cc: Keith Briffa ,p.jones@uea.ac.uk date: Fri, 29 Jul 2005 15:17:35 +0100 from: Tim Osborn subject: Re: Bristlecones! to: "Tett, Simon" At 14:27 28/07/2005, Tett, Simon wrote: > John Houghton is being quized by bits of the US senate. One > question is >"Whats the status of the review of the Mann hockey stick temperature >curve? I understand that studies by Stephen McIntyre and Ross McKitrick >suggest that it relied on the statistically insignificant bristlecone >pine. Is the IPCC taking another look at that work, which forms the >basis for much of todays climate change debate?" > >My current thoughts on an answer is to say that other reconstructions >show a similar pattern (though not magnitude). However how many of the >other reconstructions use the bristlecone data? [I suspect yours does >not] Hi Simon - I was away yesterday, so couldn't answer then. Hopefully it isn't too late to answer today. (1) I don't understand what they mean by describing the bristlecone pine as "statistically insignificant". (2) The Mann, Bradley and Hughes (MBH1999) reconstruction is only one small piece of information in today's climate change debate. (3) As far as I understand, then yes the MBH1999 reconstruction does give quite a lot of weight to a few western US tree-ring series, which are mostly bristlecone pines for the longest records. (4) Other reconstructions show similar shape (though not magnitude) and support similar conclusions (regarding the unprecedented nature of recent warmth/warming trend). This is the main argument to make, as you thought. Some of these other reconstructions do not include these bristlecones (e.g. Briffa, 2000; Crowley et al., 2003; Moberg et al., 2005; Briffa et al., 2001). Crowely and Moberg use different Bristlecone records I think. Other reconstructions do use the same Bristlecone pines (e.g., Mann and Jones, 2004). BUT the critical thing is that the studies either do not use these Bristlecone pines, or if they do use them, then they give them much more similar weighting to the other records used. I think MBH1999 is the only one that might give them a dominant weighting. (5) IPCC is assessing all published work that relates to these issues in preparation for the AR4 in 2007. This includes the McIntyre and McKitrick papers as well as papers that report results contrary to McIntyre/McKitrick, such as the paper in press by Wahl and Amman that shows the Mann et al. results are reproducible. cc'd for additional comments to Phil and Keith (when he's back). Cheers Tim Dr Timothy J Osborn Climatic Research Unit School of Environmental Sciences, University of East Anglia Norwich NR4 7TJ, UK e-mail: t.osborn@uea.ac.uk phone: +44 1603 592089 fax: +44 1603 507784 web: http://www.cru.uea.ac.uk/~timo/ sunclock: http://www.cru.uea.ac.uk/~timo/sunclock.htm