Barnoud Anne (Magellium, France); Bouih Marie (Magellium, France); Fraudeau Robin (Magellium, France); Larnicol Gilles (Magellium, France); Cazenave Anny (LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, France); Meyssignac Benoit (LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, France); Blazquez Alejandro (LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, France); Horwath Martin (TUD Dresden University of Technology, Germany); Thorben Döhne (TUD Dresden University of Technology, Germany); Jonathan Bamber (University of Bristol, UK); Antonio Bonaduce (NERSC, Norway); Roshin P. Raj (NERSC, Norway); Leroux Stéphanie (DATLAS, France); Kolodziejcyk Nicolas (UBO-LOPS, France); Llovel William (UBO-LOPS, France); Rémy Asselot (UBO-LOPS, France); Andrea Storto (CNR, Italy); Chunxue Yang (CNR, Italy); Spada Giorgio (UNIBO, Italy); Marco Restano (ESA/ESRIN, Italy); Jerome Benveniste (ESA/ESRIN, Italy)

Closing the Sea Level Budget (SLB) at monthly, yearly and interannual time scales, at the best level of accuracy and precision is an essential and central problem of modern physical oceanography. First because closing the SLB is a prerequisite for stating that all the important causes for sea level variability are identified and well quantified. Second, closing the SLB is a useful tool to cross-validate worldwide complex observing systems such as the Argo network, the satellite gravimetry missions GRACE/GRACE-FO and the satellite altimetry constellation, and to keep a close watch on their performances. Third, because closing the SLB is an efficient approach to test the consistency of different observed variables of the climate system such as sea level, ocean temperature and ocean mass, land ice melt and land water storage changes, with regard to conservation laws including those of mass and energy.
Since 2010, ESA has developed the Climate Change Initiative (CCI) programme in order to produce consistent and continuous space-based records for Essential Climate Variables (ECVs). The Sea Level Budget Closure CCI (SLBC_cci) project was conducted from 2017 to 2019 as the first cross-ECV project within CCI. The project aimed at taking advantage of the improved quality of sea level-related Earth observation datasets produced within the CCI programme to assess the closure of the global mean SLB over 1993-2016.
Rencently, a second phase of the SLBC_cci project (so-called SLBC_cci+) has been launched for a 3-year period (2023-2026). Here, we will present the main objectives of the SLBC_cci+ project to pursue the work initiated in the first phase: i) to improve the closure of the global mean SLB and extend the global mean SLB time series, ii) to assess the closure of the SLB at regional scales and iii) to explain the time and space variability in SLB both at global and regional spatial scales. More specifically, the global SLB will be updated up to 2023. We also intend to go further by extending the SLB exercise at regional scale for the 2002-2023 period (called GRACE/Argo era). Extending the SLB to regional spatial scales will allow us to identify regions where the SLB does not close, leading to a regional breakdown of the assessment of the CCI products that represent a large part of the individual components used in the SLB. In addition, the SLBC_cci+ project aspires to tackle questions such as “Is the SLB non-closure due to a structural deficiency of the observing system associated with inconsistent effective resolution across the different observing sub-systems such as Argo, GRACE and satellite altimetry? Or is it due to measurement errors in a single observing sub-system? Can we isolate in terms of time and space the potential errors?”. The project also aims at tackling scientific questions such as the attribution of sea level variations and the assessment of the Earth’s energy budget.