The ozone hole in Antarctica has reached its lowest annual peak since observation began in 1982, announced on Monday by the National Oceanic and Atmospheric Administration and NASA, although we are making progress in reducing the use of ozone-depleting chemicals, the milestone does not mean that we have solved the problem, alerted agencies.
Instead, scientists attribute a relatively tiny ozone hole to an unusually mild temperature in this layer of atmosphere.
According to NASA and NOAA, the annual ozone hole, which consists of an area of highly depleted ozone high in the stratosphere above Antarctica, at altitudes of 11 to 40 kilometres above the surface,
"For many years, under normal weather conditions, the ozone hole tends to increase to a maximum of about 8 million square miles,"
The Federal Scientific Authority states that this is the third time in 40 years that meteorological systems have caused heat stratospheric temperatures to slow ozone loss, and they reported that such weather conditions resulted in unusually small ozone holes in 1988 and 2002.
"It's a rare event we're still trying to understand,"
"If warming had not occurred, we would probably have looked at a much more typical ozone hole."
The Stratospheric Ozone Layer helps to reflect ultraviolet radiation from the Sun by protecting life on Earth from its harmful effects, such as skin cancer, cataracts and plant damage.
However, chemicals used for cooling purposes, such as chlorofluorocarbons, destroy stratospheric ozone molecules, thereby exposing the planet ' s surface to more ultraviolet radiation.
The Montreal Protocol, a landmark international environmental treaty that entered into force in 1988, had reduced CFC emissions worldwide.
These chemicals have an atmospheric life expectancy of several decades and can destroy an extraordinary amount of ozone in that time; the ozone layer has been slowly but steadily recovering since the entry into force of the Montreal Protocol, but still has a long way to go.
Each year, at the end of winter, an ozone hole is formed in the southern hemisphere, as solar rays initiate chemical reactions between ozone molecules and artificially created reactive forms of chlorine and bromine.
These chemical reactions peaked on high-flying cloud surfaces, but were softer than the average conditions in the stratosphere above Antarctica this year, preventing the formation and retention of clouds, according to NASA, which helped to prevent the loss of a significant amount of ozone.
For example, unlike what usually happens, this year there was no area above Antarctica that was completely free of ozone, according to NOAA measurements using meteoroids.
The weather systems that minimized ozone depletion in September, known as "surprise stratospheric warming", were unusually strong this year. Nearly 19 kilometres above the Earth's surface, the temperature in September was 29 degrees higher than average, reported NASA, "which was the warmest in a 40-year historical record in September with a large margin".
As with the stratospheric warming in the northern hemisphere, this weather phenomenon helped to weaken the Antarctic polar wind, a high-speed tape surrounding the South Pole, which usually concentrates the coldest air near or above the Pole itself.
Instead, the Antarctic polar vortex was out of balance and slowed down considerably.
The slow wind allowed the air to sink into the lower stratosphere, where it heated and prevented cloud formation, and the modified weather map helped to import ozone-rich air from other parts of the southern hemisphere rather than completely isolate the polar region; it also helped to raise the ozone level.
Interestingly, climate change will not cause more sudden warming in the stratosphere over the South Pole, and instead it may increase rather than weaken the polar wind as a whole.
Unlike global warming, the discovery of the ozone hole by scientists in the British Antarctic Service in 1985 stimulated international action, which quickly led to a binding international treaty, which many experts consider to be the most successful environmental agreement to date.
In fact, policymakers are even using it to address HFCs, ozone-depleting chemicals, which are also pollutants of global warming.
Since 2000, levels of CFCs in the atmosphere had declined slowly, but they were still large enough to cause annual ozone holes in the North and South Poles.
Assuming that the use of CFCs has continued since recently and that ozone-depleting chemical substitutes have not been detected and widely used, scientists expect that the ozone hole will be reduced to around 1980 levels by 2070, as CFCs still in the upper atmosphere are gradually decreasing.