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Scientists have long tossed around the idea of battling global warming by injecting sulfate aerosols—little drops of sulphate—into the sky. It's a risky solution that might backfire.

Mother Jones explained back in March that the idea started as something of a lark. In the early-1990s, Mount Pinatubo erupted in the Philippines, sending sulphates into the air that had a temporary cooling effect. A few years later, climate scientist Ken Caldeira set out to disprove that by artificially recreating the scenario could help fight global warming. But his results showed that it could. He told Mother Jones, "our original goal was to show that it was a crazy idea and wouldn't work… much to our surprise, it worked really well."

He and his team detailed the findings in a paper published in 2000.

There are, however, problems with filling our air with sulfuric acid. In 2008, climate scientist Alan Robock detailed the issues with the solution in an article published in the Bulletin of the Atomic Scientists. Among his 20 arguments against sulfate aerosols are that it could deplete the ozone layer, negatively affect plant growth, make solar power less effective, and lead to political strife on Earth. And, in his words, "there's no going back." Robock wrote:

We don't know how quickly scientists and engineers could shut down a geoengineering system — or stem its effects — in the event of excessive climate cooling from large volcanic eruptions or other causes. Once we put aerosols into the atmosphere, we cannot remove them.


But climate change models are terrifying. Most predict catastrophe if we don't change our emissions habits—and we haven't been doing a great job of that. So it's not surprising that scientists are still going back to the sulfate solution, and that some are working to tweak the idea into something that could actually work: like replacing sulfate aerosols with diamond dust.

In a paper published in Atmospheric Chemistry and Physics this week, a team of Harvard scientists explained why diamond dust is a better alternative. Co-author Debra Weisenstein explained to Nature, "Our paper is really geared towards removing the mindset that it has to be sulphate that's used to do solar radiation management." Diamond dust isn't the only alternative —alumina dust also works—but it seems to be the best. With either, Weisenstein said, "you could have significantly less impact on ozone, less heating of the stratosphere and less of an increase in diffuse light at Earth’s surface."

But even this option is problematic. Nature explains:

The scientists warn, however, that both alumina and diamond nanoparticles carry unknown risks. Sulphates are reasonably well understood, thanks to research on volcanoes. By contrast, the chemistry of the solid particles—such as how their surfaces catalyse chemical reactions—is not as clear, although the Harvard researchers are doing lab tests to remedy that.


Plus, diamonds are expensive. But our planet? Priceless.

Danielle Wiener-Bronner is a news reporter.