Alternative climatic steady states near the Permian-Triassic Boundary

TL;DR

This study uses a climate model to identify multiple stable climate states near the Permian-Triassic Boundary, revealing potential explanations for geological climate variations and discrepancies in previous simulations.

Contribution

It demonstrates the existence of multiple climate steady states in deep-time conditions and explores their stability and feedback mechanisms around the PTB.

Findings

Identified three alternative steady states with 10°C temperature difference.

Constructed a bifurcation diagram showing stability ranges and tipping points.

Showed how feedbacks like vegetation and carbon exchange modify these states.

Abstract

Due to spatial scarcity and uncertainties in sediment data, initial and boundary conditions in deep-time climate simulations are not well constrained. On the other hand, the climate is a nonlinear system with a multitude of feedback mechanisms that compete and balance differently depending on the initial and boundary conditions. This opens up the possibility to obtain multiple steady states under the same forcing in numerical experiments. Here, we use the MIT general circulation model with a coupled atmosphere-ocean-thermodynamic sea ice-land configuration to explore the existence of such alternative steady states around the Permian-Triassic Boundary (PTB). We construct the corresponding bifurcation diagram, taking into account processes on a timescale of thousands of years, in order to identify the stability range of the steady states and tipping points as the atmospheric CO$_2$ content is varied. We find three alternative steady states with a difference in global mean surface air temperature of about 10 $^\circ$C. We also examine how these climatic steady states are modified when feedbacks operating on comparable or longer time scales are included, in particular vegetation dynamics and air-sea carbon exchanges. Our findings on multistability provide a useful framework for explaining the climatic variations observed in the Early Triassic geological record, as well as some discrepancies between numerical simulations in the literature and geological data at PTB and its aftermath.