Climate Solution Methods
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ScoreMethodsReferences
57Stratospheric Aerosol Injection (SAI) of SO2 by aircraft

Aircraft designed to disseminate sulphur dioxide gas into the stratosphere, aerosols from which would cool the world by reflecting a portion of sunlight from it.
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Develop-
ment Status 		Net Cooling Status Net Carbon Status Feasib-
ility 		Effect-
iveness 		Scal-
ability 		Time-
liness 		Gating/ Reversi-
bility 		Risk Gover-
nance & Social Accept-
ance 		Cost SCORE, sum D:L
3 9 1 9 9 9 9 3 1 1 3 57
This resembles the commonly-used Technical Readiness Level (TRL) classification system, but has three levels, not nine. Moreover, as it will typically include the consideration of several technologies, concepts and information thought useful for the Method, these are rolled into a single, overall measure of technical readiness.
This provides an indication of what is the individual Method’s potential contribution to global cooling at its maximum feasible scale. Its typical measurement unit would be negative watts per square metre (-W/m2).
This roughly coincides with the number of gigatonnes of carbon (GtC/yr) that the Method could be expected to sequester at its maximum scale, from the atmosphere, for a period equal to or greater than a century. GtC for a fraction of a century are reduced by that fraction. For simplicity, the criterion omits consideration of other important greenhouse gases (such as methane) and airborne particulates. A red score indicates a value <1, yellow 1-5, green >5 GtC/yr.
This is a composite measure indicating how achievable is the negative Net Radiative Forcing (equals Global Cooling) that combines the effects of Solar Radiation Management (SRM), or Earthly albedo enhancement, and Thermal Radiation Management (TRM) measures designed to increase heat (long wave) radiation off-planet when the Method is deployed at maximum feasible scale. Where quantitative estimates or surrogates are unavailable, qualitative estimates are made.
This is the likely Cost-Effectiveness of the Method. When it can be quantified, it is an estimate of the current US dollar cost per negative watts per square metre ($/(-W/m2)) or the Net Negative Radiative Forcing of all the cooling effects of the Method, wherever they occur on the planet above the base of the marine mixed layer. Provisionally, Red might be >$10a, Yellow $1-10a, and Green <$1a/(-W/m2), where “a” is an appropriate factor changed to reflect the actual likely range of costs. If not readily quantified, then qualitative estimates or guesses are to be made.
Scalability has several different parameters or components, any of which may be or become limiting. One component of scalability is the proportion of the world’s surface or volume that can be used to deploy it. A second is whether there is/could be sufficient raw materials/chemicals, concentrations, available energy, temperature, pressure, space or habitat, and manufacturing capability to deploy it at optimum scale in a useful timeframe. A third is whether the species, diversity and biomass of them are, or could be made sufficient, and sufficiently capable, to carry out their part in the Method. This includes humanity, its robotic helpers, laws/regulations, agreements/conventions, finances, and politicosocioeconomic practices. A fourth is whether there is, or could be constructed, whatever is required in the way of software, AI/algorithms, datastores, supporting technologies, and communications necessary for optimal scalability. A fifth is a requirement for modicum of peace&security, health, civil order, and cooperation needed for the scalability to be achieved and maintained, together with limits to food, environmental and social stresses in key populations.
This relates to how quickly the Method could be researched, developed, deployed globally, and take substantial effect - noting that many Methods will typically have some effects, both positive and negative, that are delayed by years or longer. Initially, and for a crash or moonshot program (though with existential urgency, funding, and possibly widespread participation), a Green score might have a strongly, net beneficial effect by the deployed Method occurring in <5 years, Yellow in 5-25 years, and Red in >25 years. GATING/REVERSIBILITY: Gating is whether the Method can be tested at increasing scale, whilst learning by doing to address adverse effects or cost. Reversibility relates to whether, and how quickly, a trial can be stopped and/or its effects reversed. Reversibility might be scored thus. Major adverse effects cease or substantially decline within: Green <1 month, Yellow 1- 12 months, Red >1 year.
Gating is whether the Method can be tested at increasing scale, whilst learning by doing to address adverse effects or cost. Reversibility relates to whether, and how quickly, a trial can be stopped and/or its effects reversed. Reversibility might be scored thus. Major adverse effects cease or substantially decline within: Green <1 month, Yellow 1- 12 months, Red >1 year.
