"Even when simulations of SAI in climate models are sophisticated, they're necessarily going to be idealized," explained V. Faye McNeill, an atmospheric chemist and aerosol scientist at Columbia's Climate School and Columbia Engineering. "Researchers model the perfect particles that are the perfect size. 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."
Published in Scientific Reports, the study evaluates the complex variables that would shape SAI's real-world behavior - from the altitude, latitude, and timing of aerosol release to the chemical composition and abundance of materials available for deployment. The researchers found that latitude is a particularly sensitive factor. Aerosol injections near the poles could disrupt tropical monsoon systems, while equatorial releases might interfere with jet streams and global heat transport.
"It isn't just a matter of getting five teragrams of sulfur into the atmosphere. It matters where and when you do it," McNeill noted. The team argues that a globally coordinated SAI effort would be essential to minimize harmful side effects, but such coordination is unlikely given current geopolitical tensions.
Most modeling studies to date have assumed the use of sulfate aerosols, similar to those formed after volcanic eruptions like Mount Pinatubo in 1991, which cooled Earth by nearly one degree Celsius. Yet that same eruption also disrupted monsoon cycles and depleted the ozone layer - consequences that underscore the potential risks of large-scale atmospheric intervention.
To mitigate sulfate-related hazards, researchers have explored mineral alternatives such as calcium carbonate, alpha alumina, rutile and anatase titania, cubic zirconia, and even diamond. While these materials have promising optical properties, the Columbia team warns that their practical feasibility is limited.
"Scientists have discussed the use of aerosol candidates with little consideration of how practical limitations might limit your ability to actually inject massive amounts of them yearly," said lead author Miranda Hack. "A lot of the materials that have been proposed are not particularly abundant."
The team found that while calcium carbonate and alpha alumina could theoretically meet supply demands, producing and dispersing the necessary sub-micron particles poses severe technical challenges. These particles tend to clump together into larger aggregates, sharply reducing their sunlight-reflecting efficiency and introducing new uncertainties into climate response predictions.
Gernot Wagner, a climate economist at Columbia Business School, summarized the dilemma: "It's all about risk trade-offs when you look at solar geoengineering. Given the messy realities of SAI, it isn't going to happen the way that 99 percent of these papers model."
Research Report:Engineering and logistical concerns add practical limitations to stratospheric aerosol injection strategies
Related Links
Columbia Climate School
Climate Science News - Modeling, Mitigation Adaptation
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