As the planet warms and political will to cut emissions lags, some scientists have shifted their attention toward the stratosphere as a last-ditch effort to cool planet Earth.
A controversial proposal known as stratospheric aerosol injection (SAI) involves dispersing reflective particles into the stratosphere to bounce sunlight back into space. In theory, it could mimic the cooling effect of major volcanic eruptions and rapidly offset global temperature rises.
However, according to a new study published in Scientific Reports, the real-world challenges of making such a scheme work safely and effectively may be far greater than most previous models have assumed.
Geoengineering proposals to mitigate the symptoms of climate change have received severe criticism from scientists in the past, who argue that such ideas serve only to distract from addressing the root causes of climate change. However, the Columbia researchers’ new paper suggests that the difficulties of such approaches are woefully underestimated.
The study by researchers from Columbia University finds that the technical, logistical, and economic constraints of stratospheric aerosol injection could dramatically narrow the window for what might be considered a “low-risk” or even feasible deployment strategy.
“We find that the risk and design space for SAI may be considerably constrained by factors like supply chains and governance,” researchers write. “Logistical and technical considerations, most significantly difficulties in dispersing solid aerosols at scale in the desired size range, and the radiative properties of potentially formed aggregates, introduce uncertainties in the outcomes of solid-based SAI strategies more so than sulfate.”
The concept of stratospheric aerosol injection dates back to 1974, when Soviet climatologist Mikhail Budyko first proposed that reflecting sunlight with aerosols in the upper atmosphere could counteract global warming.
The idea was reinforced by natural events, such as the massive volcanic eruption of Mount Pinatubo in 1991, which released vast quantities of sulfur dioxide (SO₂) into the stratosphere. As the gas oxidized into reflective sulfate aerosols, it temporarily cooled the planet by roughly 1 °F (0.5 °C) for nearly two years.
That volcanic cooling effect became the model for modern geoengineering research. Climate engineers later expanded on Budyko’s proposal, suggesting deliberate, sustained injections of reflective materials using high-altitude aircraft or balloons.
In theory, such a planetary sunshade could reduce global temperatures for about $10 billion per degree Celsius per year—a fraction of the projected economic costs of unchecked climate change.
However, the new Columbia-led study cautions that these optimistic projections ignore messy realities.
Researchers found that the success or failure of stratospheric aerosol injection depends as much on governance as on physics. Their simulations compared centralized, globally coordinated efforts to decentralized “wild west” scenarios where multiple countries, or even private actors, might attempt injections independently.
A coordinated approach, researchers argue, would allow precise control over where, when, and how aerosols are released. Injection latitude, altitude, and timing all strongly influence how long particles linger in the stratosphere and how evenly they distribute sunlight-reflecting haze. In theory, centralized management could optimize those parameters to minimize side effects such as disrupted rainfall patterns or ozone depletion.
However, in contrast, a fragmented, unregulated deployment could lead to uneven cooling, “shorter lifetimes and poorer radiative properties, increasing requisite burdens, lifetimes, and associated risks,” researchers note. That means more material would be required to achieve the same temperature reduction, escalating both cost and risk.
To reduce the well-known downsides of sulfate aerosols, especially their potential to damage the ozone layer, scientists have proposed using solid minerals such as calcium carbonate (CaCO₃), titanium dioxide (TiO₂), or alumina (Al₂O₃). These materials are thought to scatter sunlight more efficiently while absorbing less heat.
However, the new analysis suggests that dispersing solid aerosols at the necessary scale presents formidable engineering challenges. In laboratory tests and simulations, researchers found that these fine powders tend to clump into large aggregates that scatter sunlight less efficiently and fall out of the atmosphere more quickly.
Breaking up those aggregates requires tremendous energy. Achieving the proper flow conditions to keep particles under a micron in diameter could demand in-flight compression systems hundreds of times more powerful than current aircraft compressors. That added weight and complexity would cut payloads and multiply costs.
In practical terms, researchers conclude that the very physics that make solid aerosols appealing in theory could render them nearly impossible to distribute effectively.
The Columbia team also examined global supply and demand for potential aerosol materials. Some, like limestone, sulfur, and alumina, are relatively abundant. However, others, such as zirconium oxide or industrial diamond (both proposed for their high reflectivity), could strain existing markets.
The researchers calculate that for a 15-year stratospheric aerosol injection program designed to halve the rate of global warming, annual material requirements could consume up to 40% of global zirconium ore production and vastly exceed the world’s current output of industrial diamond.
That kind of demand shock could trigger ‘demand-pull inflation’ in key industrial sectors, leading to increased prices for goods and services. This could create new geopolitical vulnerabilities in mineral supply chains. Even common substances like lime could become problematic if stratospheric aerosol injection were scaled up tenfold under poorly coordinated conditions.
Even assuming successful dispersal, the study shows that once in the atmosphere, mineral particles may still clump into fractal-like structures, reducing their cooling efficiency by up to 90%. These aggregates would settle faster and could warm the stratosphere or interfere with ozone chemistry in unpredictable ways.
“In an injection scenario where aggregates are not broken up pre-dispersal or are formed rapidly in a concentrated diffusing plume, mineral candidates often lose their shortwave scattering advantages over sulfate,” researchers write.
In effect, stratospheric aerosol injection could trade one set of uncertainties —sulfate-induced ozone depletion —for another: inefficient, unpredictable mineral behavior at high altitudes.
All told, the new findings cast doubt on the practicality of near-term solar geoengineering. If solid aerosols require ten times as many flights per year as the models suggest, that alone could multiply deployment costs by an order of magnitude, potentially erasing stratospheric aerosol injections’ supposed cost advantage.
Researchers emphasize that the problem is not just technological but systemic. Without global coordination, clear governance frameworks, and thorough testing of microphysical behaviors, stratospheric aerosol injection could create more problems than it solves.
“The development of technical and governance-based approaches to mitigate risks associated with deployment strategy, candidate selection, and aggregate injection is critical to the design or discussion of any realistic ‘low-risk’ SAI strategy,” the authors conclude.
The study does not dismiss solar geoengineering entirely. It highlights specific research areas, such as developing more effective dispersal methods, testing particle aggregation under realistic stratospheric conditions, and modeling the risks of decentralized deployment, which could inform future debate.
However, researchers argue that, for now, the practical and political complications suggest stratospheric aerosol injection is not a legitimate substitute for cutting greenhouse gas emissions at their source.
“Even when simulations of SAI in climate models are sophisticated, they’re necessarily going to be idealized. Researchers model the ideal particles, the perfect size. And in the simulation, they put exactly how much of them they want, where they want them,” co-author and atmospheric chemist and aerosol scientist at Columbia’s Climate School and Columbia Engineering, Dr. V. Faye McNeill, explained in a press release. “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 said, “and we’re arguing that the range of possible outcomes is a lot wider than anybody has appreciated until now.”
“It’s all about risk trade-offs when you look at solar geoengineering,” concludes co-author Gernot Wagner, who adds that “it isn’t going to happen the way that 99 percent of these papers model.”
The paper, “Engineering and Logistical Concerns Add Practical Limitations to Stratospheric Aerosol Injection Strategies,” appeared in Scientific Reports on October 21, 2025.
Ryan Whalen also contributed reporting for this article.
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com