Ozone levels looked like they were stabilizing, but this year a bigger than normal hole could open above the South Pole.
Scientists still disagree on the stability of ozone layer levels
The protective ozone layer over the earth has thinned to its lowest level ever, alarming scientists who believed it had begun to heal. They’re warning that increased ozone loss is allowing additional harmful ultraviolet light to reach us and making us more vulnerable to sunburn, skin cancer and cataracts.
About 20 kilometers (12.4 miles) thick, the layer of ozone gas is like a giant umbrella 15 to 35 kilometers over the earth and like any good pair of sunglasses, it acts like a filter by blocking out most ultraviolet rays.
A thin layer of ozone protects from numerous health problems
The loss of ozone was discovered over the polar regions 20 years ago and has been closely watched ever since. Scientists continue to disagree about the causes and effects of the ozone level's thinning, with some stating depletion levels have peaked.
Scientists divided on ozone depletion
According to the United Nations World Meteorological Organization's latest bulletin, the seasonal hole above the South Pole and Antarctica is shrinking.
"It is the third largest ever, more or less as one would expect from present levels of chlorine and bromine in the atmosphere," Geir Braathen, the WMO's top ozone expert, told reporters Tuesday. "It doesn't look as if the ozone hole is going to get any bigger (in coming years). It seems like we have reached a plateau."
Others scientists, such as Frank Jürgen Diekmann of the European Space Agency, expect this year's hole over the South Pole to be the biggest ever, and doubt the danger is over.
"If anything, the ozone concentration has stabilized," he said. "But especially in 2005 we’re expecting record ozone holes above the Antarctic. Going on the latest data, we can’t say the danger is gone."
Scientists can agree that levels seem to have stablized
Especially bad in south
It’s been more than 18 years since 180 countries signed up to the Montreal Ozone Protocol on reducing emissions of chlorofluorocarbons, (CFCs), which up until then were considered indispensable chemicals for modern living.
Though there's no actual "hole" in the ozone layer and only a slight thinning occurs over the rest of the world, climatic conditions are especially dangerous at the South Pole. It would take forty to fifty years for the ozone shield to recover completely -- the same amount of time chlorofluorocarbons stay in the atmosphere.
Polar-stratospheric clouds, which form above the South Pole when air masses cannot mix in the dark winter months and end up collecting more and ore chlorine compounds, are struck by the southern spring's sunlight from September to November. That causes them to break into "radicals" that split ozone into an oxygen molecule and an oxygen atom, making it disappear.
Greenhouse gases dangerous in north
These meteorological conditions can also be dangerous in the northern hemisphere, according to Christoph Brühl, of the Max Planck Institute for Chemistry in Mainz.
Greenhouse gasses like CO2 endanger the northern hemisphere
"The public is looking more and more at the Antarctic in connection with the ozone hole," he said. "In principle though, the danger is just as great in the northern hemisphere, except that it doesn't arise there every year because of various meteorological conditions."
Greenhouse gas emissions can also influence the ozone, particularly in the northern hemisphere. The gasses cool the upper stratosphere, the layer important for the formation of ozone. If the layer gets too cold, a closed area similar to that over the South Pole can form in winter, meaning air masses over the northern hemisphere can no longer exchange, damaging the ozone filter over Europe, Brühl explained. "Up to now we've always been lucky that the weather put an end to it in March, but that needn’t always be so," he added. "It could quite easily run into April and that would certainly raise the ultraviolet radiation into Germany over the June level."