By Naomi Mihara
As global heating worsens, interest in solar engineering is rising, including from private companies and investors. But the technique remains controversial and lacks regulation.
The planet is heating up faster than expected. Greenhouse gas concentrations continue to rise at record rates, leaving the world off track to limit warming below 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. The latest data shows 2025 was the third hottest year on record.
That growing gap between climate targets and reality is fueling renewed interest in geoengineering — interventions that intentionally alter the Earth’s climate system. Among them is solar geoengineering, which aims to cool the planet by reflecting sunlight back into space.
The technology remains largely experimental and could have far-reaching social, political, and environmental impacts if deployed at scale, according to scientists.
Until recently, most solar geoengineering research was carried out by nonprofits and public research institutions, funded by governments and philanthropies. But that landscape is shifting.
Over the past three years, two commercial startups — Israeli-US Stardust Solutions and California-based Make Sunsets — have emerged. As reported by media outlet Heatmap News, Stardust Solutions recently announced it had raised $60 million (around €52 million) in venture capital.
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Much of the SAI research to date has focused on injection of sulfate particles — the same type emitted by volcanoes. However, there are side effects associated with sulfate aerosols, including possible damage to the ozone layer and increased air pollution. This could in turn lead to higher rates of respiratory illnesses.
“We don’t believe this is a safe or responsible option for policymakers to consider,” said Stardust Solutions CEO Yanai Yedvab in an emailed response.
Stardust Solutions claims it has developed a different kind of particle, made of components that are “abundant in nature, chemically inert in the stratosphere, and safe for humans and ecosystems.”
The company has so far not released any information about the composition of the particle it is developing. Yedvab said they will begin publishing research this year. But some scientists are skeptical about the safety claims.
“Even if you put something into the atmosphere which is safe in the stratosphere, by the time it’s processed and come down to the lower atmosphere, it may be an active particle that’s dangerous,” said David Keith, a professor of geophysical science at the University of Chicago.
Yedvab said no outdoor testing will take place for now.