World Ozone Day, also known as the International Day for the Preservation of the Ozone Layer, is observed annually on September 16. This date was designated by the United Nations General Assembly in 1994 to commemorate the signing of the Montreal Protocol in 1987, which addressed substances depleting the ozone layer. The need for action arose due to ozone layer depletion. By 2017, 30 years after the protocol, the hole in the ozone layer began to close, with effects projected to last up to 100 years.