The bifurcation structure and noise induced transitions in the Pleistocene glacial cycles

TL;DR

This paper presents an empirical nonlinear model of Pleistocene glacial cycles, highlighting the role of bifurcation structures and stochastic noise in transitions, especially during the Mid-Pleistocene transition.

Contribution

It introduces a bifurcation-based empirical model that explains the dynamical origin of the MPT and the interplay of noise and orbital forcing in glacial cycles.

Findings

Transitions are noise-assisted before the last five cycles.

The MPT involves a change in the climate system's bifurcation structure.

The model explains the shift from 41 kyr to 100 kyr cycles.

Abstract

The glacial cycles are attributed to the climatic response of the orbital changes in the irradiance to the Earth. These changes in the forcing are to small to explain the observed climate variations as simple linear responses. Non-linear amplifications are necessary to account for the glacial cycles. Here an empirical model of the non-linear response is presented. From the model it is possible to assess the role of stochastic noise in comparison to the deterministic orbital forcing of the ice ages. The model is based on the bifurcation structure derived from the climate history. It indicates the dynamical origin of the Mid-Pleistocene transition (MPT) from the '41 kyr world' to the '100 kyr world'. The dominant forcing in the latter is still the 41 kyr obliquity cycle, but the bifurcation structure of the climate system is changed. The model indicates that transitions between glacial and interglacial climate are assisted by internal stochastic noise in the period prior to the last five glacial cycles, while the last five cycles are deterministic responses to the orbital forcing.