It has long been known that the ozone layer protects the earth from harmful ultraviolet radiation, and that molecules known as chlorofluorocarbons (CFCs), which were once used in refrigerators and spray cans, can destroy the ozone. The worldwide ban on CFC production agreed in the late 1980s has had a positive effect. Measurements now show that the ozone layer over Antarctica is recovering. But many questions remain unanswered. One is: what role does ozone play in climate change?