Just decades ago, the idea of artificially cooling the planet to help fight climate change was viewed as science fiction. But as climate change impacts grow more severe, and become irreversible, the once-fringe topic of Solar Radiation Modification (SRM) is increasingly in vogue.<\/p>\n
SRM is now a commercial industry. In October, U.S.-Israeli startup Stardust announced<\/a> that it raised $60 million in financing to test a new way of fighting climate change: deploying specially-designed, proprietary particles high into the atmosphere, where \u2014 if all goes to plan \u2014\u00a0 solar-reflecting clouds will form.<\/p>\n Like many startups, Stardust wants regulatory certainty. In an interview, its CEO pledged<\/a> not to deploy the technology without approval from governments<\/a>. But SRM is one of the most complex emerging governance issues. Following the failure of this year\u2019s United Nations Climate Change Conference in Belem to meaningfully reduce the world\u2019s greenhouse gas emissions, we break down the current state of SRM governance discussions at different levels and what they mean for solar geoengineering in the startup phase. As the number of commercial actors in the largely unregulated arena of SRM grows, so do the security risks associated with this technology.<\/p>\n SRM as a (Partial) Climate Solution<\/p>\n Global average temperatures are increasing as greenhouse gases accumulate in the atmosphere, trapping a higher fraction of solar energy that would otherwise escape back into space. In principle, SRM could partially offset these temperature increases by creating more cloud cover, which reflects incoming solar radiation before it reaches the lower atmosphere and contributes to warming near the Earth\u2019s surface. Most SRM proposals<\/a> envision using aircraft to inject particles into the upper atmosphere, where they act as nuclei for cloud formation \u2014 essentially replicating the effect of a large volcanic eruption.<\/p>\n Few climate scientists believe that SRM is a complete or unproblematic solution to climate change. It would not prevent other climate change impacts like ocean acidification, and the effect of SRM will last only as long as humans keep injecting particles into the atmosphere. Additionally, SRM will likely have side effects, including reduced rainfall and damage to the ozone layer. Many climate activists, moreover, object to SRM because they fear it gives politicians an excuse<\/a> to avoid cutting emissions.<\/p>\n For these reasons, SRM has long been viewed as a fanciful rather than realistic solution to climate change. But it is quickly gaining credibility, for two reasons. First, there is a growing body of scientific evidence that Earth\u2019s systems are near<\/a> several climate \u201ctipping points\u201d that, once reached, will become impossible to reverse. Second, global climate governance has suffered a number of body blows \u2014 such as the United States\u2019 latest withdrawal from the Paris Agreement and the European Union\u2019s weakened climate targets \u2014 over the past year, making the prospect for international cooperation to stem the climate crisis increasingly fraught.<\/p>\n In this context, SRM has attracted attention from a growing array of serious organizations. In 2021, the Office of the Director of National Intelligence\u2019s Global Trends 2040 report warned <\/a>that demand for SRM is growing, despite inadequate understanding of its impacts. Harvard University has emerged<\/a> as a hub for SRM research, receiving several grants to study the subject. In the United Kingdom, the Nuffield Council on Bioethics is working<\/a> to understand the ethical considerations of SRM, and 60 scientists have also signed<\/a> an open letter calling for increased research into the topic. Despite this growing attention, there are few rules for who can conduct SRM, where, at what scale, and with what safeguards.<\/p>\n United States<\/p>\n SRM sits in a regulatory grey zone in the United States, with no singular<\/a> law regulating its deployment. The National Oceanic and Atmospheric Administration (NOAA) has limited authority over atmospheric experiments and the \u00adEnvironmental Protection Agency (EPA) regulates emissions, but there is no statute tailored to intentional solar-reflection interventions.<\/p>\n While the Biden administration had issued an initial research governance framework<\/a> emphasizing the importance of international cooperation on SRM in 2023, the Trump administration has not yet issued any policies explicitly relating to this technology. SRM is not necessarily at odds with this administration\u2019s \u201cEnergy Dominance\u201d agenda, which may create an opening to pursue additional policy action on the topic. Furthermore, the administration\u2019s deregulatory approach to energy and climate activities may create ground for private companies to undertake SRM research and development. On the other hand, some U.S. Republicans have called for a ban on weather modification<\/a>, which may extend to SRM.