Advanced analysis methods applied to reconstructed and simulated paleoclimatic time series

Abstract

The results of a simulated CO₂ (C) and a global ice volume (V) time series, derived from a simple relaxation model of the glacial-interglacial cycles (García-Olivares and Herrero, 2013), have been analyzed using linear and non-linear techniques to evaluate the ability of the model on simulating the dynamics embedded on the climate system. On a first approximation, we have compared simulated time series with the corresponding paleoclimatic reconstructions, obtaining correlations of 0.88 between proxy-record δ¹⁸O (Lisiecki and Raymo, 2005) and simulated V, and 0.79 between reconstructed atmospheric CO₂ concentration (Petit et al., 1999; Indermuhle et al., 2000; Monnin et al., 2001; Siegenthaler et al., 2005; Luthi et al., 2008) and simulated C. Spectral analysis using Fourier transform and continuous wavelet transform are useful tools to quantify the performance of a model for reproducing the dynamics embedded in reconstructed time series. The analysis shows that the model reproduces closely the dynamics embedded in the ice volume time series, but the coherence between the simulated and reconstructed CO₂ is only sporadic, indicating that both time series do not follow the same dynamical behaviour, although in the deglacial periods the two carbon series become dynamically close. The analysis reinforces the hypothesis that some specific mechanisms included in the model are able to closely reproduce the glacial-interglacial oscillations and thus suggests which specific mechanisms should be more seriously investigated in the climate system. These techniques may be applied to other climatic time series to quantify the performance of a model simulating the dynamics of the climate system.