Ozone Hole Recovery May Be Delayed

ATMOSPHERIC CHEMISTRY

The seasonal hole in the protective stratospheric ozone layer that appears over Antarctica may take longer to recover than previously anticipated, scientists announced on Dec. 6 at the American Geophysical Union meeting in San Francisco.

Based on a combination of new ozone measurements and computer models, they revised the standard estimate of Antarctic ozone recovery from 2050 to 2065—15 years longer than originally predicted.

The production of ozone-depleting chemicals has been banned since 1996, as specified by the Montreal protocol, and global emissions of chlorofluorocarbons dropped 60% between 1989 and 1995.

But stores of the chemicals, which include chlorofluorocarbons (CFCs) and bromine compounds, still exist in sources such as fire extinguishers, automobile air conditioners, and refrigerators—particularly in developing countries that don’t yet have CFC alternatives. These stores, which will continue to be emitted until they are exhausted, may be larger than previously thought, said Dale Hurst, a researcher at the National Oceanic & Atmospheric Administration in Boulder, Colo.

The panelists made no predictions about the effect of the delay beyond the already well-known dangers of exposure to UV radiation, which would otherwise be absorbed by ozone. “It means that ozone levels will be lower in later years,” said Paul A. Newman, atmospheric scientist at NASA Goddard Space Flight Center in Greenbelt, Md.

The situation is more difficult to assess over the Arctic pole, where ozone loss is also evident but where warmer temperatures create powerful winds that redistribute the ozone. “The Arctic ozone recovery is expected to be somewhat earlier, but there’s a large uncertainty,” said John Austin, a researcher with NOAA in Princeton, N.J.

NASA researchers also announced at the meeting that this year’s ozone hole over Antarctica peaked at 9.4 million sq. miles, down from the largest recorded hole of 10.1 million square miles in 1998, but slightly larger than last year’s peak.