Have any states passed legislation authorizing research or pilot tests of solar geoengineering despite bans on deployment?
Executive summary
No U.S. state has, in the reporting provided, enacted stand‑alone laws that expressly authorize outdoor solar geoengineering research or pilot deployments while simultaneously banning full deployment; instead, recent state action has largely moved toward prohibitions or restricted definitions, even as federal agencies and scientific bodies press for carefully governed research programs [1] [2] [3].
1. What the question really asks and why it matters
The user is asking whether subnational governments have created legal space specifically to permit field tests of solar geoengineering even where deployment is proscribed — a narrow question about legislative carve‑outs for research versus blanket bans — because such carve‑outs would change who can legally run outdoor experiments and under what oversight (this distinction between research and deployment is central to governance debates) [3] [4].
2. The state legislative landscape: bans, proposals, and where the text actually matters
Since early 2024 dozens of state bills mentioning solar geoengineering or “weather modification” have been introduced and more than 30 states considered measures, but enacted bans are limited — reporting counts three states with outright bans (Tennessee, Florida and Montana in various forms) and several others passing a single chamber or considering bills, while many proposals died in committee or remain pending [1] [5] [6]. Those state laws and proposals have mostly been framed as prohibitions on large‑scale interventions such as stratospheric aerosol injection or “solar radiation modification,” rather than as affirmative authorizations of trials; the tracking projects that map these bills emphasize status (introduced, died, passed chamber) because bill language and exceptions vary widely [7].
3. Narrow exceptions exist for legacy practices such as cloud seeding — not necessarily solar geoengineering research
Some state statutes and recent bills explicitly preserve or allow traditional weather‑modification activities like cloud seeding for water management while banning broader forms of geoengineering; Montana’s legislation, for example, bans certain interventions like stratospheric aerosol injection but permits cloud seeding under water‑management rules — a distinction that lawyers and scientists stress matters because cloud seeding is localized and short‑term whereas solar geoengineering aims for regional or global radiative effects [8] [4]. Those carve‑outs do not amount to explicit state authorization for controlled outdoor experiments of solar radiation management (SRM) designed to inform potential deployment.
4. Federal research momentum contrasts with state prohibitions
At the federal level, Congress directed the Office of Science and Technology Policy and agencies to develop a five‑year research plan on solar and rapid climate interventions, and the Biden administration’s 2023 report urged a federal research program to study risks and benefits — signaling that the U.S. executive branch and research agencies are moving toward structured, federally coordinated study rather than leaving outdoor testing to states [2] [9]. Influential scientific bodies, including the National Academies, have called for small, carefully overseen experiments with significant oversight, public engagement, and risk assessment — an approach that contrasts with the wave of state bills aiming to prohibit deployment [3].
5. Case studies, gray areas, and local pushback
Local controversies have already appeared: a proposed experiment near Alameda was blocked by the city council amid transparency concerns and reporting suggests it was tied to a sequence of private projects that drew municipal resistance — showing that even absent clear state authorization, local politics and permitting can halt field efforts [10]. Internationally, other governments (for example the UK) are funding outdoor SRM trials, underscoring why U.S. federal coordination matters if researchers are to avoid a patchwork of state bans and local opposition [11] [10].
6. Bottom line and limits of available reporting
Based on the sources reviewed, there is no clear example of a U.S. state passing legislation that affirmatively authorizes solar geoengineering research or pilot tests while also banning deployment; the dominant recent trend in state legislatures has been to propose or pass restrictions and bans, with limited, traditional exceptions like cloud seeding, and federal agencies and scientific bodies are the principal drivers of any formal research pathway [1] [8] [2] [3]. This assessment is limited to the reporting provided; where bill text differs or where very recent state actions post‑dating these sources exist, those specifics are not covered here [7].