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

Impacts Observations

Securing continuity in climate monitoring

Maintaining continuity in monitoring capabilities for the stratospheric processes and climate effects of SAI

Est. direct cost: Not yet scoped
Duration

Why it’s on the roadmap

Understanding how stratospheric aerosol injection (SAI) affects Earth's climate depends on continuous, uninterrupted observational records spanning years or decades. Satellites and other monitoring systems have finite operational lifespans, and gaps — even brief ones lasting months or a year — create discontinuities that undermine researchers' ability to detect trends, validate model predictions, and separate natural climate variability from SAI-induced changes.

Under current schedules, several important monitoring systems will reach the end of their operational lives before replacements are operational. This problem is particularly stark in the stratosphere (Salawitch et al., 2025), but monitoring capabilities for other parts of the Earth system are also at risk (e.g., ocean observing networks; Witze, 2026). These gaps could obscure information needed to assess whether SAI is producing the effects that modeling, theory, and experiments predict, and to detect unexpected consequences.

Rather than developing entirely new observational systems, this activity ensures that resources are available to bridge gaps in existing monitoring infrastructure — for both stratospheric processes and surface climate effects — through temporary supplementary measurements, such as aircraft campaigns or enhanced balloon launches. The continuous records it preserves are the inputs to the sustained monitoring activities for stratospheric processes and climate effects.

Scope of work

This activity conducts periodic assessments every few years over the period before and during deployment, to identify potential disruptions to the monitoring systems critical for evaluating SAI's effects, across both stratospheric processes and surface climate. For any gaps identified, researchers will develop strategies to maintain continuous data streams during instrument transitions and to mitigate the effects of reduced capabilities where possible. The work involves assessing the end-of-life dates and replacement launch schedules of current monitoring systems, identifying periods of data discontinuity, and designing and ultimately deploying cost-effective supplementary monitoring — such as targeted aircraft flights, enhanced balloon profiling networks, or other temporary systems — to bridge these gaps.

This activity assumes existing instruments cannot always be saved; its role is to predict gaps in the record and provide temporary fixes that smooth transitions. It is a coordination and gap-filling effort rather than new instrument development; building large-scale observing systems or permanent replacements for current systems is factored in elsewhere. The scope extends throughout Phase 1, Phase 2, and Phase 3, as maintaining observational continuity is an ongoing requirement before and throughout any deployment.

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