of anomalously high temperature that can occur at any time of the year. “Under SSP2–4.5 warm spells are projected to become increasingly frequent, intense and longer. In simulations, warm spells occur, on average, up to approximately three times per year over many land regions in both models. Warm spell occurrence, however, exhibits considerable spatial heterogeneity, with more frequent occurrence over regions such as the western United States, the Sahara and the Indian subcontinent, and less frequent occurrence over regions such as the eastern U.S., southern Australia and central Asia. Under SSP2–4.5, warm spell occurrence is projected to increase globally by the end of the simulation period (i.e., the 2060s), except over Iceland in CESM2, with increases of up to 10 warm spells per year. Increases in warm spell frequency are largest at lower latitudes over regions such as the Amazon, central Africa and southeast Asia, although increases are up to five warm spells per year over Northern Hemisphere high latitudes. There are some regions where future projections of warm spells are noticeably different between the two models, such as over western North America and some tropical rainforests. When SAI is deployed, future increases in warm spells are reduced globally. In CESM2, there is little change in warm spell event occurrence between the 2060s under SAI and the reference period, with the largest change being a slight increase (no more than four warm spells per year) over west-central South America. In contrast, in UKESM1, there is a slight decrease in warm spell occurrence relative to the reference period over most land regions (Glade et al., 2025).”

“By 2100, the frequency of extreme droughts is projected to increase by 7.33% under the high-emission Shared Socioeconomic Pathways 5 (SSP5-8.5) scenario relative to present day. SAI-induced cooling alone reduces extreme drought frequency by 3.42% in GeoMIP6 and 4.28% in GLENS relative to their respective high-emission scenarios, outweighing the 2.12% increase driven by SAI-induced precipitation reductions under the same conditions. SAI in G6sulfur mitigates only 42.8% of the SSP5-8.5 warming but offsets 88.9% of the rainfall increase under SSP5-8.5, indicating a disproportionate suppression of the water cycle. While cooling directly reduces evaporation, aerosol-induced increase in atmospheric stability indirectly weakens monsoon circulation (Tilmes et al., 2013; Krishnamohan and Bala, 2022), such as India and China. Consequently, SAI may inadvertently degrade hydroclimate security in vulnerable regions under a high-emission scenario. Countries with less development experience smaller reductions, or even increases, in economic and population exposure to extreme drought under SAI relative to SSP5-8.5 or RCP8.5. These findings suggest that the current SAI strategies in GeoMIP6 and GLENS may induce the risk of unintentionally worsening regional hydroclimatic disparities (Fu et al., 2025).”

“Based on the simulations from the G6sulfur experiment that employs SAI to reduce the global mean surface temperature, SAI effectively offsets the greenhouse gas‐induced aridity trend by increasing the climate water balance at the global scale. Drought duration and severity decrease but drought frequency increases under SAI forcing. Robust wetting responses occur over most regions, especially the Sahara, South America, southern Africa and Australia, while Alaska, Greenland, Southeast Asia, and tropical Africa face enhanced drought due to SAI (Liu et al., 2024).”

“After SAI deployment, increases in extreme fire weather event frequency from climate change are dampened over much of the globe, including the Mediterranean, northeast Brazil, and eastern Europe. However, SAI has little impact over the western Amazon and northern Australia and causes larger increases in extreme fire weather frequency in west central Africa relative to the moderate emissions scenario. Variations in the impacts of warming and SAI on moisture conditions on different time scales determine the spatiotemporal differences in extreme fire weather frequency changes, and are plausibly linked to changes in synoptic-scale circulation (Touma et al., 2023).”

The Shiveluch Volcano in northeast Russia expelling a stream of aerosols into atmosphere. Courtesy of NASA Earth Observatory.
The Ambrym Volcano in the archipelago of Vanuatu expelling a stream of aerosols into atmosphere. Courtesy of NASA Earth Observatory.
The erupting Gaua Volcano in the Vanuatu Archipelago. Courtesy of the NASA Earth Observatory.

