Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 2 5 2006 10.5194/cpd-2-1001-2006 http://www.clim-past-discuss.net/2/1001/2006/ http://www.clim-past-discuss.net/2/1001/2006/cpd-2-1001-2006.html http://www.clim-past-discuss.net/2/1001/2006/cpd-2-1001-2006.pdf 1001 1049 2006-10-26 Millennial temperature reconstruction intercomparison and evaluation M. N. Juckes M. R. Allen K. R. Briffa J. Esper G. C. Hegerl A. Moberg T. J. Osborn S. L. Weber E. Zorita British Atmospheric Data Centre, Rutherford Appleton Laboratory, UK Atmospheric, Oceanic and Planetary Physics, University of Oxford, UK Climatic Research Unit, University of East Anglia, UK Swiss Federal Research Institute for Forest, Snow and Landscape, Bern University, Switzerland Dept. Earth and Ocean Sciences, Duke University, NC, USA Department of Meteorology, Stockholm University, Sweden Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands GKSS Research Centre, Geesthacht, Germany There has been considerable recent interest in paleoclimate reconstructions of the temperature history of the last millennium. A wide variety of techniques have been used. The interrelation between the techniques is sometimes unclear, as different studies often use distinct data sources as well as distinct methodologies. Recent work is reviewed with an aim to clarifying the import of the different approaches. A range of proxy data collections used by different authors are passed through two reconstruction algorithms: firstly, inverse regression and, secondly, compositing followed by variance matching. It is found that the first method tends to give large weighting to a small number of proxies and that the second approach is more robust to varying proxy input. A reconstruction using 18 proxy records extending back to AD 1000 shows a maximum pre-industrial temperature of 0.25 K (relative to the 1866 to 1970 mean). The standard error on this estimate, based on the residual in the calibration period is 0.149 K. Two recent years (1998 and 2005) have exceeded the estimated pre-industrial maximum by more than 4 standard errors.