September 16th is the International Day for the Preservation of the Ozone Layer. The World Meteorological Organization’s latest bulletin indicates that Earth’s ozone layer is recovering, and the ozone hole in 2024 will be smaller than in recent years.
The bulletin states that the lower levels of ozone depletion observed in 2024 are partly due to year-to-year fluctuations caused by natural factors, but this long-term positive trend reflects the success of concerted action by the international community.
Compared with previous years, total stratospheric ozone coverage was higher over most of the world in 2024. In 2024, the Antarctic ozone hole was deeper than the 1990-2020 average and smaller in area than during the 2020-2023 period.
The latest scientific assessment indicates that the ozone layer is expected to return to 1980s levels by the middle of the 21st century, significantly reducing the risks of skin cancer, cataracts, and ecosystem damage caused by excessive ultraviolet radiation exposure. This has important implications for the health and well-being of human society.
What is the Ozone Layer?
Ozone is a pale blue gas with a strong irritant and a foul odor. It has two most important properties: first, it is a strong oxidizing agent, reacting with a wide range of substances even at room temperature and pressure; second, it absorbs ultraviolet light. As humans, we owe ozone a debt of gratitude—it is these two properties that have saved Earth from becoming a desert like Mars.
Sunlight contains a significant amount of high-energy ultraviolet light, which not only destroys complex life molecules but also breaks down water molecules, transforming them into hydrogen and oxygen. Earth’s small size and lack of gravity cause hydrogen to escape into space—over time, this effect should have reduced the amount of water on Earth.
But the ozone layer prevented this from happening. It intercepts ultraviolet light from above, preventing most of it from reaching the Earth’s surface, and it intercepts hydrogen from below, allowing it to fall back to Earth as water. Compared to these benefits, ozone’s other benefit—preventing ultraviolet light from harming life on Earth—is almost negligible.
That said, preventing water loss takes time, after all, to achieve its effects over vast geological timescales, whereas UV damage is immediately noticeable. Therefore, the ozone layer first attracted widespread global attention precisely because of its direct impact on human health.
Benefits of Ozone Layer Recovery for Humanity
In 1987, 43 countries signed the Montreal Protocol on Substances that Deplete the Ozone Layer (Resolution 49/114). September 16th, International Day for the Preservation of the Ozone Layer, commemorates its signing. The protocol initially stipulated a halving of chlorofluorocarbon (CFC) use by the year 2000. It has since been revised several times, with detailed regulations for different types of substances, including the phase-out of CFCs by 2010 and the less harmful hydrochlorofluorocarbons (HCFCs) by 2030.
The Montreal Protocol is the most successful global environmental treaty in human history, demonstrating the international community’s resolve and ability to collectively address environmental challenges. It is the only treaty in UN history to be ratified by all member states. Since its signing, all major industries worldwide have abandoned the legal use of CFCs, and the levels of all the most important CFCs and their derivatives in the atmosphere have either stabilized or begun to decrease.
Because CFCs are extremely long-lived, recovery from them will take time. However, the latest projections suggest that the ozone layer will return to 1980 levels around 2040 over most of the world, with the Antarctic ozone hole returning to 1980 levels by 2066. One study estimates that by 2100, actions to protect the ozone layer in the United States alone could prevent 280 million cases of skin cancer and 1.6 million deaths from skin cancer, significantly impacting future public health burdens.
Decades of scientific research on the ozone layer by the World Meteorological Organization have been built on the foundations of trust, international cooperation, and free data sharing—the cornerstones of the world’s most successful environmental agreements and a model for how the international community can work together to address global challenges.
