Deliberately reflecting sunlight into space to cool the planet—solar radiation modification (SRM)—is now under serious exploration/investigation as a solution to the climate crisis. In theory, firing sulfur droplets into the stratosphere, spraying salty water into clouds, or scattering glass over polar ice could slow global warming. But as these experiments involve risks at a planetary scale, we should proceed with abundant caution, communication and transparency, regulated by globally agreed standards. Instead, we see ethical and legal boundaries being crossed by unregulated experiments.
Over the past decade, influential institutions—Harvard University, the University of Washington and a four-university partnership in the U.K. that includes the University of Oxford—have come close to conducting outdoor SRM experiments. But these initiatives ended up pausing their work following reconsideration of the scientific and political risks and pushback from local activists. Yet some groups involved in solar deflection experiments have recklessly opted to move their projects away from academic oversight.
Since 2017 a private initiative, initially called Ice911 Research and later the Arctic Ice Project, has scattered tiny glass spheres to reflect sunlight over 17,500 square meters (or three football fields) of Arctic ice, drawing protests from Alaska Native leaders. Full deployment would involve spheres over up to 100,000 square kilometers of the Arctic, an area the size of Kentucky. More recent experiments only exceed this disregard. In 2022, an independent researcher in the U.K. released sulfur dioxide from a high-altitude weather balloon into the stratosphere and named it SATAN (Stratospheric Aerosol Transport and Nucleation). Around the same time, Make Sunsets, a Silicon Valley-backed start-up, began launching similar balloons. This company now plans to sell “cooling credits” for such launches.
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The start-up’s response to the question “Is this legal?” is: “Yes, we've been in contact with multiple U.S. government agencies (FBI, FAA and NOAA). They are aware of our business and activities.” This non-answer uncovers the heart of the solar radiation modification problem. Here’s why: experiments that pose planetary risks violate international laws such as the 1985 Vienna Convention protecting upper atmosphere ozone, if those risks are not clearly assessed, communicated, and consulted on beforehand, which these startups and individuals have not done. This is true even in the absence of specific national regulation, which some wrongly believe gives them free rein.
Two significant scientific assessments published in 2023 underlined the hazards of such sunlight deflection ventures. The first, the One Atmosphere report of the U.N. Environment Programme (UNEP) found that “even as a temporary response option, large-scale SRM deployment is fraught with scientific uncertainties.” To address the evident “critical unresolved issues around equity, ethics and consent,” around SRM, it recommended a “robust, equitable and rigorous trans-disciplinary scientific review process” based on a precautionary approach.
The second, the World Meteorological Organization’s 2022 Scientific Assessment of Ozone Depletion, found that while injecting sulfur into the stratosphere “could reduce some of the impacts of global warming, it cannot restore past climatic conditions and would very likely cause unintended consequences, including changes in stratospheric ozone concentrations.” It also found that the certainty of damage to the ozone layer increases with more prolonged and more intense use of these methods. This finding sits uncomfortably with a finding from UNEP’s report: that SRM would need to be maintained for several decades to centuries to limit warming effectively and that abruptly stopping the intervention would lead to “rapid climate change that would increase risks for humans and ecosystems.” Therefore SRM poses a binary choice: short-term use could exacerbate global warming, whereas long-term deployment risks significantly damaging the ozone layer.
Credit: Lucy Reading-Ikkanda
These findings have legal implications. Solar radiation modification cannot be contained to the air above the country from where it is deployed. The duty to avoid cross-border harm is enshrined in multiple international environmental agreements. These agreements support the precautionary regulation of activities threatening large-scale modification of planetary systems such as oceans, the ozone layer, climate and biodiversity, even if their precise effect is not fully understood.
Consider the London Convention on the Prevention of Marine Pollution. In 2008 its parties agreed to prohibit a type of geoengineering known as ocean fertilization, except for research that undertakes a risk assessment, develops a risk management plan, and commits to sharing and publicizing findings through peer review. In 2010, because of its inherent high risks and potential impacts on biodiversity and people, parties to the Convention on Biological Diversity (CBD) agreed to prohibit geoengineering in general, with a narrow exception for research.
Because the U.S. is not a party to the CBD, and the London Convention only regulates ocean fertilization, there is a perception that spraying sulfur into the stratosphere from U.S. territory is not covered by international law. This is wrong. The U.S. and all other countries are a party to the Vienna Convention on Protection of the Ozone Layer and the Montreal Protocol. A key feature of the convention is that it obligates countries to cooperate on research on “substances, practices, processes and activities that may affect the ozone layer, and their cumulative effects”. Therefore, unregulated unilateral experiments that affect the ozone layer, such as SRM, violate this obligation.
Unfortunately, as the Vienna Convention currently lacks a structured research assessment process similar to the London Convention, its provisions have been ignored. Therefore, rebooting the Vienna Convention to govern SRM research is essential. Such regulatory processes are also critical at the national level because government support for SRM research is growing. While the scale of experiments is currently small, they will likely grow more ambitious. Without a robust regulatory process, the fuzzy line between researching and carrying out geoengineering will be crossed without warning. The potential impacts—such as degradation of the ozone layer and sudden shifts in global climate—will affect populations around the world, most of whom have had no say in whether such experiments should proceed.
This is especially important because many countries already use technologies to modify local weather. China plans to bring about 5.5 million square kilometers of its territory under a weather modification program by 2025. A team in Australia is injecting saltwater into clouds over the Great Barrier Reef to prevent its disappearance. The leap from weather modification to SRM is close. Therefore, the world must start putting in place a multilateral framework to govern geoengineering like SRM. The starting point of this is to regulate outdoor experimentation.
Recent years have seen record deployments in solar and wind power—demonstrated, cost-effective solutions that, unlike SRM, are accessible to developing countries. We desperately need massive investments in carbon-free energy to decarbonize the global economy. This is the moral hazard in solutions like SRM: they draw attention and resources away from what should be a singular focus in a critical decade: decarbonization.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.