The possible role of sea-ice feedbacks in the climatic response to orbital forcing at high northern latitudes is studied with a coupled climate model (ECBilt-CLIO). It is found that boreal summer insolation is critical for the sea-ice response. When summer insolation is high (low) the sea-ice fraction decreases (increases) at the margins of the permanent sea-ice cover during the whole year. More importantly, rapid shifts in GIN (Greenland-Iceland-Norway) Sea ice cover are found to be less (more) frequent for relatively high (low) summer insolation. These events, which are characterized by a sudden expansion in sea-ice cover, result in reduced GIN Sea convection, a reduction of the Atlantic thermohaline circulation by 5--10 Sverdrups and decreased air temperatures at high latitudes.