Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 2 5 2006 10.5194/cpd-2-879-2006 http://www.clim-past-discuss.net/2/879/2006/ http://www.clim-past-discuss.net/2/879/2006/cpd-2-879-2006.html http://www.clim-past-discuss.net/2/879/2006/cpd-2-879-2006.pdf 879 921 2006-09-26 Numerical reconstructions of the Northern Hemisphere ice sheets through the last glacial-interglacial cycle S. Charbit C. Ritz G. Philippon V. Peyaud M. Kageyama LSCE/IPSL, CEA-CNRS-UVSQ, UMR 1572, CE Saclay, Orme des Merisiers, Bat. 701, 91191 Gif-sur-Yvette cedex, France LGGE, CNRS, 54, rue Molière-BP96, 38402 Saint Martin d’Hères cedex, France A 3-dimensional thermo-mechanical ice-sheet model is used to simulate the evolution of the Northern hemisphere ice sheets through the last glacial-interglacial cycle. The ice-sheet model is forced by the results from six different atmospheric general circulation models (AGCMs). Two climate snapshots simulations performed for the last glacial maximum (LGM) and for the present-day periods are interpolated through time using a glacial index calibrated against the GRIP δ¹⁸O record to reconstruct the climate evolution over the period under study. Since it is driven by the timing of the GRIP signal, the temporal evolution of the ice volume and the ice-covered area is approximately the same from one simulation to the other. However, both ice volume curves and spatial distributions of the ice sheets present some major differences from one AGCM to the other. The origin of these differences, which are most visible in the maximum amplitude of the ice volume, is analyzed in terms of differences in climate forcing. The analysis of the results allows an evaluation of the ability of GCMs to simulate climates consistent with the reconstructions of past ice sheets to be evaluated. Although some models properly reproduce the advance or retreat of ice sheets in some specific areas, none of them is able to reproduce both North American or Eurasian ice complexes in full agreement with observed sea-level variations and geological data. These deviations can be attributed to shortcomings in the climate forcing and in the LGM ice-sheet reconstruction used as a boundary condition for GCM runs, but also to missing processes in the ice-sheet model itself.