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 to: keith.williams@metoffice.com Subject: Title and Abstract BCC: simon.tett@metoffice.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.tett@metoffice.com http://www.metoffice.com