Subaerial continental flood basalt volcanism is distinguished from all other volcanic activity by the repeated effusion of huge batches of basaltic magma (∼102-103 km3 per eruption) over short periods of geologic time (<1 Myr). Flood basalt provinces are constructed of thick stacks of extensive pahoehoe-dominated lava flow fields and are the products of hundreds of eruptions. Each huge eruption comes from a dyke-fed fissure tens to hundreds of kilometres long and lasts about a decade or more. Such spatial and temporal patterns of lava production do not occur at any other time in Earth history, and, during eruptions, gas fluxes of ∼1 Gt per year of SO2 and CO2 over periods of a decade or more are possible. Importantly, the atmospheric cooling associated with aerosols generated from the SO2 emissions of just one flood basalt eruption is likely to have been severe and would have persisted for a decade or longer. By contrast, warming due to volcanogenic CO2 released during an eruption is estimated to have been insignificant because the mass of CO2 would have been small compared to that already present in the atmosphere.