16 September 2025
On 16 September, the world marks the International Day for the Preservation of the Ozone Layer - a day of action initiated by the United Nations. This year's theme is "From science to global action" - a reference to the fact that scientific findings have underpinned successful political action to protect the ozone layer for decades.
Dr. Jens-Uwe Grooß from the Institute of Climate and Energy Systems - Stratosphere (ICE-4) is a member of the International Ozone Commission and has been researching the chemistry of the stratosphere for many years. Together with his team, he has recently made significant improvements to an atmospheric model that will enable even more accurate predictions of ozone depletion in the future. In this interview, he explains why the ozone layer is vital for all of us, how current research is solving new mysteries, and why - 38 years after the Montreal Protocol came into force - we must remain vigilant.
Dr. Grooß, why is the ozone layer so important for all of us - and what condition is it in today?
The ozone layer filters out the harmful UV radiation from sunlight, making life on Earth possible as we know it. Without this protective UV filter, far more harmful rays would reach the Earth, with serious consequences for our health - skin cancer being one example - as well as for agriculture and our ecosystems. One of the main causes of the ozone hole is chlorofluorocarbons (CFCs), which were previously used in aerosols, refrigerators, and air conditioners. Thanks to the implementation of the Montreal Protocol, CFCs have been gradually phased out worldwide and their concentration in the atmosphere has been declining steadily for around 25 years. However, due to the long lifespan of CFCs, we will have to wait around 40 to 50 years before the ozone hole ceases to reappear above Antarctica each springtime.
The International Ozone Commission, of which you are a member, has published a statement on the occasion of "Ozone Day" warning against cuts in research funding. How dangerous are such cuts for the global protection of the ozone layer?
When it comes to the ozone layer, you could say that we have essentially understood the processes involved and all we need to do now is implement the Montreal Protocol. If we can do that, the ozone hole would no longer be a problem in 50 years' time. This might be possible without further accompanying research - but then cases such as illegal CFC production would go unnoticed, like the ones uncovered a few years ago thanks to atmospheric measurements. The Montreal Protocol therefore stipulates the need for scientific monitoring alongside measures to reduce emissions. Had British scientists not carried out ozone measurements in remote Antarctica for three decades starting in the 1950s, the ozone hole might never have been discovered - or at least not as early. That is why the many measuring stations dotted around the world are so important - including for detecting potential new environmental threats in good time. Unfortunately, funding for many measuring stations is currently at risk. In the USA, for example, the current administration has severely cut funding for climate and atmospheric research. This threatens to restrict the operation of measuring stations, and there is even talk of prematurely decommissioning functioning satellites.
The theme for this year's Ozone Day is "From science to global action". How does this relate to your work and the role of science more generally?
In environmental research in particular, it is important not to stay in the ivory tower and only understand findings on a scientific level, but to draw consequences from these findings and formulate recommendations for policymakers. Just as the Intergovernmental Panel on Climate Change (IPCC) regularly presents the results of climate research, the findings of ozone research and the policy recommendations derived from them were also communicated to policymakers in the 1980s. Of course, there was also resistance to the planned measures back then. A noteworthy factor was that the then British Prime Minister Margaret Thatcher - despite her conservative stance and many controversial decisions - was able to follow the scientific arguments as a trained chemist. Her support was an important cornerstone for the success of the Montreal Protocol.
You and your team have just made a significant improvement to an atmospheric model. What was your research about - and why was this improvement necessary?
Although the processes involved in stratospheric ozone depletion are largely understood, there were still some discrepancies. Atmospheric models simulate complex chemical processes to better understand how the composition of the atmosphere is changing. Model calculations now generally agree quite well with experimental observations. However, measurements in winter in the core of the polar vortex showed a significant decline in hydrogen chloride (HCl) every year - something that existing models had so far been unable to reproduce. In our study, we proposed additional chemical reactions that resolve this discrepancy in the Jülich atmospheric model known as CLaMS, which stands for the "Chemical Lagrangian Model of the Stratosphere." This is a small piece of the puzzle which helps to improve our understanding of atmospheric processes. Only in this way can reliable predictions be made about the impact of certain measures in the future.
Looking to the future, what are the biggest challenges for ozone research - and what motivates you personally to stay engaged with this topic?
The implementation of the Montreal Protocol and its subsequent amendments are a major success for international diplomacy. However, in about 50 years, we will not be exactly where we were in 1980, since the atmosphere has continued to change due to anthropogenic emissions. Rising carbon dioxide levels, global warming, and other factors all interact with ozone in the atmosphere. The challenge is to gain a better understanding of these interactions with the climate. I still find it fascinating to unravel this complex relationship. Achieving this requires the close interplay of modelling and measurements: only when observations and simulations go hand in hand can we truly comprehend atmospheric processes. Increasingly fast supercomputers can help us with this, but reliable observational data are equally crucial. One problem is that a number of important satellite-based measuring instruments have reached the end of their service life and no equivalent successors are yet available. This makes ground-based measurements all the more important, the funding of which is currently under discussion. It's impossible to say whether current and future measurements will lead to another "surprise" like the discovery of the ozone hole. But without atmospheric measurements, we might not even notice it in the first place.
