Unusual weather over Antarctica has helped make the ozone hole the largest seen in a decade, according to scientists from NOAA and NASA.
At its peak, recorded between September 7 and October 13, the damaged area covered about 9.6 million square miles (25 million square kilometres).
That is more than twice the total land area of the United States.
Researchers say the seventh-largest ozone hole recorded in 48 years has been amplified by an exceptionally strong polar vortex.
“The annual ozone hole has been appearing later in the season in recent years, suggesting that the ozone layer is recovering,” said Paul Newman, a senior scientist at the University of Maryland and head of NASA’s ozone research team.
“However, an unusually powerful polar vortex prolonged ozone loss over Antarctica this year, allowing the hole to expand to a size not seen for a decade.”
An unusually strong polar vortex and atypical weather over Antarctica helped the ozone hole reach its largest size in a decade, NOAA and NASA scientists say
NOAA and NASA data indicate that the ozone hole reached its maximum extent on September 18.
On that date, it covered approximately 10.5 million square miles (27.1 million square kilometres).
That is roughly three times the size of the United States and about 90 per cent of the largest ozone hole ever measured, which occurred on September 9, 2000.
Dr Newman said the 2026 ozone hole could have been another 1 to 2 million square miles (3.5 million square kilometres) larger if levels of ozone-depleting chemicals had remained at their 2000 peak.
Those substances include chlorofluorocarbons, or CFCs, along with other compounds once commonly used in refrigerators, air-conditioning systems and building insulation.
Although some of these chemicals remain in the atmosphere, scientists expect them to disappear by the 2070s, allowing the ozone layer to recover fully.
Ozone high in the stratosphere functions as Earth’s natural sunscreen, protecting life from dangerous solar radiation.
That protection is weakened when human-made chemicals containing chlorine and bromine enter the atmosphere and break down ozone molecules.
NOAA and NASA measurements, including data collected with weather balloons shown here, identified September 18 as the date when the ozone hole was at its largest
Atmospheric currents transport these gases into the stratosphere, where ultraviolet light breaks them apart.
The released chlorine and bromine atoms then react with particles in polar clouds, triggering chemical processes that destroy ozone.
Although the Antarctic ozone hole forms each year during the southern autumn, scientists believe its exceptional size this season was driven by the unusually persistent polar vortex.
“The polar vortex was unusually extensive this year, partly because the large-scale weather systems that normally rise from the lower atmosphere and disrupt it were particularly weak during August and September,” said Amy Butler, a research scientist at NOAA’s Chemical Sciences Laboratory.
“The lack of those atmospheric waves kept the strongest winds of the vortex several degrees of latitude farther from the South Pole, creating a larger region where ozone-depleting conditions could develop.”
The findings come as forecasters warn that changes in the polar vortex could also influence winter weather in Britain, potentially bringing snow earlier than usual.
Some forecasts suggest the vortex could weaken sharply, with its winds possibly reversing direction by the middle of November.
Such a shift could allow the jet stream to move away from its normal path, raising the chance of Arctic air spilling southward.
It may also create a “blocked weather pattern”, allowing high pressure to settle over the UK and usher in cold, dry conditions.
Speaking to the Daily Mail, Dr Regan Mudhar, a weather scientist at the Université de Lausanne, said the possibility of snowfall “certainly can’t be ruled out”.
The ozone layer lies in the stratosphere, around 25 miles above Earth, where it provides a vital shield against solar radiation
Ozone is a naturally occurring molecule made up of three oxygen atoms.
Located in the stratosphere, roughly seven to 25 miles above Earth’s surface, the ozone layer acts as a protective barrier against harmful ultraviolet radiation. Excess exposure can contribute to skin cancer and cataracts, weaken the immune system and harm plants.
Most stratospheric ozone is formed in the tropics before being carried around the globe by atmospheric circulation.
Near the ground, however, ozone can form when sunlight reacts with pollution from vehicle exhausts and other sources, producing a harmful component of smog.
Warmer-than-average conditions in the stratosphere have limited ozone loss over the past two years, but the current Antarctic ozone hole remains considerably larger than those recorded in the 1980s, when scientists first identified depletion above the continent.
The ozone layer, found approximately seven to 25 miles above Earth, absorbs much of the ultraviolet radiation that would otherwise reach the planet’s surface
Concentrations of ozone-depleting chemicals, including chlorine and bromine compounds, remain high enough to cause substantial ozone loss.
Scientists recognised in the 1970s that CFCs, widely used in products such as refrigeration systems and aerosol sprays, were breaking down ozone in the stratosphere.
The 1987 Montreal Protocol established a global plan to phase out CFCs. The agreement has since produced the first clear signs that the Antarctic ozone layer is beginning to recover.
The upper stratosphere at lower latitudes is also showing strong evidence of recovery, demonstrating the effectiveness of the Montreal Protocol.
However, a new study published in Atmospheric Chemistry and Physics concluded that the ozone layer may not be recovering between 60°N and 60°S — a zone that includes London, located at 51°N.
The reason remains uncertain. Researchers suggest that climate change may be altering atmospheric circulation, carrying more ozone away from the tropics.
Another possibility is that very short-lived substances, or VSLSs, containing chlorine and bromine are destroying ozone in the lower stratosphere.
VSLSs are found in products including solvents, paint removers and industrial degreasing agents.
One of these chemicals is also used to manufacture a replacement for CFCs that is considered less damaging to the ozone layer.