The new space age could thin the ozone layer

Research on the effects of rocket emissions on the ozone layer began over 30 years ago, but for a long time, these effects were considered small.¹ This perception is starting to change as launch activity accelerates. In 2019, there were just 97 orbital space rocket launches globally. By 2024, that number had surged to 258, and is expected to keep rising rapidly.²

A long-underestimated concern

In the middle and upper atmosphere, emissions from rockets and re-entering space debris can remain up to 100 times longer than emissions from ground-based sources due to the absence of removal processes such as cloud-driven washout. While most launches occur in the Northern Hemisphere, atmospheric circulation spreads these pollutants globally.

To better understand the long-term impact of increasing rocket emissions, we collaborated with an international research team led by Laura Revell from the University of Canterbury. Using a chemistry climate model developed at ETH Zurich and the Physical Meteorological Observatory in Davos (PMOD/WRC) we simulated how projected rocket emissions will affect the ozone layer by 2030.³

Assuming a growth scenario with 2,040 annual launches in 2030 ¡ª about eight times the figure for 2024 ¡ª global average ozone thickness would decline by almost 0.3%, with seasonal reductions of up to 4% over Antarctica, where the ozone hole still forms each spring.

While these numbers may seem modest at first sight, it¡¯s important to remember that the ozone layer is still recovering from past damage caused by long-lived chlorofluorocarbons (CFCs), which were successfully banned by the Montreal Protocol in 1989. Yet today, the thickness of the global ozone layer is still roughly 2% below pre-industrial levels and is not expected to fully recover until around 2066.⁴ Our findings indicate that emissions from rockets ¡ª currently unregulated ¡ª could delay this recovery by years or decades, depending on the rocket industry growth.

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.⁵

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.⁶

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.⁴ 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 ¨C one of the Earth¡¯s most vital natural shields.

Sandro Vattioni has written this article together with external page Timofei Sukhodolov from the external page Physical Meteorological Observatory Davos.