Reflective publishes a road map for deciding on solar geoengineering

The San Francisco nonprofit Reflective has published its SAI Research Roadmap, a detailed plan of the experiments, studies and infrastructure it says are needed before the world can make informed decisions about deploying stratospheric aerosol injection (SAI), a form of solar geoengineering that would release reflective particles into the stratosphere to mimic the cooling effect of volcanic eruptions. Dakota Gruener, Reflective's cofounder and chief executive, said the group's mission is to equip the world with the data and tools for informed decisions about sunlight reflection fast enough to matter, warning that consequential decisions may arrive on timelines shorter than the research system is prepared for.

If all the proposed work is done in a coordinated way, the road map estimates it would take about a decade and cost around $370 million; done without coordination, it would take roughly 20 years and nearly $1.4 billion. The plan lays out four phases. The first, "foundational knowledge," would run two to three years and cost $30 million to $75 million, covering computer simulations and lab work on impacts to ocean circulation, ice sheets and crop yields, plus new tools for measuring baseline stratospheric conditions. The second phase would use modified aircraft to release 10 metric tons of sulfur dioxide into the stratosphere, four times over two seasons; it would take four to eight years, cost $70 million to $150 million, and is projected to cut uncertainty about the technology's cooling efficacy (how much the planet cools per ton of sulfur released) by about 25%. The third phase would scale releases up to 25,000 tons of sulfur dioxide over one season, done at least once and possibly twice; it would run four to 11 years, cost $270 million to $1.1 billion, and is projected to cut efficacy uncertainty by around 66%. The final phase would be ongoing monitoring of any full-scale deployment, gathering real-world data to update models and catch unexpected consequences. Gruener said the road map has firm "stage gates" between the later phases so that research does not advance if results show worrisome downsides or fail to resolve key uncertainties, and described the document as a first version meant to be "concrete enough for people to argue with," open to revision as feedback comes in.

Gruener stressed that Reflective itself does not advocate using solar geoengineering, but the road map does argue for outdoor experiments, a position that remains contested. Since 2002, hundreds of academics have signed an open letter calling for a ban on outdoor SAI experiments and an international non-use agreement, arguing the technology could never be governed equitably. Aarti Gupta, a co-initiator of that non-use campaign and a professor of global environmental governance at Wageningen University, said the core questions are not technical but about who would control, develop and deploy a planet-altering technology, and to whose benefit. Wil Burns, a research professor and legal scholar at American University and a signatory to the non-use agreement, argued that outdoor experiments at the scales proposed cannot answer the questions that matter most, including effects on the ozone layer and regional rainfall, and that only full deployment could do that, which he considers never tenable. He also raised the risk of "termination shock": if the world keeps emitting greenhouse gases while relying on geoengineering to mask the warming, halting it abruptly would trigger a sudden surge in temperature that future generations, who had no say in its use, would have to absorb. The article notes that other researchers have argued termination shock is less likely than often assumed and that geoengineering could be dialed down gradually instead of stopped abruptly.

Other experts who reviewed the road map were more supportive. Ilan Gur, the former CEO of the UK's Advanced Research and Invention Agency (ARIA), which funded 21 geoengineering research projects last year, said the goal should be to answer the biggest scientific questions as quickly and efficiently as possible and called Reflective's approach the right one. Sebastian Eastham, an associate professor in sustainable aviation at Imperial College London who leads an ARIA-funded project on a different cooling approach, agreed the proposed outdoor experiments cannot resolve every unknown, but said the road map helps start a conversation about decision-making under unresolved uncertainty, and warned that relying only on computer simulations risks researchers learning too little about the technology's real effectiveness and dangers.

Reflective, incorporated in late 2023, has raised more than $20 million from charities and individuals and has provided around $4 million to several dozen research groups, alongside its own projects such as an open-source solar geoengineering simulator. Earlier this year it released a database of SAI uncertainties that the new road map builds on. Gruener acknowledged the risk that solar geoengineering could worsen inequality, but said unchecked warming also threatens to disproportionately harm developing regions, and noted that the 10 tons of sulfur dioxide proposed for a phase-two experiment amounts to less than 2% of what the global aviation industry releases into the atmosphere in a single day.

Key facts

Reflective's SAI Research Roadmap estimates a coordinated research program would take about a decade and cost around $370 million, versus roughly 20 years and nearly $1.4 billion if uncoordinated.
The plan has four phases: foundational simulations and lab work ($30M-$75M, 2-3 years), a first outdoor test releasing 10 metric tons of sulfur dioxide four times ($70M-$150M, 4-8 years, cutting cooling-efficacy uncertainty about 25%), a larger test releasing 25,000 tons ($270M-$1.1B, 4-11 years, cutting uncertainty around 66%), and ongoing monitoring of any full deployment.
Since 2002, hundreds of academics have signed an open letter demanding a ban on outdoor SAI experiments and an international non-use agreement, and critics like Wil Burns argue experiments can never answer the real question of who controls and benefits from the technology.
Reflective, founded in late 2023, has raised over $20 million and distributed about $4 million to research groups; its CEO Dakota Gruener says the group does not advocate deploying solar geoengineering, only building the evidence base for a decision.
Supporters including former ARIA CEO Ilan Gur and Imperial College's Sebastian Eastham back the road map's approach, while critics warn of 'termination shock' if geoengineering is used to mask continued greenhouse gas emissions.

Why it matters

Solar geoengineering, specifically stratospheric aerosol injection, has been studied for decades but has never had a coordinated research plan. Reflective's road map is the first attempt to lay out, phase by phase, what experiments, budgets and timelines would actually be needed before anyone could claim to have enough evidence to decide whether to deploy a technology capable of altering the planet's climate.

Who it affects

The road map is aimed at scientists, philanthropies and government research agencies who might fund or conduct the work, such as the UK's ARIA, which already funds 21 geoengineering projects. It also matters to critics like the signatories of the 2002 non-use letter, and ultimately to future generations, who Wil Burns argues would inherit the risk of termination shock without having had any say in deployment.

How to use it

Reflective describes the document as a Version 1, deliberately 'concrete enough for people to argue with,' and says it will revise the plan based on feedback submitted through a mechanism on its site. The road map also builds directly on Reflective's earlier SAI Uncertainties database, which catalogued the scientific and engineering unknowns the new plan is designed to resolve.

How solid is it

The cost and timeline figures come from Reflective itself, a nonprofit that funds and advocates for solar geoengineering research, not from an independent body. Its CEO says the group does not advocate actual deployment, and the road map includes 'stage gates' meant to halt progression if experiments show worrisome downsides. Independent reviewers such as Ilan Gur and Sebastian Eastham broadly endorsed the approach, though Eastham noted that even the proposed outdoor experiments cannot resolve every unknown.

Risks and caveats

The plan's own third phase, releasing 25,000 tons of sulfur dioxide, is far larger than anything attempted before, and its outdoor experiments remain politically contested: earlier proposals like Harvard's SCoPEx and the UK's SPICE project were halted amid opposition. Critics led by Wil Burns argue that scaled experiments cannot answer the central governance question of who controls the technology, and warn of termination shock if the world leans on geoengineering while continuing to emit greenhouse gases, though other researchers say that risk is often overstated and that a deployment could be dialed down gradually rather than stopped abruptly.

“The core question is: Who would control a planet-altering technology like stratospheric aerosol injection? Who would develop it, and who would deploy it, and to what end? To serve what purposes, and whose purposes? Those questions are very fundamental, because this planet-altering technology will have winners and losers.”

— Aarti Gupta, professor of global environmental governance at Wageningen University