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

===== 4.2.2.2.2 Ocean mass observations from GRACE and GRACE Follow-On =====

The ocean mass changes correspond to the sum of land ice and terrestrial water storage changes. Since 2002, the GRACE and GRACE follow-on missions provide direct estimates of the ocean mass changes and thus they provide an independent estimate of the sum of land ice and terrestrial water storage contributions to sea level. Since AR5, GRACE-based estimates of the ocean mass rates are increasingly consistent (WCRP Global Sea Level Budget Group, 2018 <sup>[[#fn:r194|194]]</sup> ) because of the extended length of GRACE missions’ observations (over 15 years), the improved understanding of data and methods for addressing GRACE limitations (e.g., noise filtering, leakage correction and low-degree spherical harmonics estimates), and the improved knowledge of geophysical corrections applied to GRACE data (e.g., GIA). The most recent estimates (Dieng et al., 2015b <sup>[[#fn:r195|195]]</sup> ; Reager et al., 2016 <sup>[[#fn:r196|196]]</sup> ; Rietbroek et al., 2016 <sup>[[#fn:r197|197]]</sup> ; Chambers et al., 2017 <sup>[[#fn:r198|198]]</sup> ; Blazquez et al., 2018 <sup>[[#fn:r199|199]]</sup> ; Uebbing et al., 2019 <sup>[[#fn:r200|200]]</sup> ) report a global ocean mass increase of 1.7 (1.4 – 2.0) mm yr <sup>–1</sup> over 2003–2015 (see also Table 4.1). The uncertainty arises essentially from differences in the inversion method to compute the ocean mass (Chen et al., 2013 <sup>[[#fn:r201|201]]</sup> ; Jensen et al., 2013 <sup>[[#fn:r202|202]]</sup> ; Johnson and Chambers, 2013 <sup>[[#fn:r204|204]]</sup> ; Rietbroek et al., 2016 <sup>[[#fn:r205|205]]</sup> ) , uncertainties in the geocentre motion and uncertainty in the GIA correction (Blazquez et al., 2018 <sup>[[#fn:r205|205]]</sup> ; Uebbing et al., 2019 <sup>[[#fn:r206|206]]</sup> ) . The consistency between estimates of the global mean ocean mass on a monthly time scale has also increased since AR5.

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