While the hole in the Earth's protective ozone layer is slowly healing, its recovery might have a downside, scientists say: Climate change could change wind patterns and send ozone from high in the atmosphere down to the surface, where it is a major component of smog.

The discovery of a hole in the ozone layer above Antarctica was announced by a team of British scientists in 1985. The cause of the hole was attributed to ozone-depleting chemicals like chlorofluorocarbons (CFCs), which were primarily used in cooling units and propellants. When CFCs reach the ozone layer, they release chlorine atoms that rip ozone apart and peel away layers of Earth's natural sunscreen.

Simulations of life without the ozone layer, which is located in the Earth's stratosphere, are not pretty. The stratosphere (the second layer of the Earth's atmosphere, just above the one in which we dwell, the troposphere) contains 90 percent of the Earth's ozone at altitudes between 6 and 31 miles (9.6 and 50 kilometers) above us, where it traps most of the sun's harmful ultraviolet (UV) rays before they can reach the Earth's surface.

Without this shield, we'd be sunburned within 5 minutes of exposure, according to NASA's Earth Observatory.

The Antarctic ozone hole is the closest real-life glimpse at a world without UV protection. Since its discovery in the 1980s, it has spread over parts of Australia, New Zealand, Chile and South Africa where the threats of skin cancer, cataracts, and damage to have raised concerns.

Major efforts have been initiated to speed up the ozone hole's recovery, including the 1987 Montreal Protocol and the phasing out of CFCs. Even so, a study by Guang Zeng and her colleagues from New Zealand's National Institute of Water and Atmospheric Research shows that that the recovery, in concert with climate change, may do harm as well as good.

The study, detailed in the May edition of Geophysical Research Letters, revealed that variations in atmospheric circulation due to climate change will cause a 43-percent increase in gas exchange between the stratosphere and the troposphere, the layer of Earth's air at the surface and our air supply. As more and more ozone is replenished in the stratosphere it will also have more opportunities to seep into the air we breathe.

Some ozone is currently present in the troposphere, though mostly as smog from car emissions and other pollutants. It can be harmful to human respiratory systems and the environment.

If carbon dioxide levels in the atmosphere increase as expected from unabated emission, Zeng said the ozone layer will cool off, blurring the temperature boundary that separates it from the troposphere. Within the next century, more ozone than ever before will surge into our air, her computer model study predicts.

Zeng hopes that future studies of the impacts of climate change will account for the atmospheric composition of both the stratosphere and troposphere, as well as the movement of ozone between the two, to paint a better, more accurate picture of the Earth's environmental future.

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