Analysis of several different satellite records and surface monitoringinstruments indicates that the ozone layer is no longer declining,according to a study by scientists working with the Center forIntegrating Statistical and Environmental Science (CISES) at theUniversity of Chicago.
In some parts of the world, the ozone layer has increased a smallamount in the past few years, although it still well below normallevels.
The results will be published Aug. 31 in the Journal of GeophysicalResearch and follow 18 years after an international agreement, theMontreal Protocol, was established to limit the production of chemicalsdetermined to be harmful to the atmosphere.
The work, funded by the National Oceanic and AtmosphericAdministration, the National Aeronautics and Space Administration andthe Environmental Protection Agency, is a collaboration betweenatmospheric scientists and statisticians through CISES. "The work ofthis team of scientists and statisticians is widely recognized as someof the most authoritative in the statistical analysis of stratosphericozone," said Michael Stein, director of CISES at the University ofChicago.
"These early signs indicate one of the strongest successstories of international cooperation in the face of an environmentalthreat," said retired Navy Vice Adm. Conrad C. Lautenbacher, Ph.D.,undersecretary of commerce for oceans and atmosphere and NOAAadministrator.
For the past few years, studies have focused on ozone decliningin the topmost layer of the atmosphere where there is naturally verylittle ozone. However, this study addresses the total ozone columnlayer that has significant impact on how much ultraviolet radiation iscoming through the atmosphere, said BetsyWeatherhead of the University of Colorado.
"Our work focuses on the thickness of the ozone layer and is thereforerelevant to the amount of harmful ultraviolet (UV) radiation reachingthe surface of the Earth," said Weatherhead, a co-author on the paper.
Overexposure to UV radiation can cause an increase in skin cancers andcataracts in the eyes. Scientists warn that skin and eye precautions,such as wearing sunscreen, wide-brimmed hats and sunglasses, still needto be taken.
"This news about the ozone layer is encouraging, but people should notget a false sense of security. Ultraviolet radiation is still dangerousand we urge people to be 'sun smart' when outdoors," said dermatologistClay J. Cockerell, M.D., president of the American Academy ofDermatology.
Scientists say that ozone in some areas is still quite low compared tohistorical times and that the return of ozone to normal levels will beslow--likely taking several decades. The chemicals responsible for theozone depletion can take years to filter up to the stratosphere, wheremost of the ozone is located, said Weatherhead.
"Some of these chemicals remain in the stratosphere for many decades,meaning that chemicals produced years ago will continue to be harmfulfor decades to come," said Sherwood Rowland, who, along with MarioMolina and Paul Crutzen, won the 1995 Nobel Prize in chemistry fortheir work identifying the threat to the ozone layer.
Other factors can affect the recovery process, such as changes intemperature, clouds, volcanic particles, water vapor, methane, andnatural variability. Internationally, scientists continue to work tounderstand the recent changes and the likely future concentrations ofozone.
The lead author of the study, Greg Reinsel of the University ofWisconsin-Madison, was one of the first scientists to quantify thedecline in ozone in research papers published more than 20 years ago.
He died unexpectedly after completing this study, the first to show theleveling off of the total ozone layer, Weatherhead said. "The findingof positive signs about the ozone layer represents a bittersweetculmination to over twenty years of effort by Greg and his colleagues,"said Michael Stein.
Other co-authors are Alvin Miller, Lawrence Flynn, and Ron Nagatanifrom NOAA, George Tiao, Professor Emeritus in the Graduate School ofBusiness at the University of Chicago, and Don Wuebbles of theUniversity of Illinois.
The Center for Integrating Statistical and Environmental Science wasestablished in 2002. Affiliated with a number of universities andfederal agencies, the center develops multidisciplinary statisticalmethods for more precise environmental risk assessments. CISES iswholly funded through a Science to Achieve Results (STAR) grant fromthe United States EPA.
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