Magazine article UNESCO Courier

Earth's Ozone Shield under Threat

Magazine article UNESCO Courier

Earth's Ozone Shield under Threat

Article excerpt

The ozone layer, the tenuous layer of gas that surrounds our planet between twelve and forty-five kilometres above our heads, is being rapidly depleted. Seasonally occurring holes have appeared in it over the Poles and, more recently, over the temperate regions of the northern hemisphere. The threat is a serious one since the ozone layer acts as a filter that traps almost all in-coming ultraviolet radiation, which is harmful to all living organisms--humans, animals and plants.

Even though the ozone layer is some twenty-five kilometres thick, the atmosphere in it is very tenuous and the total amount of ozone, compared with other atmospheric gases, is quite small. If all of the ozone in a vertical column reaching up through the atmosphere were to be compressed to sea-level pressure, it would form a layer only a few millimetres thick.

Monitoring and forecasting

Ozone ( chemical formula [O.sub.3] ), from the Greek ozein, meaning "to smell", consists of oxygen ([O.sub.2]) which under the effect of solar radiation acquires a free atom of oxygen. Ozone is highly reactive to chlorine, hydrogen and nitrogen. Of these chlorine is the most dangerous since it is very stable and has a very long life. When they reach the stratosphere, chlorine atoms attach themselves to the ozone molecules and destroy them, with consequent repercussions on the quality of life on Earth.

Detailed study of the ozone layer began comparatively recently, in 1930, the earliest observations being made by the English scientist Sydney Chapman. These initial observations were taken up by the World Meteorological Organization (WMO) which established the Dobson Network consisting of one hundred observation stations. Since 1983, on the initiative of WMO and the United Nations Environment Programme (UNEP), seven of these stations have been entrusted with the task of making long-term forecasts of the likely evolution of our precious shield.

In 1958, the researchers who permanently monitor the ozone content of the layer above the South Pole began to observe certain seasonal variations. From June there was a slight reduction in ozone content which reached a minimum in October. In November there was a sudden increase in the ozone content. These fluctuations appeared to result from the natural phenomena of wind effects and temperature change.

However, although the October minimum remained constant until 1979, the total ozone content over the Pole was steadily diminishing until, in 1985, public opinion was finally roused by reports of a "hole" in the ozone layer and observations were intensified.

The culprits responsible for the hole had already been identified as being supersonic aircraft, such as Concorde, (although these have now been exonerated) and the notorious compounds known as chlorofluorocarbons, or CFCs. Synthesized in 1928 by chemists working at General Motors in the United States, CFCs are compounds of atoms of chlorine and fluorine. Having the advantage of being non-flammable, non-toxic and noncorrosive, they came into widespread use in the 1950s. They are widely used in refrigerators (15% ), air-conditionets ( 20% ) and to make the "bubbles" in the foam plastic used, for example, in car seats and as insulation in buildings (24%). They are also used as propellants in aerosol sprays and as a cleansing solvent in the computer industry ( 24% ).

In 1989 they represented a market valued at over $1.5 billion and a labour force of 1.6 million. Of the twenty-five countries producing CFCs, the United States, France, the United Kingdom, Japan and Germany account for threequarters of the total world production of some 1.2 million tons.

The economic issues

These figures give some idea of the importance of the economic interests that are at stake in any decision to ban the industrial use of CFCs. But, with CFCs incriminated by scientists, the question arose as to whether we were prepared to take the risk of seeing an increase in the number of cases of skin cancer, eye ailments such as cataract, or even a lowering of the human immune defence system, all effects that would follow further depletion of the ozone layer. …

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