What are the Side Effects of Stratospheric Aerosol Injection based on Climate Models?

Conducting simulations using the Community Earth System Model (CESM1), Drs. Jadwiga H. Richter, Simone Tilmes, Michael Mills, Ben Kravitz and Douglas G. MacMartin (Kravitz et al., 2017) of the National Center for Atmospheric Research it’s partners (NCAR) show that stratospheric aerosol injection has the potential to prevent further atmospheric warming and maintain a relatively stable climate. Please see the NCAR YouTube video below of a model comparison between severe Global Warming (RCP 8.5) and stratospheric aerosol injection geoengineering (Feedback Simulation).

Video Courtesy of the National Center for Atmospheric Research (NCAR)

NCAR model simulations (Kravitz et al., 2019/Tilmes et al. 2018) also show that stratospheric sulfate aerosol geoengineering could also prevent the loss of Arctic sea ice by the end of this century (see NCAR YouTube video below). Preventing the loss of Arctic sea ice is very important because it helps reflect sunlight into space and maintain Earth’s Energy Budget.

Video Courtesy of the National Center for Atmospheric Research (NCAR)

Is Stratospheric Aerosol Injection Currently Feasible?

Stratospheric Aerosol Injection is feasible with existing technologies. It could also be implemented in a very short period of time and at a relatively low cost. Because stratospheric aerosols naturally fall out of the atmosphere, the benefits/effects of this approach are temporary, generally lasting between 1 to 2 years. It is considered relatively safe for the environment because volcanoes have been injecting sulfate aerosols into the stratosphere for eons and the biosphere naturally processes sulfates using multiple pathways in the sulfur biogeochemical cycle. Besides sulfate, other reflective aerosols that are being considered for this solar radiation management approach. These aerosols include black carbon, metallic aluminum, aluminum oxide and barium titanate (Effiong and Neitzel, 2016).

Volcano Shiveluch in Kamchatka Krai, Russia releasing aerosols into the atmosphere. Courtesy of the NASA Earth Observatory.
The Klyuchevskoy Volcano on the Kamchatka Peninsula of Siberia releasing aerosols into the atmosphere. Courtesy of the NASA Earth Observatory.
The eruption of the Momotombo Volcano in Nicaragua. Courtesy of the NASA Earth Observatory.

What are the Dangers Associated with Stratospheric Aerosol Injection?

Unfortunately, there are dangers associated with stratospheric aerosol injection. This approach may reduce rainfall in some areas of the world. Loss of crops and access to fresh water due to reduced rainfall could lead to starvation and suffering. If this approach were used, it would be important to develop and implement measures to protect people and save lives and livelihoods. Despite the potential problems with this method, the benefits could exponentially outweigh its downsides.

The Raung Volcano on the island of Java in Indonesia emitting gases into the atmosphere. Courtesy of NASA Earth Observatory.
Volcano Paluweh on the small island of Palu'e in East Nusa Tenggara, Indonesia spewing gases into the air. Courtesy of NASA Earth Observatory.
The eruption of Volcano Sakurajima in southern Kyushu, Japan. Courtesy of NASA Earth Observatory.

References

  1. Bednarz, E.M., Goddard, P.B., MacMartin, D.G., Visioni, D., Bailey, D. and Danabasoglu, G., 2025. Stratospheric aerosol injection could prevent future Atlantic meridional overturning circulation decline, but injection location is key. Earth’s Future, 13(8), p.e2025EF005919.

  2. Effiong, U. and Neitzel, R.L., 2016. Assessing the direct occupational and public health impacts of solar radiation management with stratospheric aerosols. Environmental Health, 15(1), p.7.

