What are the legal limits on private solar geoengineering experiments in the United States?
Executive summary
Private solar geoengineering experiments in the United States operate in a fragmented legal gray zone: no single federal statute expressly authorizes or comprehensively regulates outdoor SRM testing, but a patchwork of existing laws and agency authorities—most notably NOAA reporting rules and pollution statutes enforced by EPA—can apply depending on methods, location, and materials used [1] [2] [3]. States have begun to act independently with bans and restrictions, and private actors have already tested or attempted tests, exposing gaps in transparency, permitting, and enforcement that critics and some policymakers find alarming [4] [5] [6].
1. Federal landscape: no single governing statute, only relevant authorities
Congress has not enacted a law that exclusively governs solar geoengineering research or deployment, leaving federal governance to a mix of existing statutes and agency programs rather than a tailored regulatory regime [1] [2]. Federal research is largely observational and laboratory-focused, and the U.S. government says it is not conducting outdoor testing of SRM, although agencies are studying the issue and the need for new authorities is under consideration [2] [5].
2. Existing federal laws that can bite: reporting, pollution, and marine permits
A number of existing laws can constrain private experiments: the Weather Modification Reporting Act requires non‑federal actors to notify NOAA before activities that modify solar radiation or clouds, and NOAA tracks such reports [2] [3]. EPA authorities under the Clean Air Act or Title VI provisions could become relevant if released substances (e.g., sulfur compounds) harm air quality or ozone, and the Marine Protection, Research and Sanctuaries Act may require permits where materials are disposed into ocean waters or sea ice [2] [1].
3. Agency roles and practical permitting requirements
NOAA’s current rule framework stemming from 1970s law requires reporting but does not provide a robust permit-and-review regime for SRM, prompting petitions to tighten rules and clarify their application to modern private SRM activities [3] [7]. EPA has publicly stated that the federal government is not conducting outdoor testing and has identified potential applicability of existing environmental statutes, while noting that decisions remain about whether new congressional authority or a designated lead agency are needed [2] [5].
4. State-level patchwork and bans changing the calculus for private actors
Several states have moved ahead with statutory restrictions or outright bans on geoengineering activities within their jurisdictions—examples include Florida’s 2025 Senate Bill 56 and Montana’s Senate Bill 473—creating a mosaic where legality depends on state lines as well as federal compliance [4] [8]. Local governments have also taken action: Alameda, California canceled a planned outdoor experiment amid controversy, showing how sub-federal politics can block private tests even where federal law is vague [6].
5. Private actors, opaque practices, and enforcement gaps
Private companies and startups have attempted or carried out experiments—most prominently firms like Make Sunsets—that have launched aerosols or weather balloons, illustrating how entrepreneurial actors can move before comprehensive rules are in place; NOAA and EPA have reported awareness of a small number of private releases [5] [3] [6]. Critics argue reporting requirements are thin—a one‑page notice in some interpretations—and that current rules do not demand the level of transparency or environmental assessment needed to evaluate risks [9] [7].
6. Competing policy pressures, governance proposals, and implicit agendas
Scholars and advocacy groups are split between calls for expanded research under strict oversight and demands for non‑use or moratoria; over 500 academics have backed international non‑use proposals, while some U.S. policy actors and private funders press for permissive research pathways, reflecting competing agendas between climate risk mitigation advocates, environmental justice critics, and venture-funded startups [10] [11] [12]. National security and geopolitical concerns—worry that unregulated private SRM could spark international disputes—add another pressure point pushing for clearer governance [8].
7. Bottom line: constrained but inconsistent limits, with enforcement driven by where and how tests are done
Legally, private SRM experiments in the U.S. are not categorically banned at the federal level but are constrained by a web of reporting rules, environmental and marine statutes, and state prohibitions; gaps remain in permit rigor, transparency requirements, and a single enforcement authority, which means legality often turns on the experiment’s scale, materials, and jurisdictional footprint [1] [2] [4]. Absent new federal legislation or consolidated agency authority, private actors face a risky regulatory landscape where some activities may proceed under existing reporting regimes while others run afoul of state bans, EPA oversight, or international backlash [3] [8] [6].