Final answer:
The current value of the control variable for stratospheric ozone depletion is in recovery due to the successful global reduction of ozone-depleting substances under the Montreal Protocol. There has been a ~20% improvement since 2005, with projections indicating continued recovery of the ozone layer.
Step-by-step explanation:
Stratospheric Ozone Depletion and Control Variable
The control variable for stratospheric ozone depletion refers to the level of ozone-depleting substances (ODS) in the atmosphere, which are regulated by global agreements like the Montreal Protocol. Ozone depletion was first noted in the late 1970s and became a major concern with the discovery of a large ozone hole over Antarctica. The adoption of the Montreal Protocol in 1989 resulted in significant reductions in the use of chemicals that damage the ozone layer, such as chlorofluorocarbons (CFCs). Figure 2.3.1, which illustrates the ozone hole recovery projection from 1960 to 2100, shows that the ozone concentration in Dobson units is expected to recover over time due to these efforts.
Scientific research indicates that there has been an approximate 20% improvement in ozone depletion since 2005, and models predict a continuous recovery, assuming continued adherence to international agreements. Various sources of pollution, which include CFCs and other ODS, are the primary causes of ozone depletion, with activities such as the use of CFCs in aerosol sprays having been largely phased out. The Montreal Protocol's success demonstrates how concerted global action can reverse and possibly fix environmental issues.
The current value of the control variable is therefore in a state of recovery thanks to the Montreal Protocol and its subsequent amendments, which have managed to control and reduce the presence of ODS in the atmosphere. While challenges still remain, the global policy has set a path toward restoring the ozone layer, ultimately protecting human health and the environment from harmful UV radiation.