A hole in the ozone layer that appeared above Antarctica in the 1980s has shrunk thanks to a worldwide ban on damaging chemicals, Nasa has confirmed.
Research found that levels of ozone-damaging chlorine are rapidly declining in the planet’s atmosphere, a direct indicator that Earth’s protective layer is on the mend.
Last year, satellite images seemed to show that the ozone hole had begun to close up, with some scientists suggesting it could fully recover by 2060.
Until now it was not clear if this was the result of the Montreal protocol, a 1989 initiative to phase out ozone-depleting chemicals called chloro-flurocarbons (CFCs).
‘All of this is evidence that the Montreal Protocol is working – the chlorine is decreasing in the Antarctic stratosphere, and the ozone destruction is decreasing along with it,’ the researchers, led by Dr Susan Strahan of Nasa’s Goddard Space Flight Centre in Greenbelt, Maryland, wrote.
Earth’s ozone layer acts like a sunscreen, shielding the planet from potentially harmful UV radiation that can cause skin cancer, cataracts, and damage wildlife.
During the 1980s researchers spotted a hole forming in the protective layer, which many blamed on global usage of chloro-flurocarbons (CFCs).
CFC’s were widely used in aerosols, fridges, air conditioning and packing materials until the Montreal protocol.
They are broken down by the sun’s ultraviolet radiation when they rise into the stratosphere, releasing chlorine atoms that destroy ozone molecules.
Since 2005, Nasa has permanently monitored the hole in the ozone layer with its Aura satellite.
Ozone depletion occurs in cold temperatures, meaning it varies with the weather year-on-year, making changes over time difficult to study.
Previous research has used statistical analyses of changes in the ozone hole’s size to argue that ozone depletion is decreasing.
But the new study used Aura readings of the chemical composition of the hole, finding that the hole is decreasing in size thanks to a drop in atmospheric CFC levels.
Ozone-damaging chlorine concentrations over the Antarctic are declining at a rate of 25 parts-per-trillion each year, equivalent to 0.8 per cent, the study found.
This resulted in a 20 per cent drop in ozone destruction since the Montreal protocol came into effect.
‘CFCs have lifetimes from 50 to 100 years, so they linger in the atmosphere for a very long time,’ said study coauthor Dr Anne Douglass.
‘As far as the ozone hole being gone, we’re looking at 2060 or 2080. And even then there might still be a small hole.’
