E. V. Dmitriev and A. I. Chavro
Institute of Numerical Mathematics, Russian Academy of Sciences, ul. Gubkina 8, Moscow, 119991 Russia
e-mail: yegor@inm.ras.ru; chavro@inm.ras.ru
Received July 22, 2005; in final form, September 29, 2005
Abstract—The Northern Hemisphere mean surface temperature has shown a significant positive trend over the
past two centuries. On the basis of the well-known reconstructions of global climate from proxy data, the con-
clusion is made that the current warming has been unprecedented during at least the past two millennia. On the
other hand, it was demonstrated in [6] that the existing statistical models strongly underestimate the low-fre-
quency variability of global annual mean temperature, thus making the conclusion drawn above questionable.
At present, the results of [6] are interpreted as evidence that the Mann reconstruction is invalid [1]. To our
knowledge, however, it is too early to draw such conclusions. What is the cause of smoothing low-frequency
variability? To what extent are various statistical models used for paleoclimate reconstruction that is subject to
this effect? To answer these questions, numerical experiments are performed with data sets of annual mean sur-
face temperature over the past millennium that are simulated with the ECHO-G coupled ocean–atmosphere
general circulation model.
DOI: 10.1134/S0001433806050057
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