The largest hole ever observed in the ozone layer over the Arctic has closed, says Copernicus’ Atmospheric Monitoring Service.

A rare hole in the ozone layer, spreading over 1 million square kilometres in area, was discovered by scientists earlier this month. 

The hole was created by unusually low atmospheric temperatures above the north pole, which created a stable polar vortex. With ozone-destroying chemicals such as chlorine and bromine left relatively stable in the atmosphere – brought on by human activities – the large hole formed.

But on April 23, Copernicus – the EU’s earth monitoring programme – announced the hole had now closed.

The closing has nothing to do with the reduction in pollution caused by having much of the world on COVID-19 lockdown.

Instead, it’s down to the polar vortex, the high-altitude currents that normally bring cold air to the polar regions. This has split in two giving the Arctic region a relative heatwave, with temperatures up to 20ºC higher than is normal for this time of year.

Copernicus ECMWF explains that the polar vortex experienced this year was extremely powerful, with very cold temperatures inside it. This further resulted in the generation of stratospheric clouds that destroyed the ozone layer by reacting with CFC gases. Note that the use of CFC gases by humans was banned by the 1987 Montreal Protocol.

Now, that polar vortex has weakened, causing the normalcy to return in the ozone layer in the polar region. Copernicus ECMWF predicts that it will form again, but it would not affect the ozone layer as much the next time.

A more ever-present ozone hold can be found over Antarctica, which last year was at its smallest size in decades. However, similar to the current Arctic hole, this was described by researchers as “just a fluke of the weather”.