We propose a programme of observations, combined with analysis of past and ongoing time series, to discover the magnitude of surface pH variations at seasonal-up-to-decadal time scales. We will address the Atlantic, UK shelf and slope waters, and selected locations in the Southern Ocean and Nordic Seas, using data from time series stations and volunteer observing ships (VOS), measuring three parameters of the marine carbonate system. The programme will be integrated with the efforts of colleagues in other European countries, and with the Surface ocean carbon atlas project (SOCAT) which aims to produce the most comprehensive and up to date data base to access all the quality data relevant to ocean carbon uptake and pH. Estimation of change will be set against the background of intra- and inter-annual variation.