Scientists Propose Silica Microspheres as Solar Geoengineering Intervention

On May 14, 2026, a startup called Stardust Solutions published what amounts to a manufacturing manual for planetary climate intervention: a feasibility study detailing how to produce and disperse up to 10 million metric tons of engineered amorphous silica particles into the stratosphere each year to reduce the amount of sunlight reaching Earth's surface [1][2]. The study — not yet peer-reviewed — specifies reactor sizes, chemical supply chains, deployment aircraft, atmospheric persistence engineering, and a cost target of roughly $5 to $5.70 per kilogram at industrial scale [1].

The proposal has brought solar geoengineering from academic abstraction to industrial planning. It has also drawn immediate condemnation from environmental groups, governance scholars, and scientists in the Global South who argue the technology threatens to upend monsoon systems, undermine emissions reductions, and hand a small number of wealthy actors control over the planet's thermostat.

What Stardust Is Proposing

Stardust Solutions, a US-incorporated, Israeli-based company founded in 2023 by a team of physicists including CEO Yanai Yedvab — a former deputy chief scientist at the Israeli Atomic Energy Commission — has raised $75 million to date [3]. A seed round of $15 million came from Canadian and Israeli investors, including Awz Ventures, a fund with ties to Israeli military and intelligence agencies. In October 2025, Stardust closed a $60 million venture round led by Lowercarbon Capital, the firm of tech billionaire and former Google executive Chris Sacca. Other backers include Exor (the Dutch holding company that is the largest shareholder in Ferrari and Juventus), former Facebook executive Matt Cohler, and the US firms Future Positive and Future Ventures [3][4].

The company's SEASP study (Submicronic Engineered Amorphous Silica Particle) describes particles 250 to 500 nanometers in diameter with hydrophobic surface coatings engineered for approximately one year of stratospheric residence time [1][5]. The proposed rollout timeline projects 250,000 metric tons per year within five years, one million tons within seven years, and eventual scaling to 10 million tons annually — a quantity the authors associate with a roughly 1% reduction in incoming solar flux [1][2].

For context, the seminal 2018 study by Wake Smith and Gernot Wagner on stratospheric aerosol injection (SAI) logistics estimated that a sulfate-based program would begin with approximately 4,000 dedicated high-altitude aircraft flights per year, increasing linearly, using a purpose-built tanker aircraft (the "SAIL") with a 25-ton payload [6]. No existing aircraft can perform the mission at the altitudes required. Smith and Wagner estimated average costs of approximately $2.25 billion per year over the first 15 years for a sulfate program [6]. Stardust's silica proposal would require substantially more mass — silica is heavier than sulfate aerosols — but the company argues its manufacturing costs could offset the difference [1].

Why Silica Instead of Sulfur?

Most SAI research has focused on injecting sulfur dioxide (SO₂), which forms sulfate aerosols that reflect sunlight. But sulfate aerosols carry well-documented drawbacks: they absorb infrared radiation, warming the stratosphere; they accelerate ozone depletion; and they produce acid rain [7][8].

A 2025 study published in Communications Earth & Environment modeled solid particles — including alumina and calcite — as alternatives. It found that solid particle injection reduces stratospheric warming by up to 70% and diffuse radiation by up to 40% compared to SO₂ [8]. For achieving −1 W/m² of radiative forcing (enough to offset a significant fraction of current warming), the ozone impact of solid particles would likely be small. However, the study flagged "sizable uncertainties" from poorly understood heterogeneous chemical and microphysical processes, which could produce global ozone column changes ranging from −14% to +4% [8].

Silica, as a specific solid particle candidate, shares these potential advantages over sulfate but has been studied far less rigorously. The question of how silica particle surfaces change once exposed to stratospheric conditions — UV radiation, extreme cold, trace reactive gases — remains largely unanswered. Particle aggregation behavior, which would affect both settling rates and optical properties, has not been validated through stratospheric field experiments [8][9]. Stardust's SEASP study is an engineering feasibility assessment, not a climate science study, and the atmospheric claims it makes await independent verification.

The Research Landscape

Academic publication on solar geoengineering and stratospheric aerosols has grown sharply over the past decade. According to OpenAlex data, 345 papers were published on the topic in 2025, up from just 53 in 2011 — a more than six-fold increase reflecting both growing climate urgency and increased funding [10].

