Fully coupled climate–ice sheet simulation of North American ice-sheet evolution during the last glacial inception

The mechanisms governing the initiation and subsequent growth of Northern Hemisphere ice sheets during the last glacial inception remain incompletely understood, in particular, the transition from single, scattered ice nuclei to developed, large-scale ice sheets. Here we present fully coupled climate–ice sheet simulations spanning 127–65 ka BP, performed with the Earth system AWI-ESM. To make the long transient simulations computationally feasible, orbital and greenhouse gas forcing are accelerated by a factor of 20. A bias correction is applied for monthly near-surface air temperatures over North America.

The simulation produces extensive North American ice sheets, with initial ice-sheet development beginning around 120 ka over Baffin Island and the Quebec region. Rates of ice-sheet growth closely follow variations in boreal summer insolation at 65°N, reflecting the dominant role of the precession cycle during early glacial inception. During this phase, ice-sheet nucleation and early expansion are primarily controlled by reductions in summer near-surface air temperature, allowing persistent snow cover and positive snow–albedo feedbacks. At later stages, once a continental-scale ice sheet is established, a self-sustaining feedback emerges. The presence of the ice sheet enhances precipitation along its southern and southwestern margins, promoting further ice advance into lower latitudes and reinforcing ice-sheet growth.

Our results suggest a two-phase glacial inception: an insolation-driven initiation phase followed by a dynamically maintained growth phase governed by ice-atmosphere feedbacks. These findings provide new insights into the processes involved in the last glacial inception and highlight the importance of fully coupled climate–ice-sheet models.