Over the past few years, the ozone hole over Antarctica has varied considerably in size and severity. In 2002, both its size and the time it stayed in position were less than usual (Angell and others 2002). In 2003, however, the ozone hole developed comparatively early and in September was one of the biggest on record. The resulting depletion covered the entire Antarctic area by mid-September (BAS 2003a) (Figure 3). Some scientists believe that it will take a decade or more before it will be clear whether the ozone layer is recovering – assuming that the global phase-out of ozone-depleting chemicals continues successfully (BAS 2003b).