Waves affect marine operations and coastal communities; they can cause coastal erosion and structural damage. They influence stratification and enhance air-sea fluxes; in shallow waters they cause near-bed currents and suspend sediment, so affecting nearshore and benthic habitats, communities and demersal fish. Wave heights in winter (when largest) increased through the 1970s and 1980s: in the NE Atlantic (significant increase between the 1960s and early 1990s); in the North Sea (increase from 1973 to the mid-1990s); at Seven Stones off Land’s End (increase of about 0.02 m/y over 25 years to 1988). However, recent trends are not clear and may depend on region; some series appear to show a decrease. Winter wave heights correlate significantly with the North Atlantic Oscillation Index (a measure of the strength of westerly winds at UK latitudes), in the west and the Irish Sea; the correlation is particularly strong in the north west. In very shallow waters (e.g. near coasts) trends are reduced; wave heights are limited by water depth (as waves break); however, if sea levels (raised by climate change) increase depths nearshore, then larger waves may approach the shore. Climate change may affect storminess, storm tracks and hence wave heights. Some climate models suggest more frequent very severe storms but there is little confidence in predicted changes of wave height
