Transient simulation of the last glacial inception. Part I: glacial inception as a bifurcation in the climate system |
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Authors: | Reinhard Calov Andrey Ganopolski Martin Claussen Vladimir Petoukhov Ralf Greve |
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Institution: | (1) Potsdam Institute for Climate Impact Research, P.O. Box 601203, 14412 Potsdam, Germany;(2) Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku Sapporo, 060-0819, Japan;(3) Department of Mechanics, Darmstadt University of Technology, Darmstadt, Germany |
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Abstract: | We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which
encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional
polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky
BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO2 forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly
over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at
a rate which corresponds to a change in sea level of 10 m per millennium. We have shown that the simulated glacial inception
represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo
feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold
value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that
for the present-day orbital parameters at least two different equilibrium states of the climate system exist—the glacial and
the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium
state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model.
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