Articles | Volume 9, issue 1
Clim. Past, 9, 393–421, 2013

Special issue: Progress in paleoclimate modelling

Clim. Past, 9, 393–421, 2013

Research article 14 Feb 2013

Research article | 14 Feb 2013

Large-scale temperature response to external forcing in simulations and reconstructions of the last millennium

L. Fernández-Donado1, J. F. González-Rouco1, C. C. Raible2,3, C. M. Ammann4, D. Barriopedro1,5, E. García-Bustamante6, J. H. Jungclaus7, S. J. Lorenz7, J. Luterbacher6, S. J. Phipps8, J. Servonnat9, D. Swingedouw9, S. F. B. Tett10, S. Wagner11, P. Yiou9, and E. Zorita11 L. Fernández-Donado et al.
  • 1Dpto. Física de la Tierra, Astronomía y Astrofísica II, Instituto de Geociencias (CSIC-UCM), Universidad Complutense de Madrid, Spain
  • 2Climate and Environmental Physics, University of Bern, Switzerland
  • 3Oeschger Center for Climate Change Research, University of Bern, Switzerland
  • 4National Center of Atmospheric Research, Climate and Global Dynamic Division, Boulder, USA
  • 5Instituto Dom Luiz, Universidade de Lisboa, Lisbon, Portugal
  • 6Department of Geography, Justus Liebig University of Giessen, Germany
  • 7Max- Planck- Institute for Meteorology, Hamburg, Germany
  • 8Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, Australia
  • 9Laboratoire des Sciences du Climat et de l'Environnement,CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 10School of GeoSciences, University of Edinburgh, UK
  • 11Helmholtz-Zentrum Geesthacht, Germany

Abstract. Understanding natural climate variability and its driving factors is crucial to assessing future climate change. Therefore, comparing proxy-based climate reconstructions with forcing factors as well as comparing these with paleoclimate model simulations is key to gaining insights into the relative roles of internal versus forced variability. A review of the state of modelling of the climate of the last millennium prior to the CMIP5–PMIP3 (Coupled Model Intercomparison Project Phase 5–Paleoclimate Modelling Intercomparison Project Phase 3) coordinated effort is presented and compared to the available temperature reconstructions. Simulations and reconstructions broadly agree on reproducing the major temperature changes and suggest an overall linear response to external forcing on multidecadal or longer timescales. Internal variability is found to have an important influence at hemispheric and global scales. The spatial distribution of simulated temperature changes during the transition from the Medieval Climate Anomaly to the Little Ice Age disagrees with that found in the reconstructions. Thus, either internal variability is a possible major player in shaping temperature changes through the millennium or the model simulations have problems realistically representing the response pattern to external forcing. A last millennium transient climate response (LMTCR) is defined to provide a quantitative framework for analysing the consistency between simulated and reconstructed climate. Beyond an overall agreement between simulated and reconstructed LMTCR ranges, this analysis is able to single out specific discrepancies between some reconstructions and the ensemble of simulations. The disagreement is found in the cases where the reconstructions show reduced covariability with external forcings or when they present high rates of temperature change.