Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 6 3 2010 10.5194/cpd-6-767-2010 http://www.clim-past-discuss.net/6/767/2010/ http://www.clim-past-discuss.net/6/767/2010/cpd-6-767-2010.html http://www.clim-past-discuss.net/6/767/2010/cpd-6-767-2010.pdf 767 800 2010-05-11 On misleading solar-climate relationship B. Legras legras@lmd.ens.fr O. Mestre E. Bard P. Yiou Laboratoire de Météorologie Dynamique, UMR 8539, IPSL, CNRS/ENS/UPMC/Ecole Polytechnique/ENPC, Paris, France Ecole Nationale de la Météorologie, Météo France, and Institut de Mathématiques de Toulouse, Toulouse, France CEREGE, UMR 6635, CNRS/Université Aix-Marseille/IRD/Collège de France, Aix-en-Provence, France Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212, IPSL, CEA/CNRS/UVSQ, Gif-sur-Yvette, France A key issue of climate change is to identify the forcings and their relative contributions. Solar-climate relationship is currently the matter of a fierce debate. We address here the need for high quality observations and adequate statistical approach. A recent work by Le Mouël et al. (2010) and its companion paper by Kossobokov et al. (2010) show spectacular correlations between solar activity and meteorological parameters. We question both the data and the method used in these works. We stress 1) that correlation with solar forcing alone is meaningless unless other forcings are properly accounted and that sunspot counting is a poor indicator of solar irradiance, 2) that long series of temperature require homogenization to remove historical artefacts that affect long term variability, 3) that incorrect application of statistical tests leads to interpret as significant a signal which arises from pure random fluctuations. As a consequence, we reject the results and the conclusions of Le Mouël et al. (2010) and Kossobokov et al. (2010). We believe that our contribution bears some general interest in removing confusion from the scientific debate. 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