The recovery of the ozone layer: a story of cooperation that continues

What is the ozone layer and why is it essential to protect it?

The ozone layer is a region of the atmosphere located mainly in the stratosphere, approximately 15 to 35 kilometres above the Earth's surface, where a significant proportion of atmospheric ozone is concentrated.

Its role is essential for life on Earth: it absorbs much of the ultraviolet (UV) radiation from the Sun, reducing the amount of harmful radiation that reaches the surface and thereby protecting human health and ecosystems.

Its depletion became one of the world's major environmental problems during the final decades of the 20th century. Today, four decades after the first evidence of the ozone hole over Antarctica, its evolution also offers reasons for optimism.

From a global problem to a global response

During the 20th century, the widespread use of substances such as chlorofluorocarbons (CFCs), then commonly found in products such as aerosols and refrigeration systems, caused significant depletion of stratospheric ozone.

The international response began to take shape even before the true scale of the problem was known. In March 1985, the Vienna Convention for the Protection of the Ozone Layer was adopted, establishing a framework that committed countries to research and cooperation. Just two months later, the publication of observations showing severe ozone depletion over Antarctica revealed the scale of the challenge and accelerated the process: in 1987, the Montreal Protocol was adopted, establishing specific phase-out schedules for nearly one hundred substances.

In 2009, this framework reached an unprecedented milestone: the Vienna Convention and the Montreal Protocol became the first treaties in United Nations history to achieve universal ratification.

The results show that the measures adopted have worked. Nearly 99% of the consumption and production of controlled ozone-depleting substances has been phased out, and there is clear evidence of recovery in the upper stratosphere.

According to the international scientific assessment, if current policies remain in place, the ozone layer is expected to return approximately to 1980 values by around 2040 for the near-global average, around 2045 in the Arctic and around 2066 in Antarctica.

Recovery is under way, but remains complex

Talking about recovery does not mean that the problem has been completely resolved. Many of the substances responsible for ozone layer depletion remain in the atmosphere for decades, and their evolution depends on complex chemical and climatic processes. This is why continued scientific monitoring remains essential.

An international study led by the Blas Cabrera Institute of Physical Chemistry (IQF-CSIC) and published in 2026 in Nature Communications analysed one of these factors: the role of natural halogens, such as bromine and iodine originating from oceans and other ecosystems.

Although they are present in much lower concentrations than human-made compounds, they can be highly effective at destroying ozone. The study indicates that their influence could mean that the recovery of Antarctica's natural seasonal ozone cycle is slower than previously expected.

These findings do not call into question the effectiveness of the measures adopted. On the contrary, the reduction of human-made substances continues to support the recovery of the ozone layer, while science enables us to better understand the factors that will determine its future evolution.

Protecting the ozone layer and protecting the climate

Although ozone layer depletion and climate change are different phenomena, the two are interconnected.

Many of the substances that damaged the ozone layer are also potent greenhouse gases. Their gradual phase-out has therefore helped not only to protect stratospheric ozone, but also to limit additional global warming.

This relationship became even more significant with the Kigali Amendment, adopted in 2016 to gradually phase down hydrofluorocarbons (HFCs). These gases do not directly deplete the ozone layer, but many have a high global warming potential.

In 2026, marking the tenth anniversary of the Kigali Amendment, the United Nations celebrates the International Day for the Preservation of the Ozone Layer under the theme “Global action for a cooler planet”, highlighting how international cooperation can deliver benefits for both ozone protection and the climate.

A lesson for major environmental challenges

The story of the ozone layer is still being written. Its recovery will take decades, and science continues to uncover factors that may influence its evolution. But it also provides an example of how scientific evidence, international agreements and sustained action over time can deliver results on a global scale.

The International Day for the Preservation of the Ozone Layer reminds us that major environmental challenges require knowledge, cooperation, innovation and long-term commitments, as well as the ability to adapt decisions as our understanding of the planet improves.