From: Jonathan Overpeck <jto@u.arizona.edu>
To: Keith Briffa <k.briffa@uea.ac.uk>
Subject: Re: response to your question
Date: Tue, 1 Aug 2006 22:05:40 -0600
Cc: "Susan Solomon" <Susan.Solomon@noaa.gov>, Eystein Jansen <eystein.jansen@geo.uib.no>

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Hi Keith - thanks. This makes sense to me. I'll 
cc Susan so she understands the issue better, and 
also can advise on any strategy we should adopt 
to make sure we communicate effectively.

thanks again

best, peck

>Peck,
>
>The TAR was, in my opinion, wrong to say 
>anything about the precedence (or lack thereof) 
>of the warmth of the individual year 1998.
>
>The reason is that all reconstructions have very 
>wide uncertainty ranges bracketing 
>individual-year estimates of part temperature. 
>Given this, it is hard to dismiss the 
>possibility that individual years in the past 
>did exceed the measured 1998 value. These errors 
>on the individual years are so wide as to make 
>any comparison with the 1998 measured value very 
>problematic, especially when you consider that 
>most reconstructions do not include it in their 
>calibration range (curtailed predictor network 
>in recent times) and the usual estimates of 
>uncertainty calculated from calibration (or 
>verification) residual variances would not 
>provide a good estimate of the likely error 
>associated with it even if data did exist.
>
>I suspect that many/most reconstructions of NH 
>annual mean temperature have greater fidelity at 
>decadal to multidecadal timescales (based on 
>examination of the covariance spectrum of the 
>actual and estimated data over the calibration 
>period. This is the reason many studies 
>implicitly (Hegerl et al.,) or explicitly (Esper 
>et a;., Cook et al.) choose to calibrate 
>directly against decadally-smoothed data.
>
>The exception is the Briffa et al (tree-ring 
>density network based) reconstruction back to ~ 
>1400. This has probably the best year-to-year 
>fidelity – but for summer land only and does not 
>go back anyway to the MWP.
>
>We are on much safer grounds focusing on 
>decadal/multi-decadal timescales and so this is 
>where we place the emphasis. As for the ‘warmest 
>decade’ – this is likely to be the 1990s or the 
>last 10 years – but again, the proxies do not 
>cover this period, and we do anyway state that 
>post 1980 is the warmest period – which I think 
>is fair enough.
>
>
>--
>Professor Keith Briffa,
>Climatic Research Unit
>University of East Anglia
>Norwich, NR4 7TJ, U.K.
>
>Phone: +44-1603-593909
>Fax: +44-1603-507784
>
>http://www.cru.uea.ac.uk/cru/people/briffa/


-- 
Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences

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