Protective ozone layer is beginning to recover (8/30/2006) | | |
 A layer of ozone in the upper atmosphere that protects Earth from the sun's ultraviolet radiation is beginning to recover after decades of erosion caused by pollution. Phil Gentry, (256)824-6420 | A layer of ozone in the upper atmosphere that protects Earth from the sun's ultraviolet radiation is beginning to recover after decades of erosion caused by pollution. A new study published this week shows that about half of the improvement is attributed to international action to reduce or eliminate ozone-depleting chemicals, while the other half has to do with recent changes in mixing patterns in the atmosphere. "This is the most important environmental success story of the past century," said Dr. Mike Newchurch, a member of the research team and a professor of atmospheric science at UAH. "It would have been a global catastrophe if we had lost an appreciable portion of the ozone layer." If the destruction of the ozone layer between seven and 15 miles high had not been slowed, it has been estimated that the extra high-energy ultraviolet radiation reaching Earth's surface by 2020 would have caused an additional 3.5 million cases of skin cancer worldwide every year, including 150,000 in the U.S., according to a 2002 international assessment of ozone depletion. The study, which was led by a Georgia Tech research scientist and UAH alumnus, Dr. Eun-Su Yang, '01 Ph.D., atmospheric science, used data from several NASA and NOAA satellites and from instruments carried aloft by balloons to look at ozone in the stratosphere over the mid-latitude regions of the northern and southern hemi-spheres. The research results are published in the Aug. 30 issue of the American Geophysical Union's Journal of Geophysical Research — Atmospheres. Data from the study, which looked at ozone in the two most important layers of the atmosphere, indicate that stratospheric ozone has stopped decreasing in one layer and is increasing in the other. Scientists attribute the stabilization of ozone levels in the stratosphere between 11 and 15 miles high (18 to 25 kilometers) to the Montreal Protocol and its amendments. The treaty, enacted in 1987, phased out the use of certain ozone-depleting chemicals used in several places, including spray can propellants, air conditioning and refrigerator coolants, and foam insulation. These chemicals contain chlorine, which destroys ozone. "The Montreal Protocol is working where we expected it to be working, in the mid-stratosphere," said Newchurch. "At altitudes below that, however, ozone is improving faster than we expected for reasons we don't understand but which have nothing to do with chlorine. That was the real surprise of this research." Some scientists believe the ozone improvement in the stratosphere between seven and eleven miles high (11 to 18 kilometers) might be related to global climate change. Ozone depletion is temperature sensitive, Newchurch said, and warming in the lower atmosphere cools the stratosphere. "When you cool the stratosphere you slow ozone depletion, so one of the unintended results of warming near the surface is to improve ozone higher up," he said. "Warming also affects air circulation patterns in ways we don't understand and can't predict very well, and those worldwide patterns also have an impact on ozone." Although the destruction of the ozone layer has been slowed or stopped, depending on location, scientists estimate it will take about 50 years (plus or minus 20) for ozone in the stratosphere to return to its 1980 level. Globally, the protective ozone layer had dropped about 3 percent between 1980 and 2001. "We do think we're on the road to recovery of stratospheric ozone, but we don't know exactly how that recovery will happen," said Derek Cunnold, a professor of earth and atmospheric science at the Georgia Institute of Technology. Detailed Graph Video Model EDITORS: Additional information about this story is available at: http://www.jpl.nasa.gov/news/news.cfm?release+2006-102 http://www.nasa.gov/vision/earth/environment/ozone_resource_page.html http://gtresearchnews.gatech.edu/
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