Final answer:
Stratospheric ozone changes between 1979 and 2017 show a mixture of depletion and recovery due to the ban on chlorofluorocarbons (CFCs) through the Montreal Protocol. Ozone depletion has improved since 2005, demonstrating the effectiveness of global policy measures.
Step-by-step explanation:
The stratospheric ozone changes between 1979 and 2017 show a mixture of depletion and recovery. In the latter part of the twentieth century, there was an alarming decrease in stratospheric ozone, especially over the Antarctic, leading to the formation of the "ozone hole." However, the global agreement known as the Montreal Protocol, which was enacted in 1989, banned the use of chlorofluorocarbons (CFCs), which were major contributors to ozone depletion. As a result, ozone depletion has improved by 20% since 2005, showing that global policy measures can help reverse and potentially fix the problem.