Final answer:
The Montreal Protocol has contributed positively to the restoration of the stratospheric ozone layer by banning harmful substances like CFCs, resulting in a reduction of ozone holes and a gradual healing process, albeit with the need for ongoing vigilance due to illegal emissions.
Step-by-step explanation:
Based on the analysis of the graph, the Montreal Protocol has had a significant positive effect on the stratospheric ozone layer. The protocol, which banned the use of ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs), has led to a recovery process where the ozone layer is healing, and the size of the ozone holes is shrinking.
Despite this progress, the recovery is slow because CFCs have a long lifespan in the stratosphere. However, since the adoption of the protocol, ozone depletion has stopped, and a 20% improvement has been observed since 2005.
While the Montreal Protocol has been effective in reducing emissions of ODS, constant vigilance is necessary to maintain this success. Illegal production and emissions continue to pose a threat, as seen with the reported increase in CFC emissions from regions in eastern Asia.
Nevertheless, the protocol is an example of global cooperation that has evidently produced meaningful action against a large-scale environmental issue, and scientists expect the ozone layer to be fully healed by 2070 if current protections are maintained.