<\/p>\n SRM has also received attention from local decisionmakers in the United States. Last year, the City Council of Alameda, California, voted<\/a> to stop tests of a form of SRM that were planned for the area. At the state level, 34 states have proposed bans on solar geoengineering, with Tennessee, Louisiana, and Florida having successfully<\/a> passed bans. The lack of popular support for SRM in the United States has also complicated its development. A 2025 study<\/a> in Nature found that solar geoengineering research faces more opposition than support among politicians and the public. Despite this backlash, private investment in SRM startups is growing<\/a>, likely leading to a dynamic in which the private sector continues development and testing for SRM without any federal level regulation.<\/p>\n Europe\u00a0<\/p>\n The European Union, generally a leader on climate action, has taken a precautionary approach to SRM research and development. In 2023, the European Commission\u2019s Group of Chief Scientific Advisors released a scoping<\/a> paper finding that the E.U. does not see SRM as a solution to the climate crisis, with member States united in their skepticism of the technology. Indeed, German Chancellor Friedrich Merz has made clear his opposition <\/a>to SRM as a way to fight climate change, while the French Academy of Sciences has called for its outright ban<\/a>. However, it recommends further research into SRM, including governance issues.<\/p>\n Non-E.U. members, most notably the United Kingdom, have gone against this trend. For example, the country\u2019s Natural Environment Research Council said<\/a> it would invest more than $13 million over five years into SRM deployment through modelling and lab work. The Advanced Research and Invention Agency has similarly dedicated over $74 million to research<\/a> if climate cooling is proved feasible, scalable, safe, and governable.<\/p>\n Global South<\/p>\n Though still largely unclear, the views of major economies in the Global South, such as China and India, will likely be decisive in shaping the regulation of SRM. Some Indian researchers have expressed caution<\/a> in proceeding with SRM, finding that its use could reduce rainfall during the Indian monsoon. Meanwhile, Chinese professor and former U.N. Overshoot Commissioner Xue Lan wrote<\/a> that the international community \u201cmust proceed carefully\u201d by adopting a moratorium on SRM deployment. Other Chinese commentators have expressed similar caution<\/a>, urging that any moves toward SRM must take place in accord with multilateral agreements.<\/p>\n Other Global South countries have taken a more forceful stance against SRM. When Switzerland proposed<\/a> establishing an expert advisory panel on SRM at the 2024 U.N. Environmental Assembly, a group of African nations and other supported countries criticized<\/a> the move, resulting in the resolution\u2019s withdrawal.<\/p>\n No Global Cooperation but Global Risks<\/p>\n At the global level, international legal and regulatory provisions regarding SRM are few and far between. In 2010, the parties to the Convention on Biological Diversity adopted<\/a> a non-binding resolution urging countries to consider prohibiting SRM pending further research and greater risk assessment. However, the resolution\u2019s non-binding nature has meant it has had little effect in practice. Looking elsewhere, an amendment <\/a>to the London Convention \u2014 which regulates marine dumping and pollution \u2014 would manage several forms of marine geoengineering, but ratification at the national level remains minimal, and it does not directly pertain to SRM.<\/p>\n Perhaps the most applicable international agreement is the International Convention on Environmental Modification<\/a> (ENMOD), which aims to regulate and restrict artificial human modifications of the natural environment. However, ENMOD applies only to \u201chostile<\/a>\u201d environmental modifications that have\u00a0 \u201cwidespread, long-lasting or severe effects as the means of destruction, damage or injury to another State.\u201d But ENMOD has never <\/a>been enforced, with no violations against the treaty ever having been lodged. ENMOD raises the question if SRM would be considered \u201chostile.\u201d<\/p>\n Stardust\u2019s insistence that it will proceed only if and when permitted by international governance arrangements is encouraging. However, as interest in SRM develops, competitors may not feel so constrained by the lack of international regulation. This scenario could produce a significant security risk<\/a> if states feel that their interests are threatened by unregulated, private-sector SRM activity. This risk is accentuated by the fact that future private sector SRM interventions could conceivably be mounted from areas beyond national jurisdiction, such as the high seas, where they could fall outside of national government control.<\/p>\n