Study: Stratospheric Aerosol Injection Is More Unpredictable and Risky Than Modeled

Study Warns Stratospheric Aerosol Injection Is More Unpredictable and Risky Than Modeled

Overview

Why SAI has been proposed

SAI aims to imitate the temporary global cooling that followed large volcanic eruptions, notably Mount Pinatubo in 1991, which injected sulfur dioxide into the stratosphere and lowered global temperatures by roughly 0.5 °C for about two years. Some prior studies have suggested that deliberate injections could reduce warming at a relatively low annual cost compared with the broader economic impacts of unchecked climate change. The Columbia study examines whether that picture survives realistic operational and material constraints.

Main findings

• Material behavior: Fine mineral particles proposed as alternatives to sulfates (for example, calcium carbonate, titanium dioxide or alumina) tend to aggregate into larger clumps in concentrated plumes. Those aggregates scatter sunlight far less efficiently and fall out of the stratosphere faster.
• Engineering difficulty: Preventing or breaking up aggregates at scale would require compression and dispersal systems far beyond the capability of existing aircraft, substantially reducing payload and raising energy and cost requirements.
• Supply-chain impacts: A multidecade SAI program at scales modeled in some scenarios could consume large fractions of global production for certain materials. The study estimates that a 15-year program designed to halve warming rates could demand up to 40% of global zirconium ore production and exceed current industrial diamond output.
• Economic and geopolitical risks: Large sudden demand for specific minerals could drive prices higher, strain industrial sectors, and create new strategic vulnerabilities in mineral supply chains.

Operational and governance considerations

Implications for solid vs. sulfate aerosols

Solid mineral aerosols have been proposed to avoid some known drawbacks of sulfate injections, including potential ozone depletion. The Columbia analysis shows that the very properties that make solids attractive in models—high reflectivity and low heating—may not survive real-world dispersal and atmospheric chemistry. If aggregates form or cannot be reliably dispersed at micron scale, mineral candidates may lose their modeled benefits.

Conclusions and recommendations

The study concludes that SAI faces substantial practical limitations that are often absent from idealized climate-model simulations. Key recommendations include:

1. Focused research on aerosol microphysics under realistic stratospheric plume conditions, including aggregation dynamics and radiative consequences.
2. Development and testing of dispersal technologies capable of delivering and maintaining target particle sizes without producing large aggregates.
3. Assessment of material supply chains and the potential economic impacts of large-scale demand for specific minerals.
4. International governance frameworks to manage coordination, deployment standards and risk trade-offs, since decentralized activity could greatly increase hazards.