Final answer:
The control variable in studies of stratospheric ozone depletion includes factors like atmospheric conditions that are kept constant. Ozone layer recovery efforts have been aided by the Montreal Protocol, which enforced the phasing out of ozone-depleting substances, leading to a significant improvement in ozone levels since 2005.
Step-by-step explanation:
The control variable in the context of stratospheric ozone depletion refers to the factors that are kept constant and not changed during scientific research or policy action to ensure a clear understanding of the effects of specific independent variables. In case studies concerning ozone depletion, control variables could include aspects such as atmospheric pressure or temperature, which should remain constant to accurately assess the impact of ozone-depleting substances (ODS) like chlorofluorocarbons (CFCs) and their alternatives.
It is crucial to understand that ozone depletion is primarily caused by man-made chemicals, particularly ODS, which release chlorine and bromine when exposed to UV light. These substances have been significantly reduced thanks to the Montreal Protocol, an international treaty established in 1989, which has helped the recovery of the ozone layer. The ozone layer is vital for absorbing harmful ultraviolet radiation from the sun, and its degradation poses serious risks, including increased rates of skin cancer and other health hazards.
The effectiveness of the Montreal Protocol is evidenced by a 20% improvement in ozone depletion since 2005, demonstrating that global policy measures can have a positive impact. The protocol has successfully phased out the production and usage of CFCs, leading to a gradual shrinking of the ozone hole over Antarctica. This concerted effort underscores the potential of international collaboration to address and mitigate environmental concerns.