A San Francisco nonprofit has released a comprehensive road map outlining the experiments, studies, and infrastructure needed to make informed choices about solar geoengineering, a controversial climate intervention that would release reflective particles into the stratosphere to mimic volcanic eruptions. Reflective, which funds solar geoengineering studies, estimates that coordinated research would take roughly a decade and cost around $370 million, while an uncoordinated approach would require nearly 20 years and close to $1.4 billion. The organization published its SAI Research Roadmap on September 10, aiming to guide scientific work and encourage funding for high-priority projects, though the plan has already drawn criticism from researchers who question whether outdoor experiments can ever be ethically justified.
The road map divides research into distinct phases, starting with foundational work lasting two to three years at a cost of $30 million to $75 million, including computer simulations, lab experiments, and development of observational tools to establish baseline stratospheric conditions. The second stage would use modified aircraft to release 10 metric tons of sulfur dioxide into the stratosphere four times across two seasons, spanning four to eight years and costing $70 million to $150 million while reducing uncertainty about cooling efficacy by roughly 25%. The third phase would dramatically scale up to 25,000 tons of sulfur dioxide released over one season at least once, possibly twice, lasting four to 11 years and running $270 million to $1.1 billion while cutting efficacy uncertainty by around 66%. A final phase would involve ongoing monitoring if full-scale solar geoengineering moves forward, gathering real-world data and watching for unexpected consequences.
"Our mission is to equip the world with the data and tools required for informed decision-making about sunlight reflection fast enough to matter," says Dakota Gruener, Reflective's cofounder and CEO. The organization incorporated in late 2023 and has since raised over $20 million from prominent charities and individuals while distributing approximately $4 million to dozens of research groups. The report includes firm stage gates between later phases, meaning research shouldn't advance if experiments fail to show the hoped-for impact, reveal troubling downsides, or don't resolve critical uncertainties. Gruener notes that 10 tons of sulfur dioxide represents less than 2% of what the global aviation industry releases into the atmosphere daily, suggesting early experiments carry minimal environmental risk.
The plan faces substantial opposition from scientists who argue outdoor experiments can't answer fundamental governance questions about who would control planet-altering technology and who would win or lose from its deployment. Since 2002, hundreds of academics have signed an open letter demanding a ban on outdoor experiments and an international non-use agreement, with critics contending that meaningful answers about regional precipitation changes and ozone layer impacts won't emerge until deployment at full scale. Wil Burns, a research professor at American University who signed the non-use agreement, worries that using the technology would violate intergenerational equity by masking continued warming, preventing future generations from turning it off without triggering sudden temperature surges known as termination shock. Reflective's road map acknowledges it won't resolve all scientific unknowns but argues that rising climate dangers could pressure nations to deploy solar geoengineering without proper research, making decisions in panic rather than based on evidence. The organization positions the experiments as necessary to determine whether stratospheric aerosol injection could ever work effectively, with supporters arguing that appropriately designed outdoor tests can teach researchers far more than endless computer simulations about both the technology's potential and its dangers. The broader debate now centers on whether scientific uncertainty about effectiveness justifies moving forward when governance questions about global equity and long-term consequences remain unresolved, a tension that will likely shape how aggressively philanthropies and governments fund the work ahead.