Which countries or organizations are researching or testing stratospheric aerosol techniques?
Executive summary
A discrete but growing ecosystem of universities, government labs and a few national research programmes are researching stratospheric aerosol injection (SAI) using modeling, lab studies and limited outdoor experiments; major national capacity to deploy SAI at scale is concentrated in a handful of wealthy states, most prominently the United States and China [1] [2] [3]. Public-facing experiments have so far been small and contested—some balloon-based releases have been reported, while many researchers and advocacy groups continue to call for strict limits and governance before any large outdoor tests [4] [5].
1. Who is doing the modelling and lab science: U.S. national labs, universities and international research consortia
Leading institutional players in SAI research are university groups and national research centers that focus on atmospheric modeling, delivery technologies and impacts; for example, an international team led by NSF’s National Center for Atmospheric Research has published recommended criteria to evaluate proposals to inject sulfur dioxide and has steered multi-disciplinary assessments [1], and multiple academic reviews and modelling projects continue to drive the field [6] [7].
2. The United Kingdom’s visible programme: modelling funding and small-scale studies
The UK government has funded modelling and environmental-response projects under UK Research and Innovation that explicitly study solar radiation modification and SAI impacts, and the NERC programme announced projects beginning in 2025 that will model SAI scenarios while emphasising that the UK has no plans to deploy SRM [8]; civil-society trackers and press reports also flagged UK researchers conducting at least small open-air balloon experiments aimed at understanding aerosol transport and nucleation (the SATAN launches), which attracted controversy for their public-relations framing as normalizing outdoor trials [4].
3. Who might be able to deploy at scale: geopolitical capacity concentrated in a few states
Analyses of deployment capability argue that while many countries can research SAI, only a very small number—most notably the United States and China—have the logistical, industrial and aerial capacity to carry out a sustained, planetary-scale SAI deployment unilaterally, with Harvard-related work explicitly naming those states as the most plausible actors for a large “PLUS” deployment scenario (Planetary, Large-scale, Uninterrupted, and Speedy) [2] [3] [9].
4. Other national and regional research activity: Europe and multilateral modelling efforts
Beyond the U.S., China and the UK, research activity includes European university consortia, independent research groups and NGO trackers that publish syntheses and critiques; organisations such as Geoengineering Monitor catalogue experiments and campaigns, while the scientific literature and policy reviews show multiple modelling centres in Europe and elsewhere contributing scenarios, aerosol chemistry studies and regional impact assessments [4] [10] [6].
5. Civil-society, ethical and governance actors shaping the research landscape
A broad set of actors outside the physical sciences—ethics centres, Indigenous and environmental groups, and policy institutes—have influenced what research proceeds and how, arguing that governance, justice and the “moral hazard” of diverting attention from emissions cuts require strict limits on field tests; some reviews state that as of early recent years there were few or no large field tests because of pushback, even as small-scale experiments and expanded modelling continue [5] [4].
6. What is actually being tested versus modelled: small balloons, aircraft concepts and lab work
Most concrete activity to date consists of modelling studies, lab measurements of aerosol microphysics and a handful of limited outdoor trials such as balloon-borne releases to study particle formation and transport; proposals for delivery platforms (custom high-altitude aircraft, lofting concepts) are well-developed on paper and in engineering studies, but full-scale, climate-altering deployments remain hypothetical and constrained by governance debates [11] [8] [10].
7. The contested public narrative and competing agendas
Reporting and advocacy often frame SAI either as an urgently needed stopgap or as an ethically fraught techno-fix; pro-research voices (some academic programmes and national labs) argue for targeted experiments to reduce uncertainty, while critics and many civil-society groups warn that small tests can be used to normalize deployment and that impacts—especially on precipitation, ozone and regional climate—remain uncertain [1] [4] [12].