Risk is used in the Risk Management or risk impact assessment sense of being compared to what would be likely to happen without the intervention. It deals with probabilities and consequences of risk events if they are realised. It compares the products of the likelihood of the risk occurring within a given time (meaning perhaps millennia for climate risks) and its impact. As climate risk is now an existential one that is now happening, our interest lies in determining quickly which Methods have acceptable risks and ones which do not risk the social acceptance of most other interventions. Green means start gated testing urgently now, Yellow means seek ways to reduce likely adverse aspects, Red means research now, but do not deploy more widely unless equivalent Methods are insufficiently effective at cooling.
This refers to the likelihood that existing forms of governance can be enhanced to satisfy the bulk of the global community of the necessity to deploy the more prospective of the Methods, first at local, then national and then international levels. Extensive community engagement is likely to be required, following proof of concept, and explanations of its likely costs, opportunities and effects. Green = (eventually) potentially acceptable and with little downside, Yellow = has some modest downsides, most of which can be offset. Red = social acceptance is unlikely unless other, comparable Methods fail.
As the Effectiveness criterion refers to the developed and globally-scaled cost of direct cooling by the Method in question, this Cost refers more to the RD&D and capital costs of researching, then deploying it at different scales and in different variants, together with the costs of Measuring, Reporting and Verifying (MRV) the results of using the Method, probably by independent bodies. It also includes insurance and recompense costs and the likely cleanup costs afterwards, together with reductions for any revenues gained, including possible carbon and cooling credits, should they eventuate. Green = likely to be profitable, Yellow = requires modest subsidies for industry and NGO participation, Red = would require extensive and ongoing public subsidy. Source TBD.
A summation of the above scores, using Red = 1, Yellow = 3, and Green = 9. Total possible = 99.
Short DescriptionAircraft designed to disseminate sulphur dioxide gas into the stratosphere, aerosols from which would cool the world by reflecting a portion of sunlight from it.
DescriptionThe most-publicised variant of SAI intends high-flying aircraft to release sulphur dioxide gas (SO2) into the stratosphere that transforms into highly-reflective tiny droplets of sulphuric acid (H2SO4) that change the atmosphere's albedo, thereby cooling the planet. Longevity of the aerosol in the stratosphere is between months and years. Wherever released, the aerosol would tend to spread over, at least, the hemisphere of release, thereby partially destroying the protective layer of ozone there that shields plants and animals from harmful UV radiation, at the same time as whitening the skies and reducing the effectiveness of photovoltaic panels. As the acid was eventually rained out, it would also produce an appreciable level of acid rain. Teleconnection effects might also affect regional precipitation across most of the land, leading to mixed, but often net harmful effects, such as reducing or varying monsoon rains on which crops depend. A conceptual method of increasing the safety and dissemination effectiveness of an aircraft would be for it to carry solid sulphur, to warm it to melting point in flight, and then to inject liquid streams of it into a jet engine's afterburner, where it would oxidise.
Key FunctionsGlobal cooling
Innovation DependenciesCustomised, high-flying aircraft.
Quantification
Graphics:
TechnologyEffectsProjects
Stratospheric Aerosol Injection (SAI)
This involves injecting sulfate aerosols or other reflective particles into the stratosphere to reflect a portion of incoming sunlight, thereby reducing global temperatures.
Danger if stop
No monsoon rain
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Pending
Uses sulfur dioxide gas emitted from high-flying aircraft or balloons. May be improved by spraying liquid sulfur onto jet engine afterburners.
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Aircraft designed to disseminate sulphur dioxide gas into the stratosphere, aerosols from which would cool the world by reflecting a portion of sunlight from it.
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Develop-
ment Status 		Net Cooling Status Net Carbon Status Feasib-
ility 		Effect-
iveness 		Scal-
ability 		Time-
liness 		Gating/ Reversi-
bility 		Risk Gover-
nance & Social Accept-
ance 		Cost SCORE, sum D:L
3 9 1 9 9 9 9 3 1 1 3 57
This resembles the commonly-used Technical Readiness Level (TRL) classification system, but has three levels, not nine. Moreover, as it will typically include the consideration of several technologies, concepts and information thought useful for the Method, these are rolled into a single, overall measure of technical readiness.
This provides an indication of what is the individual Method’s potential contribution to global cooling at its maximum feasible scale. Its typical measurement unit would be negative watts per square metre (-W/m2).
This roughly coincides with the number of gigatonnes of carbon (GtC/yr) that the Method could be expected to sequester at its maximum scale, from the atmosphere, for a period equal to or greater than a century. GtC for a fraction of a century are reduced by that fraction. For simplicity, the criterion omits consideration of other important greenhouse gases (such as methane) and airborne particulates. A red score indicates a value <1, yellow 1-5, green >5 GtC/yr.
