Stratospheric Aerosol Injection (SAI)

Geoengineering Technology BriefingNov 2020

GEOENGINEERINGMONITOR.ORG Analysis and critical perspectives on climate engineering [email protected]

Stratospheric Aerosol Injection (SAI)Description and purpose of the technologyStratospheric Aerosol Injection(SAI) is a theoretical solargeoengineering proposal to spraylarge quantities of tiny reflectiveparticles into the stratosphere, anupper layer of the Earth’satmosphere, in order to cool theplanet by reflecting sunlight backinto space. Proposals range fromspraying reflective particles, suchas sulphur dioxides, finelypowdered salt or calciumcarbonate, from aircraft, shootingparticles from artillery guns, orusing large hoses to reach the sky.None of those solargeoengineering approaches address theunderlying causes of climate change. Insteadthey aim to control the amount of incomingsolar radiation by emulating the sulphur-richdust cloud that remains in the atmosphere afterlarge volcanic eruptions. In contrast to avolcanic outburst, SAI assumes continuousmaintenance of the particle layers by regularinjections.

SAI using sulphur dioxide is the most-studiedoption. Computer simulations suggest that thistechnique would likely causedroughts in Africa and Asia andestimate that the SAI couldendanger the source of foodand water for two billion people.Because of the unequal globalimpacts and its potential to beweaponized, solargeoengineering carriesunsurmountable challenges forgovernance. Therefore, severalhundred civil societyorganizations from around theworld are calling for amultilateral ban on solargeoengineering.1

Actors involvedResearch on SAI is largely based on modelling,mostly conducted in the Northern hemisphereand at U.S. institutions, in particular HarvardUniversity, and largely supported by fossil fuel(burning) industries, billionaires and otherwealthy individuals, such as Bill Gates. Thesame sources of funding launched theDeveloping Country Impacts Modelling Analysisfor Solar Radiation Management (DECIMALS)Fund, to appear as if the research on SAI has

expanded to the Southernhemisphere, although it is onlyhappening because of thegrants from a Northernorganization managed by amajority of geoengineeringadvocates. The U.S.government is the mostimportant public funding sourcefor financing research andmodelling of SAI on global andregional scale since 2008.

Reality Check:

Its justa theory

Its beingimplemented

SAI using a tethered balloon, one way of geoengineering the climate Illustration by Hugh Hunt / Wikipedia

Point ofIntervention:


In 2019, the U.S. government allocatedUS$ 4 million to the National Oceanic andAtmospheric Association (NOAA) to conductresearch on solar geoengineering, SAI withsulphur dioxide is one of the approaches NOAAis going to explore. The only known SAI fieldexperiment injected sulphate into thetroposphere and was conducted by a Russianinstitution in 2009.2

SCoPEx: Stratospheric aerosolinjection experimentDavid Keith, based at Harvard University, is theforemost geoengineering advocate advancingsolar geoengineering. He is an investor in thetechnology, has lobbied governments, andmanages, along with Ken Caldeira, the Fund forInnovative Climate and EnergyResearch (FICER), a multimillion geoengineeringfund provided by Bill Gates since 2007. He hasalso commissioned a study by anU.S. aerospace company that argued for thefeasibility of large-scale deployment of solargeoengineering technologies. In early 2017, helaunched Harvard’s Solar GeoengineeringResearch Program, which aims to raiseUS$ 20 million in funding from severalbillionaires and private foundations to executethe open-air experiment SCoPEx.3

Alongside other engineers and researchers,Keith has proposed a number of fieldexperiments,4 including the “StratosphericControlled Perturbation Experiment” (SCoPEx).The explicit aim of this experiment is to acquirefurther data for modelling solar geoengineeringand predicting larger-scale effects of SAI, bymonitoring the reflective properties of injectedparticles and their impact on the surroundingatmosphere. The envisaged field test aims todisperse various particles of differentchemicals, from a balloon into the stratosphere,at an altitude of 20 kilometres above the Earth.The balloon will be steered from ground andequipped with scientific instruments, includingsensors for data collection.5

However, more than just a scientificexperiment, this outdoor solargeoengineering experiment has been pointed toas a public relations exercise – a way of buildingacceptance for outdoor experiments, to pavethe way for large-scale and longer experimentsthat ultimately would lead to large-scaledeployment.6

Other actorsThere are large companies for whom ”saving theworld” – exclusively through some sort oftechno-fix – is increasingly becoming astructural prerequisite for continuing theirbusiness, particularly when those companiesdepend heavily on fossil fuels. They try to shiftpolicy norms so that previously unthinkablenotions and activities – like solargeoengineering and other proposals– start tobecome more mainstream and acceptable.

