Thursday, December 29, 2011

1246458696.txt

From: Tim Osborn <t.osborn@uea.ac.uk>
To: Luterbacher J�rg <juerg.luterbacher@giub.unibe.ch>
Subject: Re: IPCC Fig. 6.10
Date: Wed Jul 1 10:31:36 2009

Hi Juerg,
At 21:56 16/06/2009, you wrote:

I hope you are very well. Douglas arrived savely here and hopefully he
will be starting officially soon. I am looking very much forward
having him here and of course working together with you on different
topics!

Yes, that sounds great to me too.

I have a chinese paleo climatology researcher (Zhinxin Hao) with me
for a couple of weeks.
She is working on the comparison with different chinese long
temperature reconstructions and would like to present a similar figure
as in the IPCC Fig 6.10.
Keith told me that he might not be able to work for the next time, so
I thought I could address this issue to you as you were also much
involved.

That's fine. Indeed I designed and drew the figure.

She asked me if I could ask you whether you could have a look at the
attachment where she tried to explain how she calculated and plotted
the curves for China. As she did not fully understand the way it was
done in the IPCC report, would you mind having a look at the text and
let me know if she applied it correctly?

It is a little hard to follow (some symbols got replaced by squares -- perhaps a PDF file
would work better than a Word Doc?) but I think that the method looks approximately right
but not quite right. Some things that look a bit different:
Se: it appears that the same value is used for all 4 reconstructions (in the example,
Se=1.3165 is used). Why would the uncertainty on one reconstruction be the same as the
uncertainty on all the others? Perhaps she has used the standard deviation of the
instrumental temperature rather than the standard error of each reconstruction? Did the
authors actually publish estimated uncertainties along with their best-estimate
reconstruction series? You should also note that reconstruction errors/uncertainties may
depend on time scale -- the IPCC fig 6.10 showed variations on timescales of 30-yrs and
longer, so I attempted to use uncertainties estimated for that timescale (or a similar
multi-decadal timescale).
IPCC wanted to mostly standardise on the 90% range (5%-95%), so for my scoring I awarded
100%/N to any temperature that falls within the +- 1 SE reconstruction range (the same as
noted in her document) but awarded 0.5*100%/N to any temperature that falls within +-
1.6448 SE reconstruction range (this differs from the +-2 SE in her document). I
originally used +- 2 SE, but (under assumption of normality), +- 1.6448 SE should encompass
5%-95% range, while +- 2 SE is of course approx 2.5%-97.5%. Either is of course equally
defendable, but if you want to reproduce IPCC, then its +- 1.6448 SE for the half score
(0.5*100%/N).
This is of course repeated for all N reconstructions.
I was a little unsure about the actual plot produced too. When the Xu2003 curve is very
low or very high, the brown shading extends in both directions (to very low *and* very high
values at once). e.g. AD 650 (but there are others too). Also the range is very narrow at
about AD 1050; although the 3 recons are quite similar here, it still looks too narrow,
especially when you add on the reconstruction SE (and +- 1.6448 SE or +- 2 SE).
Hope this helps,
Tim

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