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30.06.2006

The Antarctic ozone hole will not disappear before 2068, nearly 20 years later than previously estimated, according to scientists using a new computer model. The ozone hole is caused by chlorine and bromine gases that destroy ozone in the stratosphere (an upper layer of Earth's atmosphere) during the southern hemisphere springtime.

The gases come from human-produced chemicals such as chlorofluorocarbons (CFCs). The Montreal Protocol, an international agreement adopted in 1987, limited the production of ozone-depleting substances. Amendments in 1990 and 1992 completely eliminated legal production and use of most of these chemicals, although there will be continued emissions from previously produced and stored quantities of those chemicals that have not been destroyed or recycled.

Researchers from NASA, the National Oceanic and Atmospheric Administration (NOAA), and the National Center for Atmospheric Research (NCAR) have simulated the ozone hole in a new math- based computer model. They used estimates of chlorine and bromine levels over Antarctica from NASA and NOAA satellite observations, NOAA ground-level observations, NCAR air-based observations taken from airplanes, and the temperature of the Antarctic stratosphere in late spring, when the ozone hole begins to form.

The model accurately reproduced the ozone hole area in the Antarctic stratosphere over the past 27 years. The researchers then made projections of ozone-depleting substances in the future, leading to their prediction that the ozone hole will recover in 2068, not in 2050, as previously estimated. Their findings will be published 30 June in Geophysical Research Letters, a journal of the American Geophysical Union.

"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 in Greenbelt, Maryland. "Over areas that are farther from the poles like Africa or the U.S., the 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, improving the ozone hole."

The researchers also show that the ozone hole has not yet started to significantly shrink, which they predict will not occur until approximately 2018. They also concluded 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's surface. This solar radiation can cause skin cancer and genetic and eye damage, and it can impact marine life.

"My job is to track ozone-depleting CFCs 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, a 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 as long as 100 years are affecting ozone. This new prediction model is a very useful step forward to refining our understanding of ozone hole recovery time scales."

Harvey Leifert | Source: American Geophysical Union
Further information: www.agu.org

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