The largest-ever hole in ozone layer over the Arctic has closed, the Copernicus' Atmospheric Monitoring Service announced recently.   In late March, scientists spotted signs of a rare hole forming and it was thought to be the result of low temperatures at the north pole, reports Euro News.   Earth’s ozone layer shields it from most of the Sun's ultraviolet radiation, a major cause of skin cancer. A hole in ozone layer would pose a direct threat to humans if it moves to populated areas.   Copernicus, the EU's earth monitoring programme, announced the closure of the hole on April 23. The development is unrelated to the reduction in pollution because of lockdown across much of the world.

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Instead, it's down to the polar vortex, the high-altitude currents that normally bring cold air to the polar regions, the report said. This has split in two giving the Arctic region a relative heat wave, with temperatures up to 20ºC higher than is normal for this time of year.
 
Scientists said this year’s polar vortex was “extremely powerful” and temperatures inside it have been very cold. This generates stratospheric clouds that destroy the ozone layer by reacting with CFC gases, banned by the 1987 Montreal Protocol.

In recent days, the polar vortex has broken up and weakened. Copernicus ECMWF (European Centre for Medium-Range Weather Forecasts) has predicted that it will form again, but without affecting the ozone layer as much.
 
Copernicus scientist Antje Inness told Euronews that it is “very unusual for such a strong ozone depletion to occur in the northern hemisphere”, but this year's polar vortex was “exceptionally strong and persistent, and temperatures were low enough to allow stratospheric clouds to form for several months".

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The better-known ozone hole is above the Antarctic at the South Pole and occurs during July-September period, known as austral spring, when the stratosphere is naturally much colder. In general, the conditions for ozone destruction on this scale do not happen at the North Pole.
 
This year, the strong and stable polar vortex has caused the concentration of more ozone-depleting chemicals than usual, which added to the extreme cold creating conditions for this unprecedented hole.
 
Scientists say it is too early to attribute this phenomenon to climate change or to assess the consequences, either in the short, medium or long term.