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Add to Preferred SourcesThe record-breaking 2020 Antarctic ozone hole finally closed at the end of December after an exceptional season due to naturally occurring meteorological conditions and the continued presence of ozone-depleting substances in the atmosphere.
The 2020 Antarctic ozone hole grew rapidly from mid-August and peaked at around 24.8 million square kilometres on 20 September 2020, spreading over most of the Antarctic continent.
It was the longest-lasting and one of the largest and deepest holes since the ozone layer monitoring began 40 years ago. It was driven by a strong, stable, and cold polar vortex and very cold temperatures in the stratosphere (the layer of the atmosphere between around 10 km and round 50 km altitude). The same meteorological factors also contributed to the record 2020 Arctic ozone hole.
This is in contrast to the unusually small and short-lived Antarctic ozone hole in 2019.
“The last two ozone hole seasons demonstrate the year-to-year variability of the ozone hole and improve our understanding of the factors responsible for its formation, extent, and severity,” said Oksana Tarasova, head of WMO Atmospheric Environment Research Division, which oversees WMO Global Atmosphere Watch network of monitoring stations.
Strong Polar Vortex
Ozone depletion is directly related to the temperature in the stratosphere, which is the layer of the atmosphere between around 10 km and round 50 km altitude. This is because polar stratospheric clouds, which have an important role in the chemical destruction of ozone, only form at temperatures below -78°C.
During the Southern Hemisphere spring season (August – October) the ozone hole over the Antarctic increases in size, reaching a maximum between mid-September and mid-October (NASA Ozone Watch image of 2020 ozone hole at its September peak pictured left). When temperatures high up in the atmosphere (stratosphere) start to rise in late Southern Hemisphere spring, ozone depletion slows, the polar vortex weakens and finally breaks down, and by the end of December ozone levels have returned to normal.
However, in 2020, a strong, stable and cold polar vortex kept the temperature of the ozone layer over Antarctica consistently cold, preventing the mixing of ozone depleted air above Antarctica with ozone rich air from higher latitudes.
The EU Copernicus Atmospheric Monitoring Service reported that ozone analyses showed the ozone hole had closed on 28 December.
Every season, the appearance of the ozone hole and its evolution is monitored by means of satellites and a number of ground-based observing stations.