Rocket emissions and re-entry pollutants threaten to delay ozone recovery, but coordinated action and cleaner propulsion could prevent long-term damage.
The sharp increase in global rocket launches may hinder the recovery of the ozone layer, warns Sandro Vattioni. Although the risk is being underestimated, he notes that it could be reduced through proactive and coordinated measures.
In recent years, the expansion of satellite constellations in low Earth orbit has transformed the night sky, fueled by the rapid growth of the space industry. This progress creates major opportunities but also raises environmental challenges. Pollutants released during rocket launches and from burning debris during re-entry accumulate in the middle atmosphere, where they can damage the ozone layer — Earth’s shield against harmful ultraviolet radiation. Scientists are only beginning to fully assess the scale of this threat.
Investigations into how rocket emissions affect ozone began more than three decades ago, but for many years the impact was considered minimal. As the frequency of launches continues to rise, this view is shifting. In 2019, only 97 orbital launches were recorded worldwide, but by 2024 the figure had climbed to 258, with projections pointing to continued rapid growth.
A long-underestimated concern
Unlike ground-level pollutants, emissions from rockets and re-entering satellites can persist in the middle and upper atmosphere up to 100 times longer, since removal processes such as precipitation do not occur at those altitudes. While most launches take place in the Northern Hemisphere, atmospheric circulation eventually distributes the pollutants globally.
To investigate long-term effects, researchers from ETH Zurich and the Physical Meteorological Observatory in Davos (PMOD/WRC), in collaboration with Laura Revell’s international team at the University of Canterbury, used a chemistry–climate model to simulate how future emissions might impact the ozone layer by 2030.
In a high-growth scenario with 2,040 annual launches by 2030 — roughly eight times the 2024 total — the model predicts that global average ozone thickness would decrease by nearly 0.3%. Seasonal losses could reach as much as 4% over Antarctica, where the ozone hole continues to reappear each spring.
While these reductions may appear small, the context is critical. The ozone layer is still recovering from earlier depletion caused by long-lived chlorofluorocarbons (CFCs), which were banned under the 1989 Montreal Protocol. Even today, global ozone thickness remains about 2% below pre-industrial levels, and full recovery is not expected until around 2066. The study suggests that unchecked rocket emissions — which currently remain unregulated — could push this timeline back by several years or even decades, depending on how quickly the space industry expands.
With rockets, too, the choice of fuel matters
The main contributors to ozone depletion from rocket emissions are gaseous chlorine and soot particles. Chlorine catalytically destroys ozone molecules, while soot particles warm the middle atmosphere, accelerating ozone-depleting chemical reactions.
While most rocket propellants emit soot, chlorine emissions primarily come from solid rocket motors. Currently, the only propulsion systems that have a negligible effect on the ozone layer are those which use cryogenic fuels such as liquid oxygen and hydrogen. However, due to the technological complexity of handling cryogenic fuels, only about 6% of rocket launches currently use this technology.
Re-entry effects are still uncertain
We would like to mention that our study only considered emissions released from rockets during ascent into space. But this is only part of the picture. Most satellites in low Earth orbit re-enter the atmosphere at the end of their operational life, burning up in the process.
This process generates additional pollutants, including various metal particles and nitrogen oxides, due to the intense heat generated upon re-entry. While nitrogen oxides are known to deplete ozone catalytically, metal particles may contribute to forming polar stratospheric clouds or serve as reaction surfaces themselves, both of which can intensify ozone loss.
These re-entry effects are still poorly understood and not yet incorporated into most atmospheric models. From our point of view, it is clear that with increasing satellite constellations, re-entry emissions will become more frequent, and the total impact on the ozone layer is likely to be even higher than current estimates. Science is called upon to fill these gaps in our understanding.
Needed: Foresight and coordinated action
But that alone will not be enough. The good news: We believe a launch industry that avoids ozone-damaging effects is entirely possible: Monitoring rocket emissions, minimizing the usage of chlorine and soot-producing fuels, promoting alternative propulsion systems, and implementing the necessary and appropriate regulations are all key to ensuring that the ozone layer continues its recovery. This will take coordinated efforts between scientists, policymakers, and industry.
The Montreal Protocol successfully demonstrated that even planetary-scale environmental threats can be addressed through global cooperation. As we enter a new era of space activity, the same kind of foresight and international coordination will be needed to avoid harmful effects on the ozone layer – one of the Earth’s most vital natural shields.
Reference: “Near-future rocket launches could slow ozone recovery” by Laura E. Revell, Michele T. Bannister, Tyler F. M. Brown, Timofei Sukhodolov, Sandro Vattioni, John Dykema, David J. Frame, John Cater, Gabriel Chiodo and Eugene Rozanov, 9 June 2025, npj Climate and Atmospheric Science.
DOI: 10.1038/s41612-025-01098-6
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