Hazy Ideas: Addressing the Risks of Solar Radiation Modification

Why We Must Pause, Not Panic, on Intentional Solar Geoengineering

The Earth is running a fever, and the prognosis is increasingly grim. Decades of warnings about climate change have largely failed to catalyze the radical decarbonization our planet desperately needs. Global emissions reduction efforts, while not insignificant, are falling perilously short of the Paris Agreement’s already ambitious targets. As the window to avert catastrophic warming narrows, a new, more desperate class of interventions is being thrust into the spotlight: solar radiation modification (SRM), often called solar geoengineering. These are technologies designed to act as a planetary sunshade, reflecting a tiny fraction of incoming sunlight back to space to rapidly cool the Earth.

The allure is undeniable: a potential quick technological fix, a way to dial down the global thermostat while we (theoretically) get our emissions house in order. Yet, this siren song carries notes of profound peril. To deliberately manipulate the Earth’s climate system on such a scale is to venture into uncharted territory, armed with incomplete maps and facing risks that could dwarf the problem we seek to solve.

This isn’t a call to abandon research — quite the opposite. Instead, it is a case for a carefully constructed, internationally agreed moratorium on the deployment of SRM technologies — a moratorium that, crucially, permits and actively encourages robust, transparent, and globally governed research. This isn’t a Luddite rejection of technology, but a strategic pause, an act of collective prudence. It is a recognition that our capacity for planetary-scale intervention has outstripped our wisdom and our cooperative frameworks. Such a moratorium, far from being a sign of defeat, would be a foundational step towards what astrobiologists David Grinspoon, Adam Frank, and Sara Walker term a “mature technosphere” — a state where a technologically advanced civilization achieves a sustainable, self-regulating relationship with its host planet. Our current uncoordinated, often destructive, impact on the Earth system vividly illustrates an “immature technosphere,” highlighting the urgent need for this evolution in our planetary self-management.

The Toolkit: A Quick Tour of Current SRM Tech

SRM is not a single technology but a suite of concepts, each with its own proposed mechanism, level of understanding, and array of potential consequences.

The most discussed method is Stratospheric Aerosol Injection (SAI). This involves dispersing tiny reflective particles — sulfates, similar to those ejected by large volcanic eruptions like Mount Pinatubo, or perhaps more benign materials like calcium carbonate or even diamond dust — into the stratosphere, roughly 15-50 kilometers up. These aerosols would scatter a small percentage of sunlight, inducing a cooling effect. While SAI is the most researched SRM approach, with some models suggesting it could limit warming to below 1.5°C, the technology for sustained, controlled delivery is still largely conceptual.

Marine Cloud Brightening aims to enhance the reflectivity of low-lying marine stratocumulus clouds. By spraying fine seawater droplets or other aerosols into the marine boundary layer, the idea is to increase the number of cloud condensation nuclei. This would, in theory, create clouds with more, smaller droplets, making them brighter and potentially longer-lived, thus reflecting more sunlight. Research is ongoing, with significant uncertainties about scalability and regional side effects.

Cirrus Cloud Thinning (CCT) takes a different tack, targeting outgoing longwave (heat) radiation rather than incoming solar (shortwave) radiation. High, thin cirrus clouds trap heat. CCT proposes injecting ice nucleating particles (like bismuth triiodide) to encourage the formation of fewer, larger ice crystals that would fall out of the atmosphere more quickly, thinning the clouds and allowing more heat to escape. The science here is considered less robust than for SAI or MCB, with a risk that over-seeding could inadvertently thicken clouds and cause warming.

Other, less globally impactful or more speculative methods include Surface Albedo Modification — painting roofs white, deploying reflective coverings, or planting more reflective crops, which can have localized cooling benefits but are unlikely to counter global warming on a large scale — and Space-Based Methods, such as deploying giant mirrors or swarms of reflective spacecraft at the L1 Lagrange point. These are technologically daunting and likely prohibitively expensive for the foreseeable future.

The primary allure of these technologies is their potential for rapid cooling, offering a way to “shave the peak” of global temperature rise. In scenarios where emissions reductions and carbon dioxide removal (CDR) prove too slow, SRM is posited as a temporary measure to avoid overshooting critical warming thresholds, potentially reducing severe impacts like runaway ice sheet melt or extreme weather events. Some econometric models even suggest SAI could, under specific deployment scenarios, reduce inter-country income inequality, though such findings are highly sensitive and contentious.

