The ozone layer over much of the northern hemisphere has suffered its worst ever damage this winter, European scientists reported yesterday.
Over the past few weeks, they have witnessed the Arctic atmosphere making its closest approach yet to the type of ozone hole that now appears each winter over the Antarctic.
Up to 30 per cent of the protective ozone shield has been stripped out of the upper atmosphere because of a combination of extreme cold and a build up of chlorine and fluorine containing industrial chemicals.
The cold weather has allowed high-level ice clouds to form above the Arctic, and it is in those clouds that the complex cycle of chemical reactions which destroy ozone takes place.
The stratospheric ozone layer, extending from a height of 10,000 metres upwards, absorbs much of the sun's ultraviolet radiation, which can damage genes in all plants and animals and cause skin cancers and cataracts in people.
The observations have been made by about 300 scientists from 21 countries participating in Sesame, the Second European Stratospheric Arctic and Mid- latitude Experiment.
"The Arctic ozone depletion this year certainly looks different,'' said Dr Tony Cox, an atmospheric chemist at Cambridge University who advises the Government. He added that it resembled the early stages of ozone hole formation in the Antarctic.
Joe Farman, the British Antarctic Survey scientist who discovered the formation of Antarctic ozone holes 10 years ago, said the latest findings showed further and faster progress was needed in phasing out ozone-depleting chemicals. ``We've still got at least a decade to go before the risks decline significantly.''
Almost all of the major developed and developing countries have signed up to a UN treaty, the Montreal Protocol, which commits them to phasing out the chlorofluorocarbons (CFCs) and some other chemicals which do most damage. By the century's end, the concentration of ozone-damaging pollutants in the upper atmosphere should stabilise and gradually start falling.
The ozone depletion in the Arctic and Antarctic takes place in winter and spring within a pulsating, shifting continent-sized area of static upper air. This is cut off from the rest of the atmosphere by a band of wind which circles the globe, forming the polar vortex.
This stratospheric wind falls off in spring and the system breaks up. But the Arctic vortex is inherently less stable than the Antarctic one, which explains why there have - as yet - been no Arctic holes.