Modeling Paleocene-Eocene Hyperthermals with the PlaSim-LSG Earth System Model of Intermediate Complexity

Hyperthermal events, such as the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) and Early Eocene Climatic Optimum (EECO, 52 million years ago), are of significant interest because they offer critical insights into how the Earth’s climate reacts to rapid increases in greenhouse gas concentrations. These events, marked by intense global warming and ocean acidification, improve our understanding of the long-term effects of sudden carbon releases and help assess the potential impacts of today's human-driven climate change.

In this study, we use a version of the Planet Simulator (PlaSim), an Earth Model of Intermediate Complexity (EMIC) improved with a 3D ocean model (Large-Scale Geostrophic ocean model, LSG), to simulate these hyperthermal periods. This modeling approach allows for detailed analyses of ocean-atmosphere interactions and their role in shaping global climate patterns under extreme GHG scenarios. The simulations include boundary conditions derived from Herold et al. (2014) and use an experimental approach similar to the DeepMIP protocol. We explore a range of atmospheric CO2 levels (from 1× to 16× pre-industrial concentrations) to evaluate the sensitivity of the climate system to these factors.

The focus is on understanding feedback mechanisms and climate dynamics under extreme greenhouse gas forcing, while also considering equilibrium climate sensitivity (ECS) and polar amplification, with attention to Antarctic warming and its implications for ice-free conditions during the late Paleocene–early Eocene. Current work involves testing and refining paleoclimate boundary conditions in the Planet Simulator, particularly adjusting paleogeography, vegetation parameters, and ocean circulation to match the climate conditions of that period. This study improves our understanding of past extreme greenhouse climates and evaluates the ability of modern Earth System Models (ESMs) to predict future climate changes.