cc: c.goodess@uea.ac.uk,k.briffa@uea.ac.uk,t.osborn@uea.ac.uk
date: Thu, 25 Sep 2003 14:13:58 +0100
from: Phil Jones <p.jones@uea.ac.uk>
subject: Fwd: Re: new scientist
to: m.hulme@uea.ac.uk,h.j.schellnhuber@uea.ac.uk

    Dear All,
        The issue has moved on a little. The editor of NS will not accept another piece, only
    a letter, which Stefan Rahmstorf has drafted. I've not had a chance to look at it, but if
   anyone
    wants to join Stefan can they get in touch with him directly.
        I am going to sit this one out.  I am a little alarmed by Mike Mann at times, but his
    comments are only ever in this friendly email context.
    Cheers
    Phil

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     Date: Thu, 25 Sep 2003 08:25:28 -0400
     To: Stefan Rahmstorf <rahmstorf@pik-potsdam.de>
     From: "Michael E. Mann" <mann@virginia.edu>
     Subject: Re: new scientist
     Cc: Gavin Schmidt <gavin@isis.giss.nasa.gov>, cindy@stopesso.com,
             Andr Berger <berger@astr.ucl.ac.be>,
             Phil Jones <p.jones@uea.ac.uk>, Maraun <maraun@agnld.uni-potsdam.de>,
             mann@virginia.edu
     Stefan,
     It looks great to me, I wouldn't change anything except perhaps, the final clause of
     sentence #1:
     which received a disproportionate amount of media coverage due to the unfounded claims
     the authors made in their press releases ("Only about a third of the warming over the
     past century should be attributed to man").
     to
     which received a disproportionate amount of media coverage due to the unfounded claims
     the authors made in their press releases that "Only about a third of the warming over
     the past century should be attributed to man".
     Your point about the problems in using a regression of empirical estimates of response
     against forcing is an important one. The main problem here is that the authors supposed
     "global temperature" estimate is nothing of the sort. I actually did some research into
     this issue and here are my comments:
     Veizer's estimates are almost certainly not representative of the quantity claimed by
     Veizer (i.e., tropical mean sea surface temperature). Going back to Veizer's original
     (1999) "Chemical Geology" paper describing the data, I found some troubling issues in
     the description of the data. The data were collected from a highly irregular and
     inhomogenous spatial network of locations over the  modern continents. The authors
     argue, based on paleogeographic reconstructions, that "most of the data come from the
     tropics". That is a disturbingly poor basis on which to define a composite of the data
     as  a supposed estimate of tropical mean SST! No account seems to have been taken for
     whether or not a simple mean over the available sites is likely to represent a
     representative areal average of the tropical oceans (it can easily be shown that a
     similar random sampling of site-based SST measurements from the modern instrumental data
     base will generally give a substantially biased estimate of the true tropical mean SST
     variations). Climate scientists take great pains to insure that they average a set of
     site measurements in such as way that a meaningful areal (e.g. tropical, Northern
     Hemisphere, or global) average can be computed. A tropical SST estimate based mostly on
     tropical Pacific instrumental data, for example, would overly emphasize SST variations
     related to ENSO, and give a biased picture of  global tropical SST. There is no evidence
     in anything I've read in Veizer' papers, that care was taken to insure a meaningful
     spatial mean estimate of tropical SST. Equally problematic is the changing distribution
     of sites and data sources over time, which may considerably bias the record. Veizer
     himself (2000) notes, in fact, that the Neogene estimates may be overly dominated by
     data from the North Pacific. These are all possible reasons for why the Veizer estimates
     may not be reliable estimates of the quantity (tropical mean SST) claimed. This may
     contribute to why they do not show good agreement with other (e.g. glacial) evidence
     (i.e., Figure 2A vs Figure 2C) even after correcting for the Ph effects, and thus cannot
     be used to infer (as in Shaviv and Veizer) an estimate of the sensitivity of the global
     climate to co2.
     In fact any estimate of sensitivity from a regression analysis will in general
     underestimate the sensitivity (unless the forcing and response are self-consistently
     estimated, as in a forced model simulation). This has to do with the fact that the
     uncertainties in the forcing and response are independent, and while the uncertainties
     in the numerator of the expression used to derive the sensitivity from the data
     covariances cancel, the uncertainty in the forcing series artificially increases the
     estimated variance in the forcing series, which increases the dominator. I discussed
     this issue at some length in this paper:
     Waple, A., Mann, M.E., Bradley, R.S., [1]Long-term Patterns of Solar Irradiance Forcing
     in Model Experiments and Proxy-based Surface Temperature Reconstructions, Climate
     Dynamics, 18, 563-578, 2002.
     available here: [2]ftp://holocene.evsc.virginia.edu/pub/mann/WMB2002.pdf
     cheers,
     mike
     At 01:37 PM 9/25/2003 +0200, Stefan Rahmstorf wrote:

     Hi everyone,
     I'm thinking of sending the following letter to New Scientist. Please check critically
     what I say to make sure it stands up under fire. Your comments will be most welcome.
     Stefan
     ---
     Stott claims that the paper by Shaviv & Veizer is important science that did not get
     enough attention from media and policy makers. The opposite is true: it is a paper of
     little scientific credibility, which received a disproportionate amount of media
     coverage due to the unfounded claims the authors made in their press releases (Only
     about a third of the warming over the past century should be attributed to man).
     Shaviv and Veizer claim to have found a correlation between cosmic ray flux and
     temperature. Even if we accept their (questionable) data, it should be noted that this
     correlation was constructed by arbitrarily stretching the time scale to shift the maxima
     of cosmic ray flux by up to 20 million years, to make them coincide with temperature
     minima. The unadulterated data show no significant correlation (we checked this).
     Shaviv and Veizer then proceed to estimate the climate sensitivity to a doubling of CO_2
     concentration through regression analysis, which for a number of reasons is not
     possible. If it were, far better data could be used for this analysis: the Antarctic ice
     core data, which are more accurate, show variations on more relevant time scales (not
     tens of millions of years) and closer to present CO_2 levels, and apply to the
     present-day configuration of continents. This would yield a climate sensitivity
     exceeding 10C, but no climatologist has suggested this is a viable method.
     Climatologists agree that doubling CO_2 concentration would heat global climate by
     ~2-4C, not because this is a hegemonic myth but simply because this conclusion is based
     on sound science: the known radiative properties of CO_2 and an understanding of the key
     physical feedbacks in the climate system.
     --
     Stefan Rahmstorf
     Potsdam Institute for Climate Impact Research (PIK)
     For contact details, reprints, movies & general infos see:
     [3]http://www.pik-potsdam.de/~stefan

     ______________________________________________________________
                         Professor Michael E. Mann
                Department of Environmental Sciences, Clark Hall
                           University of Virginia
                          Charlottesville, VA 22903
     _______________________________________________________________________
     e-mail: mann@virginia.edu   Phone: (434) 924-7770   FAX: (434) 982-2137
              [4]http://www.evsc.virginia.edu/faculty/people/mann.shtml

   Prof. Phil Jones
   Climatic Research Unit        Telephone +44 (0) 1603 592090
   School of Environmental Sciences    Fax +44 (0) 1603 507784
   University of East Anglia
   Norwich                          Email    p.jones@uea.ac.uk
   NR4 7TJ
   UK
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