The Devil in the Details: Unpacking the Risks

The promise of a planetary thermostat comes with a formidable list of potential downsides, many of which are poorly understood. To begin with, we presently lack proper foresight methods for imagining the futures that SRM might create. But here are a few of the most discussed dangers, risks, and uncertainties associated with the potential deployment of SRM technologies.

The most cited danger is termination shock. If a large-scale SRM deployment, masking significant underlying warming, were suddenly halted — due to technical failure, geopolitical conflict, economic collapse, or sabotage — global temperatures would skyrocket at a rate far exceeding anything experienced under greenhouse gas warming alone. Ecosystems and human societies would have little capacity to adapt to such an abrupt shift. This creates a perilous dependency: the more warming SRM offsets, the greater the shock upon cessation, effectively committing future generations to maintaining the intervention indefinitely or facing catastrophic consequences. Deploying SRM entails opting in to becoming the planetary-scale equivalent of an insulin-dependent diabetic: you better pray that the supply never runs out for any reason.

SRM also cannot perfectly counteract greenhouse gas warming. While global average temperatures might be stabilized, regional climates could be significantly disrupted in asymmetric ways. Reducing incoming sunlight is not the same as reducing trapped heat. Some areas might overcool, others continue to warm, and precipitation patterns could be dangerously altered. Weakened monsoons, for instance, could threaten the livelihoods of billions. The very notion of a globally “optimal” SRM deployment becomes an ethical minefield, as choices would inevitably benefit some regions at the expense of others.

For SAI, stratospheric ozone depletion is a major concern. Sulfate aerosols provide surfaces for chemical reactions that destroy ozone, potentially delaying the recovery of the ozone hole by decades and increasing harmful UV radiation at the surface, with attendant risks for human health and ecosystems. While alternative aerosols like calcite might mitigate this, research is far less advanced.

The broader planetary consequences are also vast and uncertain. Altered temperatures, rainfall, and even the quality of sunlight (e.g., the ratio of diffuse to direct radiation) would impact plant growth, agricultural productivity, and marine ecosystems, including vital phytoplankton at the base of the food web. Critically, SRM doesn’t address the root cause of climate change: rising atmospheric CO2. Thus, ocean acidification, the “other CO2 problem,” would continue unabated, threatening marine life with calcium carbonate shells, like corals and shellfish.

Beyond these specific risks lie pervasive scientific and technological uncertainties. We lack precise knowledge of how much intervention is needed for a desired cooling, the full range of side effects, and the reliability of deployment technologies, which are largely conceptual or embryonic. Climate models, our primary tools for prediction, show considerable divergence in SRM simulations, especially for MCB and CCT. This is exactly why we need more research.

Finally, there’s the moral hazard (or mitigation displacement) argument. The mere prospect of an SRM “techno-fix” could diminish the urgency and political will for essential emissions reductions and adaptation efforts. While studies on individual public perception are mixed , the systemic risk that powerful actors with vested interests in fossil fuels might exploit SRM to delay decarbonization is very real.

A Planet Adrift: The Governance Void

As Jonathan Blake and I have written about extensively, perhaps the most daunting challenge is the profound lack of global governance mechanisms capable of managing technologies with such far-reaching consequences. The Earth’s atmosphere and climate are “planetary commons,” yet no agreed-upon rules, institutions, or decision-making processes exist for SRM.

This vacuum creates a high-stakes environment ripe for unilateral action. A single nation or a small coalition — with the United States and China often cited as possessing the capacity — might decide to deploy SRM, potentially optimizing the climate for its own benefit and triggering geopolitical instability, mistrust, and even conflict. The choices inherent in any SRM deployment (how much cooling, where, and by what method) are of legitimate concern to every nation.

Deep justice and equity issues are also at play. The Global South, least responsible for historical emissions but often most vulnerable to climate impacts, could also bear a disproportionate share of SRM’s negative side effects. Intergenerational equity is another casualty, as deployment could lock future generations into maintaining a risky intervention. The question of “who decides” is paramount, and current structures are ill-equipped for such momentous choices in a way that ensures legitimacy and fairness, particularly for marginalized communities.

