Sea Level on the Human Scale: Tidal Measurements and Satellite Altimetry

Sea levels have been measured over the past 50-100 years by tide gauges and over the past two decades via satellite altimetry. Averaged over the globe, these measurements record changes in the volume of the ocean as a response to climatic changes. Taken together, these data indicate that the volume of the ocean is expanding at an accelerated rate. The evidence for this conclusion will be reviewed. The difficulties, meaning the uncertainties, in interpreting these data will also be assessed, and the prospects for improved projections of sea level change in the coming decades will be discussed.