Does ozone hole leads to global cooling?

False-color view of total ozone over the Antarctic pole. Purple and blue represent areas where there is the least ozone, yellows and reds where there is more ozone. Credit: NASA Ozone Hole Watch.

Role of Chlorofluorocarbons (CFCs) in global warming and ozone-hole formation

Chlorofluorocarbons (CFCs) play a role in both global warming and ozone-hole formation.

In the troposphere, chlorofluorocarbons (CFCs) act as greenhouse gases. They absorb infra-red radiation coming from the surface of the Earth and, by trapping this heat close to the Earth they contribute to global warming.

In the stratosphere chlorofluorocarbons (CFCs) are broken down by high intensity ultra-violet radiation from the Sun into chlorine radicals and these have the ability to destroy ozone. Other greenhouse gases, such as carbon dioxide and methane, do not have a comparable role in ozone depletion.

Ozone depletion and the formation of ozone hole don’t lead to a further warming of the troposphere

Since ozone prevents high intensity ultra-violet radiation from reaching the surface of the Earth and causes stratospheric warming, it can be assumed that formation of the ozone hole changes the total radiation budget of the Earth. This is, indeed, the case. However, ozone depletion and the formation of the polar ozone holes don’t lead to a further warming of the troposphere, but to a slight cooling. It can be discussed as under:

1 . Absorption of ultra-violet radiation by ozone molecules causes warming in the stratosphere. Some of this heat emitted in the stratosphere is transferred to the troposphere causing slight tropospheric warming as well. This warming gets lessened due to formation of ozone hole.

2 . In the lower stratosphere, ozone can still act as a greenhouse gas and absorb infra-red radiation coming from the Earth’s surface. So absorption of both ultra-violet and infra-red radiation by ozone leads to a warming of the upper troposphere. If ozone levels decrease, the upper troposphere will, therefore, get cooler.

3 . Backscattering of solar radiation is particularly strong over the Antarctic where the strongest ozone depletion occurs. This is because the snow and ice covered ground has a very high albedo. Because of this high backscattering, only a small fraction of the extra ultra-violet radiation that enters the troposphere from ozone loss causes heating.

Overall, the cooling effect of ozone loss is the highest and decreases in ozone levels cause cooling not only in the stratosphere but also slight cooling in the troposphere.

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