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The ozone layer

What is the ozone layer?

Ozone is a naturally occurring molecule containing three atoms of oxygen. Ozone molecules form a gaseous layer mostly in the upper atmosphere (the stratosphere) 15-30 km above the surface of the earth, and protects life on earth by absorbing ultra-violet (UV) radiation from the sun.

The stratospheric ozone layer protects life on Earth by absorbing ultra-violet (UV) radiation from the sun. UV radiation is linked to skin cancer, genetic damage and immune system suppression in living organisms, and reduced productivity in agricultural crops and the food chain.

Scientific evidence has proven that the natural balance of stratospheric ozone has been upset by the production and release into the atmosphere of ozone depleting substances, including chlorofluorocarbons CFC, halons, CH₃CCl₃ (Methyl chloroform), carbon tetrachloride, hydrochlorofluorocarbons (HCFCs) and methyl bromide. These substances have applications in refrigerators, airconditioners, fire extinguishers, aerosols, agricultural fumigants, in foam and as solvents for cleaning electronic equipment.

• Twenty Questions and Answers about the ozone layer  - from the World Meteorological Organisation website

Ozone layer depletion

CFCs (chlorofluorocarbons), halons, CH₃CCl₃ (Methyl chloroform), CCl₄(Carbon tetrachloride), HCFCs (hydro-chlorofluorocarbons), hydrobromofluorocarbons and methyl bromide are directly implicated in the depletion of the ozone layer. These gases deplete the ozone layer by releasing chlorine and bromine atoms into the stratesphere, which destroy ozone molecules. These and other ozone depleting substances also contribute to varying extents to the enhanced greenhouse effect.

The two largest Antarctic ozone holes on record occurred in 2000 (29.8 million km2) and 2006 (29.6 million km2). The two smallest Antarctic ozone holes in recent times occurred in 2002 and 2004, due largely to disruption of the hole by atmospheric meteorological conditions around Antarctica at the time.

• More about the enhanced greenhouse effect  - CSIRO
• The Hole Truth: The role of ozone depletion in Australia's changing climate
• More information on the ozone layer and the work of the World Meteorological Organisation in ozone layer monitoring

The ozone layer is depleted in two ways. Firstly, the ozone layer in the mid-latitude (e.g. over Australia) is thinned, leading to more UV radiation reaching the earth. Data collected in the upper atmosphere have shown that there has been a general thinning of the ozone layer over most of the globe. This includes a five to nine per cent depletion over Australia since the 1960s, which has increased the risk that Australians already face from over-exposure to UV radiation resulting from our outdoor lifestyle. Secondly, the ozone layer over Antarctica is dramatically thinned in spring, leading to the `ozone hole’.

Every four years, the World Meteorological Organisation and the United Nations Environment Programme review the state of the ozone layer in their quadrennial review. In brief, it concludes that the Montreal Protocol has successfully controlled the global production and consumption of ozone depleting substances and the abundance of these ODS in the atmosphere are now declining. Ozone depletion will continue for many more decade however, as several ODS last a long time in the atmosphere after emissions end.

• Report of the 2010 Assessment of the Scientific Assessment Panel  

Antarctic ozone hole

What is it?

The Antarctic ozone hole is a dramatic thinning of ozone in the stratosphere over Antarctica each spring. This damage is due not only to the availability of ozone-depleting substances in the stratosphere, but also specific meteorological conditions that facilitate the destruction of ozone over Antarctica.

What has happened so far?

The ozone holes in 2000 and 2006 were the largest on record, measuring around 29.8 and 29.6 million square kilometres respectively (more than three and a half times the size of Australia), and at times extended over populated areas.

The 2002 and 2004 ozone holes were much smaller, due in large part to the disruption of the hole by other weather conditions in the troposphere and stratosphere.

The future

Prospects for the long-term recovery of the ozone layer are good. Non-essential consumption of major ozone depleting substances ceased for developed countries in 1996, and for developing countries in 2010.

Scientists predict that if the international community continues to comply with the Montreal Protocol, the ozone layer should recover to pre-1980 levels between 2050 and 2065.