Environment Counts | Acceleration of sea level rise in last two decades underestimated :

Tide gauges provide records of local sea-level changes that extend back to the eighteenth century. Using tide gauge records to estimate historical GMSL rise is complicated by missing data, non-uniform distribution of sites, and the need to take into account tectonic, anthropogenic and other effects. Different approaches have been used to address these complexities, but uncertainty remains. Estimates of twentieth-century GMSL range from 1.6 to 1.9 mm/yr. In addition for the period before 1990 the sum of independent estimates of the contributions (GMSL budget) from glaciers and ice sheets, thermal expansion of oceans, and changes in land water storage, are insufficient (AR5) to account for the GMSL rise estimated from tide gauge records. In this study the authors apply a statistical technique called Kalman smoothing that naturally accommodates spatially sparse and temporally incomplete sampling to analyze annual records from 622 tide gauges for 1900 to 2010.

Kalman Smoothing (blue line) and previous estimates GPR (black line), Church and White (magenta line) and Jevrejeva et al(red line). Shading represents uncertainty

The estimated GMSL trend for the period 1901–90 is 1.2 ± 0.2 mm/yr which is lower than previous estimates. This estimate resolves the sea-level budget issue for 1901–90 without recalculating individual contributions from ocean thermal expansion, glacier melting, or ice sheet mass balance. For the period 1993–2010 when satellite altimetry has been used to measure sea surface height changes the authors estimate a sea level rise of 3.0 ± 0.7 mm/yr. This result suggests that the rate of GMSL rise during the last two decades has accelerated more than previously recognized. C. C. Hay et al, Nature(2015) doi:10.1038/nature14093