The probable effects on ocean productivity of a possible 2°C rise in average sea-surface temperature accompanied by a 30 cm rise in mean sea-level over the next 30 years are considered. It seems unlikely that there will be any perceptible change in total primary productivity and changes in secondary productivity seem unpredictable. It is thought unlikely that changes in the nitrogen cycle will be sufficient to affect total biomass over this short time-scale. A2°C change is, however, likely to bring about considerable alterations in the composition of marine communities, and shifting patterns of water movement will bring about changes in the spatial distribution of biomass, communities and productivity. We may expect changes in traditional fishing grounds and marked changes in flora and fauna in British waters, but probably no increase or decrease in general productivity.