A recent study has revealed that the ozone hole over the Antarctic has not only grown larger, but has also become thinner during most of the spring, despite a general trend of recovery in area and depth since the 2000s.

The study, published in Nature Communications, highlighted that the Antarctic ozone hole has been exceptionally massive in the last four years.

Lead author Hannah Kessenich from the University of Otago pointed out, "We find that the concentration of ozone at the centre of the ozone hole has reduced, which means the ozone layer has notably thinned."

The ozone hole is an area of severely depleted ozone in the stratosphere over the Antarctic, occurring from August to October at the beginning of the Southern Hemisphere spring.

While the United Nations Environment Programme (UNEP) predicts the ozone layer's recovery within four decades, recent years have shown a surprising trend. Despite an overall positive trajectory in recovery, the ozone hole has been notably large from 2020 to 2022, with the 2022 hole exhibiting similar characteristics to the large holes observed in 2020 and 2021.

Even though the study includes data up to 2022, observations in 2023 continue to reflect the same trend. According to NASA, from September 7 to October 13, the hole averaged 23.1 million square kilometres, roughly the size of North America, making it the 16th largest over this period.

This phenomenon is not only an environmental worry, but is also intertwined with the climate and dynamics of the Southern Hemisphere.

Kessenich stated, "With the remarkably large Antarctic ozone holes during 2020-2022, we quickly noticed that adding these years onto the observational record impacted previous trends toward ozone recovery. This spurred us to look into the issue further and determine where and when ozone depletion was worsening."

To gain insights, the research group conducted a comprehensive analysis of monthly and daily ozone changes at various altitudes and latitudes within the Antarctic ozone hole from 2004 to 2022. The findings revealed a substantial 26% reduction at the core of the ozone hole during this period.

This decline is notable, considering global efforts outlined in the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. The protocol aims to regulate the production and consumption of human-generated chemicals known to contribute to ozone depletion.

The 2022 quadrennial assessment report of the Montreal Protocol affirmed the phase-out of nearly 99% of banned ozone-depleting substances.

Despite these efforts, meteorological conditions, springtime temperature, wind patterns, aerosols from natural events like wildfires and volcanic eruptions, and changes in the solar cycle could be influencing the fluctuations in the size of the Antarctic ozone hole.

The complex interplay of these factors, especially within the polar vortex, where air from the mesosphere impacts ozone chemistry, necessitates further research.

Kessenich also highlighted the need to explore the descent of air from the mesosphere within the polar vortex and its potential impact on the ozone hole in the future. This ongoing research aims to unravel the intricate mechanisms contributing to ozone depletion in Antarctica and its broader implications for the Southern Hemisphere's climate dynamics.