How do state-level bans on solar geoengineering interact with federal authority and international climate policy?
Executive summary
State-level bans on solar geoengineering have proliferated across the U.S., with more than 30 states introducing bills and a handful enacting or passing measures (for example Tennessee in 2024 and Florida in 2025), while federal law remains patchy and international governance is fragmented or contested (Congressional and EPA reporting notes no single federal statute or binding international framework governing solar geoengineering) [1] [2] [3] [4]. These dynamics create legal tension: states assert local police and environmental authority, the federal government retains delegated regulatory tools (e.g., WMRA reporting, Clean Air Act channels cited by analysts), and international law debates range from calls for a non‑use regime to arguments that existing treaties or customary international law could constrain large‑scale deployments [3] [5] [6].
1. State bans: a patchwork of prohibition and political signaling
Since 2024 dozens of state legislatures have proposed or considered bans on solar radiation modification and related weather‑modification activities; a small number have enacted laws—Tennessee in 2024 and Florida in 2025 among the most visible—and many other states have bills that differ in scope (some ban broad weather modification, others target only SRM or stratospheric aerosol injection) [2] [1] [7]. These laws often mix criminal penalties, reporting requirements for airports or aircraft, and restrictions on state agencies’ ability to fund or conduct research, signaling political opposition as much as creating enforceable technical barriers [8] [7] [1].
2. Federal authority: gaps, existing tools, and uncertain preemption
Congress has not enacted a single, comprehensive law specifically for solar geoengineering; instead, federal agencies possess a suite of potentially relevant but piecemeal authorities. The Weather Modification Reporting Act requires prior notification for weather modification activities and NOAA tracks reports under Part 908.3 of Title 15, and the EPA notes reporting and permitting pathways when activities may affect oceans or air quality [3]. Legal commentators and analysts point out that statutes like the Clean Air Act, NEPA, and other federal environmental laws could regulate projects the federal government funds or approves, but there is no clear preemption framework that automatically nullifies state bans—leading to a gray area where state and federal rules could collide [5] [3].
3. How conflicts could play out in U.S. courts
Legal questions center on whether state bans interfere with federal foreign‑policy or interstate commerce powers, or whether federal law occupies the field for activities with national reach. Scholarly work and CRS reporting emphasize that federal treaties and statutes are binding when Congress acts, but absent a single federal statute addressing SG, states retain latitude under traditional police powers to regulate health, safety, and property within their borders [4] [5]. If a federal agency later authorizes or funds outdoor experiments, that could trigger preemption litigation; conversely, states could rely on criminal or administrative enforcement to block in‑state activities unless overridden by federal action [4] [8].
4. International law and governance: contested norms, not yet a binding regime
Internationally, there is no single binding treaty exclusively governing solar geoengineering; multiple scholars and reports say existing multilateral instruments (CBD moratoriums, customary international law, no‑harm principles) may constrain or be interpreted to limit large‑scale deployment, while advocacy groups push for a formal non‑use agreement [4] [9] [6]. Debates split between those arguing that SG at scale would violate no‑harm obligations and those arguing governance can be negotiated or adapted—so global legal constraints remain unresolved and politically fraught [10] [11].
5. Practical implications: research, private actors, and cross‑border risks
Because federal regulation is incomplete and international rules are unsettled, private actors and small experiments have become focal points for controversy: EPA has flagged at least one start‑up (Make Sunsets) for reporting concerns, and analysts warn unilateral or private experiments could provoke domestic legal enforcement and international diplomatic fallout [3] [2]. Advocates for strict controls cite transboundary harm and attribution problems as central reasons to ban field experiments, while proponents of controlled research argue that governance should enable safe, transparent study to inform policy—two competing priorities that state bans leap into [5] [12] [13].
6. Where disagreement matters most and what to watch next
Key disagreements in the sources concern whether state bans are primarily substantive safeguards or political theater (Legal Planet and Science News stress the odd politics and limited federal appetite for new regulation) and whether international law already prohibits deployment (CIEL and some scholars assert strong prohibitions or moratoria while other academics argue binding rules are not yet established) [2] [14] [9] [10]. Watch for three developments that would clarify the landscape: [15] any new federal legislation or agency rulemaking specifically addressing SG, [16] major court challenges testing state‑vs‑federal authority, and [17] international diplomacy toward a non‑use or governance agreement [3] [4] [6].
Limitations: available sources map law and policy through mid‑2025 and commentary into 2025–2026; they do not provide a final judicial ruling on preemption or a single authoritative international treaty that resolves the tension, so concrete legal outcomes remain contingent on future federal action, litigation, or multilateral negotiation [3] [4].