Humanity now has so many reasons for concern that the news that the hole in the ozone layer is on its way to closing has received little attention. And yet, it is a milestone that deserves to be celebrated, because of the serious threat that is disappearing and because of the precedent it represents for other global challenges such as climate change. The latest report from the Montreal Protocol Scientific Assessment Group maintains that by the year 2040 the ozone layer in the space located between the two poles will have recovered its pre-1980 values and that the two large holes that had formed over the Arctic and over Antarctica will have closed in 2045 and 2066, respectively.
The first evidence that the ozone layer in the stratosphere was weakening was published in the 1970s, and already in 1985 an investigation in Nature demonstrated the existence of a large hole in the ozone layer located over Antarctica, which reached 30 million square kilometers, three times the area of the United States. Awareness of the seriousness of the problem led to the approval of the Montreal Treaty , which entered into force in 1989. The agreement has made it possible to stop using a hundred chemical substances that have been shown to be harmful. The release from 2012 of unrecognized emissions of CFC-11 from China jeopardized the targets, but finally the emissions ceased from 2018 and this incident has only pushed back the planned recovery schedule by one year. If everything continues as before, within 40 years the ozone layer will have fully recovered and concerted global action will also have contributed to mitigating global warming by 0.5 degrees Celsius.
What is decisive is the evidence that international treaties based on scientific knowledge are an effective instrument for tackling major environmental challenges. Climate change implies an even greater challenge because it requires dispensing with fossil fuels. But strict compliance with the 2015 Paris Agreements is the only possible way to avoid disaster. The success of the ozone layer treaty shows that, if there is political will, it can be achieved.