Why are some states introducing bans on stratospheric aerosol injection?

1. Why lawmakers say “not here”: acute environmental harms and unequal impacts

Legislative drafters point to peer-reviewed modeling and expert summaries showing that SAI could alter precipitation, worsen droughts in Africa and Asia, shift monsoons, and threaten food and water for billions, even while cooling global average temperatures; these asymmetric consequences form a core reason for bans ^[1]. Lawmakers and environmental lawyers highlight potential ozone depletion and human-health hazards from aerosols and their chemical precursors, arguing that national prohibitions are necessary to prevent actions at scales that would produce irreversible ecological damage and cross-border harm. Advocates for bans frame the issue not as scientific curiosity but as a governance problem: the distribution of harms is politically salient, and domestic prohibitions are a way to signal precaution while international rules remain incomplete ^{[1] [2]}.

2. Governance gaps: who gets to control the thermostat?

Policy analysts emphasize that SAI would require century-scale, continuous intervention to avoid rapid warming if stopped, creating a permanent liability and centralizing climate control in entities that operate the “thermostat” ^[2]. International frameworks referenced by commentators—such as the Convention on Biological Diversity moratoria and the London Convention/London Protocol—illustrate existing restrictions and a governance appetite for caution, but they do not provide clear, enforceable, democratic mechanisms to decide deployment, substances, or monitoring regimes. The governance vacuum fuels state-level bans as stopgaps: legislators prefer prohibiting domestic research or testing to cede less authority to potential unilateral deployments by other actors ^{[2] [4]}.

3. Security and geopolitics: the worry about weaponization and unilateral action

Security scholars and journalists warn that SAI poses geopolitical risks because a single state or coalition could unilaterally alter regional climates, gaining leverage or provoking conflict if weather patterns shift to the detriment of other countries ^{[1] [2]}. This potential for coercive use or strategic manipulation makes some policymakers view SAI less as a scientific option and more as a national-security concern. The fear of a small group exercising disproportionate control over global or regional climates pushes states to adopt bans to prevent domestically based research trajectories that could accelerate deployment capabilities or legitimize unilateral action.

4. U.S. state actions: precautionary laws, contested tradeoffs

As of 2025, at least 22 U.S. states introduced bills to ban geoengineering, with Tennessee adopting the first state ban in April 2024 and additional states such as Florida enacting prohibitions on actions intended to affect temperature, weather, or sunlight ^{[3] [5]}. Supporters say state bans are prudent given the absence of robust international oversight; critics caution that halting research forecloses the ability to understand risks and potential emergency uses. Observers note this tradeoff: bans reduce near‑term deployment risk but also constrain scientific learning that could inform safer governance, leaving a policy tension between precaution and knowledge generation ^[3].

5. The international context and the path forward: law, norms, and contested agendas

Internationally, civil‑society groups, academic consortia, and some treaty bodies advocate for restrictive frameworks or moratoria to prevent premature deployment while negotiating governance mechanisms ^{[1] [4]}. Proponents of research argue for transparent, internationally governed programs to assess risks; opponents emphasize the absence of accountable, equitable decision‑making and favor bans until such mechanisms exist. The debate is not purely technical: it encompasses values about who decides, how harms are weighed, and whether global environmental management should be constrained as a matter of justice and security. The competing agendas—researchers seeking knowledge, states seeking precaution, and activists seeking prohibition—explain why subnational bans have proliferated amid slow international progress ^{[2] [4]}.