Thanks, John. It is reassuring to know that geoengineering using stratospheric sulphate aerosols would have much less effect on ozone depletion that the Pinatubo eruption had. However there are still problems over the ozone.
John Davies told me about Joe Farman, who did some of the research, and helped to get the Montreal Protocol implemented. Here is an article by him, but I do not have a date for it: http://www.unep.org/OurPlanet/imgversn/104/farman.html "The prospects for ozone recovery remain poor. Though chlorine reached its peak in the atmosphere in 1994 and has since decreased slowly, bromine (which also depletes ozone) is still increasing. There needs to be a fresh impetus to attempts to control its sources - halons and methyl bromide. " "Such is our industrial capacity that we can, in just a decade or two, affect the world so severely that it may take a century or more to recover. This is what happened over ozone depletion, where we performed what in retrospect will surely be seen as an unnecessary experiment. That the consequences have not been more severe must be attributed to luck rather than good judgement. When will we learn?" That leads to one of the points I was making. Should we not learn a lesson from this, just how fragile our existence is on this planet, thanks to our own interference? This too is the lesson from books like "The Weather Makers" by Tim Flannery. We have been lucky over ozone depletion, but we may not be so lucky over Arctic sea ice disappearance, if we don't try to prevent it pretty damned quickly. As Ken Caldeira says, on another thread, there is no alternative to geoengineering for this: > .... I think John's argument is correct that if we want to prevent > further warming of the Arctic over the next decades there is essentially no > alternative to direct intervention in the climate system. Cheers, John ----- Original Message ----- From: John Gorman To: [email protected] ; geoengineering Cc: Davies, John Sent: Sunday, January 11, 2009 10:10 AM Subject: Re: [geo] Ozone depletion near catastrophe I read through the referenceyou gave and there was no suggestion of a runaway ozone loss. there was an un quantified negative statement. There was lots of discussion in this group about a year ago, particularly at the time of the publication of the Tilmes paper. Not being an expert in this are a I rely a lot on Paul Crutzen's comment in his 2006 paper; (he did after all get his Nobel prize for his work on the ozone layer!) "Among possible negative side effects, those on stratospheric ozone first spring to mind. Fortunately, in this case one can build on the experience with past volcanic eruptions, such as El Chich´on in 1982 and Mount Pinatubo in 1991, which injected 3-5 Tg S (Hofmann and Solomon, 1989) and 10 Tg S (Bluth et al., 1992), respectively, in the stratosphere. Local ozone destruction in the El Chich´on case was about 16% at 20 km altitude at mid-latitudes (Hofmann and Solomon, 1989). For Mount Pinatubo, global column ozone loss was about 2.5% (Kinnison et al., 1994). For the climate engineering experiment, in which the cooling effect of all tropospheric anthropogenic aerosol is removed, yielding a radiative heating of 1.4 W/m2 (Crutzen and Ramanathan, 2003), a stratospheric loading of almost 2 Tg S, and an input of 1-2 Tg S/yr is required, depending on stratospheric residence times. In this case, stratospheric sulfate injections would be 5 times less than after the Mount Pinatubo eruption, leading to much smaller production of ozone-destroying Cl and ClO radicals, whose formation depends on particle surface-catalyzed heterogeneous reactions (Wilson, 1993). Compensating for a CO2 doubling would lead to larger ozone loss but not as large as after Mount Pinatubo. Furthermore, the amounts of stratospheric chlorine radicals, coming from past production of the chloro-fluoro-carbon gases, are now declining by international regulation, so that ozone will significantly recover by the middle of this century. ALBEDO ENHANCEMENT BY STRATOSPHERIC SULFUR INJECTIONS: A CONTRIBUTION TO RESOLVE A POLICY in Climat Change 2006 ----- Original Message ----- From: John Nissen To: geoengineering Cc: Davies, John Sent: Friday, January 09, 2009 5:39 PM Subject: [geo] Ozone depletion near catastrophe Hi all, John Davies has told me that after Pinatubo, we nearly had a runaway ozone depletion event. The depletion is mentioned here: http://en.wikipedia.org/wiki/Mount_Pinatubo but does anybody have references to the near disaster? It is salutary to think that we have managed to avert one disaster, while we are now allowing another to happen before our eyes - with the Arctic sea ice disappearing and methane threatening to emerge from permafrost. Did we not learn a lesson from before, just how fragile our existence is on this planet? John --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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