ExxonMobil is one of those companies. Thecompany's Senior Scientific Advisor, Dr. HaroonKheshgi is the company’s point person ongeoengineering, recruited from the LawrenceLivermore National Laboratory.7 Through hisefforts, ExxonMobil has influenced“independent” reports on geoengineering andhas funded a report that advocates for carbondioxide removal and solar geoengineering.Khesgi has also been an author of severalIPCC reports and has been denounced by civilsociety for this involvement. ExxonMobil’sformer CEO and former U.S. Secretary of StateRex Tillerson has described climate change asan “engineering problem” with “engineeringsolutions.”8

Shell’s chief lobbyist, David Hone, is evangelicalabout “negative emissions” and increasinglyopenly supports solar geoengineering.9 SteveKoonin, by then chief scientist at BP, led aproject to determine hardware feasibility forsolar geoengineering experiments.10

SAI would modify the Earth’s radiative balance,

and is also associated withsignificant potential risks and

uncertainties, such asimpacts on extreme weather

events, ecosystems, rainpatterns, agricultural yields,

ozone chemistry, solarenergy output, human health

and many more.

“

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Boeing’s Integrated Defense Systems ChiefScientist and Vice-President David Whelan(formerly of DARPA) is also active ingeoengineering debates, claiming there is asmall team at Boeing studying the issue. He haspublicly mused about the technical feasibility ofgetting mega-tonnes of aerosol sulphates up todifferent stratospheric levels via aircraft orlarge cannons.11

Impacts of the technologyAs with all solar geoengineering technologiesthat only address global surface temperatures,dramatic perturbations in the climate systemcan be expected if SAI is deployed. SAI wouldmodify the Earth’s radiative balance, and is alsoassociated with significant potential risks anduncertainties, such as impacts on extremeweather events, ecosystems, rain patterns,agricultural yields, ozone chemistry, solarenergy output, human health and many more.12

Early research into SAI from the UK’s Met OfficeHadley Centre found that SAI could lead tosevere drought in the Sahel region of Africa.While researchers found that this could possiblybe countered by injecting particles into thesouthern hemisphere’s stratosphere instead,this would likely cause a failure of the rains innortheast Brazil.13

A recent modelling study simulating the climateeffects of SAI found similar potential negativeconsequences. Injection in the northernhemisphere would lead to fewer hurricanes inthe North Atlantic, which might be good newsfor the Caribbean, but it would likely createdrought in Sub-Saharan Africa and parts ofIndia. Injecting aerosol in the southernhemisphere wouldn’t create drought, but itwould create more hurricanes in the NorthAtlantic.14

Regional warming is also likely, based on theresults of the Geoengineering ModelIntercomparison Project published in 2014. Itpredicted that temperatures in the tropicswould cool as a result of SAI, but higherlatitudes would warm, with ice sheets andArctic sea ice still declining, and extremetemperature anomalies also still increasing.

The so-called termination effect is anothermajor risk: “If geoengineering were halted all atonce, there would be rapid temperature andprecipitation increases at 5–10 times the ratesfrom gradual global warming.”15 A scientificstudy published in Nature in 2018, showed thatthe shock caused by sudden terminationof solar geoengineering would have graveimpacts on biodiversity. This means thatstopping SAI once it had started could be moredangerous than starting it in the first place.Ozone depletion is another important sideeffect of SAI.16

Studies on the impacts of SAI on public healthare limited, but a recent analysis suggests thatadverse public health impacts may be expected.Little is known about the toxicity of someaerosols that have been suggested, and there isno consensus on what acceptable levels forpublic exposure to these aerosols are. There arealso very few means of evaluating potentialpublic health impacts should SAI be deployed.17

Exacerbates global power imbalancesThe prospect of controlling global temperaturesraises serious questions of power and justice: if solar geoengineering functions, who gets tocontrol the Earth’s thermostat and adjust theclimate for their own interests? Who will makethe decision to deploy if such drastic measuresare considered technically feasible, and whoseinterests will be left out?

Volcanoes also inject aerosols into the stratosphere – anderuptions have been followed by terrible droughts and famine

Photo: R Clucas / Wikipedia


The risk for weaponization of SAI isconsiderable. The premise of controlling theweather originated with military strategies,which led to the signing of the internationalEnvironmental Modification Convention(ENMOD). Military leaders in the United Statesand other countries have pondered thepossibilities of weaponized weathermanipulation for decades. If the explicit aim of atechnology is to “combat climate change,” itdoesn’t guarantee its use will be limited only tothat application. Historian James Flemingargues that if anybody can control the Earth’sthermostat, this can and will be used for militarypurposes. Even before hostile use, any state oractor claiming to be able to alter global weatherpatterns will hold a powerful geopoliticalbargaining chip with which to threaten andbully. The concept to establish capacities forcounter-geoengineering was established inview of the aforementioned risks and meansanother step towards militarization.18

Solar geoengineering is the perfectexcuse for inaction on climate changeSolar geoengineering, and geoengineeringmore broadly, is a “perfect excuse” for climatechange deniers, industries and governmentsseeking to avoid the political costs of carbonreductions and to continue business as usual.For those looking to stall meaningful climateaction, the active development ofgeoengineering tools and experiments will bepresented as a preferred pathway to addressclimate change and be used as an argument toease restrictions on high carbon emittingindustries. This line of argument was alreadyput forward by conservative think tanks in theUnited States such as the American EnterpriseInstitute.

