  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.
