Ozone holes: Why they occur and what to do about them

What are ozone holes?

Ozone holes are localized thinnings of the ozone layer. This layer is particularly important for Earth because it acts as a sunscreen, preventing the sun’s ultraviolet radiation from reaching the troposphere in full. By protecting Earth from this radiation, the ozone layer protects plants, animals, and humans from sunburn and a variety of diseases, including skin cancer [1].

As satellite images show, ozone holes are not literal holes. Scientists use the term as a metaphor for places where ozone concentrations are extremely low. The thickness of the ozone layer is measured in “Dobson units” (1 Dobson unit equals a 10-micrometer layer of ozone). Ozone holes are places where ozone levels are 220 Dobson units or lower [2].

The first ozone hole appeared in the early 1980s. Then, thanks to ground-based and satellite measurements, scientists from the British Antarctic Survey (BAS) observed that each spring, the Earth’s natural sunscreen over the South Pole was sharply thinning [3]. This change was called the ozone hole. Since then, the study of ozone holes has continued. They are monitored by:

• World Meteorological Organization (WMO);
• United Nations Environment Programme (UNEP);
• National Aeronautics and Space Administration (NASA);
• National Oceanic and Atmospheric Administration (NOAA);
• Russian Arctic and Antarctic Research Institute (AARI).

Changes in the ozone layer are studied locally and remotely. For local measurements, air is pumped into an ozonesonde (an instrument for measuring the vertical distribution of ozone in the atmosphere), and the amount of ozone in the air is calculated based on how much UV radiation or electric current the air absorbs. Ozone sondes are launched on small balloons to reach the stratosphere. Research aircraft are sometimes used for the same purpose. [4]

Remote measurements also rely on ozone’s key property  —  its ability to absorb UV rays. The source of UV radiation used in research can be not only the Sun but also lasers or starlight. For example, satellites use solar UV rays, absorbed by the Earth’s atmosphere, to measure ozone levels daily over almost the entire globe. Ground-based research stations often use lasers that transmit light over long distances.

Where are ozone holes located?

The most famous ozone hole is located over Antarctica. NOAA satellite measurements showed that the total area of ​​the polar ozone hole peaked on October 7, 2021 [5]. At that time, its size was 24.8 million km². This is roughly the size of North America. Below, on the NOAA map, the ozone hole is highlighted in dark blue.

Ozone hole over Antarctica (NOAA) (Photo: National Oceanic and Atmospheric Administration).

In July 2022, Canadian scientists from the University of Waterloo in Ontario discovered another ozone hole in the tropics. Here, ozone at the center of the hole is depleted to approximately 80% of its normal level, and its size is comparable to the Antarctic polar hole. However, its area is approximately seven times larger. [6]

The international scientific community is debating the validity of the Canadian colleagues’ study. “There is no such thing as a tropical ozone hole,” says Paul Young, an atmospheric scientist at Lancaster University in England and one of the authors of the “Scientific Assessment of Ozone Depletion 2022” report, jointly prepared by the WMO and the UN.

The distrust of scientists stems from the new definition of the ozone hole introduced by Canadian meteorologists in their report. “The study’s author found a tropical ozone hole because he looks at percentage changes in ozone, not absolute changes. And absolute changes are more important for calculating harmful ultraviolet radiation reaching the Earth’s surface,” Young asserts. Thus, according to the old approach, a tropical ozone hole does not exist, while measurements based on percentage losses suggest that the ozone layer is thinning. [7]

How ozone holes form

Natural causes

359 million years ago, at the junction of the Devonian and Carboniferous geological periods, an unexplained mass extinction occurred on Earth. Recently, scientists found deformed spores of land plants from that era in eastern Greenland. They examined them under a microscope and saw dark spots and spines on the spores, which would not be present in a healthy plant. This change in appearance suggests that the extinction coincided with increased levels of UV-B radiation (medium-wave ultraviolet) [8]. This is only possible if the Earth’s ozone layer is weakened.

Unlike other mass extinctions, this period did not involve cataclysmic events that could have significantly affected ozone levels, such as planet-wide volcanic eruptions. However, there was another event  —  a strong global warming that ended the Ice Age. Therefore, ozone loss during rapid warming is a natural and inevitable property of the Earth.

Sunspots, stratospheric winds, and volcanic eruptions continue to affect the ozone layer today. However, they do not deplete it as severely. Meanwhile, global climate change and human-caused chemical use have a more destructive impact [9].

Anthropogenic Causes

In 1974, Mario Molina and Sherwood Rowland discovered that chlorofluorocarbons (CFCs), released into the atmosphere, trigger a chemical reaction upon exposure to sunlight, destroying ozone [10]. Previously, such substances were used in aerosols and refrigerators. But after Molina and Rowland’s discovery, the international community began to collect additional information about CFCs.

