004 | Regulating the Sky: How the Ozone Regime Could Govern Stratospheric Aerosols
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Regulating the Sky: How the Ozone Regime Could Govern Stratospheric Aerosols
📘 Summary of: "Rockets, Satellites, and Stratospheric Aerosol Injection: Regulating Human Impacts on Stratospheric Aerosols Under the Ozone Regime" from Environment: Science and Policy for Sustainable Development, Volume 67, 2025 by Daniel Bodansky and Nicolás Esguerra.
A tale of two approaches
The stratospheric ozone layer faces a new threat fifty years after scientists first warned about damage from chlorofluorocarbons. This time, the danger comes from the booming commercial space industry, accumulating space debris and potential future attempts to cool the planet by injecting reflective particles into the upper atmosphere. A new legal analysis finds that the Vienna Convention and Montreal Protocol are the right framework to address these emerging challenges for the ozone layer.
An Emerging Problem in the Stratosphere
Stratospheric aerosols are tiny particles suspended 10-50 kilometers above Earth. They provide surfaces where chemical reactions can destroy ozone molecules and also influence atmospheric temperature and circulation, affecting ozone-destroying reaction rates.
Human activities are altering and introducing new sources of these aerosols. Rocket launches emit soot and materials that form aerosols or interact with existing ones. As commercial space companies launch satellite constellations numbering in the thousands, these impacts will multiply. Space debris reentering Earth's atmosphere releases metal particles that settle into the stratosphere and accumulate on aerosols, potentially enhancing their ozone-depleting effects.
Looking ahead, some scientists and others have proposed deliberately introducing reflective particles into the stratosphere to cool the planet, sometimes referred to as stratospheric aerosol injection (SAI). While proponents focus on the climate effects, such interventions could significantly impact the ozone layer through both direct chemical interactions and indirect effects on stratospheric conditions.
How the Ozone Regime Works
The ‘ozone regime’ operates through a well-established institutional framework built around two core treaties, the Vienna Convention and the Montreal Protocol, and ultimately serves to protect the Earth's stratospheric ozone layer by phasing out the production and consumption of ozone-depleting substances. The Vienna Convention provides the overarching legal framework, while the Montreal Protocol contains the specific regulatory provisions and control measures. Both treaties work in tandem through a network of governing bodies, subsidiary organs, and expert assessment panels that enable science-based decision-making.
As illustrated in the figure below, the Conference of the Parties to the Vienna Convention and the Meeting of the Parties to the Montreal Protocol serve as the regime's decision-making bodies. These are supported by several key institutions: the Ozone Secretariat coordinates activities, the Open-Ended Working Group prepares decisions and three Assessment Panels (Scientific, Environmental Effects, and Technology and Economic) provide expert guidance. The Multilateral Fund assists developing countries with implementation, while a Non-Compliance Procedure ensures adherence to commitments
Figure 1: Institutional framework of the ozone regime under the Vienna Convention and Montreal Protocol, showing the main decision-making bodies and supporting mechanisms for coordination, implementation, compliance, and financial assistance. Adapted from Bodansky and Esguerra, 2025.
Why the Ozone Treaties Work
In this paper, legal scholar Daniel Bodansky and policy specialist Nicolás E. Esguerra review the existing ozone treaties with respect to aerosols, finding that they are the right governance framework for addressing the impacts of stratospheric aerosols on the ozone layer. In particular, they are relevant as the existing international system designed to protect the stratospheric ozone layer, enjoying near-universal participation and with a proven track record of phasing out ozone-depleting substances.
The regime's scientific and technical advisory panels possess the expertise needed to assess how aerosols affect the ozone layer and what those changes mean for human health and ecosystems. The regime already includes processes for building national scientific capacity, evaluating research, and identifying knowledge gaps. The Scientific Advisory Panel (SAP) has already begun analyzing this issue, having incorporated an initial review of SAI in the 2022 Ozone Assessment in conjunction with a request by countries for assessment of SAI's effects on stratospheric ozone.
Three Pathways For Addressing Stratospheric Aerosols under the Ozone Regime
The comprehensive structure, outlined in Figure 1, demonstrates how the regime could be extended to address stratospheric aerosols’ impact on the ozone layer. The authors outline three legal options, each with distinct tradeoffs.
Decisions by the Parties would be the fastest approach. The governing bodies could adopt regulations that take effect immediately without requiring individual countries to ratify them. However, these decisions generally aren't legally binding: they function as recommendations. While voting rules allow decisions by two-thirds majority, parties have traditionally operated by consensus, which could slow action if the issue was controversial.
Amending the Montreal Protocol would fit the Protocol's regulatory character. The Protocol has been amended before to address newly identified substances. However, regulating aerosols would require a fundamental shift. Unlike substances phased out through production limits, aerosols would require regulating "upstream" activities like rocket launches. This would be a technically and politically complex undertaking and raise new enforcement questions.
Adopting a New Protocol would insulate the successful Montreal Protocol from potential controversies and allow parties to design different institutional mechanisms if needed. However, negotiating a new treaty would take more time and could open more areas for disagreement than the other options.
The SAI Question
The analysis raises a thorny issue: should the ozone regime also govern potential future use of stratospheric aerosol injection for climate purposes? The authors avoid taking positions on whether SAI should be pursued or whether the ozone regime should make such decisions. They make two narrower points: the regime is the appropriate body to assess SAI's risks to the ozone layer, and it has already begun doing so. However, if parties amend the Montreal Protocol to address existing aerosol sources like rockets, that amendment might be seen as a precedent for regulating SAI. This could introduce politically divisive climate engineering debates that could undermine the Protocol's effectiveness.
A Proactive Approach
Human influences on stratospheric aerosols are projected to increase substantially in coming years. The ozone regime's science-based, precautionary approach and proven track record make it well-suited to address this threat before significant damage occurs. The authors recommend the regime initially deepen its scientific assessments, then take action if effects prove significant– starting with non-binding guidance and progressing to legal regulation through either a Protocol amendment or new treaty as warranted.
The analysis offers a hopeful path for protecting the ozone layer's hard-won recovery from an entirely new category of threats: human impacts on the ozone layer via stratospheric aerosols.
The Final Cut: Rising human activity in the stratosphere, from rockets to potential aerosol injections, poses new risks to the ozone layer. This analysis argues that the Vienna Convention and Montreal Protocol provide the most effective framework to manage these threats through established, science-based governance
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