1987-09-16

The Montreal Protocol, a treaty designed to save the Earth's ozone layer by calling on nations to reduce certain chemical emissions, was signed on this date in 1987. Twenty-five nations agreed to establish a timetable for the phasing out of several groups of halogenated hydrocarbons proven to contribute to ozone depletion. Eventually, nearly 170 nations signed on to comply with the protocol, leading Kofi Annan to call it perhaps the single most successful international agreement to date.