Furthermore, once solar geoengineering isdeployed, sudden interruption would cause atermination effect, raising temperaturesrapidly, creating a situation worse than it wasbefore its deployment. Therefore, solargeoengineering will create dependency andcaptive markets.19

Governance of solar geoengineeringcould be impossibleThere is a de facto moratorium on climate-related geoengineering under the Conventionon Biological Diversity that clearly articulatesthe need for a global transparent regulatorymechanism for governance beforeexperimentation is considered. 196 countriesagree to require a global mechanism becausethey recognize that the potential impacts andside effects of geoengineering will be unfairlydistributed.

Since solar geoengineering could be a tool tocontrol the Earth’s thermostat for those whohave legal, economic and technologicalresources, any step towards realizing thosecapabilities must be agreed through consensusby all members of the UN.

Another key problem is that if all governmentscould effectively agree on such a complex issuewith so many social, economic, environmentaland intergenerational aspects at play, includinghow and who will carry the cost and burden ofthe negative impacts, and if countries had thecapacity to implement the necessary agreedclimate measures that demand persistence andcoherence over several decades or evencenturies, we wouldn’t have climate change inthe first place, because they could have agreedon clear and binding rules to stop excessemissions. Even the Paris Agreement, whichseems a miraculous convergence of politicalwill, only lasted a few months after entering intoforce before the largest historical GHG-emittingcountry declared it won’t respect it.

One geoengineering technology, Stratospheric AerosolInjection, proposes spraying particles into the upper

atmosphere to block sunlight.


The failure to manage fair and effectiveinternational climate governance is a clearargument against moving ahead withgeoengineering and particularly solargeoengineering, which is more deeply unfairand complex and for which there are poorprospects for establishing the fully democratic,multilateral, legally binding and century-longagreement needed for minimally fairgovernance. Without such a mechanism, oncethe tools are developed it will be extremelydifficult – or impossible – to stop powerfulgovernments from using it, for theirconvenience and/or against other countries.Therefore, the most appropriate governance forsolar geoengineering is a ban.

Reality checkSAI is seen as a quick way of geoengineeringthe climate. Although outdoor experimentshave been successfully opposed in severalcases, limiting research to computer modelling(though one aerosol injection field experimentin the troposphere has taken place in Russia20),there is a constant push by a few actors tonormalize this kind of research andexperiments, which could lead to thetechnology being developed quickly. SCoPEx isthe most high-profile experiment that has beenput forward on solar geoengineering.

Further readingFor more information on SAI, ScoPEx and solargeoengineering governance see

SCoPEx:http://www.geoengineeringmonitor.org/2019/08/open-letter-scopex/

The Big Bad Fix:http://www.geoengineeringmonitor.org/2017/12/3087/

Fuel to Fire:https://www.boell.de/en/2019/02/13/fuel-fire?dimension1=ds_geoengineering

Why the SDGs Require a Governance DebateBased on Precaution, Rights and Fairness:http://sdg.iisd.org/commentary/guest-articles/geoengineering-at-unea-4-why-the-sdgs-require-a-governance-debate-based-on-precaution-rights-and-fairness/

Endnotes1 Jones et al. (2017) Impacts of hemispheric solar geoengineering on tropical cyclone frequency, in: Nat Commun, Vol.

8 (1382), https://doi.org/10.1038/s41467-017-01606-0; Fuhr (2019) Geoengineering at UNEA-4: Why the SDGs Require aGovernance Debate Based on Precaution, Rights and Fairness, in IISD, SDG Knowledge Hub, published online: March5, 2019, http://sdg.iisd.org/commentary/guest-articles/geoengineering-at-unea-4-why-the-sdgs-require-a-governance-debate-based-on-precaution-rights-and-fairness/; Robock, et al. (2010) A Test for Geoengineering?, in:Science, Vol. 327(5965): 530 - 531, http://doi.org/ 10.1126/science.1186237

2 Stephens and Surprise (2019) The hidden injustices of advancing solar geoengineering research, in: GlobalSustainability, Vol. 3: 1 - 6, https://doi.org/10.1017/sus.2019.28; ETC Group and Heinrich Böll Foundation (2020)Geoengineering Map, https://map.geoengineeringmonitor.org/; Kravitz and MacMartin (2020) Uncertainty and thebasis for confidence in solar geoengineering research, in: Nat Rev Earth Environ, Vol. 1: 64 -75,https://doi.org/10.1038/s43017-019-0004-7

