Ozone depleting substances and climate change

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 The ozone layer sits in the stratosphere between 15 km and 30 km above the earth, and shields us and other living things from the sun’s harmful ultraviolet radiation. Ozone layer depletion could have serious effects on human health and the environment.



Depletion of stratospheric ozone occurs over both hemispheres of the Earth. However, this phenomenon is significantly less severe in the northern hemisphere (Arctic) than in the southern hemisphere (Antarctica). This is the case because, year-to-year, meteorological variability is larger over the Arctic than over the Antarctic. Furthermore, temperatures in the stratosphere do not remain low for a long time in the Arctic as in the case in the Antarctic.

Maximum ozone hole extent over the southern hemisphere, from 1979 to 2021


Overall, the ozone hole has shown signs of healing since 2000, which is predominantly attributable to phasing out ozone-depleting substances under the Montreal Protocol. At the same time, the extent of the ozone hole is strongly driven by stratospheric temperature, with warmer temperatures leading to a smaller ozone hole, such as in 2019. 

However, this is not directly attributable to anthropogenic climate change, since greenhouse gases generally have a cooling effect in the stratosphere, while they contribute to global warming in the troposphere. This stratospheric cooling has a positive effect on ozone recovery with the exception of the polar regions. Here, very low temperatures can lead to an increase in the formation of polar stratospheric clouds, which facilitate ozone depletion. The ozone hole can also be periodically influenced by volcanic eruptions, increasing the stratospheric particle load and thereby depleting ozone. This partially explains those occasional years during which the ozone hole is comparatively large, e.g. in 2015. 

The 2021 ozone hole has been one of the larger and deeper ones in recent years and was larger than the average over the last five and ten years (20.0 and 21.4 million km², respectively). According to researchers from the Copernicus Atmosphere Monitoring Service, colder-than-average temperatures together with strong winds in the stratosphere circling Antarctica contributed to the large 2021 ozone hole size. Ozone lossin the northern hemisphere is usually much more limited compared to the southern hemisphere. In Artic spring 2020, however, ozonesonde measurements showed ozone depletion that has been explained to occur due to unusually strong, long-lasting cold temperatures in the stratosphere.


The 2019 ozone hole has been a very small and short-lived one, which was mostly driven by special meteorological conditions. In particular, August and September 2019 showed exceptionally high temperatures in altitudes between 20 and 30 km above the ground of the Antarctic, stopping the formation of icy clouds that usually trap ozone-depleting molecules that, when released during southern hemispheric springtime, trigger ozone destruction. Taken together, the mitigation of ozone depletionis still very fragile and scientific evidence suggests that more action is still required to remove pressure on the ozone layer caused by ODS.




Blog by: Dhara Patel 
B.Tech FT, 4th sem 

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