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date: Wed, 11 Jun 2003 13:45:09 +0100 (BST)
from: Simon Tett <simon.tettatXYZxyzoffice.com>
Subject: Title and Abstract
--text follows this line--
Keith (CC co-authors) -- here is my seminar title, co-authors and
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