Il buco nell'ozono

The ozone, a shield for the planet

We explore knowledge with an essential part of the Earth's stratosphere.

by Stefano Bevacqua
22 June 2020
4 min read
by Stefano Bevacqua
22 June 2020
4 min read

Ozone is a molecule formed of three oxygen atoms. It’s found in small quantities near the ground, in the air we breathe, and in greater densities up in the sky, above all at heights of 9 to 22 miles. Hence why the part of the stratosphere nearest to us is known as the ozonosphere, or more commonly the ozone layer.

This bit of sky plays a crucial part in protecting life on earth, because it filters out the most dangerous ultraviolet rays from the sun. We’ve known for years that the depletion of this corner of space –especially where it hangs over the earth’s two poles– has had global repercussions on the climate. The effect is often and inappropriately called the “hole” in the ozone layer. The ozone layer is at the centre of a debate full of clashing opinions and theories.

The release of chlorine gas

When the ozone layer is depleted, or even broken in some places, ultraviolet rays can make their way to earth unstopped. They don’t do direct harm to humans, barely any of whom live in the Arctic or Antarctic. Most of all they hurt plankton, but that interferes with the food chain all the way from the tiniest creatures up to us, passing by way of the entire ocean ecosystem.

In the closing years of the last century, the bit of the ozone layer above the South Pole shrank considerably. Research lays the blame for this change at the door of humans. The most popular hypothesis points to our use of chlorofluorocarbons (CFCs) and the similar hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These gases were widely used in spray cans, solvents and glue. They were also the most common refrigerant gases in fridges and air conditioners. As they didn’t dissolve in water, they couldn’t return to earth as rain. Irritatingly stable, they could crop up unharmed many miles high in the stratosphere. Up there, solar radiation made them release chlorine, which destroyed the links between the oxygen atoms that make up ozone. The gases did further damage by creating a shielding effect several thousand times stronger than that of carbon dioxide, despite their low concentration in the atmosphere.

This is the most supported theory in the world of research. It’s not certain but it’s the most likely. There are competing theories, for example that the depletion of the ozone layer was the combined effect of CFC gases and a mixture of natural phenomena; chlorine would be widespread on earth even were it not for humans.

The good news

In the Montreal Protocol in 1987 it was decided to abolish most of the harmful gases used by humans and replace them with substances free of chlorine, despite many of them being less stable and highly flammable.

The most likely cause of the phenomenon now tackled, the ozone layer’s health made a noticeable and massive improvement, and the “hole” was largely stopped up. Whether it was the ban on gases in spray cans and fridges that did this is far from certain, but whatever the case, the situation now is radically different than it was in the last quarter of the past century. And not only because the shield against high-frequency UV rays, the worst kind for living species, is strong again, but because we’re seeing climate effects that until now were only suspected.

The virtues of ozone

The lower part of the ozone layer appears to act as a temperature regulator for the atmosphere down around our heads. It’s not clear how that works, though. A research team at the University of Colorado, led by a young British scientist, Antara Banerjee, managed to observe and measure how atmospheric circulation in the Southern Hemisphere has improved significantly since the year 2000. This is true especially of the jet stream, the air current channelled towards the South Pole.

The researchers gathered and compared a huge raft of data on the position of the atmospheric currents at the middle latitudes, the polar vortex and the southern edge of the tropical zone from 1980 to the present day. Then they simulated the chemical and physical changes in the Southern Hemisphere’s atmosphere over the last four decades. The result? The simulations almost perfectly reproduced the climate changes that had already been observed, including the shrinking of the jet stream around the Pole, which later slowed down at the end of the century. The researchers therefore demonstrated that the depletion of the ozone layer had had real consequences on the climate and that its recovery was helping make the earth slightly less contaminated. So, the ozone in our stratosphere has two advantages: not only does it keep UV at bay, it helps balance our climate.