By Mary Church, Geoengineering Campaign Manager
Published May 26, 2026
As well-funded actors push for normalization and private companies seek to commercialize highly speculative and controversial solar geoengineering technologies, three recent developments illustrate the growing urgency to advance restrictive governance frameworks.
Solar geoengineering — technologies designed to reflect or dim sunlight and artificially cool Earth — is inherently unpredictable. Testing its intended and unintended impacts cannot be done without prolonged, large-scale implementation, which would effectively turn the Earth into a risky laboratory. Decades of research on the risks of these extreme technologies have led hundreds of experts to conclude that solar geoengineering development and use should be prevented, and a growing number of governments agree.
European Union Council Calls for Reinforcement of Restrictions on Solar Radiation Modification
On April 21, the Council of the European Union (EU) published its conclusions on EU energy and climate diplomacy, in which it took a cautious stance on solar geoengineering. Notably, the Council expressed a concern that large-scale climate interventions — and solar radiation modification (SRM) in particular — “pose significant risks to the climate, the environment, security, and geopolitics.” The Council is calling for full application of the precautionary principle, close monitoring of initiatives, and a moratorium on deployment of SRM technologies, “in line with and reinforcing” the existing moratorium on geoengineering activities under the Convention on Biological Diversity (CBD).
The Council’s emphasis on risk and its reaffirmation of the precautionary principle are welcome developments. However, with growing political momentum for a Solar Geoengineering Non-Use Agreement that would permanently ban these technologies — most notably a series of decisions taken by African Ministers and growing support among Pacific Small Island States — the European Union must now align its policies with non-use and permanently put these extreme and dangerous interventions off limits.
UNEP Working Paper: Science Does Not Support SRM as a Climate Solution
On May 12, the United Nations Environment Programme (UNEP) published a working paper concluding that scientific evidence does not support SRM as a viable climate solution. The paper summarizes the current state of the science — highlighting the limits of modeling, the highly uncertain and speculative nature of projected scenarios, and the fundamental constraints on what small-scale outdoor experiments can actually reveal. It also draws a sharp contrast between idealized scenarios and the far messier realities of real-world deployment.
However, the paper falls short of following the evidence it lays out to its logical conclusion. Rather than underscoring precaution, UNEP controversially calls for more research — a position that risks normalizing and legitimizing SRM and encouraging further technological development.
The publication of UNEP’s working paper follows the presentation and subsequent withdrawal of two contentious United Nations Environmental Assembly (UNEA) resolutions on geoengineering, as well as a number of controversial activities on SRM under UNEP’s mandate to keep the environment under review. For example, UNEP’s 2023 One Atmosphere Report controversially recommended developing a framework for open-air experiments and potentially large-scale deployments. Subsequent workshops, issue notes, and summary reports have similarly promoted further research and experimentation while sidelining precaution and the existing constraints of international law.
Perhaps most troublingly, UNEP’s new working paper characterizes some of those calling for restrictive governance as wishing to “silence discourse.” This is a highly problematic and misleading representation. The call for a Non-Use Agreement is grounded in more than two decades of robust, peer-reviewed scientific research and structured debate on the profound climate and global governance issues, which conclude that solar geoengineering is untestable, uncontrollable, and ungovernable.
It’s time for UNEP to take its own scientific findings seriously and follow them to their logical conclusions.
Stardust Solutions Backtracks on Spring 2026 Outdoor Experiments
The emergence of US-Israeli startup Stardust Solutions in 2023 presented the first serious move towards the commercialization of solar geoengineering technologies. Stardust Solutions made headlines in autumn 2025 when its ambition to be global deployment-ready within a decade, and its US$75 million investment secured in pursuit of that goal, were revealed. This month, however, the company backtracked on plans to conduct highly controversial outdoor solar geoengineering experiments as early as spring 2026. In a recent New York Times interview, chief executive Yanai Yedbab said the company no longer intends to proceed on that timescale and would conduct outdoor trials only “in collaboration with a government that would set ground rules and guardrails.”
In the interview, the company also disclosed details of the particle it has developed for stratospheric injection — intended to reflect incoming sunlight and reduce surface temperatures — and has published a series of new papers on its website, none of which have yet been peer-reviewed, in an apparent move to inspire confidence in its activities.
The problem is that more research — whether conducted by private actors or through publicly funded projects — cannot provide the full information needed about intended or unintended impacts on the climate and their wider consequences. Nor can research resolve the broader, inherent social and geopolitical risks these technologies entail. Instead, research and experiments risk normalizing highly controversial theories and accelerating technological development and political lock-in, creating a dangerous slippery slope toward large-scale deployment. Likewise, calls for a moratorium on deployment while advancing outdoor experiments — whether private or government-funded — are a risky Trojan Horse.
Furthermore, the current international governance framework already effectively prohibits not only deployment but also experiments — under a longstanding and repeatedly reaffirmed de facto moratorium at the CBD. The International Court of Justice’s landmark 2025 Advisory Opinion (AO) underscores that states must prevent foreseeable harm, uphold precaution, and regulate private actors. The AO — affirmed by an overwhelming majority of States in a recent UNGA resolution — clarifies that where proven measures to tackle the climate crisis are available, States must use them, and when there are threats that new technologies could cause serious and irreversible harm to the environment, precaution counsels against their use.
Moves towards the commercialization of solar geoengineering are extremely concerning and should cause governments to sit up and act. Likewise, the UK Government’s channeling of £57 million into solar geoengineering via its controversial ARIA research agency — the first public funding openly directed towards outdoor SRM experiments — should also prompt other governments to reinforce the existing restrictive governance regime and avoid a treacherous and costly “arms” race.
Far from being a viable climate solution, solar geoengineering would break the climate in new and different ways. Deployment would unleash new harms at a planetary scale, impacting those most vulnerable to the climate crisis hardest. Solar geoengineering, therefore, belongs in a category with nuclear weapons, human cloning, and chemical weapons — technologies for which development must be prevented, and use must be banned.