Article

Climate Dynamics

, Volume 39, Issue 12, pp 2847-2866

The role of forcing and internal dynamics in explaining the “Medieval Climate Anomaly”

  • Hugues GoosseAffiliated withEarth and Life Institute, Georges Lemaître Centre for Earth and Climate Research, Université Catholique de Louvain Email author 
  • , Elisabeth CrespinAffiliated withEarth and Life Institute, Georges Lemaître Centre for Earth and Climate Research, Université Catholique de Louvain
  • , Svetlana DubinkinaAffiliated withEarth and Life Institute, Georges Lemaître Centre for Earth and Climate Research, Université Catholique de Louvain
  • , Marie-France LoutreAffiliated withEarth and Life Institute, Georges Lemaître Centre for Earth and Climate Research, Université Catholique de Louvain
  • , Michael E. MannAffiliated withDepartment of Meteorology and Earth and Environmental Systems Institute, Pennsylvania State University
  • , Hans RenssenAffiliated withSection Climate Change and Landscape Dynamics, Department of Earth Sciences, Vrije Universiteit Amsterdam
  • , Yoann Sallaz-DamazAffiliated withEarth and Life Institute, Georges Lemaître Centre for Earth and Climate Research, Université Catholique de Louvain
  • , Drew ShindellAffiliated withNASA Goddard Institute for Space Studies

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Abstract

Proxy reconstructions suggest that peak global temperature during the past warm interval known as the Medieval Climate Anomaly (MCA, roughly 950–1250 AD) has been exceeded only during the most recent decades. To better understand the origin of this warm period, we use model simulations constrained by data assimilation establishing the spatial pattern of temperature changes that is most consistent with forcing estimates, model physics and the empirical information contained in paleoclimate proxy records. These numerical experiments demonstrate that the reconstructed spatial temperature pattern of the MCA can be explained by a simple thermodynamical response of the climate system to relatively weak changes in radiative forcing combined with a modification of the atmospheric circulation, displaying some similarities with the positive phase of the so-called Arctic Oscillation, and with northward shifts in the position of the Gulf Stream and Kuroshio currents. The mechanisms underlying the MCA are thus quite different from anthropogenic mechanisms responsible for modern global warming.

Keywords

Paleoclimate Last millennium Medieval Climate Anomaly Climate modelling Data assimilation Atmospheric and ocean dynamics Radiative forcing