Final answer:
The existence of chlorine monoxide in the upper stratosphere indicates ozone depletion is occurring due to human activities and the release of chlorine atoms from substances like CFCs.
Step-by-step explanation:
The existence of chlorine monoxide in the upper stratosphere indicates that ozone depletion is occurring. Chlorine monoxide (ClOO) is formed when chlorine atoms react with ozone molecules, resulting in the net removal of ozone from the stratosphere. This process is a result of human activities such as the use of chlorofluorocarbons (CFCs), which release chlorine atoms into the atmosphere and contribute to ozone depletion.