Earth System Tipping Points and Instability in Past Oceans and Climates

About the Project

This PhD combines Earth system modelling and geologic records to investigate past climate instability: how the climate-ocean system responds to geologic disruption, like massive CO2 release or removal events. You’ll develop climate models and link these with data to understand how the ocean and climate have responded to disruptions – essential for understanding climate tipping points.

Understanding how the Earth system responds to disturbances (e.g., massive CO2 release) a central challenge in climate science. Although stabilising feedbacks can eventually regulate climate, the system is unlikely to exist in a perfectly steady state. Recent work suggests that past climates experienced pronounced instability (Hülse & Ridgwell, 2025), with transitions between quasi-stable states recorded in geochemical archives such as carbon-isotopes, expressed as δ13C excursions. Yet most intermediate-complexity Earth system models, including widely used ocean frameworks such as cGENIE (e.g., Pohl et al., 2022; Stockey et al., 2024), are typically configured to simulate only steady-state conditions. This limits our ability to investigate how climate instabilities arise, evolve, and interact with global biogeochemical cycles.

This PhD project will develop new modelling approaches to simulate unsteady ocean states operating on million-year timescales. The student will adapt and extend existing Earth system models to explore how disturbances propagate through the ocean–climate system. In parallel, they will analyse existing carbon-isotope excursion data and other geochemical indicators (e.g., Ce/Ce*, δ238U) to identify transient intervals of instability during key periods of the Neoproterozoic and Phanerozoic (i.e., spanning the past billion years). Achieving these aims will require generating new steady-state simulations of Neoproterozoic and Phanerozoic oceans at higher temporal resolution than is currently available.

Working alongside researchers who are separately generating new high-resolution carbon-isotope records, and potentially contributing to fieldwork/analysis, the student will compare model predictions with geological records of these events to assess how ocean-climate sensitivity and susceptibility to instability have varied through time. The project will provide new insight into how climate tipping behaviour emerges in the Earth system.