Ozone (O₃) is a gas present in both the stratosphere and troposphere that plays a crucial role in the Earth system and is significantly influenced by anthropogenic activities. 

a. [10 pts] Explain how Stratospheric Ozone Depletion is quantified within the Planetary Boundary Framework, and describe its current status (i.e. whether we are within the safe operating space or have transgressed it). Discuss the importance of stratospheric ozone in your answer.

b. [10 pts] Explain how anthropogenic and natural factors influence stratospheric ozone and how we know that long-term changes in stratospheric ozone are primarily related to anthropogenic activities. 

c. [10 pts] Describe the approach used by current international policies (i.e. the Montreal Protocol and its amendments) to mitigate stratospheric ozone depletion. Discuss whether these policies have been successful and identify at least two assumptions or uncertainties that must be considered when analyzing the long-term effect of these policies.