Global sea-level budget and ocean-mass budget, with a focus on advanced data products and uncertainty characterisation

Studies of the global sea-level budget (SLB) and the global ocean-massbudget (OMB) are essential to assess the reliability of our knowledge ofsea-level change and its contributors. Here we present datasets for timesseries of the SLB and OMB elements developed in the framework of ESA'sClimate Change Initiative. We use these datasets to assess the SLB and theOMB simultaneously, utilising a consistent framework of uncertaintycharacterisation. The time series, given at monthly sampling and availableat https://doi.org/10.5285/17c2ce31784048de93996275ee976fff (Horwath etal., 2021), include global mean sea-level (GMSL) anomalies from satellitealtimetry, the global mean steric component from Argo drifter data withincorporation of sea surface temperature data, the ocean-mass component fromGravity Recovery and Climate Experiment (GRACE) satellite gravimetry, thecontribution from global glacier mass changes assessed by a global glaciermodel, the contribution from Greenland Ice Sheet and Antarctic Ice Sheetmass changes assessed by satellite radar altimetry and by GRACE, andthe contribution from land water storage anomalies assessed by the globalhydrological model WaterGAP (Water Global Assessment and Prognosis). Over the period January 1993–December 2016 (P1, covered by the satellite altimetry records), the mean rate (linear trend) of GMSL is 3.05 ± 0.24 mm yr⁻¹. The steric component is 1.15 ± 0.12 mm yr⁻¹ (38 % of the GMSL trend), and the mass component is 1.75 ± 0.12 mm yr⁻¹ (57 %). The mass component includes 0.64  ± 0.03 mm yr⁻¹ (21 % of the GMSL trend) from glaciers outsideGreenland and Antarctica, 0.60 ± 0.04 mm yr⁻¹ (20 %) fromGreenland, 0.19 ± 0.04 mm yr⁻¹ (6 %) from Antarctica, and0.32 ± 0.10 mm yr⁻¹ (10 %) from changes of land water storage. In the period January 2003–August 2016 (P2, covered by GRACE and the Argo drifter system), GMSL rise is higher than in P1 at 3.64 ± 0.26 mm yr⁻¹. This is due to an increase of the mass contributions, now about 2.40 ± 0.13 mm yr⁻¹ (66 % of the GMSL trend), with thelargest increase contributed from Greenland, while the steric contributionremained similar at 1.19 ± 0.17 mm yr⁻¹ (now 33 %). The SLB oflinear trends is closed for P1 and P2; that is, the GMSL trend agrees withthe sum of the steric and mass components within their combineduncertainties. The OMB, which can be evaluated only for P2, shows that ourpreferred GRACE-based estimate of the ocean-mass trend agrees with the sum of mass contributions within 1.5 times or 0.8 times the combined 1σuncertainties, depending on the way of assessing the mass contributions.Combined uncertainties (1σ) of the elements involved in the budgets are between 0.29 and 0.42 mm yr⁻¹, on the order of 10 % of GMSL rise.Interannual variations that overlie the long-term trends are coherentlyrepresented by the elements of the SLB and the OMB. Even at the level ofmonthly anomalies the budgets are closed within uncertainties, while alsoindicating possible origins of remaining misclosures.