The climate emergency and the slow pace of reducing emissions have brought solar radiation modification (SRM) back into the international debate. SRM involves a range of interventions designed to reflect a portion of incoming solar radiation and temporarily cool the planet. These interventions encompass a range of technologies, including stratospheric aerosol injection, marine cloud brightening, cirrus cloud modification and orbital reflection systems.
Although these proposals have been around for decades, they have received limited attention from the scientific community for a long time. None have been deployed on a large scale, and their effectiveness is almost entirely assessed using climate models, which have significant uncertainties regarding regional effects and ecological and social impacts. Models suggest that SRM could rapidly reduce the global mean temperature, in line with the transient cooling observed after major volcanic eruptions, such as that of Mount Pinatubo in 1991. However, the same interventions could also alter precipitation patterns and the hydrological cycle unevenly, with potentially persistent effects that are difficult to attribute at regional scales.
Beyond physical uncertainties, SRM generally introduces additional social and political risks. From a geopolitical perspective, the relatively low cost of some of these measures, coupled with their potentially global impact, makes unilateral action by one or a few actors a plausible prospect in the absence of specific international rules. This could lead to diplomatic tensions, disputes over the attribution of climate-related damage or preventative action by other states.
There are examples of how even actions with no climatic impact can trigger immediate political reactions. In 2023, a US-based private company carried out a symbolic release of sulphur dioxide in Baja California, Mexico. Shortly afterwards, the Mexican government announced regulations to prohibit such activities. The absence of governance itself is considered a risk, as it highlights institutional shortcomings, limited participation and a lack of political commitment to addressing complex, highly uncertain problems that require technological innovation and profound social change.
To date, rather than moving towards the deployment of SRM, the dominant institutional response has been to seek to contain it through principles, guidelines, and non-binding control mechanisms that are largely national in scope and have limited international coordination. However, this approach coexists with a growing recognition that scientific research on SRM is unlikely to be halted globally, and that the absence of domestic analytical and evaluative capacities could undermine states' ability to anticipate developments, respond effectively and establish their position internationally.
From this point onwards, two possible scenarios emerge. In one scenario, increasing attention to SRM leads to preventive atmospheric governance based on greater international coordination, scientific transparency, strengthened public analytical capacities and an explicit consensus on not using or extremely restricting these technologies. In the other scenario, a lack of clear rules and geopolitical fragmentation would favour uncontrolled dynamics, with actors acting independently, increasing the risk of political escalation and conflicts over attribution of climate damage.
For now, the emerging trend is not the deployment of SRM, but rather the need for a collective decision on which boundaries must not be crossed. In a world characterised by inadequate mitigation efforts and geopolitical instability, anticipating how to govern, evaluate, or, where necessary, restrict these interventions could be as important for international stability as climate policies themselves.
For further information, see:
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