Multi-millennial future warming scenarios with the comprehensive Earth system model AWIESM

Numerical model simulations are an essential tool for assessing effects of global warming on the climate system in future greenhouse gas concentration scenarios. Commonly, these simulations cover only the next few centuries or use low-complexity models for longer periods. However, to assess the dynamics of Earth system components with long response times like the ocean or ice sheets, multi-millennial simulations with comprehensive Earth system models are essential.
Here, we present multi-millennial simulations with the complex Earth System Model AWIESM, covering an integration time beyond the typical CMIP time scale. The model runs on a multi-resolution grid with a horizontal resolution of up to 20 km in high latitudes. The model includes an interactive ice sheet for the Greenland domain. The simulations are forced with transient greenhouse gas concentrations obtained from model simulations with the Earth System Model of intermediate complexity CLIMBER-X with an interactive carbon cycle, covering overshoot scenarios that enable assessment of long-term ice sheet and ocean dynamics.
Our results reveal a scenario-dependent weakening of the Atlantic Meridional Overturning Circulation (AMOC), followed by partial recovery over the next millennium. All scenarios show sea ice-free or nearly sea ice-free summer conditions in the northern and southern hemispheres. Winter sea ice shows an asymmetric response under future warming. While Arctic winter sea ice changes are small in low- to medium-emission scenarios, Southern Ocean winter sea ice shows a large reduction even in low-emission scenarios. The Greenland ice sheet shows a continuing ice mass loss during the next millennium, even with decreasing greenhouse gas concentrations in medium-emission scenarios. The main area of ice loss is West Greenland.
These findings underscore the importance of long-term simulations with comprehensive Earth system models to understand the complex, delayed responses of key climate system components and their broader implications for the Earth system.