Abstract
ABSTRACTThe evolution of Northern Hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one General Circulation Model, COSMOS. By comparing the simulated results to geological reconstructions, we first show that the modelled climate is capable of capturing the main features of the ice-sheet evolution. However, large deviations exist, likely due to the absence of nonlinear interactions between ice sheet and other climate components. The model uncertainties of the climate forcing are examined using the output from nine climate models from the Paleoclimate Modelling Intercomparison Project Phase III. The results show a large variability in simulated ice sheets between the different models. We find that the ice-sheet extent pattern resembles summer surface air temperature pattern at the Last Glacial Maximum, confirming the dominant role of surface ablation process for high-latitude Northern Hemisphere ice sheets. This study shows the importance of the upper boundary condition for ice-sheet modelling, and implies that careful constraints on climate output is essential for simulating realistic glacial Northern Hemisphere ice sheets.
Highlights
During the late Pleistocene (800–12 kyr BP), the Earth’s climate went through vast changes known as glacial-interglacial cycles, with a periodicity of ∼100 kyr, accompanied by the periodic advance and retreat of large Northern Hemisphere ice sheets
Comparing the summer (JJA) surface air temperature difference between the reanalysis products and the PMIP3 PI General Circulation Model (GCM) output, we find that the MIROC-ESM PI temperatures exhibit a large warm bias over the northern hemisphere continents (Fig. S9)
We simulated the Northern Hemisphere ice sheets through the last glacial cycle using the glacial index method based on the North Greenland Ice Core Project (NGRIP) ice core
Summary
During the late Pleistocene (800–12 kyr BP), the Earth’s climate went through vast changes known as glacial-interglacial cycles, with a periodicity of ∼100 kyr, accompanied by the periodic advance and retreat of large Northern Hemisphere ice sheets. Orbital forcing alone cannot explain the strong 100 kyr cycle of Northern Hemisphere ice sheets, which have larger amplitude, slower build up and faster retreat than the insolation signal. This indicates that internal climatic feedbacks acting as nonlinear amplifiers are of vital importance (Imbrie and others, 1993; Huybers and Wunsch, 2005; Lisiecki, 2010; Huybers, 2011; Abe-Ouchi and others, 2013). The freshwater flux from ice-sheet melt and ice-rafting from ice-sheet calving can modulate the strength of Atlantic Meridional Overturning Circulation (AMOC) and result in global scale climate shifts (Bond and Lotti, 1995; Ganopolski and Rahmstorf, 2001; Carlson and Clark, 2012)
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