Monday, June 18, 2012

5284.txt

cc: david.roberts@metoffice.com, andy.jones@metoffice.com, jonathan.gregory@metoffice.com, jason.lowe@metoffice.com, richard.betts@metoffice.com, tcrowley@duke.edu, k.briffa@uea.ac.uk, t.osborn@uea.ac.uk, margaret.woodage@metoffice.com
date: Wed, 11 Jun 2003 13:45:09 +0100 (BST)
from: Simon Tett <simon.tettatXYZxyzoffice.com>
to: keith.williamsatXYZxyzoffice.com

Subject: Title and Abstract
BCC: simon.tettatXYZxyzoffice.com
--text follows this line--

Keith (CC co-authors) -- here is my seminar title, co-authors and
abstract.

Simon

------------------------------------------------------------

Simulating the Recent Holocene

Simon F. B Tett, Richard Betts, Keith Briffa (CRU, UEA),
Tom J. Crowley (Duke), Jonathan Gregory (Reading), Andy Jones,
Jason Lowe, Tim Osborn (CRU, UEA), David L. Roberts and
Margaret J. Woodage


A simulation of the last 500 years using natural forcings alone has
been carried out. The forcings considered are volcanic aerosol,
solar irraidance and orbital changes. Greenhouse gases and
land-surface values are set to "pre-industrial" values. On
multi-century timescales this simulation has a stable climate though
multi-decadal variability, driven by external forcing, is present.
If this is correct then the recent Holocene would have been stable
in the absence of anthropogenic influences. Maximum changes in
sea-level are about 2cm from 1820 to 1950. In the simulation
glaciers would have reached their maximum advance in the early 18\th
and mid-19\th centuries. No evidence of an orbital influence on
simulated climate is found.

The simulation agrees well with proxy reconstructions of temperature
though there is some evidence that the model may be over-sensitive.
Natural forcing enhances variability. In particular tropical
temperature decadal-variability is enhanced by a factor of two.
Large-scale precipitation is also enhanced but only on 50-year
time-scales is there a significant enhancement, relative to the
control simulation, of northern hemisphere land precipitation.

A second experiment from 1750 to 1999 using both anthropogenic and
natural forcings has just completed. The anthropogenic effects
considered are changes in sulphate aerosol, greenhouse gases, ozone
and land-surface changes. Preliminary results from this suggest an
anthropogenic effect as early as the late 19th century.


--
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.tettatXYZxyzoffice.com http://www.metoffice.com

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