New Delhi: The hole in the ozone layer, the protective shield in Earth's stratosphere absorbing harmful UV radiations emitted by the Sun, widens every year. But this year, the ozone layer hole is “larger than usual”, and is currently even bigger than Antarctica in size, scientists monitoring the ozone layer have said. 


Since 1979, the ozone layer hole has been monitored. This year, the hole has been observed to be developing rapidly and to be bigger than 75 per cent of ozone holes at this stage of the season since 1979, researchers from the Copernicus Atmosphere Monitoring Service (CAMS) said in a statement.


What is the status of the ozone hole this year?


CAMS said in the statement that they were closely monitoring the development of this year's ozone hole over the South Pole, which has reached an extent larger than Antarctica, and has shown considerable growth in the last week, making it larger than 75 per cent of all ozone holes at this stage of the season since 1979. 


In the statement, Vincent-Henri Peuch, Director of CAMS, said this year's ozone hole “evolved into a rather larger than usual one”, and that they were looking at a “quite big and potentially deep ozone hole”. 


He also said the hole is similar to that of previous year, which wasn't thought to be exceptional, but had evolved into one of the longest-lasting ozone holes ever recorded, later in the season. The vortex of this year's ozone hole is stable enough and the stratospheric temperatures are lower than last year, as a result of which there may be more growth in the ozone hole, over the next two or three weeks, he added.


The ozone hole formed last year, over the Arctic, was also very large and deep, and had even reached a size, approximately three times that of the continental US, according to CAMS.


An animation of the ozone layer on September 12, released by CAMS shows that the ozone hole develops from the edges to the middle, because of the Sun catalysing ozone-depleting reactions.


Why does the ozone hole widen every year?


Ozone layer is the stratospheric layer present at an altitude of about 11 to 40 kilometres above Earth's surface.


CAMS has given the first status update on the stratospheric hole which appears every year during the Austral spring, or spring in the southern atmosphere. This is the region where the greatest amount of ozone is lost annually, beginning in September. 


The UV radiations emitted by the Sun catalyse the ozone depleting reactions, which involve chemically active forms of chlorine and bromine released from man-made compounds. 


Chlorofluorocarbons (CFCs), which were first developed in the 1930 to be used in refrigeration and air-conditioning systems by humans, play a key role in the depletion of the ozone layer. Due to their stable nature, they can traverse to the stratosphere from the surface of the Earth. When CFCs reach the stratospheric ozone, high-energy UV radiation breaks them down, and a cascade of chemical reactions occurs, which destroy ozone. 


The ozone hole usually forms over the Antarctic during the spring season in the Southern Hemisphere from August to October. The hole reaches a maximum between mid-September and mid-October.


Ozone depletion slows during the late Southern Hemisphere spring, as temperatures high up in the stratosphere begin rising. The ozone layer returns to normal by December, when the polar vortex weakens and finally breaks down. 


CAMS performs satellite-based and in situ observations to monitor the ozone hole.


CAMS forecasts on September 14 show that the ozone layer hole is greater than 75 per cent of holes recorded in the dataset since 1979.


How long will it take for the ozone layer to recover?


As many as 197 countries around the world have banned the use of CFCs, as they are responsible for ozone depletion.


Ever since the 1987 Montreal Protocol put a ban on halocarbons, slow recovery has been shown by the ozone layer. A complete phase-out of ozone depleting substances will be possible by 2060s or 2070s, if monitoring efforts are maintained.


The ozone hole has been observed to increase to a maximum of 20 million square kilometres, during recent years.