Scientists fear that the ozone layer may not recover as fast as they once thought. Global warming appears to be offsetting gains from a 1996 ban on ozone-depleting chemicals. Thinning of the Arctic ozone is dangerous to Americans because the weakened ozone layer migrates south in the spring, researchers said. In some parts of the stratosphere, which begins 5 miles off the ground, the atmosphere lost 60 percent of its ozone between November 1999 and March 2000. That ties Arctic ozone losses recorded in 1997.
Ozone is a form of oxygen.
The ozone layer shields Earth from cancer-producing ultraviolet rays. Chlorine compounds, called CFCs, consume ozone. CFCs used in refrigeration units and aerosols caused much of the loss and were banned by international treaty. For the chlorine atoms to eat the ozone layer, they need to rest on clouds as sort of a platform. It usually isn't cold enough in the Arctic stratosphere for clouds to form.