cc: "Sophia (GA) Oliver" , "Johnson, Cathy (GA)" , "Warren, Rachel (GA)" , Keith Briffa date: Mon, 18 Oct 2004 15:35:01 +0100 from: "Tett, Simon" subject: RE: 'Global Warming Bombshell' to: "Warrilow, David (GA)" Hi David, I would not go so far as to say that I think M&M got it right. Their argument seemed to be very technically narrow and focused on what appeared to be small issues. They could be right or wrong in their argument -- I am not sufficient of an expert in this area to comment in detail. I also can see why Nature did not publish their comment! I think there are issues in Mann et al's approach -- recall the Esper et al paper which produced a reconstruction with lots more low frequency variability than others. From the comment on the paper by Keith Briffa and Tim Osborn (attached) you can see that Mann's reconstruction had the least variability of any of the reconstructions. What Hans von Storch did was apply the Mann et al method and found a difference between reconstructed and simulated values in ECHO-G and HadCM3. So I agree that there is a problem with the Mann et al approach. What this means in terms of true low-frequency climate variability is hard to say! In answer to your specific questions. a) Did Mann et al get it wrong? Yes Mann et al got it wrong. How wrong is still under debate and the ECHO-G/HadCM3 results may be over-exaggerating the variance loss for some model-specific reasons. b) Are M&M right? M&M may be right. However I think it unlikely that the Medieval warm period is as warm as today. It doesn't end up being so in the German simulations (which go back that far). Their criticisms seem to be extremely technical. c) How unusual is the last 50 years? I think it still likely to be the warmest period on record (see b) BUT the rate of warming may not be highly unusual. I agree that one of the important claims in the TAR looks like not being correct. This result could be spun to cast doubt on worries about anthropogenic climate change as the evidence that the 20th century is unusual becomes less clear cut. One could also take the view that paleo-reconstruction uncertainty is so high that it is very hard to say much about pre-industrial conditions....I think that may be one way to focus the science -- i.e. rigorously quantify the uncertainties to see what that allows you to say. If they are very large there is not much you can say. I think the best way forward would be for Keith Briffa and Tim Osborn (both at UEA) to give you a briefing on this and related issues. Simon On Mon, 2004-10-18 at 11:28, Warrilow, David (GA) wrote: > Simon, > > Thanks. > > This tells me that there you think M&M are right in saying that > something is wrong with the Mann et al analysis. > > Now this is a critical point - the original Mann diagram (as shown in > IPCC) has been widely shown as evidence of man -made cc. M&M have I > recall tried to show that there have been as warm periods in the past > (mediaeval warm period etc). This would encourage the sceptics to say > - so what's new and maybe recent warming is largely natural. > Simplistic I know and we have other analysis to show that recent > warming is ghg related but it will be spun as undermining the thesis > that human's are changing the climate and thus the need for action. > > It is therefore important to know whether a) Mann et al got it wrong > and b) M&M are right. and c) how unusual is the last 50 years in the > longer term context. I suspect the truth is in between somewhere. > > David > > > -----Original Message----- > From: Tett, Simon [mailto:simon.tett@metoffice.gov.uk] > Sent: 16 October 2004 22:09 > To: Johnson, Cathy (GA); Warrilow, David (GA) > Subject: RE: 'Global Warming Bombshell' > > > Cathy/David, > I had a look at the web site and the M&M website. I am > unsure what you mean by a "clear line". > > Anyhow Storch et al found problems with the methodology of > Mann and co and demostrated this in two plausible climate > model simulations. One of which wasHadCM3. Generating > pseudo-proxies from the models and applying the method of Mann > et al clearly showed there is a problem with the methodology. > > The M&M document seems to be rather technical -- which is not > to say it is invalid. I can see why Nature did not publish it. > They tend to like simple clear messages and from what I can > tell the M&M document seems to consist of a lot of small > points. Collectively they may add up to a substantial > critique. I am surprised they have not tried to publish them > somewhere else -- they are several suitable journals. > > hope this helps -- if not give me a call. I am in Exeter on > Wednsday; Reading the rest of the time but busy Monday AM and > all day Tuesday. > > > Simon > -----Original Message----- > From: Johnson, Cathy (GA) > [mailto:Cathy.Johnson@defra.gsi.gov.uk] > Sent: 15 October 2004 15:53 > To: Tett, Simon > Cc: DL - GASci > Subject: FW: 'Global Warming Bombshell' > > > Simon > please may we have your views on this? (I note the > author cites von Storch et al). > Science Team colleagues - this seems to be a more > recent critique than we have seen before. > > thanks > CAthy > -----Original Message----- > From: Say, Nick (GA) > Sent: Friday, October 15, 2004 2:48 PM > To: DL - GASci > Subject: 'Global Warming Bombshell' > > > Dear All, > > Peter Simmonds has just called and asked that I > circulate an articled entitled 'Global Warming > Bomshell' > (http://www.technologyreview.com/articles/04/10/wo_muller101504.asp). > > While Peter said it was very recent, on reading it, it > seems to be about the McIntyre and McKitrick critique > of Mann et al, about which we have already answered a > number of TOs this year. > > Peter said, however, that he would like to know our > opinion of the controversy. > > Nick Say > > Global Atmosphere Division, > Department for Environment, Food and Rural Affairs, > Zone 3/A1, Ashdown House, 123 Victoria Street, > London SW1E 6DE > GTN: 3544 8144 > Tel.: (0207) 082 8144 > Fax: (0207) 082 8151 > Email: Nick.Say@defra.gsi.gov.uk > > > Department for Environment, Food and Rural Affairs > (Defra) > > This email and any attachments is intended for the > named recipient only. If you have received it in error > you have no authority to use, disclose, store or copy > any of its contents and you should destroy it and > inform the sender. Whilst this email and associated > attachments will have been checked for known viruses > whilst within Defra systems we can accept no > responsibility once it has left our systems. > Communications on Defra's computer systems may be > monitored and/or recorded to secure the effective > operation of the system and for other lawful purposes. -- Dr Simon Tett Managing Scientist, Data development and applications. Met Office Hadley Centre (Reading Unit) Meteorology Building, University of Reading Reading RG6 6BB Tel: +44 (0)118 378 5614 Fax +44 (0)118 378 5615 I work in Exeter roughly two days/week. Mobile: +44-(0)77 538 80696 E-mail: simon.tett@metoffice.gov.uk http://www.metoffice.gov.uk Attachment Converted: "c:\eudora\attach\briffa02.pdf"