Multistability and hysteresis in the climate-cryosphere system under orbital forcing

Abstract

Using the Earth system model of intermediate complexity CLIMBER-2 we studied the stability diagram of the climate-cryosphere system in the phase space of Milankovitch forcing (maximum summer insolation at 65°N, abbreviated as MF). We have shown that the equilibrium response of the climate-cyrosphere system to MF reveals pronounced hysteresis behavior within the range of Earth's orbital parameters. Depending on MF, the climate-cryosphere system has either one (glacial or interglacial) or two different equilibrium states. The MF thresholds of the transitions between the two states depend on parameterizations of ice-sheet dynamics, but are rather insensitive to the choice of the orbital parameters used to obtain the same value of MF. A change of atmospheric CO2 concentration from its interglacial to the glacial value, shifts the hysteresis curve by about 15 W/m2. These results provide an important support to the conceptual models of glacial cycles based on multistability and hysteresis behavior. Copyright 2005 by the American Geophysical Union.