South Pole Ozone Recovery 20 Years Later Than Expected

GREENBELT, Maryland, June 30, 2006 (ENS) - The full return of the protective ozone layer over the South Pole will take nearly 20 years longer than scientists previously predicted, according to a new study from two U.S. government agencies and a university research center.

Scientists from NASA, the National Oceanic and Atmospheric Administration and the National Center for Atmospheric Research in Boulder, Colorado, have developed a new tool, a math-based computer model, to better predict when the ozone hole will recover.

"The Antarctic ozone hole is the poster child of ozone loss in our atmosphere," said the study's lead author Paul Newman, a research scientist at NASA's Goddard Space Flight Center in Greenbelt.

The Antarctic ozone hole on September 11, 2005 is shown in dark blue. The ozone thinning over Antarctica reached its maximum extent for the year on this date. (Photo courtesy NASA)

"Over areas that are farther from the poles like Africa or the U.S., the levels of ozone are only three to six percent below natural levels. Over Antarctica, ozone levels are 70 percent lower in the spring," said Newman.

"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," he said.

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 likely 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.

The ozone hole in the atmosphere's stratospheric layer, between 15 and 50 kilometers (nine and 31 miles) above the Earth's surface, is caused by chlorine and bromine gases that destroy ozone.

In 1984 the Antarctic ozone hole, shown in dark blue, was beginning to appear. (Photo courtesy NASA)

The ozone layer blocks 90 to 99 percent of the Sun's ultraviolet radiation from making contact with Earth.

The primary concern over ozone depletion is the potential impacts on human health and ecosystems due to increased UV exposure. Increases in skin cancer and cataracts in human populations are expected in a higher UV environment. Lower yields of certain cash crops may result due to increased UV-B stress.

Higher UV-B levels in the upper ocean layer may inhibit phytoplankton activities, which can impact the entire marine ecosystem.

By October 1994 the ozone hole has widened to cover nearly all of Antarctica. (Photo courtesy NASA)

The ozone layer is expected to improve based on a decrease in the production and consumption of ozone depleting gases mandated by an international treaty, the 1987 Montreal Protocol.

The protocol requires that the production and consumption of CFCs, halons, and carbon tetrachloride be phased out by 2000, with a 2005 deadline for methyl chloroform and methyl bromide. Exceptions to the methyl bromide phaseout are granted each year to a dozen countries, who say no cost-effective alternative is available.

While the Montreal Protocol has banned the production of most chemicals that destroy ozone, the NASA, NOAA, and NCAR researchers show that the ozone hole has not started to shrink much as a result. The scientists predict the ozone hole will not start shrinking a lot until 2018, but by that year, the ozone hole's recovery will begin to accelerate.