This company says it can help cool the planet for $10 billion a year; scientists are raising red flags

By Laura Paddison, CNN

(CNN) — One company has a simple-sounding plan to help save the planet: take a food additive and the mineral that makes eggshells hard, produce tiny particles out of them, spray them into the atmosphere and cool the world.

Stardust Solutions, an Israeli-US company founded in 2023 and led by two former Israeli government nuclear physicists, is pushing ahead in the race to develop solar geoengineering, a controversial technology aimed at artificially bringing down global temperatures by dimming the sun.

There are many different solar geoengineering methods, but perhaps the most researched — and the one Stardust focuses on — involves spraying tiny particles into the stratosphere from high-altitude aircraft or balloons to reflect the sun’s energy away from Earth and back into space.

It’s an artificial version of a natural phenomenon. Volcanic eruptions sometimes spew so much sulfur dioxide into the atmosphere it can temporarily lower global temperatures. In 1991, the eruption of Mount Pinatubo in the Philippines injected enough into the atmosphere to produce cooling of 0.9 degrees Fahrenheit (0.5 Celsius) for more than a year.

As humans burn fossil fuels and heat the planet, the question of whether solar geoengineering can and should move from theory to reality is gaining prominence.

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The technology is a “critical tool” for governments to consider as the global thermostat runs terrifyingly hot, said Stardust’s CEO Yanai Yedvab, although he stressed it’s neither a silver bullet for climate change nor a substitute for addressing its root causes.

Many scientists, however, have expressed fears that solar geoengineering could have disastrous global implications, including dramatically altering weather patterns. And some experts are raising red flags that a for-profit company is developing proprietary technology that could have huge and unpredictable repercussions.

“When the whole world is at stake, satisfying the needs of venture capitalists for profits should not enter at all into decisions about what, if anything, should be deployed,” said Raymond Pierrehumbert, professor of planetary physics at the University of Oxford.

Scientists have been researching solar geoengineering for decades, but private companies are starting to pop up. Of these, Stardust is arguably the most high profile, not least because it’s the best funded, having raised $75 million from investors.

The company was formed in the wake of the pandemic. Yedvab and his co-founder, Amyad Spector, landed on solar geoengineering as they explored ways to help address the climate crisis.

When it comes to spraying particles in the atmosphere, most solar geoengineering research and development focuses on sulfur dioxide, mimicking volcanic eruptions. But sulfur dioxide can have negative impacts, including contributing to acid rain and ozone layer depletion.

Stardust wanted to develop a material “that will be better, will be safer, that could be controlled,” Yedvab said. Earlier this year, it revealed its particle designs in a series of scientific papers, which await peer review.

The company has produced two particles: One from amorphous silica, commonly used as an anti-caking additive in foods, toothpaste and cosmetics; the other is made from a core of calcium carbonate, the main component in eggshells, surrounded by a shell of amorphous silica.

Both compounds occur naturally, but can be created synthetically. And these are commonly used substances, Yedvab said. Amorphous silica, for example, was released into the New York City subway in 2016, as part of a Department of Homeland Security test designed to simulate the impacts of a potential biological attack. It’s an anecdote that helps highlight how safe silica is considered to be, Yedvab said.

Every million tons of particles would lead to 0.9 degrees Fahrenheit of cooling, and would need be replenished every year, Yedvab said. Each million-ton deployment would cost roughly $10 billion. It’s a lot, he acknowledged, but still a small fraction of the damage climate change-related disasters are already causing.

But experts have raised concerns. In addition to being queasy about private business attempting to alter the climate, some are also concerned about the impacts on global climate and weather, as well as human health.

David Keith, a professor of geophysical sciences at the University of Chicago who is best known for his research on solar geoengineering, said Stardust is “greatly overclaiming to say that they’re confident the risks [of their particles] are lower than with sulfur.” One concern is the “hitchhiker hypothesis” — that particles in the air can pick up metals or other substances that can cause harm when people breathe them in.

Stardust said its particle design takes these risks into account, but whether they will work at scale and how they might behave in the atmosphere is unclear, said Kelly Wanser, executive director of SilverLining, a nonprofit climate research organization.

“Solar geoengineering engages some of the least understood aspects of the climate system,” said Pierrehumbert, adding that no small-scale experiment can indicate how Earth systems would respond to a full-scale deployment.

So far, the company has limited its tests to the lab. Launching outdoor tests is the next step, but history suggests this will be fraught. Plans by Harvard scientists to conduct test flights for solar geoengineering in Arctic Sweden were abandoned in 2021 after intense local opposition. A rogue experiment by US startup Make Sunsets in Mexico in 2022 led the country to ban solar geoengineering experiments.

Stardust, which hopes to start outdoor tests in the next few years, would only run them “under supervision and direct guidance of governments,” Yedvab said. He compared the process to testing life-saving drugs. They would start with very small-scale tests, with clearly defined success criteria, before graduating to larger-scale tests.

The company says it’s already engaging policymakers to try to build a regulatory framework around testing. Decisions on whether the tech is ever deployed belong “solely in governments,” Yedvab said.

Still, Stardust is a for-profit company with a financial incentive in the deployment of this technology, some experts say, and that has raised alarms. “Proprietary technology and profit motives are directly at odds with the transparency needed to legitimize [solar geoengineering] research,” Keith wrote in a blogpost last year.

Sarah Doherty, an associate professor of atmospheric sciences at the University of Washington, who leads a solar geoengineering research team, said “the current science does not support making financial bets on, or driving society toward, specific approaches.”

Yedvab said most groundbreaking technologies benefitting humanity have been made by for-profit companies, albeit often building on academic research.

But the stakes are achingly high. Solar geoengineering could open the door to a host of unintended consequences, including the potential to alter rainfall patterns and shift monsoons, which could have big repercussions for food production, scientists say.

Perhaps most alarming is the prospect of “termination shock.” This is the idea that, once started, solar geoengineering would have to be maintained indefinitely. If stopped suddenly, “the world is then faced with a catastrophic, sudden warming playing out over just a few years,” Pierrehumbert said.

Stardust says its technology can be tuned up or down, meaning deployment can be scaled down gradually. The particles fall out of the atmosphere after roughly a year “so the level of cooling remains a continuing, adjustable choice in the hands of governments and termination shock can be avoided,” Yedvab said.

Some remain unconvinced. Deploying the technology would bring “profound systemic uncertainty” and the “potential to destabilize the global climate system further,” a recent study concluded.

Thorny ethical issues also abound, including who gets to choose when and how solar geoengineering is deployed, who pays for it and what happens if some countries benefit while others are harmed.

“I worry that decisions about if, when, and how to deploy solar engineering will not be made by poor countries but rather by rich countries and private investors,” said Chukwumerije Okereke, professor in global governance and public policy at the University of Bristol.

Then there’s the fear this technology will be seized on as a reason not to make deep cuts to planet-heating pollution, which means significantly reducing the amount of fossil fuels we burn.

This is a “valid concern,” said Yedvab, but it should be balanced with what he called “moral imperatives.” Stardust’s argument is that as the impacts of climate change get increasingly severe and deadly, governments must have options.

Solar geoengineering could “buy humanity the decades needed” to address the underlying causes of climate change, Yedvab said. “I believe the real risk is that a decade from now governments will face a decision on whether they need to deploy this option without having properly studied it and having safe options in front of them.”

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