Most flying objects travel in this corridor, with only rockets and ballistic missiles, in particular, passing through the troposphere. Next comes the stratosphere up to 50 kilometres in altitude and then the mesosphere up to about 80 kilometres from the surface.
It is in this zone that the International Space Station orbits. The final layer, which then extends into the infinity of space, is called the exosphere.
As a general rule, the higher you go in the atmosphere, the lower the temperature, but in the stratosphere, the opposite happens, with temperatures rising as you approach the top.
This temperature inversion is due to the absorption of the sun’s ultraviolet rays. The layer of the stratosphere that absorbs this radiation and warms up is called the ozonosphere because it is made up of ozone, a cousin of oxygen, formed from three oxygen atoms that capture the sun’s ultraviolet rays.
A special feature of the stratosphere is the balance that occurs at its base between the heat transmitted by the ozone layer and the heat from the troposphere.
The relative stability of this area of the troposphere, at the edge of the stratosphere, is the preferred route for commercial aircraft, as they are not subject to the turbulence associated with the convection of heat from the troposphere.
Ozone is present in the stratosphere between 20 and 40 kilometres and captures the sun’s UV rays, protecting the Earth from excessive heat.
But the massive use of chlorofluorocarbon gases for decades because of their properties, these gases being particularly stable, non-flammable and non-corrosive, has caused a concentration of CFCs in our environment and then in the stratosphere.
Chemical reactions specific to these gases cause the destruction of the ozone layer and contribute to global warming. Despite restrictions on the use of CFCs since the 1980s, the concentration in the stratosphere continued to rise until the 1990s.
Scientists estimate that the concentration should reach an acceptable level by the middle of the 21st century. Until then, it is possible that the ozone layer will continue to suffer. Without ozone, life on Earth would only be possible in the oceans, at a depth where UV rays can be tolerated, as was the case 4,000 million years ago during the so-called Archaean period.
The stratosphere is one of the five layers of the Earth’s atmosphere, but it is also one of the most important because it is here that the ozone layer absorbs the sun’s UV rays and provides the Earth with a regulated temperature and a viable atmosphere.
However, several factors play a role in the disappearance of ozone, the use of so-called CFC gases, but also any other form of gas that promotes global warming. A recent study published in Nature Communications in June 2021 shows that global warming is accelerating the destruction of ozone.
This study follows the observation in spring 2020 of an ozone hole over the Arctic three times the size of Greenland, which closed naturally some time later.
It is confirmed that greenhouse gases while warming the troposphere, cool the stratosphere and the particular weather conditions over the poles favour ozone destruction when very cold currents flow and stabilize in the stratosphere.
The Arctic is particularly targeted because this phenomenon usually occurs less frequently than over the Antarctic, but if the stratosphere over the Arctic were to cool more regularly, it would promote further ozone destruction and increase global warming.
According to this scenario put forward in the study by German, American and Finnish researchers, all greenhouse gases causing global warming should be targeted. This amounts to considering the Montreal Protocol, signed in 1987, which reduced and banned the use of several ozone-destroying gases in the stratosphere, as insufficient to allow the ozone layer to recover properly.