Anthropogenically-derived increases in atmospheric greenhouse gas concentrations have been
implicated in recent climate change, and are projected to substantially impact the climate on a global
scale in the future. For marine and freshwater systems, increasing concentrations of greenhouse
gases are expected to increase surface temperatures, lower pH, and cause changes to vertical
mixing, upwelling, precipitation, and evaporation patterns. The potential consequences of these
changes for harmful algal blooms (HABs) have received relatively little attention and are not well
understood. Given the apparent increase in HABs around the world and the potential for greater
problems as a result of climate change and ocean acidification, substantial research is needed to
evaluate the direct and indirect associations between HABs, climate change, ocean acidification, and
human health. This research will require a multidisciplinary approach utilizing expertise in
climatology, oceanography, biology, epidemiology, and other disciplines. We review the
interactions between selected patterns of large-scale climate variability and climate change, oceanic
conditions, and harmful algae.