Atmospheric Science

The First Signs of a Recovery

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Science  15 Aug 2003:
Vol. 301, Issue 5635, pp. 896
DOI: 10.1126/science.301.5635.896c

The ozone hole in the stratosphere over the poles is caused by anthropogenic chlorine-containing compounds such as chlorofluorocarbons (CFCs). Since 1987, the production and consumption of these compounds have been controlled under the Montreal Protocol and its amendments. As a consequence, chlorine concentration near Earth's surface has decreased since 1993, and in the upper stratosphere, total chlorine has been decreasing since 1997. But have these reductions had any effect on ozone loss?

Newchurch et al. have analyzed ground-based and satellite ozone measurements for 1979 to 2003. After taking into account seasonal, solar, and quasi-biennial oscillation effects, they find that before 1997, ozone loss in the upper stratosphere (altitudes from 35 to 45 km) followed a linear downward trend, whereas after 1997, the rate of ozone depletion slowed down significantly. These data are the first indication that the ozone layer is beginning to recover. However, much of the ozone lies below the region studied here, so further analyses will be required to ascertain whether ozone is also recovering in lower atmospheric regions. — JFU

J. Geophys. Res. 108, 10.1029/2003jd003471 (2003).

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