La ozone layer It's much more than a term we recognize in the media every September 16th, International Day for the Preservation of Earth. This invisible shield located high in the atmosphere plays a vital role for life on Earth, as filters and reduces ultraviolet radiation (UV-B) that comes from the Sun. Without this natural barrier, humanity, wildlife and ecosystems would be seriously exposed to health problems and environmental imbalances.
Although its deterioration was a cause of great concern for decades, especially due to the famous "ozone hole" over Antarctica, in recent years good news has been gaining ground. Thanks to international efforts and scientific initiatives, signs of a gradual recovery are being seen. But how has the ozone layer actually evolved in different regions of the planet? What challenges does it still face? Let's discover how this protective barrier varies around the world and what the future holds.
What is the ozone layer and why is it crucial?
La ozone layer It is an area of the stratosphere, located between 15 and 40 kilometers above sea level, where concentrations of ozone (a gas composed of three oxygen atoms – O3) are especially high. Although this gas only represents about 2-8 parts per million In that atmospheric zone, its function is essential for life as we know it.
Ozone is formed thanks to the photochemical reaction induced by solar ultraviolet radiationBasically, photons of light break apart oxygen molecules (O2) generating free atoms, which then combine with other oxygen molecules to form ozone (O3). This cycle, known as the "Chapman cycle," maintains a certain balance of ozone in the stratosphere.
The reason it is so essential is because absorbs the most harmful wavelengths of ultraviolet radiation, allowing only those necessary for biological processes such as photosynthesis to reach the surface. Without the ozone layer, the increase in UV radiation would generate Skin cancer, cataracts, weakening of the immune system and significant changes in ecosystems and crops.
The process of ozone destruction: causes and consequences
The natural balance of the ozone layer can be broken relatively easily by the presence of certain synthetic chemicals, especially the chlorofluorocarbons (CFCs), halons, methyl bromide and other chlorinated or brominated compounds. Introduced into the atmosphere by human activities over the last century, these compounds are especially dangerous because they can remain unchanged for years until they reach the stratosphere, where solar radiation breaks them down and releases them. chlorine and bromine atoms.
In conditions like those of antarctic winterAt temperatures below -78°C, "polar stratospheric clouds" form. Within them, CFCs and other halogenated compounds release active chlorine and bromine atoms, which act as true ozone predators: a single chlorine atom can destroy up to 100.000 ozone molecules. When the first rays of spring arrive, the reaction intensifies, and the famous "polar stratospheric cloud" occurs. Antarctic ozone hole.
This destruction not only threatens human health, but It seriously affects crops, aquatic and terrestrial ecosystems, and may even disrupt food chains that are essential for biodiversity.
Most of the ozone is in the stratosphere, but there is approximately 10% in the troposphere, where, instead of protecting, it is dangerous to health and is part of the problem of photochemical smogTo better understand how this destruction occurs and what measures have been taken, we invite you to explore the article on the destruction of the ozone layer.
Comparison of the ozone layer in different regions of the world
The regional variations The ozone layer's depletion is due to multiple factors: temperature, atmospheric dynamics, latitude, solar activity, and the concentration of aggressive gases. Analyzing these regional differences helps us understand the magnitude and complexity of the challenge posed by both its protection and recovery.
- Antarctica: It's the most iconic and alarming place. Every southern spring (from August to October), the "ozone hole" opens, reaching its maximum extent between September and early October. In 2024, the average size was about 20 million square kilometers, almost three times the size of the continental United States, although it was one of the smallest since 1992 following the gradual recovery driven by the Montreal Protocol.
- Arctic: Although not as dramatic as in the Southern Hemisphere, there are episodes of ozone depletion associated with cold winters and particular atmospheric conditions. Some years, such as 2020, saw record lows, although the Arctic "hole" is less persistent and extensive.
- Mid-latitudes and tropics: Here, ozone is usually more stable and abundant, but decreases have also been detected, especially over large cities due to pollution and the transport of substances from polar latitudes.
In general, polar regions are the most vulnerable to depletion and mid-latitudes show a faster recovery, with estimates of a return to pre-industrial levels by the 2030s in the Northern Hemisphere.
The ozone hole: historical evolution and current status
La Global concern about the ozone hole began in the 80s, when British scientists measured a dramatic drop in ozone over Antarctica. The image of the "hole" became a symbol, prompting international action.