Other people are skeptical of calls for moratoria more reasons of implementation, though these arguments are often confused, claiming that a moratorium will be both impossible to enforce and impossible to unwind. What such practical objections mainly underscore are the problems associated with a lack of effective “planetary governance institutions,” which is in turn a stark symptom of an “immature technosphere” — a civilization that has developed world-altering tools without the corresponding wisdom or cooperative structures to manage them safely. It underscores the urgent need for a new paradigm of planetary-scale coordination and foresight.

Growing Up: The Moratorium as a Step Towards Planetary Maturity

The concept of a “mature technosphere,” as envisioned by Grinspoon, Frank, and Walker, offers a powerful framework for understanding the role of an SRM deployment moratorium. Such a state is characterized by “planetary-scale cooperative dynamics,” “operational closure” (functioning within planetary limits), the “acquisition and application of collective knowledge” (planetary intelligence), “signal-sensitive boundaries” (recognizing and responding to threats), and “autopoiesis” (a self-sustaining, harmonious relationship with the planet).

A research-permissive moratorium isn’t a retreat from this future, but an active strategy to cultivate it.

• It directly supports the acquisition of collective knowledge by channeling efforts into comprehensive, transparent research on SRM’s efficacy, risks, and societal implications.

• The very process of negotiating, implementing, and overseeing such a moratorium, alongside coordinating global research and developing governance frameworks, inherently builds planetary-scale cooperative dynamics.

• Research under the moratorium aims to identify critical thresholds and consequences, helping to define the signal-sensitive boundaries and “safe operating limits” essential for planetary stability.

• By preventing premature deployment, the moratorium provides time to develop the understanding and governance needed for operational closure, ensuring any future interventions support, rather than disrupt, Earth’s systems.

This deliberate pause, dedicated to enhancing collective knowledge and building cooperative capacity, is how we begin to evolve towards a more cybernetically self-equilibrating global system – a hallmark of planetary intelligence.

Designing the Pause: A Moratorium for a Learning Planet

A functional SRM deployment moratorium must prevent premature action while actively fostering the knowledge and governance needed for responsible future decisions.

Core Principles:

1. Prevention of “premature” deployment: A clear halt to any large-scale, climate-altering SRM deployment until risks, benefits, and governance are far more comprehensively understood and globally addressed.

2. Fostering governed research: Active encouragement and funding of transparent, internationally coordinated research across scientific, technical, social, ethical, and governance dimensions. This includes modeling, lab studies, natural analogues, monitoring technology development, and crucial social science investigations. This is basically about enhancing planetary sapience.

3. Building governance capacity and public deliberation: Utilizing the moratorium period to develop robust, legitimate, equitable international governance frameworks and to promote widespread, inclusive public engagement globally, especially involving vulnerable communities and the Global South.

4. Clear distinctions: Establishing verifiable distinctions between permitted research (especially any small-scale outdoor experiments) and activities constituting deployment or posing significant transboundary risks, overseen by independent international bodies. Any small-scale outdoor experiments must be subject to rigorous international guidelines, including mandatory impact assessments, full transparency, public consultation, independent oversight, strict limits to prevent significant environmental effects, and clear termination criteria.

Breaking the Glass: When Might We Revisit Deployment?

The moratorium shouldn’t be indefinite, but its re-evaluation should only occur under exceptionally stringent conditions, signaling both extreme climate emergency and profound advancements in understanding and governance. Meeting these thresholds would trigger a global reassessment, not automatic deployment. All conditions across all three categories below must be demonstrably met:

Category 1: Climate state exigency (indicating severe, unmanageable climate change despite maximal efforts)

• Threshold 1.1: Sustained global mean surface temperature anomaly exceeding 2.0°C–2.5°C above pre-industrial levels for 5–10 consecutive years, despite documented, globally concerted, and maximally feasible efforts in emissions reductions and CDR fully consistent with a 1.5°C pathway.

