Solar geoengineering, a concept once relegated to academic debate and the occasional maverick actor, has taken a dramatic step into the limelight. At the center of this shift is Stardust Solutions, a startup that, until recently, operated in near silence. In October 2025, the company announced a $60 million funding round—by far the largest ever for a geoengineering startup—drawing the attention of top climate investors and the wary gaze of the scientific community, according to MIT Technology Review.
For years, the idea of manipulating Earth’s climate by reflecting sunlight back into space has been both tantalizing and divisive. The basic theory is straightforward: by bouncing a fraction of the sun’s rays away from the planet, we could potentially cool the atmosphere and slow global warming. Nature has already shown this is possible—volcanic eruptions, which spew sulfur dioxide into the upper atmosphere, have temporarily cooled the planet by scattering sunlight. Scientists have long wondered if humanity could mimic that effect, intentionally releasing particles to produce a similar cooling.
But as interest in geoengineering has grown, so have concerns. The field has been largely confined to university research and policy debates, with even public projects facing steep hurdles. One high-profile example: a Harvard-led solar geoengineering research program was officially canceled in 2024 after years of controversy and public opposition, as reported by MIT Technology Review. The worry? That the risks and unknowns—ranging from unintended climate side effects to the potential for uneven impacts across countries—are simply too great.
Despite these headwinds, private companies have begun to push the boundaries. Three years ago, in a story broken by James Temple, Make Sunsets—a California-based startup—sent a weather balloon loaded with sulfur dioxide into the skies over Baja California, Mexico. The amount released was tiny, and it’s unclear whether it even reached the right atmospheric layer to reflect sunlight. Yet the mere act of a private entity unilaterally attempting climate engineering sparked a swift backlash. Within weeks, Mexico announced new restrictions on geoengineering experiments in its territory. Make Sunsets, undeterred, now sells “cooling credits” and recently secured a patent for its system, but remains largely on the fringe of climate innovation.
Enter Stardust Solutions. Unlike its predecessor, Stardust has attracted heavyweight investors and is beginning to speak more openly about its ambitions. “Stardust is serious, and now it’s raised serious money from serious people,” wrote James Temple in his recent coverage for MIT Technology Review. This influx of capital, and the credibility that comes with it, has made even seasoned geoengineering advocates uneasy. The prospect of private companies wielding the power to alter the global climate—potentially without broad public consent or oversight—raises thorny ethical and practical questions.
David Keith and Daniele Visioni, two leading voices in geoengineering research, captured this anxiety in a recent opinion piece for MIT Technology Review: “Adding business interests, profit motives, and rich investors into this situation just creates more cause for concern, complicating the ability of responsible scientists and engineers to carry out the work needed to advance our understanding.” Their message is clear: the stakes are too high for the usual Silicon Valley playbook of "move fast and break things."
Stardust Solutions, for its part, is trying to calm those nerves. The company insists it will not move forward with any actual geoengineering unless commissioned by governments and governed by clear regulations and oversight bodies. Yet, as MIT Technology Review points out, financial pressures and competitive dynamics could shift incentives over time. The company’s current approach—keeping the details of its proprietary particles secret until it secures a patent, possibly as soon as next year—has only added to the tension. Without transparency, outside experts have no way to independently assess Stardust’s claims that its particles will be safer, cheaper to manufacture, and easier to track than sulfur dioxide.
“Research won’t be useful unless it’s trusted, and trust depends on transparency,” Keith and Visioni emphasized. And that’s where the heart of the debate lies. Geoengineering, by its very nature, is a global enterprise. A single actor—whether a government, a corporation, or even a determined individual—could, in theory, make decisions that affect the entire planet. That prospect has led to calls for international governance, strict regulatory frameworks, and robust public engagement. Yet so far, progress on those fronts has been slow and halting.
Stardust’s emergence is a sign of how quickly the landscape is changing. Just a few years ago, the idea of a well-funded startup actively pursuing solar geoengineering would have seemed far-fetched. Now, with major investors on board and the company openly courting government contracts, the stakes couldn’t be higher. As MIT Technology Review notes, even those who support responsible research worry about the implications of profit-driven actors entering the field. The need for secrecy to protect intellectual property—like Stardust’s decision to withhold details about its particles—clashes directly with the scientific community’s demands for openness and reproducibility.
Meanwhile, Make Sunsets continues to operate on the margins, selling cooling credits to anyone willing to buy and touting its patented approach. The contrast with Stardust is stark: one company is seen as a rogue experimenter, the other as a potential industry leader. But both illustrate the challenges of regulating a technology that could, for better or worse, reshape the planet’s climate.
For now, Stardust says it will wait for governments and rules before acting. But as the money and momentum build, skeptics wonder how long that restraint will last. The tension between innovation and oversight, secrecy and transparency, public good and private gain is only growing sharper.
As solar geoengineering moves from theory to practice, the world faces a profound dilemma. Can society harness this powerful tool responsibly, or will the rush to innovate outpace the systems meant to keep us safe? The answers, for now, remain up in the air.
