Dansgaard-Oeschger events: tipping points in the climate system

TL;DR

This paper investigates the nature of Dansgaard-Oeschger events, suggesting they are transitions between two climate states influenced by external forcing and bifurcation dynamics, with weak early warning signals observed before abrupt changes.

Contribution

It reconstructs the climate system's attractor topology to assess bimodality and provides evidence supporting a bifurcation model driven by external forcing for these rapid climate events.

Findings

Dansgaard-Oeschger events show weak early warning signals.

Climate fluctuations are consistent with switches between two equilibrium states.

Transitions are influenced by external forcing and bifurcation points.

Abstract

Dansgaard-Oeschger events are a prominent mode of variability in the records of the last glacial cycle. Various prototype models have been proposed to explain these rapid climate fluctuations, and no agreement has emerged on which may be the more correct for describing the paleoclimatic signal. In this work, we assess the bimodality of the system reconstructing the topology of the multi--dimensional attractor over which the climate system evolves. We use high-resolution ice core isotope data to investigate the statistical properties of the climate fluctuations in the period before the onset of the abrupt change. We show that Dansgaard-Oeschger events have weak early warning signals if the ensemble of events is considered. We find that the statistics are consistent with the switches between two different climate equilibrium states in response to a changing external forcing (e.g. solar, ice sheets...), either forcing directly the transition or pacing it through stochastic resonance. These findings are most consistent with a model that associates Dansgaard-Oeschger with changing boundary conditions, and with the presence of a bifurcation point.