Utilizing a climate model of intermediate complexity, we test the hypothesis that the Pliocene closure of the Central American Seaway was a necessary precondition for orbitally triggered Northern Hemisphere glaciation. We conduct a series of sensitivity experiments in order to analyze the isolated and combined effects of Panama closure and orbital forcing on Northern Hemisphere perennial snow cover. While orbital forcing efficiently controls the extension of perennial snow cover, the model results suggest that the closure of the Central American Seaway did not intensify orbitally forced glaciation in high northern latitudes.