Yearly decrease of ozone
Since the beginning of the eighties (1980s) one notices that the ozone hole is getting deeper and that the covered surface is getting larger.
The phenomenon is observed yearly over the South Pole areas (Antarctica), whereby the amount of ozone in the atmosphere drastically decreases between September and the end of November.
Ozone destruction leading to the ozone hole
Scientific evidence exists for the fact that the release of bromine and chlorine hydrocarbons (CFC's) injects active bromine and chlorine components in the stratosphere, that destroy ozone. These destruction reactions become faster as the local temperature falls, among others by the formation of so-called polar stratospheric clouds that create reactive halogen compounds.
The phenomenon of the ozone hole is reinforced by the presence of the so-called polar vortex, a special circulation pattern in the stratosphere above the South Pole in local winter that isolates this area from its environment: the local stratosphere should be considered as a well closed reaction chamber in which the ozone destruction gets extremely efficient.
Therefore, one observes annual variations as to the size and depth of the ozone hole, as a function of the yearly fluctuations in temperature and in intensity and duration of the polar vortex.
The ozone hole is particularly strong above Antarctica; it is observed to a lesser degree above the North Pole. Reasons for this are:
- less severe temperatures
- less intense vortex
Ozone layer, protection against harmful radiations
The dangers of stratospheric ozone decrease are generally known: the stratospheric ozone layer protects the biosphere against the harmful ultraviolet radiations of the Sun, that cause, for example:
- skin cancer
- eye cataract
- damage to plants and marine life
International agreements on ozone depleting subsances, like the Montreal Protocol, aim at the gradual banning of CFC's.
Thanks to the Montreal Protocol banning emissions of the most harmful gases, the world has been able to avoid the near-disappearance of the ozone layer towards which it was slowly but surely heading.
According to atmospheric forecasting models it will take at least another fifty years for the ozone layer to return to normal. In the meantime, the ozone hole over Antarctica persists, with major variations from one year to the next: its maximum size even broke a record in 2023.
Researchers are monitoring the ozone layer
The combination of measurements from satellite instruments with numerical models of the atmosphere provide information about the state of the ozone layer like the ozone hole evolution in previous years, the ozone hole area, the ozone column minimum, the ozone mass deficit, the minimum temperature and even ozone forecasts.
Researchers use a system for global atmosphere monitoring, with detailed representation of stratospheric chemistry to understand the two-way interactions between weather, climate and stratospheric ozone chemistry. They take into account large forest fires and volcanic eruptions and the pollutants which they inject into the stratosphere.
Due to exceptional meteorology above the poles, scientists registered exceptional ozone holes in 2019 (weak and short) and 2020 (deep and long).
