A detailed analysis of the δ$^{18O}$ record of benthic foraminifera in deep sea cores from the Norwegian Sea shows that at the end of the Eemian interglacial (isotopic substage 5e), continental ice sheets experienced a significant phase of growth, which culminated during the maximum of isotopic substage 5d. The ice-volume was then about half of that of the last glacial maximum. This indicates that the 5e/5d transition marks the inception of the glaciation over the northern hemisphere. Subpolar planktonic foraminifera almost disappeared from the Norwegian Sea during the second half of isotopic substage 5e, indicating a cooling of surface waters, which began early in response to summer insolation changes and preceded the development of continental ice-sheets. As high temperatures prevailed south of the Greenland — Iceland — Faeroe strait, the thermal contrast between the warm North Atlantic and the cold Norwegian Sea reinforced natural cyclogenesis, which produces large snow storms over the subpolar continents.