D.he climate change is not only causing the earth to warm up, it is also apparently causing an increased depletion of the ozone layer over the Arctic. And this despite the worldwide ban on the use of chlorofluorocarbons (CFCs) since 1987. This was the result of the analysis of the data measured during the one-year expedition of the German research vessel Polarstern from 2019 to 2020 in the Arctic. “Our measurements show that the chemical ozone loss over the Arctic in the spring of last year was greater than ever before,” says expedition leader Markus Rex from the Alfred Wegener Institute (AWI) in Bremerhaven and head of the MOSAiC expedition.
At a height where the ozone concentration is at its maximum, around 95 percent of the triatomic oxygen molecules were destroyed. The thickness of the ozone layer, which absorbs the high-energy ultraviolet radiation and protects life on earth, was reduced by more than half as a result. A comprehensive analysis of the data has now shown that this development is also a result of the high levels of carbon dioxide in the atmosphere. While the greenhouse gas warms the lower layers of the air, the atmosphere cools down correspondingly more strongly at an altitude of 15 to 50 kilometers.
Low temperatures release chlorine and bromine
The temperatures in the north polar region naturally drop particularly sharply in the winter months, when the arctic polar vortex, a stable low pressure area in the stratosphere, determines the weather. If the temperatures drop low enough, chlorine and bromine, which had entered the upper air layers with the CFCs and are bound to harmless substances there, are released and destroy the ozone.
An effect that is sometimes stronger, sometimes weaker, depending on the winter. However, current analyzes show a significant trend towards ever lower temperatures in the Arctic stratosphere during the winter months. This has been correlated with increasing greenhouse gas emissions, especially carbon dioxide, in the past few decades. The result is an increasing loss of ozone in the upper atmosphere, according to Rex’s researchers.
So far, it has been controversial whether the winters in the Arctic are actually getting colder, which could accelerate the depletion of the ozone layer. The measurements of the MOSAiC expedition now provide clear evidence of this. Computer calculations show that the recurring ozone depletion could continue until the end of the century if CO₂ emissions are not drastically reduced. Climate change also affects the prevailing wind systems because of the decreasing temperature differences between the tropics and the Arctic in the course of global warming. The researchers assume that this also contributes to lower temperatures in the polar vortex.
As the polar vortex drifts towards Europe again and again – as it did this spring – a declining ozone layer could also have consequences for our latitudes. According to the AWI researchers, higher UV radiation could lead to more sunburns and increase the risk of skin cancer. The Polarstern spent a year in the arctic pack ice. Frozen in an ice floe, it drifted towards the North Pole.