  3. Fu, W., Yue, X., Tian, C., Xu, R. and Guo, Y., 2025. Unequal socioeconomic exposure to drought extremes induced by stratospheric aerosol injection. Atmospheric Chemistry and Physics, 25(20), pp.13103-13121.
  4. Glade, I., Hurrell, J.W. and Lombardozzi, D.L., 2025. Comparing future projections of warm spells and their characteristics under climate change and stratospheric aerosol injection in CESM2 and UKESM1. Frontiers in Climate, 7, p.1581305.

  5. Keith, D.W., 2000. Geoengineering the climate: History and prospect. Annual review of energy and the environment, 25(1), pp.245-284.

  6. Kravitz, B., MacMartin, D.G., Mills, M.J., Richter, J.H., Tilmes, S., Lamarque, J.F., Tribbia, J.J. and Vitt, F., 2017. First Simulations of Designing Stratospheric Sulfate Aerosol Geoengineering to Meet Multiple Simultaneous Climate Objectives. Journal of Geophysical Research (Atmospheres), 122(D11), p.12.

  7. Kravitz, B., MacMartin, D.G., Tilmes, S., Richter, J.H., Mills, M.J., Lamarque, J.F., Tribbia, J. and Large, W., 2019. Holistic assessment of SO2 injections using CESM1 (WACCM): Introduction to the special issue. Journal of Geophysical Research: Atmospheres, 124(2), pp.444-450.

  8. Lee, W.R., MacMartin, D.G., Visioni, D., Kravitz, B., Chen, Y., Moore, J.C., Leguy, G., Lawrence, D.M. and Bailey, D.A., 2023. High‐latitude stratospheric aerosol injection to preserve the Arctic. Earth’s Future, 11(1), p.e2022EF003052.
  9. Liu, Z., Lang, X. and Jiang, D., 2024. Stratospheric aerosol injection geoengineering would mitigate greenhouse gas‐induced drying and affect global drought patterns. Journal of Geophysical Research: Atmospheres, 129(3), p.e2023JD039988.
  10. Parry, I.M., Ritchie, P.D. and Cox, P.M., 2022. Evidence of localised Amazon rainforest dieback in CMIP6 models. Earth System Dynamics, 13(4), pp.1667-1675.
  11. Parry, I.M., Ritchie, P.D., Boucher, O., Cox, P.M., Haywood, J.M., Niemeier, U., Séférian, R., Tilmes, S. and Visioni, D., 2026. Stratospheric aerosol injection geoengineering has the potential to increase land carbon storage and to protect the Amazon rainforest. Earth System Dynamics, 17(2), pp.387-414.
  12. Rasch, P.J., Tilmes, S., Turco, R.P., Robock, A., Oman, L., Chen, C.C.J. and Stenchikov, G.L., 2008. An Overview of Geoengineering of Climate using Stratospheric Sulfate Aerosols. Geo-Engineering Climate Change: Environmental Necessity or Pandora’s Box, pp.250-285.
  13. Schoeberl, M.R., Toohey, M., Wang, Y. and Ueyama, R., 2025. Stratospheric injection lifetimes. Journal of Geophysical Research: Atmospheres, 130(18), p.e2025JD043928.
  14. Tilmes, S., Richter, J.H., Kravitz, B., MacMartin, D.G., Mills, M.J., Simpson, I.R., Glanville, A.S., Fasullo, J.T., Phillips, A.S., Lamarque, J.F. and Tribbia, J., 2018. CESM1 (WACCM) stratospheric aerosol geoengineering large ensemble project. Bulletin of the American Meteorological Society, 99(11), pp.2361-2371.
  15. Toohey, M., Jia, Y., Khanal, S. and Tegtmeier, S., 2025. Stratospheric residence time and the lifetime of volcanic stratospheric aerosols. Atmospheric Chemistry and Physics, 25(6), pp.3821-3839.
  16. Touma, D., Hurrell, J.W., Tye, M.R. and Dagon, K., 2023. The impact of stratospheric aerosol injection on extreme fire weather risk. Earth’s Future, 11(6), p.e2023EF003626.