The unprecedented Northern Hemisphere hole in the ozone layer has closed up after a month of lurking above the Arctic.
However, this is no reason for humanity to start popping the champagne. The unusual ozone hole (and its recovery) had little to do with human activity or even changes in pollution levels from the Covid-19 lockdown, but a freakishly strong polar vortex around the North Pole.
Scientists from Copernicus Atmosphere Monitoring Service (CAMS) used data from multiple ozone observations satellites to confirm that the “unprecedented 2020 northern hemisphere #OzoneHole has come to an end,” according to an announcement on Twitter on April 23.
“Although it looks like the polar vortex has not quite come to an end yet and will reform in the next few days, ozone values will not go back to the very low levels seen earlier in April,” they added.
The ozone layer is a region of the stratosphere between 15 and 30 kilometers (9.3 to 18.6 miles) above Earth's surface that has a high concentration of the gas ozone compared to other parts of the atmosphere. It effectively acts as a shield for our plant, absorbing much of the Sun's harmful ultraviolet rays.
When you hear “hole in the ozone layer,” you most likely think about the ozone hole over the Antarctic in the South Pole. Scientists first documented the hole in 1985 and it quickly became associated with certain human-made chemicals, especially manufactured refrigerants and solvents, that can act as ozone-depleting substances after they are transported up into the stratosphere. Thanks to a huge global effort, called the Montreal Protocol, the hole in the ozone layer over the Antarctic is the smallest its been in decades.
The recent situation in the North Pole, however, is a little different. While we expect to see natural variations in the ozone layer with the changing of the seasons, March 2020 brought something much more extreme than usual.
According to CAMS, the ozone hole was first opened over the Arctic in mid to late March after an unusually strong polar vortex, a low-pressure area that results in a wide expanse of swirling cold air. This trapped exceptional cold air in the North Pole for several weeks in a row and led to the formation of polar stratospheric clouds, high altitude clouds that can help to increase the chemical reactions involving the human-made chemicals that lead to ozone depletion once sunlight returns to the area. The result was dramatically dropping levels of ozone in the stratosphere in what became one of the largest ozone holes ever recorded over the Arctic.
“From my point of view, this is the first time you can speak about a real ozone hole in the Arctic,” Martin Dameris, an atmospheric scientist at the German Aerospace Center in Oberpfaffenhofen, told Nature in late March.
Now, it appears the polar vortex is starting to break down, allowing ozone-depleted air to mix around with ozone-rich air from lower latitudes. Since April 20, NASA's Ozone Watch has show notable levels of ozone returning to the Arctic pole, and the stratosphere is starting to appear how you'd expect it to look during a typical April.