In 2020 the Ozone Layer above the Antarctic was big compared to previous years, both in depth and area. Data from the Copernicus Atmospheric Monitoring Service shows the maximum occurred in October with more than 20 million square kilometers.
Every year, humans emit chemicals into the atmosphere, some of which can alter the ozone layer. But the ozone layer is pretty robust. In order for the depletion of ozone to start, temperatures in the stratosphere must be below -78°C so chemicals become active enough to destroy ozone molecules. This doesn’t always happen, but a very stable Antarctic vortex helped keep temperatures below this threshold.
Polar vortexes are low-pressure systems, which form in the upper atmosphere. Whenever the polar Jetstream (a fast-flowing, meandering, narrow wind band) is strong, the vortex is more stable. The counterpart is a wavy polar vortex due to a weaker Jetstream. When the polar vortex is wavy, North America faces a cold winter. Australia, on the other hand, faces a wetter season.
If the polar vortex is both stable and strong, stratospheric clouds get colder, which creates the perfect conditions for the chemical reactions to start depleting the stratospheric ozone. The 2020 season had such a strong vortex. Researchers feared it could keep active for a long time and reach the maximum depletion detected. Luckily, this didn’t turn out to be the case.
It’s not the first time something like this has happened. The image below shows the comparison between previous depletion and the one from 2020. The 2020 hole’s area wasn’t as big as in 2017, but it was very stable and lasted longer. It only really started receding after mid-December.
The lowest record of the ozone layer’s hole happened in 2019 . The entire season can be seen in the video bellow from NOAA Ozone Watch. The colors alter from blue/purple, smaller concentrations of ozone, to green/yellow, bigger concentrations.
From year to year, there may be a bigger or smaller hole, but in the end, if we wouldn’t produce the ozone-depleting chemicals, this wouldn’t be a problem in the first place. We still need to reduce emissions, and there’s no real substitute for this.
Making the average ozone hole small enough not to be so harmful is still a challenge, however. We still emit ozone-depleting chemicals, which may not be yet banned. The Montreal Protocol list needs to be continuously changed, policies concerning the environment need to be as developing as the science behind it.