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‘We could not have protected the ozone layer with voluntary pledges. That won’t work for global warming either. The Montreal Ozone Treaty shows that a binding treaty – with industrial countries taking the lead – all nations can successfully cut global pollution and trigger a clean technology revolution.’

David Doniger, policy director of the Climate Centre at the Natural Resources Defense Council

We hear people say, ‘It’s just too hard to stop man-made climate change. How can we possibly succeed?’ We have done it before and we can do it again.

The ozone layer is the layer of upper atmosphere, from 15 to 35km above the Earth’s surface. If all of the ozone were compressed to the pressure of the air at sea level, it would be a few millimetres thick. This fragile blanket protects us from the sun’s ultraviolet radiation and allows life to exist on Earth’s surface.

Two scientists from the University of California, Molina and Rowland, published a paper in 1974 proving the link between chlorofluorocarbons (CFCs) and ozone depletion. CFCs were widely used in air conditioning, as refrigerants, aerosol propellants and solvents.

The hole in the ozone layer was discovered in 1985. The world’s leaders created the Montreal Protocol, which limited the use of CFCs from early 1987 leading to a total phase out by 1996. Molina and Rowland were presented with the Nobel Prize for Chemistry for their work in 1995.

Since it’s implementation in 1987, the protocol has been revised and strengthened several times. The success of the Montreal Protocol is a shining example of what can be done when our world leaders come together to act for good. Importantly, the companies who produced these harmful gases were readily able to shift production to different kinds of less harmful gases.

Kofi Annan, the former Secretary General of the United Nations, called it ‘Perhaps the single most successful international agreement to date.’

In 2003, scientists determined that the depletion of the ozone layer was slowing due to the ban on the use of CFCs. These CFCs have a very long atmospheric lifetime, ranging from 50 to 120 years.

The total recovery of the ozone from the impact of CFCs will take several generations. Some CFCs have been replaced by hydro-chlorofluorocarbons (HCFCs) that have since also been linked to man-made global warming.

The Montreal Protocol was tightened in September 2007, decreeing that production of these must be halted by 2020 in developed countries. Final savings of greenhouse emissions will be in the order of several billion tons. We have not solved our problem of ozone depletion, but we have ‘stopped (some of) the rot.’