This article is from the Ozone Depletion: The Antarctic Ozone Hole FAQ, by Robert Parson email@example.com with numerous contributions by others.
First of all, even though the ozone hole is confined to the
antarctic, its effects are not. After the hole breaks up in the
spring, ozone-poor air drifts north and mixes with the air there,
resulting in a transient decrease at middle and high latitudes.
This has been seen as far north as Australia [WMO 1991][Roy et al.]
[Atkinson et al.] On a time scale of months short-wave UV
regenerates the ozone, but it is believed that this "dilution" may
be a major cause of the much smaller _global_ ozone depletion, ~3%
per decade, that has been observed. Moreover, the air from the
ozone hole is also rich in ClO and can destroy more ozone as it
mixes with ozone-rich air. Even during the spring, the air in
the vortex is not _completely_ isolated, although there is some
controversy over the extent to which the ozone hole acts as
a "chemical processor" for the earth's atmosphere.
([Tuck 1989] [Schoeberl and Hartmann] [AASE] [Randel] [Waugh].)
From a broader standpoint, the ozone hole is a distant early
warning message. Because of its unusual meteorological properties
the antarctic stratosphere is especially sensitive to chemical
perturbations; the natural mechanisms by which chlorine is
sequestered in reservoirs fail when total stratospheric chlorine
reaches about 2 parts per billion. This suggests that allowing
CFC emissions to increase by 3% per year, as was occurring during
the 1980's, is unwise, to say the least. The emission reduction
schedules negotiated under the Montreal Protocol (as revised in
1990 and 1992) lead to a projected maximum of ~4 ppb total strat.
chlorine in the first decade of the 21st century, followed by a
gradual decrease. Letting emissions increase at 3%/year would have
led to >16 ppb total stratospheric chlorine by 2040, and even a
freeze at 1980 rates would have led to >10 ppb. [Prather et al.].