The hole in the ozone layer over Antarctica is well known, but not many know that occasionally there is a hole over the Arctic as well. The last incidents happened in the string of 2011 and 2020. According to a study published in Nature Geoscience, these changes in ozone levels were responsible for weather anomalies felt across the world.
Climate researchers observe weather anomalies across the entire northern hemisphere every time this happens. Especially in central and northern Europe and parts of Russia, spring in those years was exceptionally warm and dry. In contrast, in the polar regions, wet conditions were more common than usual.
Whether this is a casual relationship between ozone destruction and these weather changes is still a matter of debate amongst the scientific community. It’s likely that the polar vortex in the stratosphere — which forms in the winter and disappears in the spring — also plays a role. So far, many research groups have studied this phenomenon and arrived at different conclusions. This is because most models developed so far only consider physical factors but do not take into consideration ozone levels, partly because it would need much more computing power.
This new study now sheds light on this situation, thanks to a team of researchers from ETH Zurich, Switzerland. The authors ran multiple simulations to examine ozone depletion in two different climate models that considered ozone levels. The new calculations make it clear: the weather anomalies in 2011 and 2020 were caused by the ozone depletion over the Arctic. The simulations largely coincided with actual data over those two years, as well as eight other events that were used for comparison purposes.
“What surprised us most from a scientific point of view is that, even though the models we were using for the simulation are utterly different, they produced similar results,” said Gabriel Chiodo, SNSF Ambizione Fellow at the Institute for Atmospheric and Climate Science.
According to the team, it all starts with ozone depletion in the stratosphere. This only happens when temperatures in the Arctic are very low. “Ozone destruction occurs only when it is cold enough, and the polar vortex is strong in the stratosphere, about 30 to 50 kilometres above the ground,” said Marina Friedel.
Under normal circumstances, ozone absorbs UV radiation emitted by the sun, warming the stratosphere and breaking down the polar vortex in the spring. However, when there’s less ozone, the temperature in the stratosphere drops, and the vortex gets stronger. “A strong polar vortex then produces the effects observed at the Earth’s surface,” said Chiodo. This study confirms that ozone levels play an important role in temperature and circulation changes around the North Pole.
According to the authors, the new findings have the potential to help climate researchers be more accurate in predicting climate changes in the future.
“It will be interesting to observe and model the future evolution of the ozone layer, said Friedel. After all, ozone depletion continues even though ozone-depleting substances — such as chlorofluorocarbons (CFCs) — have been banned since 1989. These compounds can stay in the atmosphere for 100 years. This means their potential to destroy the ozone layer can last decades even after they have been taken out of circulation. “Yet CFC concentrations are steadily declining, and this raises the question of how quickly the ozone layer is recovering and how this will affect the climate system,” concluded the researcher.
Friedel, M., Chiodo, G., Stenke, A. et al. Springtime arctic ozone depletion forces northern hemisphere climate anomalies. Nat. Geosci. 15, 541–547 (2022). https://doi.org/10.1038/s41561-022-00974-7