From: parson_r@cubldr.colorado.edu (Robert Parson)
Subject: Arctic ozone Hole? (Re: ECO Geneva (INC6) #2 Dec 10 92 (27
Organization: University of Colorado, Boulder
Date: Sat, 12 Dec 1992 23:06:59 GMT

In article <1466601971@igc.apc.org>, larris@igc.apc.org (Lelani Arris) writes:
> 
>                 CLIMATE TALKS GENEVA DECEMBER 1992
> 

> Global warming feeds Arctic ozone depletion
> 
> by Bill Hare, Greenpeace International
> 
> Scientific pressure to reduce greenhouse gas emissions, in
> particular CO2 from fossil fuel combustion has increased with
> recent research results that demonstrate a potential major
> adverse interaction between global warming and ozone depletion.
> Published in the scientific journal Nature on 19 November just
> days before the Fourth Meeting of the Parties to the Montreal
> Protocol on Substances That Deplete the Ozone Layer, the report
> predicts that a doubling of atmospheric CO2 could lead to the
> formation of an Arctic ozone hole.
 ...............
> 
> The prospect of rising greenhouse gas concentrations
> together with high atmospheric chlorine concentrations creating
> the circumstances for catastrophic losses of ozone in the Arctic
> is truly frightening.
> 
 This post is a reasonable summary of the more disturbing aspects of
 the _Nature_ paper. It leaves out some mitigating factors, however:

 1. The dimensions of the calculated "hole" are modest, by present-day
 antarctic standards. The region of extreme depletion (  < 250 DU) has
 radius of about 10 degrees, and overall the hole (which I arbitrarily
 define by a 400 DU contour) has a radius of about 20 degrees. If it
 were to be centered over the north pole the area under it would mostly
 consist of year-round pack ice. (It could be off-center, though, in which
 case there would be some open water beneath it.) Overall it looks more
 like the wimpy 1988 antarctic hole than like the big ones that have
 formed in the past three years. The 1988 hole did not produce large increases
 in UV-B at open-water latitudes.

 2. The hole is only expected to form once every five years, on the average.
  "For the remaining 80% of winters, it is unlikely that doubling of CO2
 will suppress the occurrence of stratospheric warming sufficiently to produce
 an arctic ozone hole, although even in these conditions ozone depletion
 could be enhanced." (p. 244)

 Given the complexity of this kind of calculation (it's difficult enough
 to model regional climate changes _or_ ozone depletion 50 years into the
 future, and the present problem involves the synergistic interaction of
 these two processes) one shouldn't rely too much upon detailed features
 of the results. The calculation should probably be regarded more as a
 proof-of-principle demonstration - that an Arctic ozone hole *could*
 form in the future - than as a foundation for specific policy decisions.
 There could well be phenomena left out of the simulations that make the
 actual effects quite a bit worse (too often, people assume that when a
 model is incomplete, it inevitably implies that the real effects will
 be less severe than the predictions. The history of the antarctic ozone
 hole provides a suitable counterexample.) If in the future a serious
 crisis does appear to be likely, tinkering with present CFC reduction
 schedules is not likely to yield a dramatic improvement; it'll be 
 necessary to come up with some scheme for removing the halogens that
 are up there now.

 At present, though, it looks like Steinn Sigurdsson's home waters will
 get by without serious damage :) (How far north do the Icelandic and
 Norwegian fishing fleets range?)

 Robert
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