date: Tue Nov 30 16:04:12 2004
from: Keith Briffa <k.briffa@uea.ac.uk>
subject: Re: Model stuff
to: Martin Todd <mtodd@geog.ucl.ac.uk>

   Martin
   have done minor edits to fix typos etc
   At 15:30 30/11/2004, you wrote:

     Here's the near final version of section 3
     (3) Comparison of proxy records to GCM model outputs
     3.1 Description of GCM model experiments
     We use output from two state-of-the-art  experiments using two (UK and German) coupled
     ocean-atmosphere GCMs in which best estimates of (i) natural forcings only
     (ii) natural plus anthropogenic radiative forcings are applied over the
     past 500 (UK) to 1000 (German) years. By using results from two GCMs we will be able to
     quantify some of the uncertainty in past climate simulations associated with
     model climate sensitivity. The GCMs are HadCM3 (Gordon et
     al, 2000, Pope et al, 2000) and ECHO-G (Zorita et al., 2003). Output from
     HadCM3, will be made available by the Hadley Centre. The first experiment
     (NAT500) simulating the period 1500 to 2000 is driven with natural
     forcings alone (changes in solar irradiance, volcanic aerosol and orbital
     parameters (mainly the date of perihelion). In this experiment land cover
     and greenhouse gases are set to pre-industrial conditons.  The second
     experiment (ALL250) over the period 1750-2000 includes all natural
     forcings plus additional anthropogenic forcings. These are the changes in well-mixed
     greenhouse gases , sulphate aerosols
     (both their direct effect on scattering solar radiation and their indirect
     effect on cloud albedo), changes in vegetation (mainly the replacement of
     forest with pasture) and changes in tropospheric and stratospheric ozone.
     Simon Tett  at the Hadley Centre  will provide data
     on near surface temperature and other diagnostics. The ECHO-G experiments
     are very similar except that there is no land use change , geographical structure to
     volcanic aerosol forcing and no specification of tropospheric aerosols.
     The 'natural forcings only' experiennt runs for 1000 years to the present.
     A very preliminary analysis  suggests that anthropogenic forcings have had
     a substantial effect on Arctic Siberian  climate during the 20th century.
     For the illustrative study region the ALL250 simulation indicates a
     warming of  about 0.750C since 1950 compared to the NAT500 simulation,

     Fig 2 NATURAL500 (solid) and ALL250 (dotted) simulations for 1500-2000 AD
     (Tett ref) for 60-115E and 65N to 75N
     3.2 Palaeo-data - model comparisons
     3.2.1 GCM evaluation

     Prior to proxy-model comparisons we will determine the extent to which the
     HadCM3 and ECHO-G GCMs accurately reproduce (a) the basic state of the
     regional climate (b) the timescales and structure of regional climate
     variability and the associated dynamics. We will undertake an equivalent
     analysis to that with observational data described in Section 1.4 using
     data from the GCM control and experimental runs and compare with results
     from the analysis of observations.
     3.2.2. Paleo data-model comparison
     We will test the veracity of the simulated model climate variability
     against proxy data by quantifying the coherence in regional climate
     variability estimates from HadCM3 and ECHO-G and multi-proxies at
     decadal-centennial timescales. We will compare the regional climate
     history in the GCMs and proxies in terms of (a) the magnitude of variance
     in (b) the relative variance at different timescales (c) the phase
     relationships and coherence of variability. This will employ a variety of
     timeseries approaches (including cross spectral analysis and wavelet
     analysis),correlation and  regression. We will utilise techniques for
     proxy-model comparison developed within the EU-funded SO&P projects
     (Simulations, Observations & Paloclimatic data: climate variability over
     the last 500 years) which account for the error in the GCM and proxy
     estimate. This will determine the statistical uniqueness of recent trends
     relative to past periods. We will also determine whether the spatial
     pattern  of lake response bwteen the sites is consistent with that
     recorded in the spatially more complete tree ring data and the GCM output.
     Using the timing of climate response to the natural and anthropogeic
     forcing history as simulated by the GCMs we will be able to attribute
     causes to variability observed in the proxy records. From our analysis we
     will determine whether the observed lake ecosystem response is more
     consistent with climate variability/change simulated by GCMs under natural
     or natural plus anthropogenic forcing.
     ****************************
     Martin Todd
     University Lecturer
     Department of Geography
     UCL (University College London)
     26 Bedford Way
     London WC1 8HR
     email m.todd@geog.ucl.ac.uk
     ********************************

   --
   Professor Keith Briffa,
   Climatic Research Unit
   University of East Anglia
   Norwich, NR4 7TJ, U.K.

   Phone: +44-1603-593909
   Fax: +44-1603-507784
   [1]http://www.cru.uea.ac.uk/cru/people/briffa/