Source: OpenAlex

Data as of Jan 1, 2026CSV

Harvard's Solar Geoengineering Research Program, funded by foundations including the Hewlett Foundation, the Sloan Foundation, the Open Philanthropy Project, and individual donors including Bill Gates and former Google executive Alan Eustace, was the most prominent academic effort in the field for years [11]. Its outdoor experiment, SCoPEx (Stratospheric Controlled Perturbation Experiment), was designed to test calcium carbonate aerosol behavior in the stratosphere — but it was cancelled in March 2024 without ever flying, after sustained opposition from Indigenous groups, environmental organizations, and the Swedish government [11][12].

Harvard's program maintained a policy of not accepting funding from entities whose profits primarily come from fossil fuels [11]. Stardust Solutions operates under no such restriction. The Center for International Environmental Law (CIEL) has flagged Stardust's planned outdoor experiments — projected to begin in 2026 — as "reckless," noting the absence of any international regulatory framework governing such activities [13].

Regional Impacts: Monsoons, Agriculture, and the Global South

The most consequential scientific concern about any SAI deployment is its uneven regional effects. Climate models consistently project that stratospheric aerosol injection sufficient to offset global warming would alter precipitation patterns, particularly in the tropics. Twelve climate models reviewed found that SAI deployed to offset the warming from quadrupled CO₂ could reduce rainfall in parts of the tropics by 5% to 7% annually compared to preindustrial levels [14][15].

For South Asia, the implications center on the monsoon. The Indian Institute of Science, with funding from the Indian government, has been studying the sensitivity of the South Asian monsoon to SAI [14]. One crop-climate modeling study found that solar dimming geoengineering could reduce groundnut yields in India by up to 20% relative to baseline warming scenarios — not because temperatures became too cool, but because reduced direct sunlight impairs photosynthesis and disrupts seasonal water availability [16].

In sub-Saharan Africa, models suggest that SAI deployed over the Indian Ocean to increase rainfall over the drought-affected Sahel would displace drought conditions to East Africa [14]. The fundamental problem is geographic: aerosols injected to cool one region inevitably alter atmospheric circulation elsewhere. Most models find that negative side effects would disproportionately impact the Global South — communities that bear the least responsibility for greenhouse gas emissions [15][17].

These projections carry substantial uncertainty. The specific effects of silica particles, as opposed to sulfate or calcite, on regional climate have not been modeled in published literature. Stardust's SEASP study does not include regional climate impact modeling [1].

The Cost Equation

The cost asymmetry between solar geoengineering and other climate interventions is stark — and, for critics, precisely the problem.

Source: Smith & Wagner 2018; IPCC; IEA

Data as of Jan 1, 2025CSV

SAI with sulfate aerosols has been estimated at roughly $18 billion per year per degree Celsius of cooling [6][18]. Silica-based deployment would likely cost more per degree due to higher mass requirements, though Stardust claims manufacturing efficiencies could narrow the gap. By comparison, direct air capture of CO₂ currently costs $250 to $1,000 per ton of CO₂ removed, translating to hundreds of billions of dollars for meaningful temperature reduction [18]. Global renewable energy investment, while running at roughly $500 billion per year, addresses root causes rather than symptoms [18].

This cost gap is what makes geoengineering attractive to some policymakers and investors — and alarming to others. At $1 to $10 per ton of CO₂-equivalent cooling, SAI is orders of magnitude cheaper than any mitigation or removal technology [18]. A single wealthy nation or even a well-funded private actor could theoretically deploy it unilaterally.

Governance: A Legal Vacuum

No international treaty explicitly prohibits or regulates stratospheric aerosol injection for climate purposes. The Environmental Modification Convention (ENMOD) of 1978 prohibits "hostile" environmental modification, but its language was designed for military applications and has never been enforced [19][20]. The Convention on Biological Diversity adopted a de facto moratorium on geoengineering activities in 2010, but it is non-binding and does not cover research [20].

