SAI Research Roadmap

PHASEFoundational knowledgeWhat can existing evidence tell us, and where does it fall short?Time2–3 yrsCost~$30M–$75M

PHASEAerosol microphysicsDoes data from small outdoor experiments validate the processes in our models?Time4–8 yrsCost~$70M–$150MEst. uncertainty reduction (cooling efficacy)~25%

PHASEStratospheric distributionDo sulfate aerosols mix and distribute, globally, in the way our models predict?Time4–11 yrsCost~$270M–$1.14BEst. uncertainty reduction (cooling efficacy)~66%

PHASEMonitored coolingAs cooling begins, do observed effects match predictions? Are any unexpected effects emerging?TimeOngoingCostTBD

ImpactsClimate response, impacts, and risks

AerosolsMicrophysics, chemistry, transport

ObservationsMonitoring systems, instruments, and data

EngineeringAircraft R&D, materials handling, operations

Observations

New stratospheric observing systems

Building observational systems to monitor stratospheric processes during deployment

Est. direct cost: $50M–$600M
Est. duration

Why it’s on the roadmap

Stratospheric processes are the first indicator of whether stratospheric aerosol injection (SAI) will achieve its intended surface cooling effect. Without continuous, detailed observation of stratospheric properties during deployment, decision makers cannot reliably assess whether aerosols are behaving as expected or confidently adjust injection strategies if observations deviate from predictions. Robust observational systems capable of measuring key stratospheric variables with sufficient precision and spatiotemporal resolution are prerequisites for responsible SAI deployment. The specific requirements those systems must meet will be defined through earlier modeling work.

Scope of work

This activity involves developing, testing, deploying, and operating the observational systems identified during Phases 0 and 1 of the roadmap. These systems will monitor stratospheric aerosol properties — aerosol optical depth (AOD), vertically resolved aerosol spatial and particle size distributions, aerosol composition, and spatiotemporal variability — during SAI deployment. Furthermore, stratospheric temperature, water vapor, ozone, and the chlorine reservoir ClO will need to be measured to understand the aerosol impacts on local radiation and composition. The work includes selecting or designing appropriate instruments and platforms (satellites, high-altitude aircraft, balloons, or other systems), and building or procuring these systems. Rigorous testing and validation will follow development. Once validated, the systems will be deployed strategically to provide global or near-global coverage of stratospheric aerosol properties. Critically, observational systems must be operational and validated 3–5 years before an aerosol evolution and transport experiment, so that a baseline can be established and the experiment monitored with confidence. This activity covers developing and deploying the instruments; ongoing monitoring and analysis fall under a separate activity.

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