Ozone Depletion

Stratospheric Ozone Depletion

Importance of the Stratospheric Ozone Layer

Ozone is a tri-atomic form of oxygen - it has three oxygen atoms instead of the normal two. It is formed naturally in the upper levels of the earth's atmosphere by high-energy ultraviolet radiation from the sun. The radiation breaks down oxygen molecules, releasing free atoms, some of which bond with other oxygen molecules to form ozone. About 90 per cent of all ozone in the atmosphere is formed in this way, between 15 and 55 kilometers above the earth's surface - the part of the atmosphere called the stratosphere. Hence, this is known as the "ozone layer." Even in the ozone layer, ozone is present in very small quantities; its maximum concentration, at a height of about 20-25 kilometers, is only ten parts per million.

Ozone is an unstable molecule. High-energy radiation from the Sun not only creates it, but also breaks it down again, recreating molecular oxygen and free oxygen atoms. The concentration of ozone in the atmosphere depends on a dynamic balance between how fast it is created and how fast it is destroyed.

Human life and that of most other organisms on earth depends very much on the existence of a thin protective layer of ozone within the stratosphere. This layer of ozone molecules screens out enough of the incoming ultraviolet radiation to permit the earth to be habitable to a wide range of plant and animal species.

Why is the ozone layer important for life on Earth?

The ozone layer is important because it absorbs ultraviolet (UV) radiation from the sun, preventing most of it from reaching the earth's surface. Radiation in the UV spectrum has wavelengths just shorter than those of visible light. UV radiation with wavelengths between 280 and 315 nanometers (a nanometer is one millionth of a millimeter) is called UV-B, and is damaging to almost all forms of life. By absorbing most UV-B radiation before it can reach the earth's surface, the ozone layer shields the planet from the radiation's harmful effects. Stratospheric ozone also affects the temperature distribution of the atmosphere, thus playing a role in regulating the earth's climate.

Impact of Ultraviolet Radiation on Human Health

Ultraviolet radiation, which will increase as a result of depletion of the stratospheric ozone layer, has a number of adverse effects on human health including increased risks of various forms of skin cancer, weakening of the human immune system and increased risk of eye disorders such as cataract problems.

International Actions to Protect the Ozone Layer

Probably the greatest success in international environmental protection has been the rapid action to negotiate and implement sweeping measures to eliminate or greatly reduce use of substances that threaten the stratospheric ozone layer.

In the early 1970s two scientists, Mario Molina and Sherwood Rowland, identified the potential of chlorofluorocarbons (CFCs) and other chlorine compounds to cause extensive depletion of the stratospheric ozone layer. Although their work was initially quite controversial, ultimately the scientific community recognized the validity of their analysis and in less than a generation countries spurred on by consumer action had acted decisively to respond to their warnings. This action to phase out otherwise useful industrial compounds is unprecedented in international environmental protection.

Still, except for the banning of "non-essential uses" of CFC aerosols in a handful of countries, no international controls existed to regulate the use of ozone depleting substances until the negotiation of The Montreal Protocol in September 1987. Two years earlier The Vienna Convention for the Protection of the Ozone Layer negotiated before there was a sense of urgency in the international community, created a framework for international actions to limit production and uses of substances that might contribute to depletion of the stratospheric ozone layer. Just after the signing of the Vienna Convention several developments combined to create an impetus for international action.  

The scientific community increasingly accepted the validity of the Molina-Rowland hypothesis, which was ultimately to win the two scientists and German scientist Paul Crutzen the Nobel Chemistry Prize in 1995.  In 1984 three scientists, Prather, McElroy and Wofsy in Nature magazine had already warned of a danger of a precipitous decline of the ozone layer if stratospheric concentrations of chlorine and bromine compounds moved past a certain point.

As the global economy began to recover from the recession that followed the 1979 oil price shock it became clear that model assumptions of constant CFC emissions were no longer valid. What most galvanized the world to action was the discovery by the British Antarctic survey in 1985 that ozone levels over much of Antarctica had dropped greatly during the Antarctic springtime. This "Antarctic ozone hole" which had been foreseen in none of the models brought a sense of urgency to the international discussions. In mid-1986 the solid industry resistance to international regulatory action was fractured when the Alliance for Responsible CFC Policy, the trade group representing US users and manufacturers of CFCs, called for internationally negotiated limits on the manufacture of CFCs. Although chemical companies in Europe and Japan initially viewed this action as a betrayal, industry positions changed as industry scientists worldwide joined in the consensus that the ozone layer was genuinely threatened.

Scope of International Controls

The Montreal Protocol on Substances that Deplete the Ozone Layer came into force in January 1989 and is the legal basis for the worldwide effort to safeguard the ozone layer through controls on production, consumption and use of ozone-depleting substances, known in the language of the Protocol as "controlled substances." In March 1989 a Multilateral Fund was established with funding to facilitate developing countries' introduction of substitutes for CFCs and other ozone depleting compounds.  British Prime Minister Margaret Thatcher, a chemistry major at Oxford, was a central force behind the London conference which created this fund and extended controls to developing countries who were given additional time for the phaseout. The rapid phaseout of CFCs and many other ozone depleting compounds/chemicals was given further impetus in 1992 in Copenhagen. Instead of merely a reduction in production and consumption of five CFCs and three halons, the Protocol now requires developed countries to phase out 15 CFCs, three halons, 34 HBFCs, carbon tetrachloride and methyl chloroform. A longer-term reduction schedule, also leading to complete phase out, has been agreed for 40 HCFCs. The list of controlled substances is now extended to include methyl bromide as agreed at the 7th Meeting of the Parties.

By December 1995, 150 countries had ratified the Montreal Protocol, becoming Parties to it and therefore legally bound by its requirements. About a third are developed and two-thirds are developing countries. Parties to the Montreal Protocol agreed to reduce and then eliminate the use of ODS before substitutes and alternative technologies were fully available. This has proved a successful strategy. Industries and manufacturers have already developed alternative substances and technologies for almost every former use of ODS. Many countries are already well on their way to a complete phase out of ODS.

Atmospheric concentrations of CFCs and other ozone depleting gases have leveled off and it is anticipated by the end of the 21^st century the damage to the ozone layer will be repaired as a result of concerted international action.

A remarkable aspect of this rapid phaseout of CFCs and other ozone depleting substances, including bromine compounds used in fire extinguishers and many other uses, was close cooperation among government officials in the US EPA and its international counterparts, the UN Environment Programme, and industry engineers and members of the military and navies of the world. This remarkable story of how the air forces, armies and navies of the world were leaders in the ozone protection fight was the subject of a UN conference in Brussels in February 2001 which also probed how such a collaboration might be adapted for climate protection.

Montreal Protocol Multilateral Fund

Recognizing developing countries' need for economic development and their relatively low historical use of CFCs, the Montreal Protocol grants developing countries a 'grace period' of ten years more than developed countries to implement the reduction and phase-out measures required by the Protocol. In addition, at their 1990 meeting in London, the Parties created a financial mechanism to provide technical and financial assistance to developing countries' ozone protection programs.

To be eligible to receive support under the financial mechanism, Parties must be developing countries and must consume less than 0.3 kg per capita per annum of controlled substances.

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