Holes in the ozone layer are warning signs for the way we treat the air we breathe. The last breach opened up over the Arctic, and its size was what scared scientists: almost a million square kilometers. Almost a decade ago, it was not that big and it took so long to close.
The unprecedented 2020 northern hemisphere #OzoneHole has come to an end. The #PolarVortex split, allowing #ozone-rich air into the Arctic, closely matching last week's forecast from the #CopernicusAtmosphere Monitoring Service.
– Copernicus ECMWF (@CopernicusECMWF) April 23, 2020
“The ozone layer over the Arctic is severely depleted at an altitude of 18 kilometers. The last time this was observed was during the spring of 2011, ”said the European Commission’s Atmospheric Monitoring Service (CAMS) in a statement.
The Arctic breach recorded in March was responsible for a stratospheric polar vortex that circles the pole and, this year, was exceptionally strong and long lasting. "Temperatures in the stratosphere have remained low long enough to allow the formation of polar stratospheric clouds, resulting in large ozone losses in the Arctic," says the CAMS statement.
Bromine and chlorine suspended in polluted air, in contact with these clouds, disintegrated ozone over the region. As the days get longer, these chemicals react with sunlight to deplete stratospheric ozone.
To make matters worse, the temperatures at the poles are becoming increasingly unstable, and this affects not only the formation of these holes but also the time they take to close. "Cold air strengthens the polar vortexes, allowing them to do more damage to the ozone layer," University of Maryland climate scientist Ross Salawitch told Nexus Media News.
Not only did the prolonged stay of the vortex aggravate the problem: the air currents that would normally release oxygen molecules in the affected region were stopped, unable to advance over the pole. The hole finally closed in early April.
Half a century of recovery
Ozone is naturally generated by solar radiation; when it is reduced (as in polar winters), it also decreases, mainly due to its rapid oxidation with the proximity of any element. Nature opens a hole in each pole every year; the problem is when it opens, it increases in size and it takes time to close – when it closes.
The result of the (justified) panic that the researchers instilled in the authorities and the public when they discovered in 1985 a gigantic breach over the South Pole resulted in the Montreal Protocol.
The planetary agreement called for the banning of substances, such as chlorofluorocarbons (CFCs), which were not only causing the hole in the ozone layer to widen but preventing it from closing.
Global warming, the bad guy
Below, you can see a simulation in which, on the left, we see the evolution of the ozone layer (in orange, red and yellow) thanks to the end of the use of CFCs; on the right, as it would be without the Montreal Protocol.
The hole over Antarctica gets smaller every winter, but it will take about half a century before it closes. That's the good news. The bad thing is that climate change also damages the ozone layer.
As carbon dioxide traps heat in the lower layers of the atmosphere (the greenhouse effect), the planet's surface is getting hotter and the upper atmosphere is colder. This is precisely the cause of intense and lasting polar vortexes, and more high-altitude clouds, activating the substances that disintegrate ozone.