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

[John Nissen]

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 -~----------~----~----~----~------~----~------~--~---