Influence of the choice of insolation forcing on the results of a conceptual glacial cycle model

Abstract

Over the Quaternary, ice volume variations are “paced” by astronomy. However, the precise way in which the astronomical parameters influence the glacial–interglacial cycles is not clear. The origin of the 100 kyr cycles over the last 1 million years and of the switch from 40 to 100 kyr cycles over the Mid-Pleistocene Transition (MPT) remain largely unexplained. By representing the climate system as oscillating between two states, glaciation and deglaciation, switching once glaciation and deglaciation thresholds are crossed, the main features of the ice volume record can be reproduced (Parrenin and Paillard, 2012). However, previous studies have only focused on the use of a single summer insolation as input. Here, we use a simple conceptual model to test and discuss the influence of the use of different summer insolation forcings, having different contributions from precession and obliquity, on the model results. We show that some features are robust. Specifically, to be able to reproduce the frequency shift over the MPT, while having all other model parameters fixed, the deglaciation threshold needs to increase over time, independently of the summer insolation used as input. The quality of the model–data agreement however depends on the chosen type of summer insolation and time period considered.