What causes the Antarctic ozone hole to open, and why is it bigger than usual for this time of year?
ADVERTISEMENTThe ozone hole that forms over Antarctica every year is taking an unusually long time to close, climate scientists report.
Typically, the Antarctic ozone hole begins to form in mid-August and starts to decrease gradually during November.
But this year the ozone hole area formed several days earlier than usual and has maintained an area of just over 15 million square kilometres since late October. The alarming news comes from the Copernicus Atmosphere Monitoring Service (CAMS) which is keeping a close watch on the hole.
Why is the ozone layer so vital?
Earth’s ozone layer protects us all from the sun’s harmful radiation. The realisation that certain chemicals were thinning it led to a major international intervention in 1987.
The Montreal Protocol - signed just seven years after the problem was discovered - is a rare example of speedy global accord, and the envy of today’s climate scientists.
The treaty has phased down man-made chemicals that deplete the atmosphere’s ozone molecules, leading scientists to declare a “significant milestone” in the ozone layer’s recovery last year.
But for the last three years, ozone layers have also been closing much later than usual. Climate change is one of the potential causes of this phenomenon, according to CAMS.
How has the Antarctic ozone hole changed in 2023?
The ozone hole widens during the austral spring, when ozone-depleting substances start to gather in the stratosphere over the South Pole. Alongside solar radiation, extreme cold temperatures and polar stratospheric clouds, this causes a drastic drop in the concentration of Ozone in the stratosphere.
By the end of November, stratospheric temperature increases and a change in winds tend to see the ozone hole close up.
2023 has followed a slightly different trajectory. An earlier increase in size saw the ozone hole become the sixth largest in the satellite era (since 1979) with a total area of 25.12 million km2 by mid-September.
Despite dropping in the usual fashion through early October, it increased again towards the end of the month, notes CAMS. And it has maintained an area of around 12 million km2, which is predicted to continue into the first week of December.
Why are ozone holes taking longer to close?
Although this year’s ozone hole has waxed and waned in a particular way, the unusual longevity is part of a recent trend.
Since 2020, ozone holes have been closing much later than before, around mid- to late December.
CAMS says this is due to colder than average stratospheric temperatures and a strong polar vortex - fierce winds circulating high in the atmosphere over Antarctica - lasting until December.
The reason for that stronger polar vortex is still something of a mystery. Several potential drivers have been identified by CAMS, including water vapour released into the atmosphere by the Hunga-Tonga volcano in the South Pacific; changes in wind patterns in the Southern Hemisphere; and climate change.
Further research is needed according to the monitoring service, which is delivered by the European Centre for Medium-Range Weather Forecasts on behalf of the European Commission.
"Since the signing of the Montreal Protocol, we have drastically reduced the emission of ozone depleting substances, giving space to the atmosphere to start its recovery,” says CAMS Director Vincent-Henri Peuch comments.
“This is a lengthy process that involves many fluctuating factors that should be monitored to have a proper understanding of how the ozone layer is developing. The success of the Montreal Protocol is a testament to how effective actions to protect the global climate can be."
