Shouldn't the ozone hole be repaired by now? Every Antarctic spring, the ozone hole returns. And you might reasonably wonder: why? The Montreal Protocol was agreed almost 40 years ago and successfully phased out most uses of the CFCs and other chemicals responsible for destroying stratospheric ozone. Yet this year the Antarctic ozone hole again developed rapidly. By 12 September 2026 it covered about 25 million km? — around 5 million km' above average for that point in the season. Interestingly, other measures of its severity, including the ozone mass deficit and minimum ozone column, remained close to historical averages (Source: CAMS). So why does it keep coming back - and why is the phenomenon so strongly associated with Antarctica? The answer is a remarkable combination of cold, clouds, chemistry and sunlight. During the Antarctic winter, the stratosphere becomes exceptionally cold. Strong winds encircle the continent, forming the polar vortex, which isolates the polar air and allows it to cool further. Antarctica's winter stratosphere is generally colder and its vortex more persistent than its Arctic counterpart. At temperatures below roughly -78°C, something unusual can happen: polar stratospheric clouds (PSCs) form. These are not ordinary weather clouds. They form around 15-25 km above the surface, in the normally very dry stratosphere. And their surfaces provide a chemical laboratory. Chlorine originating from human-made ozone-depleting substances is still present in the stratosphere, much of it held in relatively inactive reservoir compounds. Reactions on PSC particles convert these reservoirs into forms that can subsequently produce highly reactive chlorine. But until is dark nothing happens one ingredient is still missing: Ö sunlight. When sunlight returns to Antarctica in spring, it activates this prepared chlorine chemistry. Reactive chlorine then enters catalytic cycles that destroy ozone. And catalytic is the important word. The chlorine is regenerated by the reactions. It can therefore participate again and again, allowing a single chlorine atom to contribute to the destruction of many ozone molecules. Later in spring, the stratosphere warms and the polar vortex weakens and eventually breaks down. Air from lower latitudes mixes into the Antarctic stratosphere and the special conditions required for rapid ozone destruction disappear. The ozone hole closes — but the chlorine has not disappeared. To actually get rid of the chlorine, it must eventually make its way back into the troposphere, where it can be washed out and deposited at the surface. That journey is extremely slow, which is why the atmosphere still carries the chemical legacy of emissions from decades ago. Via Francesca Di Giuseppe

The reduction of ozone concentrations in the stratosphere and the formation of the Antarctic ozone hole each year are caused by complex meteorological and chemical processes. The status of the currently ongoing Antarctic ozone hole is displayed as a 3D rendered animation. To put this in perspective and allow for comparisons, the videos in the second and third rows show the entire process of formation and destruction of the 2017 to the 2025 ozone hole. Finally, the educational video first on the sidebar will guide you through the basics of the ozone hole and why it is important to keep monitoring the ozone layer. Below the videos you will find graphics, updated daily, showing the extent of the Antarctic ozone hole this year. atmosphere.copernicus.eu/mon…