Climate change stressors already affect the subtropical and tropical coastal, estuarine, and riverine habitats of dugongs and manatees, and are predicted to increase over the coming decades, exacerbated by co-stressors including harmful algal blooms, dam construction, hardening coastlines, phasing out coastal power plants, land clearing, and human food insecurity. These cumulative impacts will be locally variable but changes in the extent and continuity of sirenian habitats are likely to be widespread. Important features of some key manatee habitats such as warm water refuges, freshwater sources, and navigable migration routes are expected to be reduced or lost. The movement behaviors of all four sirenian species will change in response to alterations in community composition of feeding habitats, and the temporary loss of such habitats resulting from the increased intensity of extreme events. The locations of essential resources and the cues triggering the timing of movements are expected to alter rapidly as the climate changes. Some coastal habitats may become unsuitable for manatees because of the salinization of sources of freshwater for drinking. The capacity of dugongs and manatees to alter their movements in response to climate change will be essential to their survival.