Model sensitivity to North Atlantic freshwater forcing at 8.2 ka
1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
2National Oceanic and Atmospheric Administration's National Climatic Data Center, Boulder, CO, USA
3NASA Goddard Institute for Space Studies and Center for Climate Systems Research, New York, NY, USA
4Cluster Earth & Climate, Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam, The Netherlands
5Climate and Global Dynamics, National Center for Atmospheric Research, Boulder, CO, USA
Abstract. We compared four simulations of the 8.2 ka event to assess climate model sensitivity and skill in responding to North Atlantic freshwater perturbations. All of the simulations used the same freshwater forcing, 2.5 Sv for one year, applied to either the Hudson Bay or Labrador Sea. This freshwater pulse induced a decadal-mean slowdown of 10–25% in the Atlantic Meridional Overturning Circulation (AMOC) of the models and caused a large-scale pattern of climate anomalies that matched proxy evidence for cooling in the Northern Hemisphere and a southward shift of the Intertropical Convergence Zone. The multi-model ensemble generated temperature anomalies that were just half as large as those from quantitative proxy reconstructions, however. Also, the duration of AMOC and climate anomalies in three of the simulations was only several decades, significantly shorter than the duration of ~150 yr in the paleoclimate record. Possible reasons for these discrepancies include incorrect representation of the early Holocene climate and ocean state in the North Atlantic and uncertainties in the freshwater forcing estimates.