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 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.