[geo] Re: Royal Society report - Temperature rebound a myth?

[John Nissen]

Hi Ken, We may disagree about the rebound of SRM termination, but we agree about the sense.  Indeed turning off SRM has been likened to turning off the kidney dialysis machine of a patient with kidney failure.  (Thanks, Stephen, for that thought.) So why did the Royal Society report mark "Stratospheric aerosols" with an H for high risk in table 3.6; and 2/5 for safety in table 5.1?  You were a member of the working group! I note that "Cloud albedo" also gets an H for "Regional climate change".  But isn't that a huge advantage of the method over stratospheric aerosols - that it can be more targeted to cool particular areas?  Every way that a method can be tuned, or targeted more closely, means that there is more scope for avoiding side-effects - thus is a safety bonus.  (Being able to turn off the SRM may also allow you to react to unexpected side-effects - another bonus.) Cheers, John --- Ken Caldeira wrote: See attached paper ... If you turn off solar deflection you would get rapid warming (no overshoot, but a rapid rebound). This is not a myth that needs refuting. The question is:  What does this mean? There are plenty of things that we do that, were they stopped suddenly, we would be in big trouble. For example, if we stopped pumping oil today, our transportation system and therefore food distribution system would grind to a halt and there would be mass starvation. Does this mean that it would be crazy to base a food distribution system on oil? Or does it mean, if you are going to base a food distribution system on oil, you had better be pretty sure you can assure a nearly continuous flow. I think the rapid rebound means that everyone will be incented to make sure that the amount of solar radiation deflection is modulated with care. The fact that stopping SRM suddenly could bring big problems means that we would take great care not to stop suddenly. If we stopped generating electricity we would be in big trouble. If we stopped piping water we would be in big trouble. If we stopped hauling garbage we would be in big trouble. Etc, etc. Our response to these threats is not to say: no electricity, no water pipes, no garbage hauling, etc. Instead we say, let's assure continuity, as best we can, of electricity, water piping, garbage hauling, etc. ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA kcalde...@ciw.edu; kcalde...@stanford.edu http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968   On Sun, Sep 6, 2009 at 8:38 AM, John Nissen <j...@cloudworld.co.uk> wrote: At the launch of the Royal Society report, it was explained that a disadvantage of SRM was if you suddenly stopped it, because the temperature would rebound due to all the CO2 that had accrued in the meantime, with its suppressed warming effect.  This "termination effect" is expressed as a "high risk", see table 3.6 [1]  with footnote [2]. It so happens I have just looked through Tom Wigley's file on the geoengineering googlegroup: http://groups.google.com/group/geoengineering/files In this presentation he restricts geoengineering to the SRM type.  I found in his slide entitled "Global-mean temperature and sea level consequences", about 2/3 way through the presentation, a comment in yellow: "Rapid warming if geoengineering turned off - but no more rapid than A1B."  The implication of this is that the rate of temperature increase returns to the rate if there had been no SRM.  There is no rebound of temperature.  Merely the rate of temperature increase rises to the rate that you'd expect from the level of net forcing from CO2 in the atmosphere, etc. Thus I believe that this idea of rebound is a complete myth, and needs to be publicly refuted. Now, one of the dangers of SRM is that a Pinatubo-like volcanic event might occur during SRM deployment, in which case you'd want to turn off the SRM within a year, to avoid any risk of over-rapid cooling.  The ability to rapidly turn off SRM with stratospheric aerosols or cloud brightening, seems to me to be a very important advantage of these two techniques, which has not been highlighted in the report. So the very fact that you can turn off SRM improves its safety, rather than reduces it!  Yet, in the report, this very fact causes SRM engineering with stratospheric aerosols to get a low safety rating!!!  Cheers from Chiswick, John [1] Page 35 of report, table 3.6. [2] Ibid, footnote: (h) ‘Termination effect’ refers here to the consequences of a sudden halt or failure of the geoengineering system. For SRM approaches, which aim to offset increases in greenhouse gases by reductions in absorbed solar radiation, failure could lead to a relatively rapid warming which would be more difficult to adapt to than the climate change that would have occurred in the absence of geoengineering. SRM methods that produce the largest negative forcings, and which rely on advanced technology, are considered higher risks in this respect. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---