cc: Keith Briffa <k.briffa@uea.ac.uk>,p.jones@uea.ac.uk
date: Fri, 29 Jul 2005 15:17:35 +0100
from: Tim Osborn <t.osborn@uea.ac.uk>
subject: Re: Bristlecones!
to: "Tett, Simon" <simon.tett@metoffice.gov.uk>

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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

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