November 10, 2008
Posted: 09:29 AM ET
The ozone hole over the Antarctic, which grows to its maximum annual size in September, peaked at the fifth-highest size ever since measurements began in 1979 this year, according to scientists at the National Oceanic and Atmospheric Administration.
But experts say that the "fifth-largest" designation may not necessarily be bad news at all. They're sticking to predictions that the ozone hole will repair itself over the rest of the 21st Century. Colder-than-average temperatures and strong high level winds helped widen the hole this season. Warmer weather as the Antarctic summer starts up helps close up the hole each year.
It's been nearly four decades since the first research drew links between man-made chemicals and destruction of ozone in the upper atmosphere. Chlorofluorocarbons and freon - once widely used in air conditioners and spray cans respectively, were among the substances that broke down stratospheric ozone - the key to protecting us from harmful solar radiation. Projections indicate that a thinning ozone layer could lead to increases in human skin cancer, eye cataracts, and other maladies. Dutch scientist Paul Crutzen and Americans Mario Molina and Sherwood Rowland shared the 1995 Nobel Prize for Chemistry for their discoveries.
Global concern over ozone damage led to what is widely regarded as a remarkably successful international treaty. The Montreal Protocol was ratified in 1987 and took full effect nine years later, banning most uses of ozone-destroying chemicals.
Scientists have reported a substantial reduction in the levels of ozone-destroying chemicals reaching the stratosphere. But CFC's, freon, bromides, and other ozone-eaters are particularly long-lasting, and may take much of the rest of this century to dissipate. "The decline of these harmful substances to their pre-ozone hole levels ... will take decades," said NOAA chemist Stephen Montzka.
Translation: Don't lose the sunscreen. Ozone layers have thinned planet-wide, and during the late-winter weather in either hemisphere, ozone protection reaches its lowest levels near the poles. Less ozone in the upper atmosphere means more exposure to the ultraviolet radiation that can cause skin cancer.
NOAA's Ozone measurements page can be found here
NASA offers daily updated graphics and animations on the size of the ozone hole here.
Peter Dykstra Executive Producer CNN Science, Tech & Weather
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