In 1985, the scientific community noticed a problem: the ozone layer, a gas in the stratosphere that protects the planet from ultraviolet rays from the Sun, was thinning. Above the South Pole, between the end of winter and the beginning of spring (between August and December), it thinned so much that people started talking about a real hole. A discovery that scared the governments of the Earth enough to push for an unprecedented initiative: the global ban on CFCs (chlorofluorocarbons) and all other gases that contribute to the destruction of atmospheric ozone. The plan, known as the Montreal Protocol, worked for once, and with the progressive dismissal of those directly responsible, the hole in the ozone layer began to heal.
This year, for example, the European Union’s Copernicus program data reveal that the hole opened late (practically at the end of August), and for now it is proceeding slowly, with a trend similar to that seen in 2022, a season in which the hole in the ozone layer was smaller than average. As always when it comes to climate, however, one swallow does not make a summer: in 2023, for example, the hole was among the largest ever observed. In fact, the dynamics that drive the seasonal thinning of the Antarctic ozone layer are modulated by much more complex climatic phenomena than the simple presence of ozone-depleting gases in the atmosphere. And it is estimated that the damage done in decades of unwitting use of these substances will take at least 40 years to disappear completely, leaving the Antarctic winter finally free of the now traditional “hole”.
This year’s hole
Every year between August and December (in what is called the Antarctic ozone hole season), the Copernicus Atmosphere Monitoring Service of the European Centre for Medium-Range Weather Forecasts provides detailed analysis and forecasts of the thickness of the ozone layer over the South Pole. This year’s data confirm that the seasonal thinning has started very late, and is weak compared to averages recorded since 1979.
The phenomenon was expected, because this year the Antarctic stratosphere has experienced two phenomena of intense and sudden warming, in July and August, when temperatures reached 15 and 17 degrees respectively. In cases like these, the Antarctic polar vortex (an area of low pressure permanently positioned on the South Pole, which also has a similar one at the North Pole) is weakened and unfavorable conditions are created for the formation of the ozone hole, because the winds that blow in the stratosphere tend to be slower, and do not hinder the influx of ozone from other areas of the atmosphere.
Is the hole closing?
As we were saying, a good year is not enough to claim victory. The phenomena that occur in our atmosphere are due to a complex mix of chemical and physical elements, which in the case of the ozone hole include the intensity of solar radiation, stratospheric temperatures and the intensity of the polar vortex, quantity and extension of clouds, and the levels of ozone-depleting substances present. And calculating the contribution of each of these variables from year to year is a complex task.
What is certain is that several studies conducted in recent decades confirm that the ban on CFCs implemented with the Montreal Protocol is working, that emissions of these gases have fallen dramatically, and that the ozone layer is slowly recovering. Even under these conditions, however, it will take decades for the levels of ozone-depleting gases to fall below pre-industrial levels: experts’ calculations estimate about another four decades, during which meteorological variables will continue to determine the intensity and duration of the seasonal ozone hole.
What risks remain?
There are also other factors, both natural and otherwise, that can promote the deterioration of the ozone layer. Smoke from fires, as well as water vapor and sulfur dioxide from volcanic eruptions, if they reach the atmosphere in large quantities can contribute to the development of the ozone hole (in fact, it is believed that the eruption of the Hunga-Tonga volcano in early 2022 contributed to the enlargement of last year’s ozone hole).
Not only that, because alongside these natural factors, there are also other anthropogenic factors, in addition to the gases banned by the Montreal Protocol, which can contribute to the destruction of the ozone layer. Among these, emissions from space rocket launches, which are constantly increasing due to the boom in the civil aerospace industry in recent years. As well as debris caused by the re-entry of satellites into the atmosphere, which is also constantly increasing due to the success that mega satellite constellations are having.
Not to mention solar geoengineering projects, initiatives currently being studied that would involve releasing chemicals into the atmosphere that reflect sunlight. The noble goal is to reduce the amount of energy reaching the Earth, and thus alleviate the effects of climate change. But it could come at the expense of the atmospheric ozone layer, which is damaged by the presence of aerosols in the stratosphere. And since the ozone layer appears to have protective effects (albeit indirect) on the climate, this would be a paradoxical outcome, to say the least. For this reason, it is important not to consider the hole in the ozone layer as a problem of the past: the Montreal Protocol was an important move in the right direction, but continued vigilance remains essential, to avoid compromising the objectives achieved again.