Editing IPCC:AR6/SROCC/Chapter-4 (section)

===== 4.2.2.1.2 Satellite altimetry =====

High precision satellite altimetry started in October 1992 with the launch of the TOPEX/Poseidon and Jason series of spacecraft. Since then, 11 satellite altimeters have been launched providing nearly global sea level measurements (up to ±82° latitude) over more than 25 years. Six groups (AVISO/CNES, SL_cci/ESA, University of Colorado, CSIRO, NASA/GSFC, NOAA; Nerem et al., 2010; <sup>[[#fn:r138|138]]</sup> Henry et al., 2014 <sup>[[#fn:r139|139]]</sup> ; Leuliette, 2015 <sup>[[#fn:r140|140]]</sup> ; Watson et al., 2015 <sup>[[#fn:r141|141]]</sup> ; Beckley et al., 2017 <sup>[[#fn:r142|142]]</sup> ; Legeais et al., 2018 <sup>[[#fn:r143|143]]</sup> ) provide altimetry-based GMSL time series. Since AR5, several studies using two independent approaches based on tide gauge records (Watson et al., 2015 <sup>[[#fn:r144|144]]</sup> ) and the sea level budget closure (Chen et al., 2017 <sup>[[#fn:r145|145]]</sup> ; Dieng et al., 2017 <sup>[[#fn:r146|146]]</sup> ) identified a drift of 1.5 (0.4–3.4) mm yr <sup>–1</sup> in TOPEX A from January 1993 to February 1999. Accounting for this drift leads to a revised GMSL rate from satellite altimetry of 3.16 (2.79–3.53) for 1993–2015 (WCRP Global Sea Level Budget Group, 2018 <sup>[[#fn:r147|147]]</sup> ; see Table 4.1) compared to 3.3 mm yr <sup>–1</sup> (2.7–3.9) for 1993–2010 in AR5. Compared to AR5, the revised satellite altimetry GMSL estimates now show with ''high confidence'' an acceleration of 0.084 (0.059–0.090) mm yr <sup>–1</sup> over 1993–2015 (5–95% uncertainty range; Watson et al., 2015 <sup>[[#fn:r148|148]]</sup> ; Nerem et al., 2018 <sup>[[#fn:r149|149]]</sup> ) . This acceleration is due to an increase in Greenland mass loss since the 2000s (Chen et al., 2017 <sup>[[#fn:r150|150]]</sup> ; Dieng et al., 2017 <sup>[[#fn:r151|151]]</sup> ) and a slight increase in all other contributions probably partly due to the recovery from the Pinatubo volcanic eruption in 1991 (Fasullo et al., 2016 <sup>[[#fn:r152|152]]</sup> ) and partly due to increased GHG concentrations e.g., (Slangen et al., 2016 <sup>[[#fn:r153|153]]</sup> ; ''high confidence'' ). The current sea level rise is 3.6 ± 0.3 mm yr <sup>–1</sup> over 2006–2015 (90% confidence level). This is the highest rate measured by satellite altimetry (Ablain et al., 2019 <sup>[[#fn:r154|154]]</sup> ; ''medium confidence'' ). Before the satellite altimetry era, the highest rate of sea level rise recorded was reached during the period 1935–1944. It amounted 2.5 ± 0.7 mm yr <sup>–1</sup> (estimate at the 90% confidence level from sea level reconstructions; Church and White, 2011 <sup>[[#fn:r155|155]]</sup> ; Ray and Douglas, 2011 <sup>[[#fn:r156|156]]</sup> ; Jevrejeva et al., 2008 <sup>[[#fn:r157|157]]</sup> ; Hay et al., 2015 <sup>[[#fn:r158|158]]</sup> ; Dangendorf et al., 2017 <sup>[[#fn:r159|159]]</sup> ). This is expected to be smaller than the current rate of sea level rise, making the current sea level rise the highest on instrumental record ( ''medium confidence'' ).

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