Ozone Layer Decline Leveling Off, According To New Study

Betsy Weatherhead, a researcher with the Cooperative Institute forResearch in Environmental Sciences, a joint institute of the Universityof Colorado at Boulder and the National Oceanic and AtmosphericAdministration and corresponding author of the study, said the teamdocumented a leveling off of declining ozone levels between 1996 and2002, and even measured small increases in some regions.

"The observed changes may be evidence of ozone improvement inthe atmosphere," said Weatherhead. "But we will have to continue tomonitor ozone levels for years to come before we can be confident."

It most likely will be decades before the ozone layerrecovers, and it may never stabilize at the levels measured prior tothe mid-1970s, when scientists discovered human-produced chlorine andbromine compounds could destroy ozone and deplete the ozone layer,Weatherhead said.

A paper on the subject involving researchers from CU-Boulder,NOAA, the University of Wisconsin Madison, the University of Chicagoand the University of Illinois was published online Aug. 29 in theJournal of Geophysical Research.

The halt in the ozone decline follows the 1987 MontrealProtocol, an international agreement now ratified by more than 180nations that established legally binding controls for nations on theproduction and consumption of halogen gases containing chlorine andbromine. Scientists say the primary source of ozone destruction ischlorofluorocarbons, or CFC's, which once were commonly used inrefrigeration, air conditioning, foam-blowing equipment and industrialcleaning.

The new statistical study focused on levels of total-columnozone -- ozone existing between Earth's surface and the top of theatmosphere. Total-column ozone is a primary blocker of UV radiation inthe atmosphere.

The team analyzed data from a cadre of NASA and NOAAsatellites as well as ground stations in North America, Europe, Hawaii,Australia and New Zealand.

About 90 percent of total-column ozone is found between 10miles to 20 miles above Earth's surface in the stratosphere,Weatherhead said. The ozone layer protects the planet from the harmfuleffects of UV radiation, including skin cancer and cataracts in humansand damaging effects on ecosystems.

Despite the new evidence for the beginnings of an ozonerecovery, Mike Repacholi, The World Health Organization's environmentalhealth coordinator in Geneva, warned that precautions such asUV-blocking sunglasses and skin protection remain vital. "This studyprovides some very encouraging news," he said. "But the major cause ofskin cancer is still human behavior, including tanning and sunburnsthat result from a lack of proper skin protection."

Ozone depletion has been most severe at the poles, with levelsdeclining by as much as 40 percent on a seasonal basis, saidWeatherhead. But there also has been as much as a 10 percent seasonaldecline at mid-latitudes, the location of much of North America, SouthAmerica and Europe.

Other anthropogenic changes to the atmosphere such as methanelevels, water vapor and air temperatures will affect future ozonelevels, which are naturally maintained by complex chemical processessparking the continual creation, destruction and redistribution ofozone, said Weatherhead. "Even after all chlorine compounds are out ofthe system, it is unlikely that ozone levels will stabilize at the samelevels."

Scientists warn a return to significantly higher atmosphericozone levels may take up to 40 years. "Chemicals pumped into Earth'satmosphere decades ago still are affecting ozone levels today," saidSherwood Roland of the University of California, Irvine, who shared the1995 Nobel Prize in Chemistry with Paul Crutzen and Mario Molina fortheir work in identifying the CFC threat to the ozone layer. "Thisproblem was a long time in the making, and because of the persistenceof these chlorine compounds, there is no short-term fix."

Greg Reinsel, a UW Madison researcher and the lead author ofthe study, was one of the first scientists to quantify the ozonedecline more than two decades ago. He died unexpectedly in May aftercompleting the study.

Other co-authors include NOAA's Alvin Miller, Lawrence Flynnand Ron Nagatani, George Tiao of the University of Chicago and DonWuebbles of the University of Illinois.

More UV radiation information is available at: http://www.srrb.noaa.gov/UV/.