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

• Published in: Nature climate change 2015-06, Vol.5 (6), p.565-568
• Main Authors: Watson, Christopher S., White, Neil J., Church, John A., King, Matt A., Burgette, Reed J., Legresy, Benoit
• Format: Article
• Language: English
• Subjects: 704/106/694; 704/106/829; Altimetry; Climate Change; Climate Change/Climate Change Impacts; Environment; Environmental Law/Policy/Ecojustice; Gauges; Global positioning systems; GPS; letter; Marine; Sea level
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/nclimate2635

This study identifies and corrects instrumental drift for satellite altimeter missions, which affects estimates of the rates of sea-level rise. Corrected data show an acceleration in the rate of rise, counter to previous estimates and in line with projections. 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 variability 1 , 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 contributions 2 , GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref.  8 ) and reprocessed ERS-2/Envisat altimetry 9 . Second, in contrast to the previously reported slowing in the rate during the past two decades 1 , 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 .