Probabilistic reanalysis of twentieth-century sea-level rise

Abstract

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--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. The failure to close the budget of GMSL during this period has led to suggestions that several contributions may have been systematically underestimated. 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 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 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.The increase in rate relative to the 1901-90 trend is accordingly larger than previously thought; this revision may affect some projections of future sea-level rise.

Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change

“…There have not yet been any new comprehensive attempts to close the budget since 1993 with the revised satellite altimeter data, nor have there been any new assessments of the budget of GMSL rise before the satellite altimeter period. Hay et al [17] suggested that their lower rate of twentieth century GMSL rise is more consistent than earlier reconstructions with the sum of contributions. We note that there are several possible combinations of the contributions presented by Gregory et al [83] that could match the reconstruction of Hay et al Moreover, their estimated rate of sea level rise prior to 1950 is slightly larger than that of Church and White [18].…”

“…There are now more estimates of acceleration of GMSL over the nineteenth to twentieth century and these are generally larger than those available at the time of the AR5, ranging from 0.0042±0.0092 [15] to 0.02±0.01 mm year −2 [16] (see Cahill et al [29]; Hay et al [17]; Hogarth [30]; Olivieri and Spada [31]; Spada et al [32] for intermediate estimates). Jorda [33] estimated that at least 2.2 mm year −1 of the recent sea level trend estimated from altimetry cannot be attributed to unforced multidecadal variability, implying that the change in trend between 1900 and 1990 and the altimeter period is at least partly forced.…”

“…Updates of two of the GMSL reconstructions used in the AR5 give 1.77±0.28 [15] and 1.9 ± 0.3 mm year −1 since 1900 (and 3.1 ± 0.6 mm year −1 for 1993 to 2009) [16], in the upper half of the AR5 range. Hay et al [17] considered the Bfingerprints^of mass loss from glaciers and ice sheets in their reconstruction of GMSL. These effects on regional sea level are due to the change in the geopotential field (jointly determined by gravitation and Earth rotation) and the elastic response of the lithosphere, both practically instantaneous and caused by the geographical redistribution of mass on the Earth's surface when mass is transferred from land into the ocean.…”

“…Including the GeLi fingerprints is an advance over assuming geographically uniform sea level contributions from land ice (as in Church and White [18]), but estimating the magnitude of the weight factors for the many fingerprints used by Hay et al in the presence of large regional decadal variability is challenging given the time-varying and incomplete distribution of observations. Hamlington and Thompson [19] drew attention to the tide-gauges from the Arctic, Alaska and Japan that are included in Hay et al [17] but not the other reconstructions. The Arctic gauges have negative trends for 1950-1970, and high-latitude gauges in general have the most uncertain glacial isostatic adjustment [16].…”

Nonlinear subsidence at Fremantle, a long‐recording tide gauge in the Southern Hemisphere

“…For example, the vertical stability of the Australian continent and its suitability as a datum for MSL observations has been debated for decades [e.g., Emery, 1986, 1988;Bryant et al, 1988;Amin, 1993;Belperio, 1993;Feng et al, 2004;Sandiford, 2007;Moucha et al, 2008;Watson, 2011;Lewis et al, 2012]. Hay et al [2015], Haigh et al [2014], Hogarth [2014], Holgate and Woodworth [2004], Jevrejeva et al [2014], Jorda [2014], Merrifield et al [2009], Olivieri and Spada [2013], Watson et al [2015], and Woodworth et al [2009Woodworth et al [ , 2011; those that claim deceleration include Boretti [2012], Boretti and Watson [2012], Parker et al [2013], and Watson [2011]; those that claim neither include Schr€ oter [2010, 2014].…”