Chlorofluorocarbons or CFCs do not occur naturally. CFCs were made for propellants in spray cans, Styrofoam™ puffing agents, and as coolants for refrigerators and air conditioners. The usage of two CFC compounds (CFC-11 and CFC-12) decreased in the mid 1970s. When this human made, or anthropogenic, gas was found to destroy ozone, the United States banned its use, resulting in a decline of global usage.
In the 1980s other countries increased their use of CFCs. In response to the discovery of CFCs role in destroying ozone, representatives from 23 nations met in Montreal, Canada in 1987 to address concerns of ozone depletion by CFCs. The resulting Montreal Protocol called for a 50% reduction in the usage and production of this anthropogenic gas by the year 1999. This accounts for the decline in CFC usage in the late 1980s. While the use of these chemicals has declined, the atmospheric concentrations have not. This is because CFCs are very stable molecules and will stay in the atmosphere for nearly 100 years before finally declining.
