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Ozone decline stuns scientists
By Katy Human and Kim McGuire
Denver Post Staff Writers
Solar flares and frigid temperatures are believed to be working with human chemicals to eat away at the protective ozone layer above the North Pole, surprising scientists who have been looking for evidence that the planet's ozone layer is healing.
The ozone layer protects Earth from dangerous ultraviolet radiation, which can cause skin cancer.
Last winter, Arctic ozone declined more precipitously than ever in the upper atmosphere, probably because of violent storms on the sun's surface, one team reports today in the journal Geophysical Research Letters.
And in recent days, a lower layer of ozone has undergone an extraordinary thinning because of a level of bitter cold (about minus-110 degrees Fahrenheit) rarely seen in the Arctic and manmade chemicals, researchers said. One Colorado scientist has raced north to document the event, expected to sputter out within days.
The two unusual findings have experts worried that they don't fully understand the dynamics of ozone depletion.
"I don't think we can be confident about whether or not we're seeing an ozone recovery or if we're attributing recovery to the correct causes," said Cora Randall, an atmospheric scientist at the University of Colorado.
Randall and her colleagues studied a dramatic and unexpected drop in upper-level ozone levels last winter. A few months before the decline, massive solar storms had blasted high-energy particles toward Earth. Randall suspects the energetic particles helped create chemicals called nitrogen oxides, which are known ozone-gobblers.
Solar storms are natural, she said, but some scientists suspect humans also played a role in creating conditions that contributed to the historic ozone- depletion event.
Human-emitted chemicals are largely responsible for the massive ozone hole that has formed at lower levels in the Arctic atmosphere in recent days, experts said. There, unusually low temperatures are triggering reactions in which manmade chemicals quickly devour ozone, they said.
"Something like this only happens once every 20 years," said Russ Schnell, with the National Oceanic and Atmospheric Administration in Boulder.
His agency deployed Andrew Clarke to a lab in Greenland, located under the area of sky where the ozone layer is diminishing. There, Clarke is lofting testing equipment into the sky with giant balloons. It will be weeks or months before the results are understood, he said.
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