Today we celebrate not only the International Day for the Preservation of the Ozone Layer, but the greatest combined success for the planet in history.

Adopted in 1987, the Montreal Protocol on Substances that Deplete the Ozone Layer remains the only treaty to have been ratified by every country on the planet.

All 198 states working together to rid the world of ozone-depleting substances such as chlorofluorocarbons.

Ozone is a gas with two sides. At ground level, it is considered a pollutant and forms the main component of smog, but high in the atmosphere, it is our best protection against harmful UV radiation emitted by the Sun.

In the 1970s, scientists realized that humanity was causing a hole in the ozone layer through the use of aerosols and other ozone-depleting gases used in air-conditioners, refrigerators and circuit board manufacturing.

This hole could cause significant damage, including increases in skin cancer, cataracts, and damaged ecosystems.

Without the treaty in place, it was estimated that ozone depletion would be ten times worse by 2050 than what has been achieved.

Compared to levels in 1990, 98% of ozone-depleting substances have been removed from the atmosphere and greenhouse gases have been reduced by 11 gigatons a year.

So today is a mark of celebration and a symbol of what the world can achieve when working in harmony since the signing of the Montreal Protocol 36 years ago.