Abstract & Overview
The ambiguity of temperature reconstructions is assessed using pseudo tree growth series in the virtual reality of two simulations of the climate of the last millennium. The simple, process-based Vaganov-Shashkin-Lite (VS-Lite) code calculates tree growth responses controlled by a limited number of climatic parameters. Growth limitation by different ambient climate conditions allows for possible nonlinearity and non-stationarity in the pseudo tree growth series. Statistical reconstructions of temperature are achieved from simulated tree growth for random selections of pseudo-proxy locations by simple local regression and composite plus scaling techniques to address additional ambiguities in paleoclimate reconstructions besides the known uncertainty and shortcomings of the reconstruction methods. A systematic empirical evaluation shows that the interrelations between simulated target and reconstructed temperatures undergo strong variations with possibly pronounced misrepresentations of temperatures. Thus (i) centennial scale inter-annual correlations can be very weak; (ii) the decadal range of reconstructed temperatures may be as large as the range of the temperature variations over the considered time-period; (iii) decadal variability is under-represented in the reconstructions. The misrepresentations are in part due to the temporally varying temperature-growth relations and to an apparent lack of decadal scale variability in the simulated pseudo-growth series compared to the local temperatures.