New paper finds computer models are inconsistent with temperature reconstructions of the past millennium

A new paper published in Climate of the Past finds that computer model simulations of past climate are not consistent with reconstructed temperatures of past climate. Thus, either the model simulations are erroneous or the temperature reconstructions erroneous, or both.

Clim. Past, 9, 1089-1110, 2013
www.clim-past.net/9/1089/2013/
doi:10.5194/cp-9-1089-2013

Climate of the last millennium: ensemble consistency of simulations and reconstructions

O. Bothe^1,2,*, J. H. Jungclaus¹, D. Zanchettin¹, and E. Zorita<sup>3,4

1</sup>Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany
²University of Hamburg, KlimaCampus Hamburg, Hamburg, Germany
³Institute for Coastal Research, Helmholtz Centre Geesthacht, Geesthacht, Germany
⁴Bert Bolin Centre for Climate Research, University of Stockholm, Stockholm, Sweden
^*now at: Leibniz Institute for Atmospheric Physics at the University of Rostock, Kühlungsborn, Germany

Abstract. Are simulations and reconstructions of past climate and its variability consistent with each other? We assess the consistency of simulations and reconstructions for the climate of the last millennium under the paradigm of a statistically indistinguishable ensemble. In this type of analysis, the null hypothesis is that reconstructions and simulations are statistically indistinguishable and, therefore, are exchangeable with each other. Ensemble consistency is assessed for Northern Hemisphere mean temperature, Central European mean temperature and for global temperature fields. Reconstructions available for these regions serve as verification data for a set of simulations of the climate of the last millennium performed at the Max Planck Institute for Meteorology.

Consistency is generally limited to some sub-domains and some sub-periods. Only the ensemble simulated and reconstructed annual Central European mean temperatures for the second half of the last millennium demonstrates unambiguous consistency. Furthermore, we cannot exclude consistency of an ensemble of reconstructions of Northern Hemisphere temperature with the simulation ensemble mean.

If we treat simulations and reconstructions as equitable hypotheses about past climate variability, the found general lack of their consistency weakens our confidence in inferences about past climate evolutions on the considered spatial and temporal scales. That is, our available estimates of past climate evolutions are on an equal footing but, as shown here, inconsistent with each other.