'Montreal Protocol has helped slow ozone depletion'

Thanks to the Montreal Protocol, the ozone layer is in much better shape now than it would have been without the United Nations (UN) treaty, a new study says.

Without the Montreal Protocol, a very large ozone hole over the Arctic would have occurred during that cold winter and smaller Arctic ozone holes would have become a regular occurrence.

The Montreal Protocol came into force in 1987 and it restricted the use of ozone-depleting substances. But the atmospheric concentrations of these harmful substances continued to rise as they can survive in the atmosphere for many years.

Concentrations peaked in 1993 and have subsequently declined.

"Our research confirms the importance of the Montreal Protocol and shows that we have already had real benefits. We knew that it would save us from large ozone loss 'in the future', but in fact we are already past the point when things would have become noticeably worse," said lead author professor Martyn Chipperfield from University of Leeds.

For the study, researchers used a state-of-the-art 3D computer model of atmospheric chemistry to investigate what would have happened to the ozone layer if the Montreal Protocol had not been implemented.

"We have used actual observed meteorological conditions for the past few decades. This gives a more accurate simulation of the conditions for polar ozone loss," Chipperfield added.

The hole in the ozone layer over the Antarctic would have grown in size by an additional 40 percent by 2013. Had ozone-depleting substances continued to increase, the ozone layer would have become significantly thinner over other parts of the globe.

"The scientists must continue to monitor the situation to ensure all potential threats to the ozone layer are mitigated," Chipperfield said.

The study appeared in the journal Nature Communications.