The Antarctic ozone hole is the most discussed, yet the Arctic often sees ozone thinning as well. In 2020 the Arctic experienced a record-breaking drop, though overall such events are rarer there than in the Antarctic. Why is that? The ozone layer sits high in the stratosphere and blocks much of the sun’s ultraviolet radiation. It is monitored by ground stations and satellites like Sentinel-5P from the European Copernicus program, providing ongoing data on its health.
Each year, from roughly July or August to October or November, the Antarctic ozone layer develops a large thinning that later heals. The Arctic, by contrast, rarely shows a comparable event. The last significant episodes in the north occurred during spring in 1997, 2011, and 2020, and these Arctic holes have consistently been smaller than those in the southern hemisphere.
The 2020 Arctic thinning reached about one million square kilometers, according to Diego Loyola of the German Aerospace Center (DLR). That figure is small next to Antarctica, which reached roughly 24.8 million square kilometers in the same year.
Loyola is among researchers who used data from the Sentinel-5P TROPOMI instrument two years ago. They observed a peculiar opening over the North Pole, described in a study published in Atmospheric Chemistry and Physics, which reported record-low ozone values.
“From March 14 for five weeks, the Arctic ozone columns dropped to levels that would normally be called ozone holes, below 220 Dobson units,” explains an Ecuadorian scientist involved in the work.
“Ingredients” for a hole in the ozone layer
Ozone is a gas in the air; it can be protective or harmful depending on where it is. Javier García-Serrano of the Meteorology group at the University of Barcelona notes that ground-level ozone from traffic and industry is harmful, while stratospheric ozone shields us from ultraviolet radiation.
Both Loyola and García-Serrano emphasize that several conditions must align for a hole to form: extremely low stratospheric temperatures (below about -80°C), sunlight, wind patterns, and the presence of substances like chlorofluorocarbons (CFCs).
Cold temperatures in the stratosphere drive ozone depletion, especially in Antarctica where polar stratospheric clouds form. These clouds become active in the presence of sunlight and can convert ozone-destroying chemicals into reactive forms, accelerating ozone loss.
Polar stratospheric clouds contain ice crystals that help transform otherwise stable compounds into reactive species, triggering rapid chemical reactions that destroy ozone when sunlight returns. The polar vortex—strong, circular winds that trap air masses at very low temperatures—further concentrates these processes in the Antarctic region.
As stratospheric temperatures rise, ozone destruction slows, the polar vortex weakens, and conditions gradually return to normal levels.
Effect on weather
The World Meteorological Organization notes that ozone depletion would have been more severe in recent years without the Montreal Protocol. Substances that deplete ozone, such as CFCs and halons, were widely used in refrigerators and fire extinguishers and are now largely phased out. Yet these chemicals remain in the atmosphere for decades, keeping concentrations high enough to influence ozone levels.
Whether ozone changes feed into broader climate shifts is a long-standing scientific debate. In the Antarctic case, several studies have explored potential links for years. For instance, a 2011 study in Science by Columbia University researchers found that Antarctic ozone impacts atmospheric circulation down to the equator, increasing precipitation in subtropical regions. More recently, a 2020 Nature focus centered on the Arctic noted that thinning ozone often coincides with weather anomalies across the Northern Hemisphere. Springs in central and northern Europe, Russia, and especially Siberia were unusually hot and dry.
Researchers from the Federal Polytechnic University of Zurich ran climate-model simulations that included ozone depletion and found that the observed weather anomalies in 2011 and 2020 were largely tied to Arctic ozone thinning. García-Serrano and Loyola view these results as intriguing and plausible, though they acknowledge that the discussion is still evolving.
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