Transitions in the Northern Hemisphere glaciation process

We use the new Earth system model of intermediate complexity CLIMBER-X to investigate pathways of Northern Hemisphere (NH) glaciation. We perform experiments in which different combinations of orbital forcing and atmospheric CO₂ concentration are maintained constant in time. Each model simulation is run for 300 thousand years (kyr) starting from present-day conditions, and using an acceleration technique with asynchronous coupling between the climate and ice sheet model components.

We find that in the pathway to a NH glaciation, several bifurcations might occur. The bifurcations separate a diversity of stable configurations, which have different spatial and temporal prints. We identify four different bifurcations, separating five different equilibrium states: (i) completely ice-free conditions, (ii) present-day (ice only over Greenland), weak glaciation (with ice coverage north and west of Hudson Bay, Greenland and Scandinavia), (iv) Last Glacial Maximum – type of glaciation (with large North American and medium-size Eurasian ice sheets) and (v) mega-glaciation (full ice coverage over both North America and Eurasia).

The transitions are also clustered in terms of differential timescales. While the North-American continent full glaciation has a development timescale of ~ 100 kyr, an extensive ice coverage of the Eurasian continent involves a much longer time-frame of ~ 250 kyr. This could explain why a complete glaciation of the Eurasian continent was never observed. This result is also consistent with previous studies in the sense that one glaciation cycle is not long enough for the Eurasian ice sheet to fully grow.