September 16·Every year

International Day for the Preservation of the Ozone Layer

September 16th marks the 1987 signing of the Montreal Protocol, which phased out ozone-depleting substances. The ozone hole over Antarctica is now measurably healing — it is projected to return to 1980 levels by 2066. The Montreal Protocol is the only UN treaty to have been ratified by every country on Earth, and the ozone layer recovery is its proof of concept.