Unabated global mean sea-level rise over the satellite altimeter era

Abstract

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 drift^4,5). 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 projections^2,10, and larger than the twentieth-century acceleration^2,8,10.