Contribution of ice sheet and mountain glacier melt to recent sea level rise

Changes in global mean sea level primarily reflect the sum of three contributions: water mass changes in the oceans, water density changes, and variations in the volume of the ocean basins. Satellite altimetry data(1-4) suggest that sea level rose by about 2.39 +/- 0.48 mm yr(-1) between 2005 and 2011. However, previous estimates(5-9) of sea level rise from density and ocean mass changes were lower than the altimeter data indicate. Here we show that the gap in the sea level budget disappears when we combine gravity data from the GRACE (Gravity Recovery and Climate Experiment) satellite mission and temperature and salinity observations from the Argo programme collected between 2005 and 2011. The Argo data indicate a density-driven sea level rise of 0.60 +/- 0.27 mm yr(-1) throughout this period. To estimate ocean mass change from the gravity data, we developed a forward modelling technique that reduces the bleeding of terrestrial signals into the ocean data. Our reassessment suggests an ocean mass contribution of 1.80 +/- 0.47 mm yr(-1), for a total sea level rise of 2.40 +/- 0.54 mm yr(-1), in agreement with the altimeter-based estimates. On the basis of the GRACE data, we conclude that most of the change in ocean mass is caused by the melting of polar ice sheets and mountain glaciers. This contribution of ice melt is larger than previous estimates(10), but agrees with reports(11-13) of accelerated ice melt in recent years.