This is a composite measure indicating how achievable is the negative Net Radiative Forcing (equals Global Cooling) that combines the effects of Solar Radiation Management (SRM), or Earthly albedo enhancement, and Thermal Radiation Management (TRM) measures designed to increase heat (long wave) radiation off-planet when the Method is deployed at maximum feasible scale. Where quantitative estimates or surrogates are unavailable, qualitative estimates are made.
This is the likely Cost-Effectiveness of the Method. When it can be quantified, it is an estimate of the current US dollar cost per negative watts per square metre ($/(-W/m2)) or the Net Negative Radiative Forcing of all the cooling effects of the Method, wherever they occur on the planet above the base of the marine mixed layer. Provisionally, Red might be >$10a, Yellow $1-10a, and Green <$1a/(-W/m2), where “a” is an appropriate factor changed to reflect the actual likely range of costs. If not readily quantified, then qualitative estimates or guesses are to be made.
Scalability has several different parameters or components, any of which may be or become limiting. One component of scalability is the proportion of the world’s surface or volume that can be used to deploy it. A second is whether there is/could be sufficient raw materials/chemicals, concentrations, available energy, temperature, pressure, space or habitat, and manufacturing capability to deploy it at optimum scale in a useful timeframe. A third is whether the species, diversity and biomass of them are, or could be made sufficient, and sufficiently capable, to carry out their part in the Method. This includes humanity, its robotic helpers, laws/regulations, agreements/conventions, finances, and politicosocioeconomic practices. A fourth is whether there is, or could be constructed, whatever is required in the way of software, AI/algorithms, datastores, supporting technologies, and communications necessary for optimal scalability. A fifth is a requirement for modicum of peace&security, health, civil order, and cooperation needed for the scalability to be achieved and maintained, together with limits to food, environmental and social stresses in key populations.
This relates to how quickly the Method could be researched, developed, deployed globally, and take substantial effect - noting that many Methods will typically have some effects, both positive and negative, that are delayed by years or longer. Initially, and for a crash or moonshot program (though with existential urgency, funding, and possibly widespread participation), a Green score might have a strongly, net beneficial effect by the deployed Method occurring in <5 years, Yellow in 5-25 years, and Red in >25 years. GATING/REVERSIBILITY: Gating is whether the Method can be tested at increasing scale, whilst learning by doing to address adverse effects or cost. Reversibility relates to whether, and how quickly, a trial can be stopped and/or its effects reversed. Reversibility might be scored thus. Major adverse effects cease or substantially decline within: Green <1 month, Yellow 1- 12 months, Red >1 year.
Gating is whether the Method can be tested at increasing scale, whilst learning by doing to address adverse effects or cost. Reversibility relates to whether, and how quickly, a trial can be stopped and/or its effects reversed. Reversibility might be scored thus. Major adverse effects cease or substantially decline within: Green <1 month, Yellow 1- 12 months, Red >1 year.
Risk is used in the Risk Management or risk impact assessment sense of being compared to what would be likely to happen without the intervention. It deals with probabilities and consequences of risk events if they are realised. It compares the products of the likelihood of the risk occurring within a given time (meaning perhaps millennia for climate risks) and its impact. As climate risk is now an existential one that is now happening, our interest lies in determining quickly which Methods have acceptable risks and ones which do not risk the social acceptance of most other interventions. Green means start gated testing urgently now, Yellow means seek ways to reduce likely adverse aspects, Red means research now, but do not deploy more widely unless equivalent Methods are insufficiently effective at cooling.
This refers to the likelihood that existing forms of governance can be enhanced to satisfy the bulk of the global community of the necessity to deploy the more prospective of the Methods, first at local, then national and then international levels. Extensive community engagement is likely to be required, following proof of concept, and explanations of its likely costs, opportunities and effects. Green = (eventually) potentially acceptable and with little downside, Yellow = has some modest downsides, most of which can be offset. Red = social acceptance is unlikely unless other, comparable Methods fail.
As the Effectiveness criterion refers to the developed and globally-scaled cost of direct cooling by the Method in question, this Cost refers more to the RD&D and capital costs of researching, then deploying it at different scales and in different variants, together with the costs of Measuring, Reporting and Verifying (MRV) the results of using the Method, probably by independent bodies. It also includes insurance and recompense costs and the likely cleanup costs afterwards, together with reductions for any revenues gained, including possible carbon and cooling credits, should they eventuate. Green = likely to be profitable, Yellow = requires modest subsidies for industry and NGO participation, Red = would require extensive and ongoing public subsidy. Source TBD.
A summation of the above scores, using Red = 1, Yellow = 3, and Green = 9. Total possible = 99.