This study examines the climate response to different magnitudes of Atlantic Meridional Overturning Circulation (AMOC) weakening under glacial conditions using the Australian Earth System Model. A potential threshold is identified between linear AMOC slowdown and nonlinear shutdown, driven by a critical change in ocean heat loss that induces a nonlinear atmospheric response governed by energetic constraints.

We compare pollen-based reconstructions of Northern Hemisphere tree cover over the last 20 000 years with simulations from the Max-Planck-Institute Earth System Model (MPI-ESM). The model captures broad forest trends but misses key regional patterns and the mid-Holocene forest peak. Testing climate drivers reveals mismatches in how temperature, water, and CO₂ control forests, pointing to structural limits and the need for improved vegetation processes in models.