A hole in the ozone layer over Antarctica is healing and in turn reversing changes it caused to the flow of winds over the southern hemisphere, a study discovers.
Researchers from the University of Colorado Boulder say this is due in part to a ban on ozone depleting substances (ODS) in the 1980s.
The biggest impact can be seen in the southern hemisphere jet steam – it had been moving further south due to ozone depletion, but that appears to be reversing.
Antara Banerjee, lead author, says this is likely only a temporary change due to the impact of rising carbon dioxide levels and more ODS coming from China.
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This image made available by NASA shows a map of a hole in the ozone layer over Antarctica on Sunday, Oct. 20, 2019. Last year the hole had its smallest peak since 1987
Before 2000 the mid-latitude jet steam had been gradually shifting towards the South Pole and another hurricane causing jet stream was getting wider.
This was changing rainfall patterns and ocean currents in the southern hemisphere and causing countries like Australia to suffer severe drought.
Researchers used a range of computer simulations to show the jet stream stopped moving south at the same time as the ozone hole began healing.
In Australia changes to the jet stream led to an increased risk of drought by pushing rain away from coastal areas – a reverse in the moving south of the stream could bring those rains back to the country.
Last year the Antarctic ozone hole it its smallest annual peak on record – that’s since it was first discovered in 1982 – but it’s a temporary fix.
Scientists say this may be due to unusually mild temperatures in that layer of the atmosphere.
The moving of jet streams further south, caused by the ozone hole, was leading to increased droughts in places like Australia but the reverse could see rains return
There has also been a surge in ozone-depleting chemicals coming from industrial regions of China, the team confirmed.
‘We term this a ‘pause’ because the poleward circulation trends might resume, stay flat, or reverse,” says Banerjee.
“It’s the tug of war between the opposing effects of ozone recovery and rising greenhouse gases that will determine future trends.”
She said the biggest discovery from their study was the proof that a global protocol like the one in Montreal that banned ODS can pause or reverse environmental harm.
The study was published in the journal Nature.
WHAT IS THE OZONE LAYER?
Ozone is a molecule comprised of three oxygen atoms that occurs naturally in small amounts.
In the stratosphere, roughly seven to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress immune systems and also damage plants.
It is produced in tropical latitudes and distributed around the globe.
Closer to the ground, ozone can also be created by photochemical reactions between the sun and pollution from vehicle emissions and other sources, forming harmful smog.
Although warmer-than-average stratospheric weather conditions have reduced ozone depletion during the past two years, the current ozone hole area is still large compared to the 1980s, when the depletion of the ozone layer above Antarctica was first detected.
In the stratosphere, roughly seven to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation
This is because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss.
In the 1970s, it was recognised that chemicals called CFCs, used for example in refrigeration and aerosols, were destroying ozone in the stratosphere.
In 1987, the Montreal Protocol was agreed, which led to the phase-out of CFCs and, recently, the first signs of recovery of the Antarctic ozone layer.
The upper stratosphere at lower latitudes is also showing clear signs of recovery, proving the Montreal Protocol is working well.
But the new study, published in Atmospheric Chemistry and Physics, found it is likely not recovering at latitudes between 60°N and 60°S (London is at 51°N).
The cause is not certain but the researchers believe it is possible climate change is altering the pattern of atmospheric circulation – causing more ozone to be carried away from the tropics.
They say another possibility is that very short-lived substances (VSLSs), which contain chlorine and bromine, could be destroying ozone in the lower stratosphere.
VSLSs include chemicals used as solvents, paint strippers, and as degreasing agents.
One is even used in the production of an ozone-friendly replacement for CFCs.