  Are temperature reconstructions possibly biased due to regionally differing
density of utilized proxy-networks? This question is assessed utilizing a
simple process-based forward model of tree growth in the virtual reality of two
simulations of the climate of the last millennium with different amplitude of
solar forcing variations. The pseudo-tree ring series cluster in high latitudes
of the northern hemisphere and east Asia. Only weak biases are found for the
full network. However, for a strong solar forcing amplitude the high latitudes
indicate a warmer first half of the last millennium while mid-latitudes and
Asia were slightly colder than the extratropical hemispheric average.
Reconstruction skill is weak or non-existent for two simple reconstruction
schemes, and comparison of virtual reality target and reconstructions reveals
strong deficiencies. The temporal resolution of the proxies has an influence on
the reconstruction task and results are sensitive to the construction of the
proxy-network. Existing regional temperature biases can be attenuated or
accentuated by the skill of the reconstruction approach.
