Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 5 4 2009 10.5194/cpd-5-1803-2009 http://www.clim-past-discuss.net/5/1803/2009/ http://www.clim-past-discuss.net/5/1803/2009/cpd-5-1803-2009.html http://www.clim-past-discuss.net/5/1803/2009/cpd-5-1803-2009.pdf 1803 1818 2009-07-03 Limitations of red noise in analysing Dansgaard-Oeschger events H. Braun P. Ditlevsen J. Kurths M. Mudelsee Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark Heidelberg Academy of Sciences and Humanities, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany Institute of Physics, Humboldt University Berlin, Newtonstraße 15, 12489 Berlin, Germany Potsdam Institute for Climate Impact Research, P.O. Box 60 12 03, 14412 Potsdam, Germany Climate Risk Analysis, Schneiderberg 26, 30167 Hannover, Germany During the last glacial period, climate records from the North Atlantic region exhibit a pronounced spectral component corresponding to a period of about 1470 years, which has attracted much attention. This spectral peak is closely related to the recurrence pattern of Dansgaard-Oeschger (DO) events. A red noise random process was used to evaluate the statistical significance of this peak, with a reported significance of more than 99%. Here we use a simple two-state model of DO events, which itself was derived from a much more sophisticated ocean-atmosphere model of intermediate complexity, to numerically evaluate the spectral properties of random (i.e., solely noise-driven) events. This way we find that the power spectral density of random DO events differs fundamentally from a simple red noise random process. 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