As global temperatures shatter records, scientists are debating a radical Plan B: reflecting sunlight back into space. But this high-stakes climate intervention could come with catastrophic risks.
The year 2024 marked a sobering milestone: for the first time, average global warming exceeded the 1.5°C threshold that climate scientists have warned against for decades1 . With the effects of climate change intensifying, interest in once-fringe technological solutions is rapidly heating up. Among the most controversial is solar geoengineering—a set of proposed techniques to deliberately cool the planet by reflecting sunlight back into space5 .
Proponents argue it could provide a crucial emergency brake on global warming. Critics warn it could create a dangerous "moral hazard"—an excuse to delay emissions reductions—while potentially disrupting weather patterns, undermining international security, and locking humanity into centuries of planetary-scale intervention1 7 .
Solar geoengineering, formally called solar radiation management (SRM), encompasses several proposed approaches to cool the Earth by reducing the amount of solar radiation absorbed by the planet5 . Unlike methods that address the root cause of climate change by removing carbon dioxide from the atmosphere, SRM attempts to temporarily counteract the symptoms—specifically, the heat trapped by greenhouse gases.
The risks associated with solar geoengineering extend far beyond laboratory uncertainties, creating a complex web of environmental, geopolitical, and ethical dilemmas1 .
SAI could reduce tropical rainfall by 5-7% annually, threatening crops and rainforests
Catastrophic rapid warming if geoengineering is suddenly stopped1
| Region | Potential Impact | Cause |
|---|---|---|
| Tropics | Reduced rainfall, threatening crops and rainforests | Altered atmospheric circulation |
| Sahel, North Africa | Could induce drought in East Africa while relieving it elsewhere | Shifted precipitation patterns |
| Global | Shift in malaria risk from East African highlands to lowlands | Changed temperature and rainfall |
To move from computer models to real-world understanding, scientists have proposed small-scale field experiments. One of the most prominent was the Stratospheric Controlled Perturbation Experiment (SCoPEx), led by researchers from Harvard University.
A high-altitude, self-propelled balloon would be launched into the stratosphere.
The balloon would release a very small amount of material—initially planned to be less than 2 kilograms of calcium carbonate or sulfate particles.
The balloon would then maneuver back through the perturbed air mass to measure particle dispersion and atmospheric interactions.
| Tool or Material | Function in Research | Notes |
|---|---|---|
| Climate Models | Computer simulations to predict efficacy and risks2 | Primary tool for current research |
| Sulfur Dioxide (SO₂) | Primary aerosol for SAI; reflects sunlight | Mimics volcanic emissions; ozone concerns |
| Calcium Carbonate | Alternative aerosol for SAI | Potentially less damaging to ozone |
| Sea Salt Particles | Core material for Marine Cloud Brightening | Makes marine clouds more reflective |
| High-Altitude Balloons & Aircraft | Delivery systems for experiments | Current aircraft insufficient for large-scale deployment |
Solar geoengineering presents humanity with a formidable dilemma. On one hand, research reveals its potential to rapidly reduce global temperatures, buying time for emissions reductions and potentially averting worst-case climate scenarios. On the other, the same research illuminates a path fraught with catastrophic and uncertain risks—from regional climate disruptions and termination shock to geopolitical instability and the undermining of global climate action1 7 .
The debate is no longer about whether we can physically alter the stratosphere or brighten clouds; the science suggests we can. The fundamental questions are now about risk management, global justice, and collective decision-making.