Ozone Depletion in Arctic Produces Weather Anomaly

Many people are familiar with the hole in the ozone layer above Antarctica, but what is less known is that occasionally, the protective ozone layer in the stratosphere above the Arctic also disintegrates, depleting the ozone layer there. This last happened in the spring months of 2020, and before that, in the spring of 2011.

Whenever the ozone layer is depleted, climate scientists then observe weather anomalies throughout the northern hemisphere. In central and northern Europe, Russia and especially in Siberia, spring is very warm and dry. In other areas, such as the polar regions, however, wet conditions prevail. This weather anomaly is especially noticeable in 2020. Switzerland is also unusually warm and dry that spring.

Whether there is a causal relationship between the destruction of stratospheric ozone and the observed weather anomalies is a matter of debate in climate research. Polar eddies in the stratosphere, which form in winter and decay in spring, also play a role. Scientists who have studied the phenomenon so far have come to contradictory results and different conclusions.

The new findings now shed light on the situation, thanks to doctoral student Marina Friedel and Swiss National Science Foundation Ambizione Fellow Gabriel Chiodo. Both are members of a group led by Thomas Peter, Professor of Atmospheric Chemistry at ETH Zurich, and work closely with Princeton University and other institutions.

Simulation reveals correlation

To uncover a possible causal relationship, the researchers ran simulations that integrated ozone depletion into two different climate models. Most climate models consider only physical factors, not variations in stratospheric ozone levels, in part because this would require more computational power.

But new calculations make it clear: the cause of the weather anomalies observed in the Northern Hemisphere in 2011 and 2020 was largely ozone depletion over the Arctic. The researchers’ simulations with the two models largely coincided with observational data from those two years, as well as eight other similar events used for comparison purposes. However, when scientists “turned off” ozone depletion in the model, they were unable to reproduce the results.

“What surprised us most from a scientific point of view was that, although the models we used for the simulations were very different, they yielded similar results,” said co-author Gabriel Chiodo, SNSF Ambizione Fellow at the Institute for Atmospheric and Climate Science.

The mechanism is explained

Phenomena like the one the researchers are now studying began with ozone depletion in the stratosphere. For ozone to be broken down there, the temperature at the Arctic must be very low. “Ozone depletion only occurs when temperatures are cold enough and the polar vortex is strong in the stratosphere, about 30 to 50 kilometers above ground level,” Friedel said.

Normally, ozone absorbs UV radiation emitted by the sun, thereby warming the stratosphere and helping to break up the polar eddies in the spring. But as ozone decreases, the stratosphere cools and the eddies become stronger. “The strong polar eddies then produce the effects observed on the Earth’s surface,” Chiodo said. Ozone thus plays a major role in temperature changes and circulation around the Arctic.

Greater accuracy is possible for long-term forecasts

The new findings could help climate researchers make more accurate forecasts of future seasonal weather and climates. This allows for better prediction of changes in heat and temperature, “which is important for agriculture,” Chiodo said.

Friedel added, “It will be interesting to observe and model the future evolution of the ozone layer.” This is because ozone depletion continues, even though ozone-depleting substances such as chlorofluorocarbons (CFCs) have been banned since 1989. CFCs are extremely long-lived and persist in the atmosphere for 50 to 100 years; their potential to cause ozone destruction persists for decades after they are removed from circulation. “But CFC concentrations continue to decline, and this raises questions about how quickly the ozone layer recovers and how this will affect the climate system,” he said.

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