Ice-climate co-evolution during the last two glacial cycles: characterization and feedbacks via ensemble fully-coupled earth system modeling

Anthropogenic climate change, accelerating the melting glaciers and ice sheets resulting in future sea level rise, is a key concern for humanity. Over the past 700 thousand years, glacial-interglacial cycles have shaped Earth’s climate. These are marked by relatively large, at times rapid system changes. As such, the past offers an albeit fuzzy perspective on possible ice and climate system interactions and transitions. Constraints on ice-climate evolution beyond the Last Glacial Maximum, however, are sparse, and dating uncertainties increase with geologic time. Given the data limitations, the paleo community often looks to models to complement inferences from paleodata. Still, to date, no full glacial cycle simulations have been published with coupled ice and climate models of sufficient complexity to resolve synoptic scale atmospheric dynamics and ocean circulation. This thesis explores the phase space of model simulations of transient ice-climate co-evolution in response to radiative forcing during the last two glacial cycles. The novelty of our study lies in three key aspects. Firstly, we employ LCice, a fully coupled Earth system model of intermediate complexity, which incorporates all key ice-climate feedbacks. Secondly, we utilize ensemble simulations instead of a single model realization. This approach moves beyond attempting to recreate the past as closely as possible with always imperfect models. It instead offers an exploration of plausible physically-self consistent scenarios. Thirdly, our study includes transient simulations of the last two glacial cycles, encompassing both ice growth and retreat phases. This thesis documents the following contributions: 1) a detailed analysis of the potential phase space of the last two glacial inceptions, 2) a continuous record of climate fields derived from ensemble simulations across the last two glacial cycles, and 3) an analysis of the relative impact of the ice-climate feedbacks on ice evolution during the last glacial cycle.