Columbia Climate School researchers warn that proposals to inject aerosols into the stratosphere to reflect sunlight carry major uncertainties and risks. Climate models often idealize particle types, sizes and injection patterns, obscuring real‑world limits such as material scarcity and particle clumping. Sulfates, the most commonly suggested particles, could cause acid deposition and ecological harm, while engineered alternatives face practical and supply challenges. The authors stress that SAI is not a substitute for cutting emissions and accelerating clean energy.
Scientists Urge Caution: Dim‑the‑Sun Geoengineering Could Carry Major Risks
Columbia Climate School researchers warn that proposals to inject aerosols into the stratosphere to reflect sunlight carry major uncertainties and risks. Climate models often idealize particle types, sizes and injection patterns, obscuring real‑world limits such as material scarcity and particle clumping. Sulfates, the most commonly suggested particles, could cause acid deposition and ecological harm, while engineered alternatives face practical and supply challenges. The authors stress that SAI is not a substitute for cutting emissions and accelerating clean energy.
17:51, 02.11.2025Environment
Scientists Urge Caution Over Plans to Dim the Sun to Cool the Planet
As policymakers and researchers explore last‑resort ways to slow global warming, proposals to inject aerosol particles into the stratosphere — a form of solar geoengineering called stratospheric aerosol injection (SAI) — have drawn renewed attention. The idea is to mimic the cooling effect seen after large volcanic eruptions by scattering sunlight back to space. But Columbia Climate School researchers warn that the approach carries wide‑ranging uncertainties and potential harms that are poorly understood.
Models vs. reality. Laboratory and climate model simulations often assume ideal particle types, sizes and perfectly controlled injection patterns. As Columbia aerosol scientist Faye McNeill notes, those assumptions produce neat results in models but may hide substantial uncertainty when applied to the real world. “Researchers model the perfect particles that are the perfect size,” she said, “and in the simulation they put exactly how much of them they want, where they want them. But when you start to consider where we actually are, compared to that idealized situation, it reveals a lot of the uncertainty in those predictions.”
“There are a range of things that might happen if you try to do this,” McNeill added. “We’re arguing that the range of possible outcomes is a lot wider than anybody has appreciated until now.”
Complex environmental side effects. The Columbia team highlights plausible knock‑on effects: injecting particles near the poles could influence tropical monsoon systems, while tropical injections might alter the jet stream. Sulfates — the most commonly proposed material because they resemble volcanic aerosols — could increase acid deposition, harm soils, and affect ecosystems in ways climate models may not fully capture.
Alternatives and practical limits. Some researchers and startups are investigating engineered particles such as calcium carbonate or even diamond‑like materials as lower‑risk reflectors. Politico recently reported that a geoengineering startup raised $60 million to develop a new reflective particle. But coauthor Miranda Hack warns that many proposed materials are scarce or expensive to produce at the scale that would be required, and particles tend to coagulate (clump), which would reduce their reflectivity and shorten their atmospheric lifetime.
Risk trade‑offs and governance. Columbia climate economist Gernot Wagner emphasizes that SAI is fundamentally about weighing trade‑offs: it may alter weather patterns, ecosystem health, and regional climates in uneven ways, and it is unlikely to perform as perfectly as most models assume. The researchers stress that SAI should not be viewed as a substitute for aggressive emissions reductions and rapid clean‑energy deployment.
Conclusion. While solar geoengineering could theoretically lower global temperatures, significant scientific, logistical and ethical questions remain. The Columbia team calls for far more research into real‑world effects, material availability, and robust international governance before any large‑scale deployment is considered.