Final answer:
The Montreal Protocol established in 1987 called for the reduction and phase out of chlorofluorocarbons (CFCs), which were commonly used as refrigerants and in other applications but were significantly harmful to the ozone layer.
Step-by-step explanation:
The Treaty of Montreal, better known as the Montreal Protocol, was established to address the global issue of ozone layer depletion. Specifically, it called for the reduction and phase out of chlorofluorocarbons (CFCs), among other substances. CFCs were commonly used as refrigerants, as well as in aerosol sprays and other applications, and their release into the atmosphere was found to have a detrimental effect on the ozone layer. Developed nations began phasing out CFCs by 1995, and their use continued in developing nations until 2010, with further controls on less harmful substances planned until 2030.
Alternative substances such as hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) are proposed replacements for CFCs, though they still contribute to environmental issues like global warming and are currently subject to being phased down under newer amendments like the Kigali Amendment to the Montreal Protocol.