Ozone depletion in the Arctic causes weather anomalies

While many people are familiar with the ozone hole over Antarctica, the problems facing the protective ozone layer in the stratosphere above the Arctic have received comparatively little attention until recently.

In 2011 and 2020, for example, a significant thinning of the ozone layer over the North Pole led to weather anomalies across the entire Northern Hemisphere, including an exceptionally warm and dry spring in central and northern Europe and Russia, as well as unusually wet conditions in the polar regions. Whether a direct causal link exists between the destruction of stratospheric ozone and these weather anomalies, however, remains contested in climate science.

To address this question, a team of experts led by ETH Zurich carried out simulations that incorporated ozone depletion into two different climate models, and found that the most likely primary cause of the weather anomalies observed in the Northern Hemisphere in 2011 and 2020 is ozone depletion over the Arctic. The simulations were consistent with observational data from both years (as well as eight further events of this kind used for comparison purposes). When the scientists removed ozone depletion from their models, they were unable to reproduce the results.

««What surprised us most from a scientific perspective is that the models we used for the simulation are completely different from one another, yet they nevertheless produced similar results», says study co-author Gabriel Chiodo, an expert in climate dynamics at ETH Zurich.

According to the scientists, ozone depletion occurs when temperatures in the Arctic are very low. «Ozone depletion only takes place when it is cold enough and the polar vortex in the stratosphere, approximately 30 to 50 kilometres above the ground, is strongst», explains the study's lead author, Marina Friedel, a doctoral candidate in environmental sciences at the same university.

Normally, ozone absorbs the sun's UV radiation, warms the stratosphere, and helps break down the polar vortex in spring. However, when less ozone is present, the stratosphere cools and the vortex strengthens. «A strong polar vortex then leads to the effects observed at the Earth's surface», said Dr. Chiodo. Ozone thus appears to play a fundamental role in the temperature and circulation changes in the Arctic.

These findings could help climate scientists produce more accurate seasonal weather and climate forecasts, enabling better prediction of temperature fluctuations that are crucial for agriculture. However, further research is needed to understand the future development of the ozone layer. Although ozone-depleting substances such as chlorofluorocarbons (CFCs) have been banned since 1989, they are extremely long-lived and can remain in the atmosphere for up to a century, continuing to damage the ozone layer. «This raises the question of how quickly the ozone layer recovers and how this affects the climate system», Friedel concluded.