Ozone hole growing despite cuts in CFCs

STEVE CONNOR

Science Correspondent

The hole in the Earth's protective ozone layer is getting bigger, according to the latest measurements taken precisely 10 years after the problem first came to light.

Scientists at the British Antarctic Survey (BAS) in Cambridge say the ozone layer over the South Pole has now thinned to less than 40 per cent of what it was in the Sixties. The problem, which has appeared regularly during Antarctic springs, has now extended into the summer for the first time.

The "hole" is actually a thinning of the ozone layer which occupies an altitude of between about eight and eleven miles above ground and protects against the harmful ultraviolet radiation from the sun. Joe Farman and colleagues at the BAS first identified its destruction in 1985 after nearly 30 years of continuous monitoring from the Halley Research Station.

Latest measurements published in the journal Nature by scientists Anna Jones and Jonathan Shanklin found that the thinning of the ozone layer was getting worse. "Its reduction has continued since 1985 and there are no signs of it slowing down," Dr Jones said.

Since international measures have come into force to limit the production of ozone-destroying chemicals, notably chlorofluorocarbons (CFCs), scientists have predicted that recovery will take several years to begin.

Dr Jones said a continued thinning of the ozone layer over the Antarctic was expected because of the time it takes for cuts in CFCs to have an effect at the high altitudes where the damage is done. "We should begin to see a turnaround by the end of the century," she said.

When Dr Farman first identified the destruction of the ozone layer, about 30 per cent of it had already gone. Now more than 60 per cent has disappeared during October, the worst month in the Antarctic spring for ozone depletion.

Some critics have suggested that periodic ozone destruction may be a natural phenomenon, due for instance to the 11-year cycle of the sun's activity. But Dr Jones said such suggestions "don't fit the chemical theories that explain the thinning of the ozone layer".

Dr Farman said there is clear evidence that man-made substances are causing the ozone depletion as a result of a complex series of chemical reactions that take place at high altitudes in the presence of clouds of ice crystals and the sudden appearance of intense sunlight at the end of the long Antarctic winter.

Dr Farman, who is now semi-retired, criticised the slow pace of international negotiations to phase out the production of ozone-destroying chemicals still in use, such as the pesticide methyl bromide. "Much more could be done to speed things up," he said.

Because the ozone hole now extends into the Antarctic summer, scientists are worried that it will result in increased amounts of ultraviolet radiation reaching the pristine oceans where it could damage the reserves of plankton, which is a source of food for higher animals such as fish and whales.