By Wilson da Silva
IT’S bigger, nastier and it’s expanding faster than ever before: the hole in the ozone layer has reappeared over Antarctica, and it’s already the biggest yet seen at this time of the year.
If it keeps expanding at current rates, this latest gash in the Earth’s protective ozone shield could cover an area twice that of Australia within weeks up to 24 million square kilometres.
Dr Paul Lehmann, of the Bureau of Meteorology’s Ozone Studies Unit in Melbourne, said last week that scientists were observing “the greatest amount of ozone depletion ever”.
“There’s a 24 million-square-kilometre hole appearing in the sky. It’s here in front of us,” Dr Lehmann said.
The Geneva-based World Meteorological Organisation announced on Tuesday that ozone levels over the Antarctic fell to 35 per cent below normal last month, and were even 10 per cent below those of August 1994, the lowest on record.
The hole has been expanding at the unprecedented rate of 1 per cent a day, and already covers an area the size of Europe.
If current trends continue, it could reach record size within weeks, scientists said.
“In certain places in the stratosphere, the chemicals have wiped ozone out completely,” said Dr Paul Fraser, senior principal research scientist at the CSIRO Division of Atmospheric Research.
The federal Environment Minister, Senator John Faulkner, in Melbourne on Friday to announce a program to collect and destroy ozone-depleting halon gas in old fire extinguishers, said Australians faced rising rates of skin cancer, immune- system suppression and genetic damage before the damaged ozone layer could recover.
“The depletion of the ozone layer will get worse . . . perhaps through to the turn of the century and possibly beyond, “ he told reporters.
“But in 50 years’ time, given the measures and the strong international action that has been taken, we should see the damage in the ozone layer repaired.”
Ozone is a fragile shield of gas encircling the Earth that keeps out 90 per cent of the harmful ultraviolet radiation from the sun, especially the cancer-causing UV-B and UV-C rays.
Rapid depletions have been traced to industrial gases containing chlorine and bromine, such as CFCs used in refrigeration, aerosols used as industrial cleaning agents, and halon gas contained in yellow fire extinguishers.
As well as skin cancer and genetic damage, lower ozone levels are forecast to lead to higher rates of sunburn and cataracts, stunted crops and the depletion of phytoplankton, organisms essential to the marine food chain. Their depletion could be expected to lead to falling fish stocks.
Ozone levels over Antarctica have been dropping dramatically in the past few years, and there are large swathes of atmosphere over the continent six kilometres thick in some places with no ozone at all.
Depleted ozone is kept locked above Antarctica by winds that circle the poles, but eventually drifts north during December and January as these winds subside.
It carries with it active chlorine molecules that go on to eat away at the ozone layer over Australia, South America and South Africa, increasing the amount of damaging ultraviolet rays reaching the ground.
Average ozone levels over Melbourne have in the past decade dropped 5 per cent, enough to increase the level of skin cancer- causing ultraviolet-B rays by between 7.5 and 10 per cent.
United Nations scientists said earlier this year that falling ozone levels would likely trigger an extra 250,000 cases of skin cancer a year worldwide, and deplete worldwide fish stocks by some seven million tonnes.
Already, Adelie penguins in Antarctica which normally go no more than a day’s swim from their land-based nests are travelling up to nine days at sea to find food, and at times return to their young with nothing.
Earlier this year, scientists reported of the 1800 penguin chicks in one region that were expected to survive, only 70 were still alive at the end of the season.
Although 90 per cent of the ozone-depleting chemicals are released by industry over Europe, North America, Russia and Japan, it is over the South Pole that they do the most damage.
Once released, ozone-depleting chemicals rise high into the air and are blown along by jet streams in the upper atmosphere to come cascading down over the poles.
Because Antarctica is a large frigid land mass surrounded by ocean, temperatures in its upper atmosphere fall far lower than over the North Pole, which is mostly surrounded by land.
The chemicals are more efficient at destroying ozone the colder it gets, and since the air is much colder over Antarctica as low as -85 degrees Celsius ozone depletion is more dramatic and more dangerous to life.
Ozone levels have also been falling in the north. Recent measurements show ozone levels between 10 and 20 per cent lower, creating a porous ozone-thin cap that lasts well into March.
Ozone-depleting chemicals like CFCs and halon are safe and stable on the ground, but in the upper atmosphere they react with high ultraviolet light and snap apart, turning into wildly ricocheting chlorine molecules that go on to break apart surrounding ozone molecules at a frenetic pace.
Each chlorine molecule can destroy 50,000 ozone molecules, and scientists estimate that more than half a million tonnes of chlorine gas is released into the atmosphere each year.
Since 1987, when the Montreal Protocol limiting the production and release of ozone-depleting gases was signed by 149 countries, there has been some improvement. Twice amended to toughen its provisions, it has seen a 70 per cent cut in the consumption of ozone-depleting gases since 1986.
Industrialised countries have agreed to halt all production and importing of almost all ozone-destroying gases by the end of this year, and to establish timetables for phasing out the remainder.
Early indications are that the measures may be working.
Recent figures show that the amount of CFC-11 and carbon tetrachloride two of the nastiest ozone-eaters, which had almost doubled their presence in the atmosphere since 1980 has levelled off, and appears to be falling.
But scientists say it may take three to five years before ozone levels start rising again, and it will take until the middle of next century for the layer to return to normal.
“We’ve seen a decrease in the chemicals, but not in the rate of ozone depletion,” Dr Fraser said . “It’s levelled off and just started to decline. In about three to five years, the chlorine levels in the stratosphere will reach a maximum . . . and should start trending down.”
Dr Fraser doubts that this year’s hole will break the 1994 record. “If this hole were the largest on record, I don’t think it would be significantly larger,” he said. “Ultimately, I don’t think we’re going to lose a lot more of our ozone layer (over Melbourne) . . . less than 1 per cent more before the rate starts to slow down.” Dr Lehmann is not as certain. “Atmospheric loading of chlorine should be down in the next year or two that’s if they’ve got their chemistry right,” he said.
THE OZONE HOLE
How we are destroying Earth’s sunscreen.
The ozone layer stops 90 per cent of all harmful ultraviolet rays (UV) from reaching Earth’s surface. Ozone-depleting gases such as chlorofluorocarbons (CFCs) become unstable on reaching the upper atmosphere and are split by UV radiation, freeing chlorine atoms that destroy ozone molecules.
Ozone-depleting gases, including CFCs, methyl bromide, methyl chloroform, carbon tetrachloride and halons, are found in many solvents, air-conditioning units, refrigerators, aerosols and fire-extinguishing systems.
WHAT YOU CAN DO TO HELP SAVE THE OZONE LAYER
- Repair all leaks in car and home air-conditioners, many of which are still CFC-based.
- When arranging for air-conditioners to be serviced, ask if refrigerants will be recovered and recycled. If the system needs major repairs, ask for a quote for converting it to ozone-friendly substitute refrigerants.
- Remove refrigerants form fridges, air-conditioners and dehumidifiers before disposing of them.