In 1976, the US Academy of Sciences conducted its own research and confirmed the scientists’ findings [11]. In 1985, the British Antarctic Survey received data on declining ozone concentrations over the Halley Bay Antarctic Station [12]. Unexpectedly high chlorine levels were detected in the stratosphere’s chemical composition, making it clear that ozone depletion was indeed occurring.

How to Combat Ozone Holes

When the impact of CFCs was confirmed by satellite images and additional research, the 1987 Montreal Protocol was developed: an agreement to phase out the production of ozone-depleting chemicals. Additional documents with recommendations on how to reduce CFC use were later published.

The gradual phase-out of ozone-damaging substances did indeed occur, and several years ago the UN confirmed its effectiveness [13]. In May 2020, the ozone hole over Antarctica even closed, but reopened shortly afterward. CFC concentrations in the atmosphere near the poles are still too high, making it difficult to talk about stability. There are specific climatic conditions here, which, due to polar vortices and nacreous clouds, prevent the ozone layer from recovering more quickly.

Ozone holes generally have the ability to disappear or shrink. Changes in their size are due not only to human activity but also to climatic conditions. For example, because ozone is formed by oxygen and ultraviolet radiation, its amount decreases for a long time during the polar night, but then recovers on its own during the polar day. A hole can form and heal in a few weeks, but sometimes it takes months. [14]

Is the ozone hole a hoax?

Some scientists suggest that ozone holes are not as dangerous as they are made out to be. Ben Lieberman, a former senior fellow in energy and environment at the Thomas A. Rowe Institute for Economic Policy Research, is convinced that the Montreal Protocol was unnecessary and that the ozone hole problem has been greatly exaggerated: “The ozone layer thinning that occurred throughout the 1980s appears to have stopped in the early 1990s. This is too early to attribute this to the Montreal Protocol.”

He also believes that the link between ozone depletion and increased health risks for humans, animals, and plants is far-fetched: “Ozone depletion itself does not harm human health or the environment. The WMO acknowledges that no statistically significant long-term trends have been found. Therefore, it can be said that the effect of ozone layer thickness on UV radiation over populated areas is so small as to be difficult to detect.” [15]

French scientist Haroun Tazieff holds a similar opinion. He believes the appearance of ozone holes is completely normal, and nothing needs to be done about it: “The ozone hole is a natural hole that appears over Antarctica in early October and disappears by the end of December. In Europe, I think I’m the only person who refutes the main theory, but I’ve never been officially contradicted by either environmentalists or scientists.” [16]

He argues that ozone holes may be part of a larger political game. He believes the supposed problems promoted by politicians have led to millions of pounds being spent on “environmental windmills” rather than addressing the real threats of pollution.

These and other scientists point out the lack of research into the problem. They say many dire predictions about the consequences of ozone holes have failed to come true or were based entirely on myths. For example, in 1992, the New York Times reported that ozone depletion over southern Chile was causing vision problems in sheep and rabbits [17]. This story was subsequently repeated by other sources, including television. Later, Al Gore’s book, Earth in the Balance, reiterated this myth: “In Patagonia, hunters now report finding blind rabbits, and fishermen catching blind salmon” [18]. The myth was debunked when a team from Johns Hopkins University demonstrated that the animals’ blindness was related to common conjunctivitis [19].

Ozone hole  —  forecasts

According to NASA research models, the concentration of chlorine and other ozone-depleting substances in the stratosphere will not return to 1980s levels until at least the mid-21st century. Agriculture, which continues to use nitrous oxide  —  a potent ozone-depleting greenhouse gas  —  is also contributing to the problem. [20]

There are also other human activities whose impact we don’t yet fully understand but which may pose risks. These include rocket launches and sulfate geoengineering — the idea that we can prevent the worst effects of global warming by pumping aerosols into the stratosphere to cool temperatures and cause sunlight to reflect off these aerosol particles. [21]

At the same time, temporary positive dynamics are also visible. In 2019, abnormal weather conditions in the upper atmosphere over Antarctica sharply limited ozone depletion. This resulted in the smallest hole since 1982, but scientists predict that the Antarctic ozone layer will fully recover by 2040 [22]. Humanity’s main task now is to continue research and monitor the state of not only the ozone hole but also the climate as a whole.

illuminem Voices is a democratic space presenting the thoughts and opinions of leading Sustainability & Energy writers, their opinions do not necessarily represent those of illuminem.

Curious how major companies measure up on climate? On illuminem’s Data Hub™, explore verified emissions data, net‑zero targets, and sustainability performance of thousands of firms — from industry leaders to emerging innovators.