From	Jonathan T. Overpeck	Date	Tue, 1 Aug 2006 22:05:40 -0600
To	Keith Briffa
CC	Susan Solomon, Eystein Jansen
Subject	Re: response to your question
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 Mail and Fedex Address: Institute for the Study of Planet Earth 715 N. Park Ave. 2nd Floor University of Arizona Tucson, AZ 85721 direct tel: +1 520 622-9065 fax: +1 520 792-8795 http://www.geo.arizona.edu/ http://www.ispe.arizona.edu/