3 ETC Group and Heinrich Böll Foundation (2020) Geoengineering Map: Fund for Innovative Climate and EnergyResearch (FICER), https://map.geoengineeringmonitor.org/other/fund-for-innovative-climate-and-energy-research-ficer/; ETC Group and Heinrich Böll Foundation (2020) Geoengineering Map: Harvard’s Solar GeoengineeringResearch Program, https://map.geoengineeringmonitor.org/other/harvard_s-solar-geoengineering-research-program/

4 Keith, et al. (2014) Field experiments on solar geoengineering: report of a workshop exploring a representativeresearch portfolio, in: Phil. Trans. R. Soc. A, Vol. 372(2031), https://doi.org/10.1098/rsta.2014.0175

5 ETC Group and Heinrich Böll Foundation (2020) Geoengineering Map: Stratospheric Controlled PerturbationExperiment (SCoPEx), https://map.geoengineeringmonitor.org/Solar-Radiation-Management/stratospheric-controlled-perturbation-experiment-scopex/


6 Pierrehumbert (2017) The trouble with geoengineers “hacking the planet”, in Bulletin of the Atomic Scientists,published June 23, 2017, https://thebulletin.org/2017/06/the-trouble-with-geoengineers-hacking-the-planet/

7 Zundel (2017) Trump Administration – A Geoengineering Administration?, ETC Group Briefing, March 28, 2017,www.etcgroup.org/content/trump-administration-geoengineering-administration

8 Associated Press (2012) Climate change fears overblown, says ExxonMobil boss, in: The Guardian, June 28, 2012,www.guardian.co.uk/environment/2012/jun/28/exxonmobil-climate-change-rex-tillerson; ETC Group (2017) Civilsociety: “Oil companies should not author IPCC report”, published: May 3, 2017,https://www.etcgroup.org/content/open-letter-ipcc-108-civil-society-organizations

9 Hone (2017) The geo-engineering taboo” in: EnergyPost, June 26, 2017, http://energypost.eu/the-geo-engineering-taboo/

10 Blackstock, et al. (2009) Climate Engineering Responses to Climate Emergencies, Novim,https://arxiv.org/ftp/arxiv/papers/0907/0907.5140.pdf

11 Fora.tv (2010) Geoengineering: Global Salvation or Ruin? , Audio podcast produced by Commonwealth Club ofCalifornia, https://www.commonwealthclub.org/events/archive/podcast/geo-engineering-global-salvation-or-ruin

12 Kravitz and MacMartin (2020); Robock, et al. (2015) 20 reasons why geoengineering may be a bad idea, in: Bulletin ofthe Atomic Scientists, Vol. 64(2):14 - 59, https://doi.org/10.1080/00963402.2008.11461140

13 Radford (2013) Geoengineering could case drought in Sahel, in: Climate Home News, April 2, 2013,http://www.climatechangenews.com/2013/04/02/geoengineering-could-cause-drought-in-sahel/

14 Jones, et al. (2017)15 Robock (2014), Stratospheric Aerosol Geoengineering, in: Issues in Environmental Science and Technology, Vol. 38,

http://climate.envsci.rutgers.edu/pdf/RobockStratAerosolGeo.pdf16 Heckendorn, et al. (2009) The impact of geoengineering aerosols on stratospheric temperature and ozone, in:

Environ. Res. Lett., Vol. 4(4), https://doi.org/10.1088/1748-9326/4/4/045108; Trisos, et al. (2018) Potentially dangerousconsequences for biodiversity of solar geoengineering implementation and termination, in Nature Ecology &Evolution, Vol 2, https://doi.org/10.1038/s41559-017-0431-0

17 Effiong and Neitzel (2016) Assessing the direct occupational and public health impacts of solar radiationmanagement with stratospheric aerosols, in: Environ. Health, Vol. 15 (7), https://doi.org/10.1186/s12940-016-0089-0

18 Fleming (2010) Fixing the Sky: The Checkered History of Weather and Climate Control, Columbia University Press,New York, ISBN 9780231144131; Stephens and Surprise (2019); Heyen, et al. (2019) Strategic implications of counter-geoengineering: Clash or cooperation?, in Journal of Environmental Economics and Management, Vol 95,https://doi.org/10.1016/j.jeem.2019.03.005

19 ETC Group (2010) Geopiracy: The Case Against Geoengineering, Communiqué 103,http://etcgroup.org/content/geopiracy-case-against-geoengineering; Robock (2014)

20 ETC Group and Heinrich Böll Foundation (2020) Geoengineering Map: Field experiment in Russia,https://map.geoengineeringmonitor.org/Solar-Radiation-Management/field-experiment-in-russia/

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Stratospheric Aerosol Injection (SAI)