Current large-scale mammalian diversity patterns in Canada can be accurately explained using various measurements of heat energy. Unfortunately, climatic change is predicted to alter the fundamental climatic basis for contemporary diversity gradients, with the expected consequence that much of the Canadian biota will need to migrate in order to remain within climatically suitable regions. We make predictions regarding future mammal diversity patterns in Canada, and therefore provide a preliminary indication of where management intervention should be directed in order to conserve mammal diversity as climate changes. We also examine the current distributions of individual mammal species in Canada in order to determine which taxa cannot migrate farther north because of the Arctic Ocean barrier. Of the 25 species that fall into this category, we examine the predicted loss of habitat in one keystone species – Dicrostonyx groenlandicus, the collared lemming – and find that this taxon is likely to lose approximately 60% of its habitat with unpredictable but likely detrimental consequences for the arctic biota. We discuss the implications of our findings briefly.