A NEW study has confirmed that the hole in the ozone layer over the Antarctic is showing signs of shrinkage, with scientists identifying “the first fingerprints of healing” and raising hopes that the planet is on the road to recovery.
The significant development has emerged almost three decades after the Montreal Protocol came into force in 1989, phasing out numerous man-made compounds – including those containing either chlorine or bromine, such as refrigerants – which were found to be responsible for ozone depletion.
As we reported last year, leading scientists have been optimistic about a substantial recovery of the ozone layer by mid-century – or by around 2070 in the Antarctic, where it is severely affected – due to widespread international compliance with the protocol and industry’s development of ‘ozone friendly’ substitutes.
While the rate of ozone depletion has clearly slowed over the years, the latest study provides the first evidence that ozone abundance over Antarctica has begun to increase.
The study, published recently in the journal Science, found that the September ozone hole – the month chosen as the benchmark in the study – has shrunk by more than four million square kilometres since 2000, when ozone depletion was at its peak.
Volcanic eruptions have slowed the rate of recovery, with the study also finding that the unusually large Antarctic ozone hole (at 28.2 million square kilometres) recorded last year was due to an eruption in Chile.
However, as we wrote at the time and which now has the science backing it, this is not related to chlorine levels in the atmosphere.
Indeed, for the first time, there is solid evidence of ozone layer recovery brought about by the continuing decline of atmospheric chlorine originating from chlorofluorocarbons (CFCs).
More than half the shrinkage identified in the study was due solely to the reduction in atmospheric chlorine. Most of the rest appears to be due to the weather.
“We can now be confident that the things we’ve done have put the planet on a path to heal,” said lead author Susan Solomon, who is the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at the Massachusetts Institute of Technology (MIT).
Previous ozone studies have typically focused on October, when the hole is fully formed. However, this time around, Prof Solomon and her colleagues analysed September, when Antarctica has emerged from winter and the ozone-depleting chlorine chemistry gets underway, but in conditions where there are less variables such as slight changes in meteorology.
The authors are confident that this gives a clearer picture of chlorine’s effect as the ozone hole is beginning to open up, in response to the changes in light and temperature, and through a wide range of measurements and sophisticated modelling they found that from 2000 to 2015 – at this point in the annual cycle – the rate at which the hole opens up has clearly slowed down as chlorine levels have decreased.
Barring future volcanic eruptions, Prof Solomon now sees no reason why the ozone hole could not be permanently closed by 2050.