A science teacher explains: Ozone, the earth’s invisible protective shield
One of the effects of ozone depletion, which is not as discussed, is the weather change witnessed in the southern hemisphere due to shifting jet stream patterns
By Rachna Arora
Had it not been for the protective shield of the atmosphere against ultraviolet rays, just a few minutes in the sun would give severe sunburn, skin cancer would be the leading cause of death, plants would wither and die resulting in acute food shortage.
The sun gives life and it also gives a small percentage of UV rays, which like all electromagnetic radiations cannot be seen and ignored. The very powerful UV rays, which can cause more harm than good, come in a bouquet of UV A, B and C rays, with UVB being most harmful while UVC do not reach the surface of earth.
Yet again, Nature also provided the solution, in the form of an ozone layer which is at a height of 15 to 35 km from the surface of the earth. This layer absorbs about 95-97 per cent of the UV rays. (“Dobson Unit” (DU) is the measure of ozone concentration in the atmosphere).
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It was in 1976 that the depletion of the ozone layer primarily because of widespread use of Chloro-Fluro carbon, CFCs (which literally digest ozone to form oxygen) was recognised as a global threat. Considering the serious ramifications on human health and environment, the governments globally under the aegis of the UN came into action widely remembered as Vienna Convention and the Montreal Protocol. These treaties happen to be the most widely ratified treaties in United Nations history. So, thanks to international cooperation, the ozone layer began to heal.
One of the effects of ozone depletion, which is not as discussed, is the weather change witnessed in the southern hemisphere due to shifting jet stream patterns. Jet streams are strong air currents formed at heights of about 8 to 15km by the confluence of hot and cold air. These bands of air are thousands of kilometers long and hundreds of kilometers wide. Jet streams are strongest in winters as the temperature difference between the warm tropical air and cold polar air is greatest.
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The jet streams move from the west to the east. But however, due to the depletion of ozone, the air over the poles further cools, causing very cold winds, with temperature up to –80 degree, to move in a whirlpool thus forming a polar vortex whose influence can be felt even in the lower layers of the earth’s atmosphere. This causes the jet streams to move from the equator deeper into the poles changing rainfall patterns. As the jet streams move further south, this pushes the rain away from the coastal regions in Australia, causing droughts, and also widen the tropical rain belts and subtropical deserts in parts of Africa, South America and Australia in the southern hemisphere which has an adverse effect on livelihoods of people. This pattern was observed for over three to four decades in the last century.
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However, a reversal of the wind pattern was first observed in the year 2000. As even the greenhouse gases have a role to play in the southward shift of the jet stream so studies were conducted to find the cause of this reversal. Through simulations and data analysis it has now been established that it is the repairing of the ozone layer that has reversed the jet streams in the southern hemisphere. Ozone has been found to play a limited role in the northern hemisphere.
Mankind has been and continues to storm all life-threatening challenges – be it climate change or COVID-19. Undoubtedly, the human quest to surmount anything that comes in its way to save mankind is inimitable and indefatigable.
(The writer is PGT- Physics at Shiv Nadar School, Noida)
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