The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability1, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1 (refs 2, 3). However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift4,5). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results (for example, refs 6, 7), we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions2, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref. 8) and reprocessed ERS-2/Envisat altimetry9. Second, in contrast to the previously reported slowing in the rate during the past two decades1, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections2,10, and larger than the twentieth-century acceleration2,8,10.
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This work was supported by the Integrated Marine Observing System (IMOS)—IMOS is a national collaborative research infrastructure, supported by the Australian Government. Additional support was provided by the Australian Government Department of the Environment, the Bureau of Meteorology and CSIRO through the Australian Climate Change Science Programme. Part of this project was supported through an Australian Research Councils Discovery Project (DP0877381), and a Future Fellowship (FT110100207). Altimetry products were obtained from the Jet Propulsion Laboratory PO.DAAC and Centre National d’Études Spatiales AVISO archives, with additional dry path delay corrections obtained from the Radar Altimeter Database System (http://rads.tudelft.nl/rads/). We thank B. Haines (JPL) and F. Lemoine (GSFC) for their altimeter orbit solutions, S. Nerem and D. Masters for providing the University of Colorado along-track data, R. Riva for rates of elastic deformation, and J. Hunter for useful comments on the manuscript. TG data were provided by the University of Hawaii Sea Level Center, and the Australian National Tidal Centre (NTC). The authors thank suppliers of GPS data (such as IGS, TIGA, BIGF, SOPAC) and NASA/JPL for making the GIPSY software and GPS orbit and clock products available.
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Scientific Reports (2017)