Final answer:
Stratospheric ozone depletion refers to the reduction of ozone in the upper atmosphere, largely caused by CFCs and resulting in the 'ozone hole.' The Montreal Protocol successfully addressed this issue by phasing out CFCs, leading to significant ozone layer recovery.
Step-by-step explanation:
The stratospheric ozone layer, composed of ozone (O3) molecules, is vital for life on Earth as it absorbs the majority of the Sun's harmful ultraviolet radiation. In the late 20th century, scientists identified a significant decrease in this layer, particularly over the Antarctic, leading to the phenomenon commonly referred to as the "ozone hole". Industrial chemicals known as chlorofluorocarbons, or CFCs, were found to be major contributors to this depletion as they release chlorine and bromine atoms in the stratosphere, which then catalytically destroy ozone molecules. The global response to this concern was the Montreal Protocol, an international agreement to phase out the production of CFCs and other ozone-depleting substances (ODS). Since its implementation, there has been a measurable improvement in stratospheric ozone levels, with a 20% recovery since 2005, highlighting the successful impact of coordinated global policy on environmental issues.