In a world where the effects of climate change are becoming increasingly severe and the pace of emissions reductions remains frustratingly slow, a new and controversial technology is moving from the realm of science fiction to the edge of reality: solar geoengineering. This set of techniques, designed to artificially cool the planet by reflecting sunlight away from Earth, has long been seen as a last resort—a sort of planetary painkiller rather than a cure for our climate woes. But now, with the emergence of well-funded startups and a growing sense of urgency among scientists and investors alike, solar geoengineering is poised to become a central—and deeply contentious—topic in the global climate debate.
At the heart of this story is Stardust Solutions, a 25-person Israeli-U.S. startup that has rapidly become the most prominent commercial player in the field. According to POLITICO and Bloomberg, Stardust claims to have developed a novel reflective particle and the technology to release millions of tons of it high into the atmosphere. Their goal? To dim the sun's rays and, in theory, throw global warming into reverse. The company has already raised a staggering $75 million, including a record-breaking $60 million investment round in 2025 led by Lowercarbon Capital and joined by other high-profile backers such as the Agnelli family and former Facebook executive Matt Cohler.
This sudden influx of cash has catapulted Stardust ahead of its competitors, making it, as Columbia climate economist Gernot Wagner put it, "the only serious game in town." But the speed and scale of Stardust's ambitions have also triggered alarm among scientists, policymakers, and environmental advocates, many of whom worry that the technology is racing far ahead of the regulations and oversight needed to ensure its responsible use.
Solar geoengineering, also known as solar radiation modification (SRM) or stratospheric aerosol injection (SAI), involves dispersing reflective particles—traditionally sulfur dioxide—into the stratosphere to mimic the cooling effects of volcanic eruptions. The concept is not new; as POLITICO notes, the 1783 eruption of Iceland's Laki volcano sent millions of tons of sulfur into the sky, dimming sunlight and cooling the planet for years. Stardust hopes to replicate this effect, but with a particle they claim is safer and more environmentally benign than sulfates, which are known to cause acid rain, asthma, and ozone depletion.
Yet skepticism abounds. Many scientists question whether a truly inert, safe particle can be found, let alone deployed at the scale necessary to make a meaningful impact. As David Keith, a professor at the University of Chicago and a leading voice in geoengineering research, bluntly stated in Bloomberg: "Claims of an inert stratospheric particle are nonsense." Even diamonds, he argues, would alter stratospheric chemistry at high altitudes.
The potential risks of solar geoengineering go far beyond chemistry. Models suggest that while SRM could lower global temperatures, it might also disrupt regional weather patterns, exacerbate droughts in places like sub-Saharan Africa, intensify hurricanes in the North Atlantic, and trigger winter droughts in the Mediterranean. The Royal Society, in a November 2025 report cited by both POLITICO and Bloomberg, acknowledged the technique's likely effectiveness in cooling but warned of the many unknowns and possible negative side effects. As Ben Kravitz, a professor at Indiana University, told POLITICO, "There would be some winners and some losers. But in general, some amount of stratospheric aerosol injection would likely benefit a whole lot of people, probably most people." Still, others, like Martin Siegert of the University of Exeter, remain deeply uneasy, arguing that large-scale geoengineering "would mean severing the natural link between the temperature of the planet and the concentration of greenhouse gases."
Perhaps the most chilling concern is what happens if the world becomes reliant on solar geoengineering and then, for whatever reason, stops. This so-called "termination shock" could unleash a decade of rapid, catastrophic warming, outpacing humanity's ability to adapt. As Bloomberg points out, once started, solar geoengineering would need to be maintained for centuries—far longer than the typical lifespan of even the most robust corporations.
Despite these dangers, there is a growing sense among climate experts that the world may not have the luxury of ignoring geoengineering. A recent poll of climate researchers, reported by Bloomberg, found that two-thirds believe there will be an attempt to deploy large-scale SRM by 2100, with more than half predicting that a "rogue actor"—be it a private company, billionaire, or nation-state—will take the lead. This reflects mounting pessimism about the prospects for sufficient emissions cuts and a recognition that, as Janos Pasztor, a former senior UN climate official, put it: "If the situation is as bad as it is, then we might actually need this technique. If that is the case, then we have a moral imperative to study it—to understand it."
Pasztor himself has been drawn into Stardust's orbit, first as a skeptical outsider and later as a consultant hired to advise the company on governance and transparency. In a candid interview with POLITICO, he recounted his initial reluctance to get involved, fearing that Stardust's for-profit model and lack of oversight could lead to reckless deployment. Ultimately, he agreed to help on the grounds that encouraging openness and public scrutiny was better than leaving the company to operate in the shadows. "Like it or dislike it," he said, "there is a Stardust, and they are developing an A-to-Z system to do stratospheric aerosol injection. It is happening."
Yet even Pasztor remains troubled by Stardust's secrecy and the slow pace of regulatory development. While the company has pledged to publish research in peer-reviewed journals and to adhere to a voluntary code of conduct, critics note that these commitments are only as strong as Stardust's willingness to keep them. Efforts to establish international rules have so far faltered: the UN Convention on Biological Diversity has a non-binding moratorium, the U.S. is not a signatory, and a Swiss proposal for an expert group at the UN Environment Assembly failed to advance. Some U.S. states and Mexico have banned or restricted geoengineering experiments, but there is no comprehensive global framework.
Stardust, for its part, insists that it welcomes regulation and is actively working with policymakers to develop the necessary guardrails. CEO Yanai Yedvab has repeatedly stated that "sunlight reflection deployment should be conducted under established governance, guided by governments and authorized bodies." The company has also begun lobbying efforts in Washington, seeking to shape potential U.S. and international regulations. Still, the gap between Stardust's rapid technical progress and the slow, uncertain evolution of oversight remains a source of deep unease for many observers.
As the debate over solar geoengineering heats up, one thing is clear: the world is fast approaching a crossroads. Whether Stardust's technology becomes a vital tool in the fight against climate change or a cautionary tale of unintended consequences will depend not just on science and engineering, but on the ability of governments, scientists, and the public to grapple with the ethical, environmental, and geopolitical questions it raises. The stakes could not be higher.
In the end, the story of Stardust is not just about one company's quest to blot out the sun—it's a test of how humanity confronts the limits of its own power, and the responsibility that comes with it.