A punctuated equilibrium analysis of the climate evolution of cenozoic exhibits a hierarchy of abrupt transitions

Alternative climatic steady states near the Permian-Triassic Boundary

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, depending on these conditions, feedback mechanisms in the climate system compete and balance differently. This opens up the possibility to obtain multiple steady states in numerical experiments. Here, we use the MIT general circulation model 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 CO2 content is varied. We find three alternative steady states with a difference in global mean surface air temperature of about 10 °C. We also examine how these climatic steady states are modified when feedbacks operating on comparable or longer time scales are included, namely 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.

A reliable benchmark of the last 640,000 years millennial climate variability

How often have past climates undergone abrupt transitions? While our understanding of millennial variability during the past 130,000 years is well established, with precise dates available, such information on previous climate cycles is limited. To address this question, we identified 196 abrupt transitions in the δ18O record of the well-dated Chinese composite speleothem for the last 640,000 years. These results correspond to abrupt changes in the strength of the East Asian Monsoon, which align with the Greenland stadials and interstadials observed in the North Atlantic region during the last 130,000 years before present. These precise dates of past abrupt climate changes constitute a reliable and necessary benchmark for Earth System models used to study future climate scenarios.