Session: Glacial Climates (LGM, Last deglaciation, Ice sheet uncertainties, Glacial-interglacial cycles)
Author: Xu Zhang / firstname.lastname@example.org / Alfred Wegener Institute Helmholtz centre for Polar and Marine Research
Co-author: Gerrit Lohmann, Alfred Wegener Institute Helmholtz centre for Polar and Marine Research;
Various climate archives suggest that abrupt climate changes are an intrinsic characteristic over much of the last million years. Millennial-scale climate variability, known as Dansgaard-Oeschger events, has been linked to changes in the Atlantic Meridional overturning circulation (AMOC). However, whether the abrupt changes are related to the nonlinearity of climate system itself or to nonlinear forcing to a linear system remains elusive. To reproduce the abrupt transition between strong and weak circulation regimes, a common trigger mechanism in climate modelling studies is ad-hoc freshwater perturbations in the North Atlantic. This approach does not require a nonlinear climate system to trigger abrupt climate shifts because responses of ocean circulation can be just followed by the nonlinear forcing. Recently, Zhang et al (2014; 2017) find that changes in ice sheet height and atmospheric CO2 are capable of triggering abrupt circulation transitions associated with a regime of AMOC bi-stability. This indicates that climate system is intrinsic nonlinear and abrupt climate changes can be caused by gradual external forcing. Since this feature is only derived from one climate model (ECHAM5/MPIOM), it is of critical importance to evaluate its re-productivity in other climate models that are used to guide policy makers to make adaption strategy to future climate changes. Accordingly, we propose a series of simplified experiments that will provide a quantitative assessment of inter-model performances on abrupt glacial climate changes. This project will be promoted as a working subgroup within the PMIP4 framework.