Ozone hole 'set to shrink'

The biggest ozone hole yet over Antarctica in October

By BBC News Online's Helen Briggs

An international group of scientists is predicting that the hole in the ozone layer over Antarctica will shrink and close within 50 years.

Our prediction is that ozone amounts will recover over the next 50 years or so

Professor Alan O'Neill

It says a ban on the chemicals that thin the Earth's protective film of gas is showing signs of success and the ozone layer should soon start to repair itself - as long as countries stick to the ban.

The forecast was made following a conference in Buenos Aires, Argentina, where 300 climate scientists scrutinised new data.

But the experts warn that governments must tackle the wider issue of reducing greenhouse gas emissions, if any real progress on ozone is to be achieved.

Montreal Protocol

The prediction is based on evidence that levels of chlorofluorocarbons (CFCs) in the lower atmosphere are falling.

CFCs break down ozone, the three-atomed oxygen molecule, which shields the surface of the planet from harmful rays.

An international ban on CFCs, once widely used in aerosols, has been in place since 1987, when the Montreal Protocol was introduced.

Scientists studied fresh data at the Stratospheric Processes and their Role in Climate (SPARC) Second General Assembly in Buenos Aires.

'Detailed understanding'

Alan O'Neill, chair of the SPARC 2000 Scientific Committee, told BBC News Online: "Scientists have gained a detailed understanding of how man-made substances (containing chlorine and bromine) destroy ozone.

"We can explain why much more ozone is destroyed over the Antarctic than over the Arctic, and why the ozone hole is bigger during some years than during others.

"The biggest ever ozone hole was witnessed over Antarctica in early October 2000.

"But we are now seeing evidence that the international bans or controls on ozone destroying substances are now taking effect: amounts of these substances are, overall, falling in the lower atmosphere and our prediction is that ozone amounts will recover over the next 50 years or so."

Delayed recovery

The recovery was not likely to start for a few years yet, Professor O'Neill said, and it would not happen steadily because of natural fluctuations in weather patterns from one year to the next.

And a cooling of the lower atmosphere due to greenhouse gas emissions could delay the closing of the ozone hole, perhaps by a decade or so.

Commenting on the report, Brian Gardiner, one of the British Antarctic Survey scientists who discovered the Antarctic ozone hole in 1985, said political will was needed to tackle the other huge environmental issues facing the planet.

"The Montreal Protocol is the first international treaty that holds out the promise of solving a global environmental problem before it becomes a disaster," he told BBC News Online.

"We should learn from that and attack the bigger problem of climate change by achieving intergovernmental agreement to limit the burning of fossil fuels before the consequences of that become a disaster."