Monckton responding to an email about how volcanoes cause ozone depletion:
I’m not familiar enough with the inner workings of the
general-circulation models, so I’m not sure how it is that the ozone
hole appears only over the Antarctic. One possibility is that the
circumpolar circulation (which sailors take advantage of) acts as a
cage for the weather within. Another, which I’m trying to find data
for, is the volcanic activity of Mount Erebus, Antarctica’s active
volcano. In a good year for eruptions, Erebus can put out as much CFCs
as Man used to. It would be very amusing if the activity cycle of
Erebus correlated neatly with the opening and (now) the gradual
closing of the ozone hole. So your point about volcanic activity could
be right on the mark.
Volcanoes do not emit CFCs. They do emit HCl, but only a very big eruption will send this into the stratosphere. Robert Parson writes:
To conclude, we need to say something about Mt. Erebus. In an
article in 21st Century (July/August 1989), Rogelio Maduro
claimed that this Antarctic volcano has been erupting constantly
for the last 100 years, emitting more than 1000 tons of chlorine
per day. Mt. Erebus has in fact been simmering quietly for over a
century [ARS] but the estimate of 1000 tons/day of HCl only applied
to an especially active period between 1976 and 1983 [Kyle et al. 1990].
Moreover, that estimate has been since been reduced to 167 tons/day
(0.0609 Mt/year). By late 1984 emissions had dropped by an order of
magnitude, and have remained at low levels since; HCl emissions
at the crater rim were 19 tons/day (0.007 Mt/year) in 1986,
and 36 tons/day (0.013 Mt/year) in 1991. [Zreda-Gostynska et al.]
Since this is a passively degassing volcano (VEI=1-2 in the active
period), very little of this HCl reaches the stratosphere. The
Erebus plume never rises more than 0.5 km above the volcano,
and in fact the gas usually just oozes over the crater rim. Indeed,
one purpose of the measurements of Kyle et al. was to explain high
Cl concentrations in Antarctic snow.
By comparison CFCs put >0.3 Mt/year into the stratosphere.