Ms Ruchika Rajat Sharma
Visiting Research Fellow, IISD

The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains high concentration of ozone in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer is mainly found in the lower portion of the stratosphere from approximately 20 to 30 kilometres above Earth, though the thickness varies seasonally and geographically.

Ozone is a gas, in the atmosphere that protects everything living on the Earth, from harmful ultraviolet (UV) rays from the Sun. In fact, the ozone layer acts as a shield to absorb the UV rays, and keep them from doing damage at the Earth's surface. To repair the ozone layer, then, we must stop releasing ozone-depleting compounds into the atmosphere. In 1987, more than 180 countries agreed to address the problem in the Montreal Protocol. When countries began phasing out ozone-depleting Chlorofluorocarbons (CFCs), they came up with a replacement known as the HFC (Hydro fluorocarbon).

Largest-ever hole in the ozone layer above Arctic finally closes
The largest hole in the Ozone layer, spreading over 1 million square kilometres above the Arctic, was first identified by scientists in the March 2020; caused due to unusual atmospheric conditions, is observed, has closed, confirmed on 23rd April, 2020, the Copernicus Atmospheric Monitoring Services (CAMS) and Copernicus Climate Change Service (C3S) by the European Union's earth monitoring programme - European Centre for Medium-Range Weather Forecasts (ECMWF).

It is believed that the Polar Vortex, the high-altitude currents that are responsible for bringing cold air to the Polar Regions, this year's beginning period, is responsible for the healing of the layer. The ozone layer works as a protective shield for the Earth, as it prevents Sun's UV rays radiation - which can cause skin cancer - from entering Earth. The huge big hole above the Arctic Circle could have posed severe damage and a direct threat to humans, if it had of moved further south to populated areas, which possibility is at least not there anymore now.

2019 Ozone hole is the smallest ever on historic record. Abnormal weather patterns in the upper atmosphere over Antarctica, in fact had dramatically limited Ozone Depletion in September and October 2019, resulting in the smallest ozone hole, since 1982, NASA and NOAA scientists reported. Such holes in the Ozone Layer are quite common above the Antarctic at the South Pole especially during July to September but, the ozone layer hole above the Arctic at this time was unusual.

The Antarctic or South Pole's ozone hole, a layer of the atmosphere around 10-50 kilometres above the mean sea level, is mainly caused by human-made chemicals including chlorine and bromine that migrate into the stratosphere, during July to September, when the stratosphere is naturally colder. In general, the condition for ozone destruction on this scale just does not happen at the North Pole. According to Copernicus, the last time, similarly strong chemical ozone depletion was observed over the Arctic or North Pole, was during spring (January) 2011.

Why has an ozone hole formed in the Arctic?
This year the polar vortex has been 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 predicts that it may form again, but without affecting the ozone layer as much.

"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," - Copernicus scientist Ms Antje Inness told Euro news.

Is the hole related to climate change and what are the consequences?
It is still too early to attribute this phenomenon to climate change or to assess the consequences, either in the short, medium or long term.

"We don't know at the moment why the dynamics were so unusual this winter," said Inness. "I'm sure many scientists would go for modelling studies to find out the reasons for this." The direct consequence is increased UV exposure in the areas through which this ozone hole has passed: during this period - Alaska, Canada, Greenland and parts of Russia. Scientists at the University of Santiago de Chile told, Euro news that the exceptional polar vortex was likewise reinforced by the ozone hole, and this has been a determining factor in Europe having the warmest winter since records began.

How big is the Antarctic ozone hole now?
The Antarctic ozone hole in 2019 was the smallest since this atmospheric disruption caused by CFC gases was discovered in 1985. The banning of these gases by the Montreal Protocol in 1987 has allowed a reduction in the Antarctic ozone hole and even the gradual restoration of atmospheric currents in the southern hemisphere, according to a recent study.

The Author is a Research Fellow at Indian Institute of Sustainable Development (IISD), New Delhi.