• Threshold 1.2: Irrefutable scientific evidence (e.g., IPCC special report confirmation) of the imminent (within 1-2 decades) and unavoidable crossing of one or more major planetary-scale climate tipping points (e.g., irreversible collapse of West Antarctic/Greenland ice sheets, widespread abrupt permafrost thaw, large-scale Amazon dieback) leading to catastrophic global impacts, where SRM is assessed with high confidence to be the only viable means to temporarily avert or slow the transition.

• Threshold 1.3: Sustained, multi-year, globally synchronous extreme climate impacts (e.g., mega-droughts, heatwaves, floods) leading to widespread, severe food and water insecurity affecting >25% of the global population, with high scientific confidence that these impacts are directly attributable to anthropogenic climate change and are projected to worsen catastrophically without rapid intervention beyond mitigation/CDR.

Category 2: Scientific understanding & technological readiness (ensuring SRM is well-understood and controllable)

• Threshold 2.1: High-confidence (>90%) scientific consensus (multi-model, observationally-validated research) on the full spectrum of global and regional climate responses (temperature, precipitation, circulation, cryosphere) and biogeochemical impacts (ozone, ecosystems, carbon cycle) for specific, well-defined SRM deployment scenarios, including robust uncertainty quantification.

• Threshold 2.2: Demonstrated and independently verified capability to reliably model, predict, and monitor intended effects and unintended side-effects of proposed SRM methods with high resolution, including robust attribution systems to distinguish SRM impacts from natural variability and GHG changes.

• Threshold 2.3: Successful completion of a phased, transparent, internationally governed research program, including any small-scale, non-climate-altering outdoor experiments (where deemed essential and safe after rigorous assessment), validating key assumptions about SRM processes, efficacy, and localized impacts, with peer-reviewed published results.

• Threshold 2.4: Development and proven viability of deployment and termination technologies that are safe, reliable, and controllable, including strategies to minimize termination shock (e.g., gradual phase-out protocols).

Category 3: Governance & societal preparedness (ensuring global legitimacy, equity, and control)

• Threshold 3.1: Establishment and ratification of a comprehensive, legitimate, broadly accepted international legal and governance framework for SRM, with powers for deployment decisions, oversight, monitoring, enforcement, adaptive management, liability, and redress/compensation, ensuring equitable representation (especially for vulnerable nations and the Global South).

• Threshold 3.2: Documented evidence of widespread global public understanding of SRM risks/benefits, and established processes for informed, meaningful, inclusive public and stakeholder deliberation and consent/dissent in potentially affected regions worldwide.

• Threshold 3.3: International agreement on robust ethical guidelines for SRM deployment, addressing intergenerational equity, distributive justice, mitigation deterrence, and conditions for deployment/cessation, developed through inclusive global dialogue.

This multi-layered “socio-technical lock-in” ensures that any move away from the moratorium is driven by concurrent, significant advancements across the board — climate necessity, scientific certainty, and global readiness. The international process of debating and agreeing upon these very thresholds would itself be a profound exercise in building planetary-scale intelligence and cooperative capacity.

Choosing the Telescope Over the Thermostat (For Now)

The call for a research-permissive SRM deployment moratorium isn’t an admission of defeat in the face of climate change, nor is it a rejection of human ingenuity. It is, rather, an embrace of a more profound form of ingenuity: the capacity for collective foresight, cautious deliberation, and responsible stewardship of our shared planetary home. It is a recognition that before we attempt to seize the global thermostat, we must first improve our collective vision through the telescope of rigorous, ethical, and globally coordinated research.

This moratorium is an active strategy for cultivating the attributes of a “mature technosphere,” moving us from being an unconscious, destabilizing force to a conscious, potentially stabilizing intelligence within the Earth system. It’s a proposal for investment in learning, in building trust, and in developing the global cooperative frameworks that are prerequisites for navigating the complex, high-stakes challenges of the Anthropocene.

The path forward demands unwavering commitment to the fundamentals: drastic emissions reductions and scaling up sustainable carbon dioxide removal. SRM can never be a substitute for these. But by pausing on deployment while actively pursuing knowledge and building governance, we choose deliberation over desperation. We choose to evolve our planetary intelligence, striving for a future where, as Grinspoon, Frank, and Walker suggest, “wise self-management and planetary management [are] one and the same.” This is the urgent, and ultimately hopeful, task of our time.