To assess the accuracy and reliability of our knowledge about sea-level change and its causes, assessments of the sea-level budget (SLB) are indispensable. Closure of the sea-level budget implies that the observed changes of GMSL equal the sum of observed (or otherwise assessed) contributions, namely changes in ocean mass and the steric component. Closure of the ocean mass budget (OMB) implies that the observed ocean-mass change (e.g., from the Gravity Recovery and Climate Experiment, GRACE) is equal to assessed changes of water mass (in solid, liquid or gaseous state) outside the ocean, which are dominated by mass changes of land ice (glaciers and ice sheets) and water stored on the continents as liquid water or snow (land water). Misclosure of these budgets indicates errors in the assessment of some of the components (including effects of undersampling) or contributions from unassessed elements in the budget.

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 first phase of the 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. The project also developed new data products based on existing CCI products and on other data sources. SLBC_cci concentrated on datasets generated within CCI or by the consortium members as they have thorough insights into the genesis and uncertainty characteristics of the datasets. This facilitated progress towards working in a consistent framework of product specification, uncertainty characterization, and sea level budget analysis, and enabled the identification of unresolved inconsistencies as a prerequisite for future improvements.

The first phase of this project covered the precise altimetry era (starting in 1993) with a special focus given to the period 2003/2005 to 2015, coinciding with the availability of GRACE space gravimetry data and Argo drifter data.

The new project phase (SBLC_cci+) aims to improve the closure of the global mean sea level budget by: 1) lengthening the time series, 2) assessing budget closure at global and regional scales, 3) providing an explanation of temporal and spatial variability at global and local scales. Depending on the availability of the various elements, the global sea level budget will be updated up to 2022/2023. In addition, the project will address the regional variability of sea level and sea surface temperature, and investigate the contributions of natural/internal climate variability and anthropogenic forcing (detection/attribution) to the associated spatial trends. By extending to regional spatial scales, we can pinpoint areas where the sea level budget does not close, resulting in a regional breakdown of the assessment of the items
that accounts for a significant portion of the individual components used.

For further informations : https://climate.esa.int/en/projects/sea-level-budget-closure/