One of the largest ozone holes in years | Polarjournal
The 24 million square kilometre ozone hole above Antarctica on 27 September 2020. (Foto: NASA)

The hole in the ozone layer above Antarctica is one of the largest and deepest in the last 15 years, according to the World Meteorological Organization (WMO). The ozone hole above Antarctica usually starts to grow in August and peaks in October. This year it reached a peak of 24 million square kilometers and measured 22 million square kilometers on October 22, the WMO said. This means that the hole is larger than the average of the last decade and covers most of Antarctica.

The 22 million square kilometre ozone hole over Antarctica on October 22, 2020. (Foto: NASA)

WMO’s Global Atmosphere Watch program works closely with the Copernicus Atmospheric Monitoring Service, NASA, Environment and Climate Change Canada, and other partners to monitor the Earth’s ozone layer, which protects us from the sun’s harmful ultraviolet rays.

NASA’s Ozone Watch reported the lowest reading of 95 Dobson units measured on October 1. Scientists are seeing signs that the ozone hole now appears to have reached its maximum extent for 2020.

The maximum peak of 2020 is not the largest ever recorded – this had been measured already in 2000 with a hole of 29.9 million square kilometres. But it is still significant, with the hole also being one of the deepest in recent years.

“As sunlight returned to the South Pole in recent weeks, we saw continued ozone depletion over the area. After the unusually small and short-lived ozone hole in 2019, which was caused by special meteorological conditions, we are seeing again a fairly large ozone hole this year. This confirms the need to continue to enforce the Montreal Protocol banning emissions of ozone-depleting chemicals”.

The Montreal Protocol prohibits emissions of ozone-depleting chemicals. Since the ban on halogenated hydrocarbons, the ozone layer has recovered slowly; the data clearly show a trend towards reducing the area of the ozone hole.

The most recent scientific assessment of ozone depletion under the WMO/UN Environment Programme, published in 2018, concluded that the ozone layer is on the road to recovery and a possible return of ozone levels to pre-1980 levels above Antarctica.

The large ozone hole in 2020 was powered by a strong, stable and cold polar vortex that kept the temperature of the ozone layer over Antarctica constantly cold.

Atmospheric ozone measurements from the Copernicus Sentinel-5P satellite are updated daily. (Foto: ESA)

Ozone depletion is directly related to the temperature in the stratosphere, i.e. the atmospheric layer between approximately 10 km and 50 km altitude. Polar stratospheric clouds, which play an important role in the chemical destruction of ozone, only form at temperatures below -78°C.

These polar stratospheric clouds contain ice crystals that can convert non-reactive compounds into reactive ones, which can then quickly destroy ozone once the sun’s light is available to start the chemical reactions. This dependence on polar stratospheric clouds and solar radiation is the main reason why the ozone hole can only be seen in late winter and early spring.

Heiner Kubny, PolarJournal

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