CFCs, or Freon, are man-made, stable, and nontoxic chemicals used primarily as coolants. In 1984, scientists discovered CFCs to be one cause of the depletion of the ozone layer which acts as a filter for ultraviolet light. Because of this, many nations signed the Montreal-London Protocol. This treaty calls for the production of CFCs to be stopped by the year 2000 for industrialized countries and the year 2010 for developing countries. The United States stopped production of CFCs in 1995.