While many people are familiar with the hole in the ozone layer above the Antarctica, until recently less attention has been given to the problems the protective ozone in the stratosphere over the Arctic is also facing. In 2011 and 2020, for instance, a significant thinning of the ozone layer over the North Pole gave rise to weather anomalies across the entire northern hemisphere, including exceptionally warm and dry springs in central and northern Europe and Russia, or unusually wet conditions in the polar regions. However, whether there is a direct causal relationship between stratospheric ozone destruction and these weather anomalies has remained a matter of debate in climate science.
To clarify this issue, a team of experts led by ETH Zürich ran simulations which integrated ozone depletion into two different climate models, and discovered that the main cause of the weather anomalies in the northern hemisphere observed in 2011 and 2020 is most likely ozone depletion over the Arctic. The simulations coincided with observational data from these two years (as well as eight such events which were used for comparison purposes). Moreover, when the scientists removed ozone destruction from their models, they could not reproduce the results.
“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 study co-author Gabriel Chiodo, an expert in Climate Dynamics at ETH Zürich.
According to the scientists, ozone depletion occurs 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 kilometers above the ground,” explained study lead author Marina Friedel, a doctoral student in Environmental Sciences at the same university.
Usually, ozone absorbs UV radiation from the Sun, warming the stratosphere and helping to break down the polar vortex in spring. However, if there is less ozone, the stratosphere cools down and the vortex becomes stronger. “A strong polar vortex then produces the effects observed at the Earth’s surface,” Dr. Chiodo said. Thus, ozone appears to play a fundamental role in temperature and circulation changes around the Arctic.
These findings could help climate scientists build more accurate seasonal weather and climate forecasts, allowing for better predictions of temperature fluctuations, which are crucial for agriculture. However, more research is needed to understand the future evolution of the ozone layer. Although ozone-depleting substances such as chlorofluorocarbons (CFCs) have been banned since 1989, they are extremely long lived, and can linger in the atmosphere for up to a century, thus still damaging the ozone layer. “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,” Friedel concluded.
The study is published in the journal Nature Geoscience.
By Andrei Ionescu, Earth.com Staff Writer