The Montreal Protocol: the global agreement that phases out ozone-depleting substances

Background

The Montreal Protocol on Substances that Deplete the Ozone Layer is a global agreement to protect the ozone layer by phasing out the chemicals that deplete it, covering both production and consumption.
It was signed in 1987 and entered into force in 1989.
The parties meet once a year; the Protocol has been adjusted or amended six times since its creation.
The most recent amendment, the Kigali Amendment, called for the phase-down of hydrofluorocarbons (HFCs) in 2016.
HFCs do not deplete the ozone layer but are powerful greenhouse gases; they were used as replacements for ozone-depleting substances eliminated by the original Protocol.
It was preceded by the Vienna Convention of 1985, a framework convention that does not require countries to take control actions; it took effect in 1988 and reached universal ratification in 2009.