How did we deplete the ozone layer, and what are the implications for Earth's climate? An interview with Yevgeny Rozanov.

— Could you please tell us how your scientific career began and what led you to research the ozone layer and its impact on Earth's climate?

— My career started with atmospheric process modeling under the guidance of one of the country's leading climatologists, Igor Leonidovich Karol. Back in the 1980s, we worked together on a two-dimensional atmospheric model. Thanks to Professor Karol's scientific connections, Paul Crutzen, a renowned researcher of the ozone layer and future Nobel laureate, came to St. Petersburg in 1993. This led to a fascinating exchange of scientific ideas, and we had intense debates that took an unexpected turn for me: Paul invited me to collaborate at the Max Planck Institute.

During his visit, we established our then two-dimensional model of chemistry and pollutant transport, and we conducted calculations on the state of the ozone layer during the last glacial maximum. The results were discussed with equal intensity, and Paul convinced me that a two-dimensional approach was insufficient; it did not account for atmospheric waves and dynamic transport processes. We needed a three-dimensional model capable of encompassing the complexity of processes influencing the climate. Inspired by this idea, I returned to Russia to work on three-dimensional modeling at my institute (A.I. Voeykov Main Geophysical Observatory. — editor's note). Unfortunately, it was a difficult time, funding was reduced, and at one point, scientific work virtually came to a halt.

I faced a choice: either move into business or seek opportunities to continue my work abroad. I tried my hand at business, but I found that direction unappealing. Therefore, when an offer came from the University of Illinois to work with Professor Michael Schlesinger's group, I decided to join them. Schlesinger was a prominent climatologist and was acquainted with many stars of global science, including Syukuro Manabe, who had recently received the Nobel Prize, and Mikhail Ivanovich Budyko — an outstanding Russian climatologist who was also considered deserving of this award. Budyko had a special talent, and he was highly respected in our circle for his ability to intuitively grasp climatic processes.

Working with a three-dimensional climate model in Professor Schlesinger's group allowed us to consider the influences of solar radiation, volcanic eruptions, and other key factors. Without ozone in the model, we would never have understood how solar and volcanic processes impact the climate. These studies laid the foundation for my future scientific path and reinforced my belief that detailed modeling is essential for understanding the processes that determine the state of Earth's climate.

— You claim that your contribution to the famous IPCC report was modest. Nevertheless, the report received a Nobel Prize, and you were one of its reviewers. Can you tell us about your involvement in this project and why you consider this report important?

— Although I indeed joined at the review stage, working on the report proved to be an invaluable experience for me. I had to delve into thousands of pages of documentation and discuss the most intricate scientific aspects with representatives from various disciplines. The IPCC report of 2007 was a significant milestone because it was during this time that major doubts about climate warming arose. For the first time, the group of experts convincingly stated that warming had begun as early as the 1970s and that it was likely caused by the increase of greenhouse gases in the atmosphere.

Working on the report taught me how crucial international cooperation is in science. It was a turning point: to gain public trust, support from scientists around the world representing different universities and specialties is essential. I learned to discuss complex topics, seek compromises, and find solutions that satisfied all participants. Nowadays, solitary research is becoming impossible, and the role of an individual in science is that of an organizer of a large team. This understanding led me to participate in international projects, such as the World Meteorological Organization's project assessing the depletion of the ozone layer, where I served as one of the authors.

— How do you assess the contribution of Russian science to international scientific projects and programs, such as the Radiometric Center in Davos? How would you describe the differences in scientific cultures between Russia and the West?

— The contribution of Russian scientists to international research has always been significant. We possess vast amounts of data, excellent specialists, and extensive geographical opportunities for observations. For example, one of my joint studies concerned the impact of solar activity on climate, and I endeavored to be a bridge between Russian and foreign science.

As for the differences, they undoubtedly exist. Scientific communication abroad in most fields is more open and frequent than in Russia. In Europe, it is customary to reach out to colleagues, share ideas and results. In our culture, the principle of "doing everything alone" has been valued for a long time, and this is still noticeable. Nevertheless, my colleagues, with whom I work in Russia, are adapting to these changes, and we have become much closer to international standards of interaction.

However, the current geopolitical situation significantly hampers scientific collaboration. For example, in many European countries, any interaction with Russian scientists is prohibited, which I believe is a serious mistake. Science should remain separate from politics — this is the principle on which the international scientific community stands. At the level of personal communication, scientists are open and interested in collaboration, and it is crucial to maintain this despite pressure from politicians.

“We work with a digital twin of the planet”

— What happened with the ozone layer issue? It used to be a hot topic, but then it faded from view. What is the current situation?

— The ozone layer issue has not disappeared; however, some positive changes have occurred. Ozone was long considered a stable part of the atmosphere, but since the 1980s, its levels have been rapidly declining, especially after the discovery of the ozone hole over Antarctica in 1985. This posed a serious threat because ozone protects us from ultraviolet solar radiation, excessive exposure to which can lead to skin cancer and eye problems.

Society consolidated to address this issue, and the Montreal Protocol was adopted, which limited the production of chlorofluorocarbons — substances that destroy ozone. The ozone layer began to recover, and by the 2000s, stabilization reached a noticeable level. However, it is still too early to talk about complete restoration. Moreover, we have detected an increase in emissions of CFC-11, which, according to some reports, is not being produced. This means we must continuously monitor the ozone layer to prevent irreversible changes.

However, since then, environmental issues have been overshadowed by climate warming discussions. Global warming has become the primary topic, and the ozone layer has partially taken a back seat.

— What are the main challenges and issues in modeling the ozone layer and its impact on climate?

— There are still several unresolved issues in ozone modeling. For instance, why does the concentration of ozone in tropical and temperate latitudes continue to decline in the lower stratosphere? There is a hypothesis that iodine-containing substances formed in the upper ocean layers are destroying ozone, but this requires evidence. Additionally, the increase in the number of rocket launches also affects ozone, as they release substances into the atmosphere that destroy ozone. In the future, we may reach a "singularity" where the number of launches exceeds reasonable limits.

Moreover, the impact of wildfires also requires study. Recent fires in Australia and California have led to a deepening of the ozone hole, but we cannot yet accurately determine how fires affect the ozone layer as a whole. Finally, climate change itself demands innovative approaches. For instance, there are proposals to release sulfur-containing pollutants into the stratosphere to cool the climate, but we know that such pollutants can destroy ozone. It is important to find a compromise between cooling the climate and protecting the ozone layer to avoid creating new problems.

— At the regional level, how can changes in the ozone layer affect the climate?

— Ozone significantly influences regional climate, especially during winter. For example, increased solar activity leads to greater ozone and temperature in the tropical stratosphere, which strengthens the polar vortex and results in warming in northern Europe and Siberia. A reduction in ozone weakens the vortex, making the weather less predictable and increasing the likelihood of extreme cold spells.

Today, scientists continue to track changes in the ozone layer and analyze their impact on the climate using complex models and modern technologies. The ozone layer remains a vital topic in climatology, and we still have much to learn about its influence on life on Earth.

— Let's talk about climate models. How can your working climate model assist in predicting and mitigating the effects of climate change?

— As is well known, the limit of predictability in meteorology is about a week, but I am dealing with climate, not weather. Skeptics argue: if you can't predict the weather, how can you predict climate changes? These are different things. Climate is the average weather over 30 years. We conducted a "historical comparison" of the model from 1960 to 2020 and evaluated how it reproduces climate changes during this time, comparing it with observations. The agreement turned out to be