The Montreal Protocol of 1987 placed strict controls on the release of ozone-depleting substances. A new study now shows what would have happened to the ozone layer in the absence of this critically important international treaty — and it wouldn’t have been pretty.

Above: Arctic ozone without the Montreal Protocol (left) and following its implementation (right) on 26 March 2011. Credit: Sandip Dhomse.

“Our research confirms the importance of the Montreal Protocol and shows that we have already had real benefits,” noted study lead author Martyn Chipperfield of the University of Leeds in a statement. “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.”

Advertisement

In the new study, which appears at Nature Communications, Chipperfield’s team used a 3D atmospheric chemistry transport model to show what the atmosphere would have looked like if no controls were placed on the production and release of chlorine- and bromine-containing ozone-depleting substances (ODSs).

Their work shows that the ozone hole in the Antarctic — which reached its peak in 1993 and has been declining ever since — would have grown 40% bigger by 2013. What’s more, large holes would have opened-up intermittently above the Arctic, including some large enough to affect northern Europe. Ozone decline over northern hemisphere middle latitudes would have continued, more than doubling to approximately 15% by now.

Writing in the California Academy of Sciences, Molly Michelson explains the direct benefit of the Montreal Protocol to humans:

Our health. In the most populated areas of Australia and New Zealand, which currently have the highest mortality rates from skin cancer, the model predicts that surface UV could have increased by 8–12% without the treaty; and in Northern Europe, increases would have exceeded 14% by 2013. In addition, the continued reduction in atmospheric emissions of chlorine and bromine should eventually translate into an increase in stratospheric ozone, reducing the incidence of skin cancer and preserving the temperature structure of the atmosphere, with important long-term consequences for circulation and climate.

The Montreal Protocol has thus set an important precedent, one demonstrating how the international community can come together for a common cause.

More at CAS and BBC. Check out the scientific study here.