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Study highlights need to keep an eye on the ozone hole
Despite public perception, the Antarctic ozone hole has been remarkably massive and long-lived over the past four years, University of Otago researchers believe chlorofluorocarbons(CFCs) aren’t the only things to blame.
In a study, just published in Nature Communications, the group analysed the monthly and daily ozone changes, at different altitudes and latitudes within the Antarctic ozone hole, from 2004 to 2022.
Lead author Hannah Kessenich, PhD candidate in the Department of Physics, says they found there is much less ozone in the centre of the ozone hole compared to 19 years ago.
“This means that the hole is not only larger in area, but also deeper throughout most of spring.
“We made connections between this drop in ozone and changes in the air that is arriving into the polar vortex above Antarctica. This reveals the recent, large ozone holes may not be caused just by CFCs,” she says.
While the Montreal Protocol on Substances that Deplete the Ozone Layer, which has been in place since 1987, regulates the production and consumption of man-made chemicals known to deplete the ozone, the researchers believe other complex factors are also contributing to the ozone hole.
“Most major communications about the ozone layer over the last few years have given the public the impression that the ‘ozone issue’ has been solved.
“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.
“Our analysis ended with data from 2022, but as of today the 2023 ozone hole has already surpassed the size of the three years prior – late last month it was over 26 million km2, nearly twice the area of Antarctica.”
Ms Kessenich believes understanding ozone variability is important because of the major role it plays in the Southern Hemisphere’s climate.
“We all know about the recent wildfires and cyclones in Australia and New Zealand and the Antarctic ozone hole is part of this picture.
“While separate from the impact of greenhouse gases on climate, the ozone hole interacts with the delicate balance in the atmosphere. Because ozone usually absorbs UV light, a hole in the ozone layer can not only cause extreme UV levels on the surface of Antarctica, but it can also drastically impact 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.”
She is quick to allay fears about extreme UV rays, though.
“New Zealanders need not worry about applying extra sunscreen this year as the Antarctic ozone hole is generally not open above New Zealand – it is mostly located directly over Antarctica and the South Pole.”
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From: Springer Nature
Climate science: Antarctica’s ozone hole expands mid-Spring for past two decades
The core (middle stratospheric layer) of the Antarctic ozone in mid-spring (October) has experienced a 26% reduction since 2004, contrary to previously reported recovery trends in total ozone, suggests a Nature Communications paper. However, recovery trends remain in early spring (September). The findings highlight the importance of continuous monitoring and evaluation of the state of the ozone layer with the changing dynamical state of Earth’s climate.
The Montreal Protocol designated a list of controlled ozone depleting substances that were banned from future production in 1987 and is widely considered to have been successful for ozone recovery. However, the past three years (2020–2022) have witnessed the re-emergence of large and long-lived ozone holes over Antarctica in mid spring, while early spring still shows a slight ozone increase (or a slight recovery of the ozone hole). Understanding ozone variability remains of high importance, due to the major role Antarctic stratospheric ozone plays in climate variability across the Southern Hemisphere.
To assess recent changes in the Antarctic ozone hole, including during the 2022 season, Annika Seppälä, Hannah Kessenich and colleagues analysed monthly and daily ozone changes between 2001–2022. Data from 2002 and 2019 were excluded as sudden stratospheric warming broke up the ozone hole anomalously early in these years. They looked at different stratospheric layers throughout the key austral springtime months of September to November. When satellite data from 2022 is considered, they found that previously reported recovery trends in Antarctic spring total column ozone (the total ozone above a given point on Earth across all atmospheric layers) from 2001 onward disappear. The middle stratosphere has been dominated by continued, significant ozone reduction since 2004, amounting to 26% loss in the core of the ozone hole. This reduction is potentially driven by dynamical changes in the mesosphere (the atmospheric layer above the stratosphere and the ozone layer).
The findings suggest that changes in the Southern Hemisphere atmosphere are contributing to a persistent Antarctic ozone hole.
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Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
By looking at detailed, daily ozone observations from the last 19 years, we find evidence of much less ozone in the center of the Antarctic ozone hole compared to 19 years ago. This means that the hole has not only remained large in area, but it has also become deeper (i.e. has less ozone) throughout most of Antarctic spring. The especially long-lived ozone holes during 2020-2022 fit squarely into this picture, as the size/depth of the hole during October was particularly notable in all three years. On a positive note, however, we do find a delay in the ozone hole onset date and signs of increasing ozone during early-spring (September).
"Knowing when and where worsening ozone depletion is occurring (October middle stratosphere, between 20-35 km in altitude) allows us to focus on possible causes that might affect these spatiotemporal regions. We find a link between declining ozone and changes in air descending into the polar vortex during October (a dynamical effect). Altogether, our findings reveal the recent, large ozone holes may not be caused just by CFCs. So, while the Montreal Protocol has been indisputably successful in reducing CFCs over time and preventing environmental catastrophe, the recent persistent Antarctic ozone holes appear to be closely tied to changes in atmospheric dynamics.
Our results highlight the need to keep a close watch on the ever-changing Antarctic ozone hole.
Dr Martin Jucker is a lecturer at the University of New South Wales and Associate Investigator at the ARC Centre of Excellence for Climate Extremes
This new paper applies a linear trend analysis on the ozone hole area and asserts that despite the Montreal Protocol, there has been a reduction of ozone since the early 2000s. Based on those results, it questions the ozone hole recovery which is generally accepted to be on track for mid-century.
I am not convinced of the results of the study. Their results rely heavily on the large ozone holes we have seen in 2020-2022. However, existing literature has already found reasons for these large ozone holes: Smoke from the 2019 bushfires and a volcanic eruption (La Soufriere), as well as a general relationship between the polar stratosphere and El Niño Southern Oscillation: We know that during la Niña years, the polar vortex in the stratosphere tends to be stronger and colder than usual, which means that ozone concentrations will also be lower during those years. The years 2020-22 have seen a rare triple La Niña, but this relationship is never mentioned in the study.
In addition, the study removes two years in the record, 2002 and 2019, on the basis of exceptional events happening during those years; so-called Stratospheric Sudden Warmings. Those events have been shown to have strongly decreased the ozone hole size, so including those events would probably have nullified any long-term negative trend in ozone concentrations. It is questionable how the authors can remove 2002 and 2019 from the record but not 2020-22, given that all of these years have been shown to be dominated by very special and rare events.
In this context, it is important to note that the ozone hole is extremely variable from year to year, meaning that it can be large one year and small the other year. It is only over longer terms that a trend can be identified. Using only 22 years and then removing two inconvenient years does not help make this study convincing.
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