In 2000, the size of the hole reached a record high, reaching nearly 29 million square kilometers. Since then, a slow but steady recovery has been observed. According to NASA and NOAA, in 2024 the hole was smaller than the 20-year average, ranking seventh among the smallest since 1992.
This improvement is due to the progressive reduction of CFCs and other aggressive chemicals, stipulated by the Montreal Protocol. Even so, it will still take decades to return to pre-1980 values: the hole is expected to disappear completely over Antarctica by 2060-2066, and earlier (2030-2050) in other regions.
The fundamental role of the Montreal Protocol and international cooperation
El Montreal Protocol It was signed in 1987 and was the first global environmental treaty to achieve universal ratification. Its objective was Eliminate the production, use, and emission of ozone-depleting substances, such as CFCs, halons, HCFCs and methyl bromide.
The success of the Protocol lies in the fact that it was based on solid scientific evidence and in a mechanism of cooperation and continuous evaluation between countries and scientists. It not only involved the progressive replacement of everyday products, but also fostered innovation and the development of alternative technologies.
In 2019, the Kigali Amendment, which extended its commitment to reducing hydrofluorocarbons (HFCs). Although they don't directly destroy ozone, these gases have a very powerful greenhouse effect and can contribute to climate change.
More than 99% of the substances covered by the Protocol have been eliminated, although some still exist. Challenges in controlling illegal emissions or the regulation of new compounds not contemplated in the original agreement.
Impacts on health, agriculture and ecosystems
A weakened ozone layer allows greater entry of UV-B radiation, which translates into serious consequences.
- Human health: Protecting ozone is vital to reducing cases of skin cancer, cataracts and eye injuries, and immune weakeningSome studies estimate that the Montreal Protocol has prevented two million cases of skin cancer per year and that by 2030 there will be a 14% less incidence compared to the scenario without measures.
- Agriculture: Plants sensitive to ultraviolet radiation would suffer severe damage, affecting agricultural productivity and food security.
- Ecosystems: UV-B radiation disrupts phytoplankton, the base of many aquatic food chains, and harms terrestrial and marine organisms.
El environmental and social benefit of preserving the ozone layer It is incalculable, since it directly and indirectly impacts all of the Earth's vital systems.
Ozone monitoring and surveillance technologies
El monitoring the ozone layer It is carried out through an international network of satellites (such as NASA's Aura, NOAA-20 and NOAA-21, Suomi NPP) and meteorological balloons launched from polar stations, capable of measuring ozone concentrations in real time at different altitudes.
The standard reference parameter is the Dobson unit, which measures the amount of ozone in a vertical column of the atmosphere. Before widespread depletion, ozone levels over Antarctica hovered around 225 Dobson units. In October 2024, the lowest recorded level was 109 units, still far from the original levels. To learn how this measurement is evolving, check out this article on the structure of the atmosphere.
Observations show that the trend is positive, but the restoration process is slow as CFCs remain in the atmosphere for decades before completely decomposing.
Current and future challenges of the ozone layer
While the recovery progresses, not everything is resolved. They persist new threats and challenges:
- Some compounds not covered by the Protocol, such as nitrous oxide, continue to contribute to ozone depletion.
- El climate change, through increased greenhouse gases and alterations in atmospheric circulation, can modify the dynamics of the stratosphere and affect chemical processes related to ozone.
- The existence of exemptions and permitted uses of harmful substances still present in everyday life and in some industries, especially in developing countries.
- La responsible destruction of "ODS banks" (ozone-depleting substances) at the end of life of household appliances and refrigeration systems.
The connection between ozone and climate change
The ozone layer and climate change are more closely related than meets the eye.Many of the gases that destroy ozone are also potent greenhouse gases. Reducing these compounds through the Montreal Protocol has prevented a significant increase in global temperature.
However, some alternatives, such as HFCs, have a high greenhouse effect, which has led to new regulations, such as the Kigali Amendment.
There is also concern that the climate change could influence the recovery of the ozone layer by altering atmospheric circulation and stratospheric chemistry, so scientists will continue to monitor these impacts.
Lessons from the past: the ozone layer as a reference for other global challenges
La recovery of the ozone layer It is an inspiring example of how science, politics, and society can collaborate. The existence of a problem involving a limited number of substances and sectors facilitated reaching consensus. All of this was possible thanks to scientific evidence, awareness-raising campaigns, and international pressure.