date: Thu Sep  4 13:30:31 2003
from: Keith Briffa <k.briffa@uea.ac.uk>
subject: Re: Abstract for AGU
to: Simon Tett <simon.tett@metoffice.com>

   Simon
   though time short , thought it worth making the following suggested changes. The main
   ambiguity  though is your meaning about the simulated variability being too large (see
   Italic remarks ) - do you mean high-frequency? This sentence is not clear. Below changes
   shown in bold.
   Keith and Tim
   At 11:25 AM 9/4/03 +0100, you wrote:

     Dear All,
         I have submitted an abstract(see below) on our simulation/analysis of
          the last 500 years to AGU session PP11. Phil Jones has been
          co-opted through his early instrumental data. You have up to 1400
          UTC to scream! Sorry -- I left things till late in the day.
     Simon
     ============================================================
     Simulating the Last Half-Millennium
     S. Tett (1), R. Betts (2), D. Roberts(2), M. Woodage
     (2), A. Jones (2), T. Crowley (3), K. Briffa (4), T. Osborn (4), J. Gregory (5),
     J. Lowe (1) and P. Jones (3).
     (1) Hadley Centre -- Reading, Meteorology Building  University of
         Reading,  Reading  Berkshire  RG6 6BB  UK
     (2) Hadley Centre, Met Office, FitzRoy Road, Exeter, EX1 3PB, UK
     (3) Dept. of Earth and Ocean Sciences, Nicholas School of the
         Environment and Earth Sciences, Duke University, NC, USA
     (4) Climatic Research Unit, School of Environmental Sciences,
         University of East Anglia, Norwich  NR4 7TJ UK
     (5) CGAM, Department of Meteorology, University of Reading, PO Box
         243, Reading RG6 6BB UK
     To test simulated AOGCM variability and change against proxy
     reconstructions we have simulated the last half-millennium using the
     HadCM3 model forced with natural and anthropogenic forcings. The
     natural forcings used were changes in orbital parameters, volcanic
     aerosols , and solar irradiance. One simulation (NATURAL), was run from A.D.1500 using
     only natural forcing factors and with land-surface characteristics set
     to A.D.1750 values and well-mixed greenhouse gases set to pre-industrial
     concentrations. A second simulation (ALL), uses a combination of both
     anthropogenic and natural forcings starting in 1750 . In ALL, sulphate aerosols,
     greenhouse gases, ozone and land
     surface characteristics also change through time.
     The natural simulation shows general agreement with the paleo-reconstructions until the
     mid- to
     late-19th century. However, the (is something missing here?)simulated response appears
     to be too
     large while simulated decadal variability is significantly smaller
     than that reconstructed. In the simulations there is an anthropogenic
     impact on climate by the mid to late 19th century. Comparison with
     early European instrumental data appears to  confirm qualitatively the
     simulated anthropogenic (do you mean sulphate aerosol and what time?) cooling during the
     19th century.
     After correcting for long-term drift (I would not put this previous phrase in here as
     the sea level response is not dependent on this correction) The simulated sea-level
     falls
     rapidly after large volcanic eruptions (such as Tambora), then recovers
     over several decades to pre-eruption levels. A simple diagnostic
     model shows maximum glacier advance occuring during the Maunder minimum and the
     mid-19th century.  Twentieth century sea-level rise, which is dominated by
     anthropogenic forcings, is mainly due to ocean thermal expansion with a moderate
     contribution from glacier melting.
     --
     Dr Simon Tett  Managing Scientist, Data development and applications.
     Met Office   Hadley Centre  Climate Prediction and Research
     London Road   Bracknell    Berkshire   RG12 2SY   United Kingdom
     Tel: +44 (0)1344 856886   Fax: +44 (0)1344 854898
     E-mail: simon.tett@metoffice.com   [1]http://www.metoffice.com

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

   Phone: +44-1603-593909
   Fax: +44-1603-507784
   [2]http://www.cru.uea.ac.uk/cru/people/briffa[3]/

