Dimming the Sun Like a Volcano? This Climate Fix Could Backfire Horribly

New research clarifies that the use of stratospheric aerosol injections (SAI)—tiny sunlight-reflecting particles dispersed in the atmosphere—could be a very bad idea.

SAI is a theoretical technique to cool down our rapidly warming planet. The theory is that, akin to volcanic eruptions, these particles in the upper atmosphere would reflect some of the sunlight away from Earth. While some researchers are seriously considering this approach, a study published yesterday in the journal Scientific Reports sets the record straight in terms of the practical physical, political, and economic contexts.

“Even when simulations of SAI in climate models are sophisticated, they’re necessarily going to be idealized. Researchers model the perfect particles that are the perfect size. And in the simulation, they put exactly how much of them they want, where they want them,” co-author V. Faye McNeill, an atmospheric chemist and aerosol scientist at Columbia’s Climate School and Columbia Engineering, said in a university statement.

“There are a range of things that might happen if you try to do this—and we’re arguing that the range of possible outcomes is a lot wider than anybody has appreciated until now,” she added.

Unintended consequences

According to existing studies, the success of SAI would depend on crucial details such as the time of year, the total amount of particles, the altitude of the particle release, and—potentially most significantly—the latitude of the particle release. For instance, releasing SAI near the poles could interrupt tropical monsoons. Near the equator, on the other hand, it could impact jet streams and global air circulation.

As such, SAI should be released in a centralized, coordinated manner. Given the current state of global affairs, the researchers argue that that is unlikely—and I’d argue that “unlikely” is a very polite way of putting it.

When the Philippines’ Mount Pinatubo erupted in 1991, the planet’s temperatures decreased by almost 1.8 degrees Fahrenheit (1 degree Celsius) for a number of years. Researchers frequently cite the event as proof that SAI could temporarily cool the planet, but the truth is that the eruption also created problems. It disrupted the Indian monsoon system, lessened rainfall in South Asia, and played a role in ozone depletion.

If we use sulfate aerosols akin to the compounds released by volcanic eruptions, they might also lead to negative consequences, like acid rain and soil contamination. As such, researchers have proposed alternatives such as calcium carbonate, alpha alumina, rutile and anatase titania, cubic zirconia, and diamond.

However, “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 Miranda Hack, lead author of the study and an aerosol scientist at Columbia University. “A lot of the materials that have been proposed are not particularly abundant.”

Particle complexities

Diamond particles would certainly be reflective, but they’re obviously too expensive and insufficient. (Speaking of diamonds, what if the Louvre heist was actually pulled off by SAI-supporting climate experts hoping to save the planet with 19th-century jewels? Someone call President Macron.)

According to the team, only calcium carbonate and alpha alumina are plentiful enough to be realistically scalable, but these materials have other issues related to dispersion. The particles involved in SAI have to be very small, but the mineral substitutes are likely to clump together into less effective and unpredictable concentrations.

“It’s all about risk trade-offs when you look at solar geoengineering,” said Gernot Wagner, a co-author of the study and a climate economist at the Columbia Business School. Taking into account SAI’s complex reality, “it isn’t going to happen the way that 99 percent of these papers model.”

Ultimately, the study emphasizes that SAI could be more complex, unpredictable, and dangerous than it seems. Perhaps it’s also a reminder that we’re unlikely to find a one-size-fits-all solution for human-driven global warming. Plus, did people learn nothing from the postapocalyptic 2013 movie Snowpiercer?