At the sixth session of the United Nations Environment Assembly (UNEA-6) in early 2024, a Swiss-led resolution attempting to establish basic governance for solar geoengineering collapsed amid deep disagreement. Close to 60 countries in the Global South, led by the African Group and joined by Colombia, Fiji, Mexico, Pakistan, and Vanuatu, called for a non-use agreement [21][22]. The United States and Saudi Arabia, acting in concert, blocked the majority position, supporting instead a framework that would welcome geoengineering research under the World Climate Research Programme [22]. The resolution was withdrawn entirely.

More than 500 academics from over 50 countries have signed a letter calling for an International Non-Use Agreement on Solar Geoengineering [20]. Supporters argue that in the absence of governance, even research programs create path dependencies that make eventual deployment more likely — a dynamic they call "lock-in."

Termination Shock: The Withdrawal Problem

Perhaps the most frequently cited risk of solar geoengineering is termination shock: the rapid temperature rebound that would occur if deployment were suddenly halted. Because SAI masks warming without reducing greenhouse gas concentrations, stopping injection would expose the planet to the full accumulated warming within years rather than decades [23][24].

A 2018 study by Parker and Irvine in Earth's Future examined this risk in detail. The authors concluded that termination shock is frequently overstated as an argument against research, noting that relatively simple policy design — maintaining backup deployment hardware, distributing launch sites across multiple nations — could make an SAI system resilient against most plausible disruptions [23]. However, they acknowledged that extreme scenarios — simultaneous geopolitical conflict among deploying nations, for instance — could still trigger abrupt cessation.

The duration of commitment is itself a governance challenge. If emissions continue rising, SAI would need to be maintained for centuries or millennia [24]. Even under aggressive decarbonization, the system would likely need to operate for several decades while CO₂ concentrations decline. Critics argue this creates an unprecedented intergenerational obligation with no historical parallel.

The Moral Hazard Debate

The concern that geoengineering could "crowd out" emissions reductions — the so-called moral hazard — ranks among the most frequently cited objections [25][26]. The argument is straightforward: if policymakers and publics believe a technological fix exists, they will invest less in the harder work of decarbonization.

Empirical evidence on this question is mixed. A large-scale experiment on Facebook (n ≈ 340,000) found little support for a moral hazard effect: information about geoengineering did not measurably reduce support for emissions mitigation [26]. A separate study found no significant effect of SAI information on support for a carbon tax [25]. Some researchers have argued the moral hazard concern is itself a form of paternalism — assuming that the public cannot hold two ideas (geoengineering may help, and emissions must still fall) simultaneously.

But the political economy tells a different story than survey experiments. Fossil fuel interests have historically promoted technological optimism to delay regulation. While Harvard's program excluded fossil fuel funding, the broader geoengineering research ecosystem has no such norm. Stardust's investor base — dominated by Silicon Valley venture capital and technology billionaires — does not include fossil fuel companies, but the company's for-profit structure introduces a different set of incentive problems: once a firm has invested hundreds of millions in deployment infrastructure, its business model depends on continued and expanded use [3][27].

The strongest version of the scientific case against solar geoengineering, even among researchers who accept the urgency of climate change, rests on a combination of arguments: that SAI does not address ocean acidification (the ocean absorbs 25% of human CO₂ emissions regardless of temperature); that it creates winners and losers among nations with no legitimate mechanism for adjudicating those outcomes; that it locks humanity into an indefinite commitment with catastrophic failure modes; and that its apparent cheapness makes it politically toxic to the mitigation agenda even if survey evidence on individual attitudes is ambiguous [15][17][18].

What Comes Next

Stardust Solutions has announced plans to begin outdoor experiments in 2026, though the timing and location remain undisclosed [13]. The company's SEASP papers are being submitted to scientific journals for peer review — a process that will subject its manufacturing claims, atmospheric residence estimates, and safety assertions to independent scrutiny for the first time [1].

Meanwhile, the governance gap persists. No nation has enacted domestic legislation specifically regulating stratospheric aerosol injection. The UNEA process remains stalled. And the technical capacity to deploy aerosols at scale continues to advance faster than the international community's ability to agree on whether, how, or by whom it should be done.

The question is no longer whether someone will attempt solar geoengineering. It is whether the scientific evidence, governance structures, and affected populations will have any meaningful role in that decision.