A model for Dansgaard-Oeschger events and millennial-scale abrupt climate change without external forcing

TL;DR

This paper introduces a conceptual model demonstrating how millennial-scale abrupt climate changes, similar to Dansgaard-Oeschger events, can emerge internally without external triggers, through complex interactions of ocean, atmosphere, and sea-ice dynamics.

Contribution

It presents a novel self-consistent model combining ocean, atmosphere, and sea-ice interactions that reproduces key features of abrupt climate events without external forcing.

Findings

Model reproduces statistical features of ice-core data

Abrupt changes arise from internal intermittencies in sea-ice cover

Mechanism relies on emergent atmospheric noise and stochastic limits

Abstract

We propose a conceptual model which generates abrupt climate changes akin to Dansgaard-Oeschger events. In the model these abrupt climate changes are not triggered by external perturbations but rather emerge in a dynamic self-consistent model through complex interactions of the ocean, the atmosphere and an intermittent process. The abrupt climate changes are caused in our model by intermittencies in the sea-ice cover. The ocean is represented by a Stommel two-box model, the atmosphere by a Lorenz-84 model and the sea-ice cover by a deterministic approximation of correlated additive and multiplicative noise (CAM) process. The key dynamical ingredients of the model are given by stochastic limits of deterministic multi-scale systems and recent results in deterministic homogenisation theory. The deterministic model reproduces statistical features of actual ice-core data such as non-Gaussian $\alpha$-stable behaviour. The proposed mechanism for abrupt millenial-scale climate change only relies on the existence of a quantity, which exhibits intermittent dynamics on an intermediate time scale. We consider as a particular mechanism intermittent sea-ice cover where the intermittency is generated by emergent atmospheric noise. However, other mechanisms such as freshwater influxes may also be formulated within the proposed framework.