Rapid expansion of ice sheet area in transient simulations of the last glacial inception

We present transient simulations of the last glacial inception using the Earth system model CLIMBER-X with interactive ice sheets and visco-elastic solid-Earth response. The simulations are initialized at the Eemian interglacial (125 ka) and run until 100 ka, driven by prescribed changes in orbital configuration and greenhouse gas concentrations from ice core data.
CLIMBER-X simulates a robust ice sheet expansion over North America and Scandinavia through MIS5d, in accordance with proxy data. However, we show that the crossing of a bifurcation point in the ice-covered area, which leads to a rapid (~7 million square km over a few centuries) expansion of ice sheets over North America, is critical to get a large enough ice volume to match the sea level drop of ~40 m indicated by reconstructions during the last glacial inception. As a consequence of the presence of this bifurcation point, the model results are highly sensitive to climate model biases. We also show that in the model the vegetation feedback plays an important role during glacial inception.
Further results suggest that, as long as the system responds almost linearly to insolation changes during the last glacial inception, the model results are not very sensitive to changes in the ice sheet model resolution and the acceleration factor used to speed-up the climate component. This is not valid, however, when the system response is characterized by strongly-nonlinear processes, such as a rapid increase in ice-covered area.