Probabilistic reanalysis of twentieth-century sea-level rise

Estimating and accounting for twentieth-century global mean sea-level (GMSL) rise is critical to characterizing current and future human-induced sea-level change. Several previous analyses of tide gauge records(1-6)-employing different methods to accommodate the spatial sparsity and temporal incompleteness of the data and to constrain the geometry of long-term sea-level change-have concluded that GMSL rose over the twentieth century at a mean rate of 1.6 to 1.9 millimetres per year. Efforts to account for this rate by summing estimates of individual contributions from glacier and ice-sheet mass loss, ocean thermal expansion, and changes in land water storage fall significantly short in the period before 1990(7). The failure to close the budget of GMSL during this period has led to suggestions that several contributions may have been systematically underestimated(8). However, the extent to which the limitations of tide gauge analyses have affected estimates of the GMSL rate of change is unclear. Here we revisit estimates of twentieth-century GMSL rise using probabilistic techniques(9,10) and find a rate of GMSL rise from 1901 to 1990 of 1.2 +/- 0.2 millimetres per year (90% confidence interval). Based on individual contributions tabulated in the Fifth Assessment Report(7) of the Intergovernmental Panel on Climate Change, this estimate closes the twentieth-century sea-level budget. Our analysis, which combines tide gauge records with physics-based and model-derived geometries of the various contributing signals, also indicates that GMSL rose at a rate of 3.0 +/- 0.7 millimetres per year between 1993 and 2010, consistent with prior estimates from tide gauge records(4). The increase in rate relative to the 1901-90 trend is accordingly larger than previously thought; this revision may affect some projections(11) of future sea-level rise.