The walrus (Odobenus rosmarus) is classified as a focal ecosystem component of the Arctic, defined as a biological element that is considered central to the functioning of an ecosystem, is of major importance to Arctic residents and/or is likely to be a good proxy for short- and long-term changes in the environment. The Arctic is undergoing large-scale environmental changes due to rapid global warming, including a marked reduction of sea ice in several areas inhabited by walruses. This chapter reviews how walruses already have been affected by global warming, or likely will be in the future. Specifically, we review the effects on walruses of projected changes in sea ice cover, marine productivity, ocean acidification, predation, pathogens and ultraviolet radiation, whereas changes in human activity patterns are discussed elsewhere in this volume. We find that, while the Pacific walrus seems to experience negative effects of warming and decrease in sea ice, the Atlantic walruses may be less affected; also in comparison to other ice-associated pinnipeds. Hence, we concur with previous assessments that the walrus is likely to survive into the future; at least in areas where human disturbance is minimal, and suitable terrestrial haul-outs are close enough to their feeding grounds.