Thermodynamic assessment of simulations of the last deglaciation with an Earth system model of intermediate complexity

As we observe and expect severe changes in the Earth’ climate, the analyses of past climate state transitions is of major value for improving our Earth system understanding. Under this objective, the last deglaciation (~ 21 ka to 9 ka before present), the transition from the Last Glacial Maximum (LGM) to the Holocene, is an ideal case study. During this transition, the orbital configuration gradually changed and greenhouse gases have risen, which caused a sharp decline in northern hemisphere ice sheets and an increase in the global mean surface temperature.

We create an ensemble of deglaciation simulations with a modified version of the Planet Simulator, an Earth system model of intermediate complexity (EMIC). We produce single and combined forcing simulations for further investigation from a thermodynamic perspective. The response to the transiently changing radiative forcing is investigated in terms of energy and entropy budgets of the atmosphere. Here, we focus on the deglacial evolution of the material entropy production (MEP). Its contributions represent the strength of major climate features such as the kinetic energy generation rate, vertical and horizontal heat transport and the hydrological cycle. Preliminary results show an increase of the global mean MEP from the LGM to the Holocene because of a strengthening of the hydrological contribution. In contrast, the relative importance of kinetic energy dissipation and turbulent heat diffusion in the boundary layer decrease. Our work can provide the basis for investigating the MEP as a diagnostic quantity with other models and for other climate state transitions.