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SCIENTISTS FIND ANTARCTIC OZONE HOLE TO RECOVER LATER THAN EXPECTED
June 29, 2006
Bron : earthobservatory.nasa.gov

Scientists from NASA and other agencies have concluded that the ozone hole over the Antarctic will recover around 2068, nearly 20 years later than previously believed.

Researchers from NASA, the National Oceanic and Atmospheric Administration (NOAA) and the National Center for Atmospheric Research (NCAR) have developed a new tool, a math-based computer model, to predict the timing of ozone hole recovery. Their findings will be published tomorrow in Geophysical Research Letters.

The Antarctic ozone hole is a massive loss of ozone that occurs each spring in the Southern Hemisphere. The ozone hole is caused by chlorine and bromine gases in the stratosphere, an upper layer of the atmosphere, that destroy ozone in an annually recurring process that takes place in the unique meteorological conditions of the Antarctic stratosphere. Those gases come from human-produced chemicals such as chlorofluorocarbons.

"The Antarctic ozone hole is the poster child of ozone loss in our atmosphere," said lead author Paul Newman, a research scientist at NASA's Goddard Space Flight Center, Greenbelt, Md. "Over areas that are farther from the poles like Africa or the continental U.S., the annually averaged levels of upper atmospheric ozone are only three to six percent below natural levels. But, over Antarctica, ozone is 70 percent lower in the spring. This new method allows us to more accurately estimate ozone-depleting gases over Antarctica, and how they will decrease over time, reducing the ozone hole area."

For the first time, a model combines estimates of future Antarctic chlorine and bromine levels based on current amounts as captured from NASA satellite observations, NOAA ground-level observations, NCAR airplane-based observations, with anticipated future emissions, the time it takes for the transport of those emissions into the Antarctic stratosphere, and assessments of future weather patterns over Antarctica.

The model accurately reproduces the ozone hole area in the Antarctic stratosphere over the past 27 years. Using the model, the researchers predict that the ozone hole will recover in 2068, not in 2050 as currently believed.

International agreements such as the Montreal Protocol, approved in 1987, limit production of ozone-depleting substances. Later changes to those international agreements have completely eliminated legal production of most of these chemicals, though there will be continued emissions of previously produced and stored amounts of those chemicals that are not destroyed or recycled.

The researchers also show that the ozone hole has not yet started to significantly shrink, something they predict will not start to occur until 2018. Newman's team also further indicated that greenhouse gas-forced climate change will have only a small impact on the Antarctic stratosphere and recovery of the ozone hole.

The upper ozone layer is important because it blocks 90-99 percent of the sun's ultraviolet radiation from making contact with Earth. This solar radiation can cause skin cancer, genetic damage, eye damage and can impact marine life.

"My job is to track ozone-depleting chlorofluorocarbons around the globe on a weekly basis," said Steven Montzka, a research chemist in the Global Monitoring Division at NOAA's Earth Systems Research Laboratory in Boulder, and co-author of the paper. "We make calculations with that information to determine how gases containing chlorine and bromine that have life spans in the atmosphere ranging from 45 to about 300 years, are affecting ozone. This new prediction model is a very useful step forward to refining our understanding of ozone hole recovery time scales."

The researchers included ozone data from the Total Ozone Mapping Spectrometer (TOMS) on NASA's Earth Probe TOMS satellite, gas measurements from the Ozone Monitoring Instrument (OMI) aboard NASA's Aura satellite, temperature information from NOAA's polar orbiting series satellites, and data captured by NOAA ground stations and weather balloons to create the new prediction model.

To view related Antarctic ozone hole images on the Web, visit:

http://www.nasa.gov/cente(...)/ozone_recovery.html

For more information about the Antarctic ozone hole on the Web, visit:

http://ozonewatch.gsfc.nasa.gov/

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Bron : ACE.MMU
The ozone layer over Canada is normally thicker in winter and early spring, varying naturally by about 25% between January and July. Weather conditions can also cause considerable daily variations.