The focus of climate discussion is moving from prevention to adaptation and, more recently, intervention as the globe struggles with the rapidly intensifying effects of climate change. Solar Radiation Modification (SRM), a type of solar geoengineering that suggests modifying Earth’s radiation budget to cool the planet, is one of the most controversial theories gaining traction in scientific circles. The idea of purposefully reflecting some of the sun’s energy back into space to lower global temperatures is as audacious as it is divisive.
Solar radiation modification is not entirely new in it’s conception. It draws inspiration from nature itself. The 1991 eruption of Mount Pinatubo in the Philippines, for instance, spewed millions of tons of sulfur dioxide into the stratosphere, forming a reflective aerosol layer that temporarily cooled the Earth by about 0.5 degrees Celsius. Scientists took note. If a natural process could result in such a dramatic cooling effect, could it be replicated and controlled by humans?
Stratospheric aerosol injection, which involves spraying materials like calcium carbonate or sulfur dioxide into the upper atmosphere to reflect sunlight, is one of the suggested SRM techniques. Other ideas include installing reflective mirrors in space and marine cloud brightening, which aims to increase the reflectivity of clouds over oceans. However, despite the science’s potential to counteract global warming, there are still many unknowns.
Furthermore, a difficult question is brought up by the concept of solar geoengineering, who makes the final decision? SRM deployment cannot be contained within national boundaries. Both positive and negative effects would be felt all over the world. This gives rise to geopolitical worries regarding governance, consent, and accountability. Without a robust international regulatory framework, a unilateral move by a single state or coalition could spark international tension, or even conflict.
Public perception also poses a challenge. In many parts of the world, SRM is met with suspicion, often being conflated with “chemtrails” or dismissed as dangerous hubris. The moral hazard argument suggests that focusing on SRM could reduce the urgency to cut emissions, offering a technological escape hatch rather than addressing the root causes of climate change. Critics argue that this could delay hard but necessary transitions in energy, agriculture, and transportation sectors.
esearch is still being done in spite of the controversy. Aerosol behavior in the stratosphere is being tested by small-scale experiments, such as the now-canceled SCoPEx (Stratospheric Controlled Perturbation Experiment), which was designed by Harvard scientists. The experiment raised important issues regarding scientific transparency, equity, and the role of consent in environmental experimentation, but it was never carried out because of ethical and public opposition, particularly from Indigenous groups in Sweden.
Responses to SRM have been uneven in the Global South. On the one hand, in the event of heat waves, agricultural collapse, or sea level rise, vulnerable nations stand to lose the most from ongoing warming.
However, they still carry the scars of past environmental experiments that were carried out without consulting them. For example, the ability of SRM to affect rainfall may have an impact on food security in areas like South Asia or the Sahel, where millions of people rely on regular monsoons. Therefore, rather than imposing technocratic solutions from the Global North, scientists and policymakers from Africa, Latin America, and Asia have called for a more inclusive dialogue that prioritizes local knowledge and priorities.
While the technical capacity for large-scale SRM does not yet exist, discussions around governance have begun to take shape. Bodies like the Convention on Biological Diversity (CBD) have called for a moratorium on SRM experiments. Others, like the Carnegie Climate Governance Initiative (C2G), advocate for a global governance framework before any deployment is considered. The argument is not necessarily against research but for guardrails ethical guidelines, transparency, and oversight.
Some scientists maintain that research into SRM must continue precisely because of its risks. The climate system is already being disrupted; failing to explore all potential options, even risky ones, could be seen as a dereliction of scientific responsibility. In this view, understanding SRM better does not mean endorsing it means preparing for every scenario, including the desperate ones. After all, in a world where 1.5°C of warming is rapidly approaching and emissions trajectories remain bleak, extreme options may one day become the only options.
What remains unknown, however, is considerable. No one knows how long-term deployment of SRM would interact with other planetary systems, nor how easily it could be reversed. There’s also the risk of “termination shock” a rapid spike in temperatures if SRM were suddenly stopped. This could trigger even greater environmental and social chaos than the warming it aimed to prevent. And because SRM does nothing to reduce atmospheric carbon dioxide, it fails to address other climate change symptoms like ocean acidification, biodiversity loss, or glacier melt.
Still, the very existence of SRM on the scientific and political agenda reflects the gravity of the climate crisis. It is no longer a fringe idea but one being discussed in UN reports, academic journals, and diplomatic circles. Whether it becomes a tool for justice or a symbol of desperation will depend on how humanity chooses to proceed.
In the end, solar radiation modification forces us to confront a paradox. It offers a potentially powerful means to reduce global temperatures but at a cost we do not yet fully understand, and perhaps cannot control. As Earth’s climate continues to shift, the pressure to explore radical solutions will grow. The challenge, then, is not just scientific, but profoundly moral, what kind of future are we engineering, and who gets to decide?
