date: Tue, 5 Apr 2005 13:07:12 +0100 from: "Rob Wilson" subject: Re: Emailing: ECHO-G and solar weighting to: , "Tim Osborn" Hi Tim, thanks for the reply I was always under the impression that, in general, solar changes controlled long term changes in climate and volcanic events caused short term cooling. I am surprised when you say that volcanic forcing dominates the models - this seems at odds to papers by Lean and Rind etc. The 1257/59 volcanic event has an obvious effect in the model - yet the recovery is quick - i.e. no effect on the long term trend of the model output. I guess 'clusters' of volcanic events could cause a longer term response of the climate system. How are the relative weightings of the external forcing estimated in the models? Although I agree that GHGs are important in the 19th/20th century (especially since the 1970s), if the weighting of solar forcing was stronger in the models, surely this would diminish the significance of GHGs. Jeez - I sound like a sceptic - this is not my intension. I guess, ultimately, what troubles me is that of the myriad of NH recons out there now, they generally show a MWP that is NOT as warm as the late 20th century. I have no trouble with this - however, the solar activity of the MWP (excluding the Oort minimum) is also generally not as high as the recent period. I know correlation does not mean causation, but it seems to me that by weighting the solar irradiance more strongly in the models, then much of the 19th to mid 20th century warming can be explained from the sun alone. again, am I being overtly simplistic? Rob ----- Original Message ----- From: [1]Tim Osborn To: [2]Rob Wilson ; [3]K.briffa@uea.ac.uk Sent: Tuesday, April 05, 2005 12:01 PM Subject: Re: Emailing: ECHO-G and solar weighting Rob - I don't think either run is heavily influenced by the solar forcing. The apparent lack of agreement between the solar record and NATURAL is because the volcanic forcing dominates over the solar (for example, giving the cooling trend during the final 3 decades). The ALL run appears to fit better with the solar record, but the 1700-present greenhouse gas forcing is more than double the 1700-present solar forcing and hence the warming trend over that period in the model is driven mainly by GHGs. I think Irina Fast showed some solar-only runs for 1750-present in Reading and they didn't show temperature trends anywhere near so large as in the ALL run. Cheers, Tim At 11:06 05/04/2005, Rob Wilson wrote: >Dear Tim and Keith, >I was wondering if you could clarify the relative inputs of the ECHO-G >model for me. > >the attached figure compares the ALL and NATURAL ECHO-G outputs (annual >extra-tropical land temperatures) with the spliced Beryllium record from >the Crowley 2000 paper. > >I do not understand why the NATURAL run, which is weighted heavily towards >the solar input (if I understand the situation correctly), does not show >more of an increase since the early 1700s. > >The Beryllium record qualitatively compares well with the ALL forcing run. > >Perhaps I am missing something here, but from this comparison, it seems to >be that most of the long term variability in the ALL run can be explained >solely by the Beryllium record. > >I am not sure if this particular Be record was used for ECHO-G, but if we >believe the Be record (probably debatable!), then it seems to me that the >sun's activity can explain most of the NH temperature variability. CO2 and >other greenhouse gases would therefore have a weaker influence. > >I am sure I have simplified that the situation horribly, BUT have I missed >something? > >hope you can help >Rob Dr Timothy J Osborn Climatic Research Unit School of Environmental Sciences, University of East Anglia Norwich NR4 7TJ, UK e-mail: [4]t.osborn@uea.ac.uk phone: +44 1603 592089 fax: +44 1603 507784 web: [5]http://www.cru.uea.ac.uk/~timo/ sunclock: [6]http://www.cru.uea.ac.uk/~timo/sunclock.htm