Ozone layer making tentative improvements.

• Author: Chafe, Zoe
• Position: Environmental Intelligence

Two recent studies indicate that the Montreal Protocol, a 1987 treaty designed to protect the eroded stratospheric ozone layer, is finally beginning to work. Because it takes time for harmful chemicals to migrate up through the atmosphere to sensitive ozone layers, scientists are only now able to measure the effects of reductions begun in 1987. Both studies found that atmospheric concentrations of ozone-depleting substances are increasing more slowly than before. As a result, ozone in the upper stratosphere (35 to 45 kilometers above ground) is now declining at about 4 percent per decade, half the 1980s rate.

"This is the beginning of a recovery of the ozone layer," says Professor Michael Newchurch, lead author of a study on chlorine levels in the atmosphere published in the Journal of Geophysical Research. Increases in the concentration of chlorine, the ozone destroyer in CFCs, have begun to slow in the upper stratosphere. Newchurch attributes this improvement to the Montreal Protocol's global ban on chlorofluorocarbons (CFCs), compounds once widely used in aerosols and refrigerants. While scientists have recorded declining chlorine levels in the lower atmosphere for some time, this is the first study to document chlorine improvements in the higher ozone layer.

Newchurch cautions, however, that the results apply only to the upper stratosphere, which contained very lit fie ozone to begin with: "We don't see compelling evidence that the destruction of ozone is slowing in the lower stratosphere, where 80 percent of the protective ozone...