Introduction
Recently, a giant Ozone hole has been discovered over Antarctica, known as the White Continent, by satellite measurements. In this region, the amount of ozone is around 220 Dobson Units or below. (A Dobson is an ozone concentration measuring unit, consisting of a number of molecules of ozone, needed to create a layer of pure ozone, i.e., 0.01 mm thick, at a temperature of 0° Celsius and a pressure of 1 atmosphere.) As per the sources, this hole is one of the largest holes ever noticed, about 26 million square kilometre s, which is its maximum extent as of September 21, 2023. This is regarded as the 12th largest daily ozone hole extent since 1979 when satellite records were an emerging technology. Further, it is the 16th largest ozone hole when its average was taken from September 7th till October 13th, i.e., the peak of the ozone depletion event. Despite being a natural phenomenon, it is a matter of concern, as scientists think that ozone holes could reopen due to climate change.
Rather than an actual hole, the ozone hole is similar to a small spot that is formed during the spring season every year in the ozone layer of the Southern Hemisphere. In other words, the thinning of the ozone layer takes place just above Antarctica in September every year, leading to the formation of the ozone hole.
Under the environmental monitoring programme of the European Union, the observations regarding this ozone hole were made and recorded by Copernicus Sentinel-5P, a satellite developed by the European Space Agency.
Ozone Layer and its Usefulness
The ozone layer is a layer of the ozone gas (O3) in one of the four layers of the atmosphere, i.e., the stratosphere. Despite being a trace gas, it acts as a natural shield that protects us from the harmful rays of the sun. The ultraviolet (UV) radiation is absorbed by this gas, and all living organisms as well as ecosystems are saved from its dangerous effects. A large number of skin cancers, sunburns, cataracts, and cellular damages are caused among people when they are exposed to a large amount of UV radiation. The ozone layer blocks these UV rays, thereby decreasing the rates of these diseases across the world.
A trace gas is a type of gas that is found in small concentrations, such as one part per billion (ppb) or lower.
Fluctuation in the Size of the Hole
Every year, the size of the ozone hole increases and decreases. It opens in the month of August and closes in the month of November/December. It is created when special winds are formed over the surface of Antarctica due to the Earth’s rotation. Owing to these winds, a small climate gets developed around Antarctica. As a result, the continent cannot get in contact with the surrounding air. The hole gets closed down after the winds disappear.
Causes of the Giant Hole This Year
According to the scientists at the National Oceanic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA), this giant ozone hole appeared this year earlier than usual mainly because of the eruptions that occurred at Hunga-Tonga volcano in Tonga between December 2022 and January 2023. Usually, when a volcano erupts, the gases emitted from it do not rise above the level of the stratosphere. However, a large amount of water vapour was released into the stratosphere by this eruption. The water vapour chemically reacted with the ozone layer, thereby altering its heating rate. Basically, it increased the speed and frequency of chemical reactions that destroy the ozone layer. Besides, some other components of the water vapour, such as iodine and bromine, also result in the depletion of the ozone layer.
It was in the mid-1980s that the ozone holes were first detected in the world. Gradually, their sizes increased during the mid-2000s, covering a maximum area of approximately 30 million square kilometres at that time.
Human Activities
Some scientists are of the opinion that there is hardly any evidence of human activities being responsible for the ozone hole. However, there are others who came to know that huge ozone holes were created in the 1970s due to human activities. At that time, these holes had been discovered by satellite and ground-based measurements. It was also inferred that the reckless use of chlorofluorocarbons (CFCs), a type of chemical used for different purposes, such as solvents, refrigerants, and aerosol sprays, was responsible for the holes. Therefore, the use of these chemicals has been restricted as CFCs can be sustained in the atmosphere for 50 to 100 years or more.
Further, it was also discovered that the depletion of the ozone layer was due to the gases that act as propellants to push the solutions that are in the aerosol cans and not by aerosols. The propellants consist of chlorine, which rises up very high and enters the stratosphere layer of the atmosphere, and thus, diminishes the ozone.
In 1987, scientists warned people about the ozone holes, and taking immediate action, the Montreal Protocol was developed. This protocol aimed at preserving the ozone layer by prohibiting the production as well as the use of such gases and other chemicals. Consequently, the ozone layer recovered in the stratosphere. However, the ozone layer will be completely recovered only if CFCs are fully destroyed, which may take several decades.
Measuring Ozone in the Atmosphere
The ozone layer over the poles is examined by the researchers at NASA and NOAA through various instruments, installed in NASA’s Aura, NOAA-20, and NOAA-NASA Suomi NPP satellites. There is a Microwave Limb Sounder in Aura that determines the levels of chlorine in the atmosphere. The average depletion in ozone can also be estimated by scientists by evaluating the amount of ozone concentration within the hole.
Impact of Climate Change on Ozone
According to some scientists, the rising temperature on the surface of the Earth impacts ozone holes. From the 1980s till 2020, the ozone hole kept getting reduced. However, to everyone’s surprise, a very deep and persistent ozone hole was detected in 2020 caused by the wildfires that occurred the same year in the south-eastern part of Australia. These wildfires have recently become more frequent and destructive throughout the world, as the temperature on the Earth’s surface is continually rising and there seems to be no end to the climate crisis. Forest fires in the Northern Hemisphere also got worse this year. Their continuation may lead to the release of more smoke into the stratosphere, leading more ozone depletion in the coming years.
Though the impact of these ozone holes on climate is not clearly evident, some scientists have researched that these holes decrease the effect of greenhouse gases, and give a cooling effect to the atmosphere. Besides, these holes alter the seasons’ progression. So, winters may continue for a longer period of time.
Expert Comments
According to the ESA’s Copernicus Sentinel-5P’s mission manager, Claus Zehner, “The satellite measured trace gases in the atmosphere in order to monitor the ozone and climate. It showed that this year’s ozone hole started earlier than usual, and had a big extension.” Some opine that it is very unlikely that the surface of Antarctica will get warmer due to the ozone hole. Zehner says, “It’s not a concern for climate change.”
According to Paul Newman, who is leading NASA’s ozone research team and is the chief scientist for Earth Sciences at the Goddard Space Flight Centre of NASA in Greenbelt, Maryland, “It’s a very modest ozone hole. Declining levels of human-produced chlorine compounds, along with the help from active Antarctic stratospheric weather slightly improved levels this year.”
He further said that if Hunga Tonga had not gone off, the hole would likely be smaller this year. The eruption got into the Antarctic stratosphere, but we cannot yet quantify its impact on the ozone hole.
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