The more I reflect on the 23 impressive years since the signing of the Montreal Protocol, the more I realize what far-reaching lessons it holds for the global environmental agreements of today.

As we close the door on the first decade of the 21st century, the environmental crises that we face today require action beyond even the scale of the world's response to the ozone-depletion emergency in the late 20th century.

As we all know, the ozone layer is a thin layer in the atmosphere that sits about 10-50 km above the Earth. It absorbs most of the harmful ultraviolet radiation from the sun. The discovery of an ozone "hole" in 1985 shocked the world and two years later the Montreal Protocol was signed. Today, almost every country in the world has ratified the agreement.