Kondicio sine qua non (conditio sine qua non) - in Latin, a condition without which one cannot - in Serbian.
This is for life on Earth as we know it - the ozone layer, a protective wall in the sky several tens of kilometers from the surface of our planet.
"The ozone layer is a layer in the earth's atmosphere that absorbs a good part of the sun's ultraviolet (UV) radiation, which is harmful to living organisms," says Professor Vladimir Đurđević from the Faculty of Physics in Belgrade for the BBC in Serbian.
During the 1970s, scientists noticed that the ozone layer was damaged, and in the middle of the next decade, ozone holes were also discovered, places where the concentration of ozone, the gas that makes up the layer, is significantly reduced, above the poles, primarily the southern one, around the ice continent of Antarctica.
The cause is human activity and the use of chlorofluorocarbons, most often freon, chemical compounds from cooling systems, such as air conditioners and refrigerators, and deodorants.
With the abolition of their production and use by the international Montreal Protocol of 1987, the ozone layer began to recover.
The contract was signed on September 16, and this date has been marked as the World Day for the Protection of the Ozone Layer for three decades.
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"Invisible Shield"
The ozonosphere, as it is also called the ozone layer, is a layer within the stratosphere, at a height of 10 to 50 kilometers above the Earth's surface, with an increased presence of ozone.
The ozone layer was discovered by French physicists Charles Fabry and Henri Bisson in 1913.
Its properties were further investigated by the British meteorologist Gordon Dobson, after whom the unit for the amount of atmospheric ozone is named.
The highest concentration of this colorless-pale bluish gas is at an altitude of 20 to 25 kilometers, and its maximum content is in spring, minimum in autumn.
It also occurs in the lower layers of the atmosphere, and at the surface a higher concentration can be toxic to humans and plants.
"Ozone is a gas that absorbs the sun's UV radiation, and that is why these values on the Earth's surface are significantly lower than in a situation where there is no ozone layer," explains Đurđević.
Ultraviolet radiation can cause harmful effects on humans and other living organisms.
One of them is skin cancer, i.e. melanoma, which affects 132.000 people annually, while non-melanoma cancer occurs in between two and three million.
World Health Organization estimates that a 10 percent reduction in ozone levels leads to an additional 300.000 non-melanoma skin cancers and 4.500 melanoma cases.
Depletion of the ozone layer and the ozone hole
That something is wrong with the ozone layer was noticed more than half a century ago.
"It has been observed that the amount of ozone in the atmosphere is decreasing," explains Đurđević.
Scientists Mario Molina and Sherwood Rowland published a paper in 1974 where they expressed their doubt that chlorofluorocarbons, until then considered harmless chemicals, were destroying ozone in the Earth's stratosphere.
"Their release into the atmosphere damages the ozone layer because one freon molecule can destroy thousands of ozone molecules.
"Atmospheric circulation is such that these freons, which live for a long time, accumulate the most in the southern hemisphere and there the ozone hole is formed," explains Đurđević.
The ozone hole above Antarctica was discovered by three British scientists - Joseph Farman, Brian Gardiner and Jonathan Shanklin, and this information was made public in mid-1985, linking it to chlorofluorocarbons.
Satellite monitoring has shown that ozone depletion has spread over a vast area of 20 million square kilometers.
That's right confirmed assumption Molina and Rowland, for which they received the Nobel Prize for Chemistry in 1995.
The ozone hole occurs during the Antarctic spring, from September to early December, when strong westerly winds begin to circulate around the continent.
Significant reductions in ozone content in the stratosphere were also observed above the Arctic, of the North Pole, during late winter and early spring, from January to March, but far less than those in the extreme south of the Earth.
Professor Đurđević says that these "two things are incomparable" and that "in principle there is only one ozone hole".
"The atmosphere is not like Swiss cheese pierced with ozone holes," adds the meteorologist.
The Montreal Protocol as a lifeline
The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted on September 16, 1987 in this Canadian city.
It entered into force on January 1, 1989 and has had nine revisions so far.
This international agreement was supposed to prevent further degradation of the ozone layer and protect it by gradually ending the production of chemicals that damage it.
These are substances that contain chlorine or bromine, and at first these were only chlorofluorocarbons,
During the 1990s and early 2000s, their production and consumption stopped, and by 2009, 98 percent chemicals agreed in the agreement was gradually removed.
"Science and technology have found a solution so that we can continue to have refrigerators and air conditioners, but that these systems do not use gases that have a negative impact on the environment," explains Đurđević.
Later amendments resulted in strict restrictions and replacements for chlorofluorocarbons, namely - hydrochlorofluorocarbons and hydrofluorocarbons.
Although good for the ozone layer, these substitutes have turned out to be bad for the climate.
The global warming potential of the most commonly used hydrochlorofluorocarbon, for example, is almost 2.000 times stronger than carbon dioxide.
The Montreal Protocol also agreed on a phase-out schedule for developed and developing countries.
A multilateral fund was also introduced to provide financial and technical assistance to help developing countries meet their obligations.
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Ozone layer over Serbia
Đurđević says that this Montreal Protocol is one of the most important international agreements and the most successful that has ever happened.
"It demonstrated that all the countries of the world can really adopt appropriate measures and policies that will be followed and that will solve a global problem.
"If we agreed once, it means that it is possible for us to agree the next time as well," concludes Đurđević.
Before the adoption of the Montreal Protocol, the consumption of ozone-depleting substances in Serbia amounted to 2700 tons, and in 1989, when it came into force, it decreased by a third, and by 2005 it had fallen to less than two percent of the original amount.
However, in the period from 1979 to 2005, there was a cumulative drop in ozone concentration over Serbia by 7,2 percent, "which is in line with changes in neighboring countries", says the scientific paper Current state of the ozone layer on earth with a special review to Serbia from 2008.
During this time period, ozone holes occurred over the territory of Serbia once or twice, in autumn and winter, when the UV radiation index is low.
"Only three roads were of larger dimensions, but even then they occupied an area of less than half of the territory of Serbia," states the paper by authors Vladan Ducić, Snežana Đurđić and Nataša Martić Bursać.
However, the general condition of the ozone layer over Serbia is satisfactory, according to scientists.
"Although the values are lower than at the end of the 2008s, the downward trend has stopped and a slight upward trend has been present for ten years," added the paper published in XNUMX.
A happy ending on the horizon
The global action to protect the ozone layer seems to have borne fruit.
"The emission of ozone-depleting substances has practically been reduced to zero, and the ozone layer is recovering," says Professor Vladan Ducić from the Faculty of Geography in Belgrade, for the BBC in Serbian
He says that further degradation of the ozone layer "is not a realistic scenario", which does not mean that "we can expose ourselves to direct solar radiation without protection".
"Models show that the ozone layer in our latitudes could return to its previous state as early as the middle of the next decade."
The ozone hole over Antarctica continued to expand until 2000, followed by improvement and recovery, and today there is evidence that it is beginning to disappear.
Treatment is relatively slow due to the long lifetime of ozone-depleting molecules, some of which persist in the atmosphere for 50 to 150 years before disintegrating.
U United Nations joint report from 2022. it is stated that, if current policies are maintained, the ozone layer will be returned to the values of 1980, that is, before the ozone hole appeared.
Above Antarctica, where the damage was worst, in 2066, and above the Arctic in 2045.
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