Is the Recovery of the Ozone Layer Being Delayed?

Suomi NPP earth observation satellite

The Montreal Protocol of the UN in 1987 is credited with the discontinuation of the use of chlorofluorocarbons (CFCs). The renowned ozone hole was expected to become history after a certain recovery period. Some studies project the complete closure of the ozone hole by around the middle of the 21st century.

However, the thinning of the ozone layer persists more stubbornly in certain regions than anticipated, and full restoration remains distant. Investigations attribute this phenomenon to, among other factors, dichloromethane emissions and extensive wildfires, postponing the potential recovery of the ozone layer by approximately another 30 years into the future.

Protection Against Harmful UV

The ozone layer is a zone in the stratosphere with an increased concentration of the trace gas ozone (O3). Ozone is crucial because it absorbs the majority of harmful UV-B and UV-C radiation from the sun—the portion of sunlight that can cause skin cancer, cataracts, and various environmental issues.

The causes of the holes in the ozone layer are attributed to the extremely low temperatures prevailing over the poles at the beginning of spring, as well as sunlight and a number of chemical substances such as chlorofluorocarbons (CFCs). These substances were previously common in products like aerosol sprays, pesticides, flame retardants, and refrigeration devices, and some are still in use today.

Giant Holes in Two Places

In summary, the scientific community generally assumes that the ozone hole over Antarctica, which is consistently large from late August onward and recovers in the following months due to seasonal warming, is on the path to recovery. Whether the recently occasionally reached record sizes indicate a declining trend is uncertain. In 2020, for instance, the depletion had an extent of 18 million square kilometers by the end of winter, surpassing the entire Antarctic land area (approximately 14 million square kilometers). Since then, it has reached even greater dimensions in individual years.

This phenomenon is attributed, in part, to extreme cold zones in the atmosphere, with chlorofluorocarbon (CFC) molecules continuing to play a significant role. These substances have a lifespan of 50 to 100 years, explaining why their concentrations have hardly decreased since the implementation of the Montreal Protocol.

Satellite Measurements

The ozone hole over the Antarctic has also reached record-breaking proportions in 2021.

A research team from the University of Otago in Dunedin, New Zealand, speculates that CFCs and other pollutants may not be the sole culprits. The team’s recent findings suggest additional harmful factors because the recent record-breaking ozone holes over Antarctica are difficult to explain solely by these substances. Their study, published in the journal Nature Communications, delves into monthly and daily ozone variations at different altitudes and latitudes from 2004 to 2022, utilizing satellite data.

Surprisingly, the scientists, under the direction of lead author Hannah Kessenich, found that the Antarctic ozone hole’s core had significantly less ozone than it did 19 years ago. In the October months since 2004, the gas concentration in this region above the Southern Continent has decreased by over a quarter. Kessenich noted that this implies not only a larger spatial extent of the ozone hole but also a deeper presence throughout most of the spring. Additionally, the researchers found that the ozone hole appears later and closes later compared to previous years.

Changes Above the Stratosphere

The team observed a correlation between this ozone depletion and changes in the atmosphere as it entered the polar vortex over the Antarctic. This suggests that recent significant ozone holes may not be solely caused by CFCs, as stated by the atmospheric researcher. Researchers are considering changes in the dynamics of the mesosphere, the atmospheric layer above the stratosphere, as a possible cause.

Despite public perceptions that the “ozone problem” has been resolved in recent years, as noted by Kessenich, the Montreal Protocol has indeed significantly improved the situation regarding ozone-depleting CFCs. However, according to the researchers, the overall impression has changed little. “While the Montreal Protocol has vastly improved our situation with CFCs destroying ozone, the hole has been amongst the largest on record over the past three years, and in two of the five years prior to that,” as stated by the authors.

But Still Recovery?

The extent of the Antarctic ozone hole in 2023, based on data from the Copernicus Sentinel 5P satellite.
The extent of the Antarctic ozone hole in 2023, based on data from the Copernicus Sentinel 5P satellite. Image: ESA.

As other researchers have explained, the study is not novel in this regard. In fact, this study aligns with the findings of the World Meteorological Organization (WMO) ozone status reports, as stated by Ulrike Langematz, a climate researcher from the Free University of Berlin who was not involved in the study. These reports indicate that Antarctic ozone continues to recover in early winter, while in late winter and spring in recent years, there have been significant, unusually prolonged ozone holes with various possible causes.

Martin Dameris of the German Aerospace Center, who was also not involved in the study, sees no immediate signs of a sustained thinning of the ozone layer over Antarctica. He refers to the year 2019, which the New Zealand scientists did not consider in their current study. In that year, the smallest ozone hole since 1988 was observed. Although large ozone holes reappeared between 2020 and 2022, Dameris notes that, from a scientific perspective, this is not unusual. On average, the ozone hole is likely to continue shrinking in the coming years.

Consequences for the Climate

Development of the ozone distribution over Antarctica between July 1 and September 24, 2023.

Nevertheless, the group led by Kessenich points out that this year, the ozone hole has exceeded the size of the three previous years. By the end of October, its area was over 26 million square kilometers, nearly double the size of Antarctica. Investigating the mechanisms behind this peculiar development is of paramount importance, according to Kessenich. It is crucial to comprehend these ozone fluctuations because, as the researcher emphasizes, they have a significant impact on the southern hemisphere’s climate.

Although the ozone hole is not directly related to the impacts of greenhouse gases on the climate, it does influence the delicate balance in the atmosphere. Since ozone absorbs UV light, the absence of these molecules can have drastic effects on where heat is stored in the atmosphere. “Downstream effects include changes to the Southern Hemisphere’s wind patterns and surface climate, which can impact us locally,” noted Kessenich.

Featured Image: NASA.