Past Trends

nations signed a global environmental treaty called the Montreal Protocol to reduce substances that deplete the ozone layer. As of December 2012, 197 nations had signed the treaty.

The use of CFCs in the past had a destructive effect on the ozone layer. CFCs were used in refrigerants solvents and propellants. As off the late 1970's the use of CFCs has been heavily regulated. In 1987, 27