16 September 2026
Heat and drought significantly increased the risk of wildfires across many parts of Germany this summer, with fire brigades called into action in several federal states. The situation was particularly severe in North Rhine-Westphalia: Several hundred hectares of forest burned in the Hürtgen Forest in the district of Düren. In the nearby High Fens on the Belgian side of the border, several thousand hectares were affected. To mark World Ozone Day on 16 September, the UN Environment Programme is highlighting an aspect of climate protection that may seem surprising at first glance: under the slogan "Global action for a cooler planet", it is also drawing attention to the Montreal Protocol's contribution to protecting the climate.
The Montreal Protocol was adopted in 1987 to protect the ozone layer. The treaty involved countries committing to phase out ozone-depleting substances such as chlorofluorocarbons (CFCs), which were previously used in aerosols, refrigerators, and air conditioners. Ten years ago, the protocol was expanded through the Kigali Amendment to include the gradual phase-out of refrigerants that are particularly harmful to the climate. As a result, the Montreal Protocol also plays an important role in climate protection.
We spoke to atmospheric scientist Dr. Jens-Uwe Grooß from the Institute of Climate and Energy Systems - Stratosphere (ICE-4) at Forschungszentrum Jülich about how ozone protection and climate protection are connected and what the Kigali Amendment has achieved. Grooß has been conducting research into the ozone layer for many years and is involved in the international scientific assessments carried out under the Montreal Protocol.
Following a summer of prolonged heatwaves and major forest fires, the issue of climate protection is particularly prominent. This year's World Ozone Day is also celebrating ten years since the adoption of the Kigali Amendment. What exactly does an agreement to protect the ozone layer have to do with global warming?
At first glance, the connection isn't immediately obvious. The Montreal Protocol was originally concluded to protect the ozone layer. To achieve this, the production of CFCs was initially restricted internationally before being banned altogether. Hydrofluorocarbon (HFC[JUG1.1][AT2.1]) refrigerants, compounds that do not contain chlorine, were used as replacements. While HFCs pose no threat to the ozone layer and have a lower global warming potential than many CFCs, they are still very damaging to the climate.
The Kigali Amendment was therefore adopted 10 years ago to gradually reduce the use of these substances as well. This makes sense, as it meant the existing political and international infrastructure could be used - for example, for reporting requirements and monitoring mechanisms.
The Kigali Amendment is predominantly concerned with refrigerants used in refrigeration and air-conditioning systems. Why are these substances particularly problematic for the climate?
Many of these refrigerants have a very strong greenhouse effect. For example, the refrigerant R-134a, which is used in many air-conditioning systems in cars, has a very high global warming potential. Over a period of 100 years, the same amount of R-134a contributes around 1,400 times more to global warming than the same amount of CO2. With R-410A, which is used in heat pumps and air-conditioning units, for example, the factor is even higher, at more than 2,000. As long as the refrigerants remain within the cooling circuits, this is not initially a problem. However, leaks can occur during production, operation, and disposal, allowing these gases to escape into the atmosphere.
The Montreal Protocol is seen as one of the most successful international environmental agreements. What can we learn from it for climate protection?
The Montreal Protocol demonstrates that international environmental policy can work if the international community agrees on binding rules, while monitoring and reviewing their implementation over the long term. In my view, this international cooperation is one of its great strengths. The agreement had already had a positive effect on the climate even before the Kigali Amendment. The original phase-out of CFCs was important not only for the ozone layer, but also for climate protection.
When it comes to climate protection, however, the task is considerably more complex. Greenhouse gas emissions affect practically all areas of our lives and our economy - from energy supply and transport to industry and the building sector. That is why we need both a reliable political framework and sensible long-term decisions in our everyday lives. Anyone planning to install a new heating system today, for example, should not just consider the initial costs, but also which energy sources will still be economically viable and climate-friendly in 10 or 20 years' time.[AT3.1] A heat pump using a climate-smart refrigerant such as propane, for instance, can offer a sustainable solution.
As temperatures rise, global demand for air conditioning and cooling is increasing. Are we at risk of a vicious circle: the warmer it gets, the more we need to cool - and the more we contribute to global warming?
Such an effect is certainly possible: as temperatures rise, the demand for air conditioning increases - and with it, energy consumption. How we cool is therefore crucial. On hot, sunny days, for example, we can use the high output from photovoltaic systems. At the same time, we should use appliances that are as energy-efficient as possible and refrigerants with a low global warming potential. This helps prevent the growing demand for cooling from further exacerbating climate change. However, the truth is that greenhouse gases are generally much more difficult to regulate than CFCs. This makes climate protection more complicated - but no less necessary.
The Montreal Protocol is widely regarded as a success story when it comes to protecting the ozone layer. What is the current status of its recovery?
As far as the ozone layer is concerned, I can say with conviction that the Montreal Protocol is working. And it shows that international environmental agreements are possible. However, it will still take some time for the ozone hole to disappear completely. We expect the ozone layer to return to 1980 levels by the start of the second half of this century. This is something we can estimate using various observations and models. We now have a good understanding of the processes taking place in the atmosphere. However, all of this depends on countries continuing to adhere to the agreements of the Montreal Protocol.
The next international scientific assessment of ozone depletion is due to be published at the end of this year. You and other Jülich researchers are involved in compiling the report What exactly are you investigating - and which questions regarding the future of the ozone layer are particularly interesting at present?
An important component of the Montreal Protocol is that the current state of research on the ozone layer[JUG4.1][AT5.1] is comprehensively assessed every four years. This involves researchers from all over the world compiling findings from the past few years. The findings range from measurements of the ozone layer and ozone-depleting substances to model simulations and projections of future developments - everything that has been published on the subject in the scientific literature over the last four years. The results are also summarized for policymakers and can provide the basis for amending existing regulations. The central question is, of course, how far has the ozone layer recovered, and how will it develop in the future? But new findings on individual processes are also incorporated. These include, for example, my study on chlorine chemistry[AT6.1], which allowed us to resolve a discrepancy that had previously existed in ozone depletion models. Alongside me, our institute director at ICE-4, Prof. Dr. Michaela Hegglin, and my FZJ colleague Dr. Johannes Laube are also working on the current report.
The report, which is due to be published at the end of the year, once again highlights the importance of ongoing research in this field. [JUG7.1]At any rate, the development of the ozone layer shows that long-term, collaborative action pays off. This is an important lesson that can also give us encouragement when it comes to climate protection - even if there is still a great deal to be done in that area.
