Research

Global Sea Level Budget and Ocean Mass Budget, with Focus on New Data Products and Uncertainty Characterization.

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Abstract

Studies of the sea-level budget are a means of assessing our ability to quantify and understand sea-level changes and their causes. Closure of the total sea level budget implies that the observed changes of global mean sea level (from satellite altimetry) equal the sum of observed (or otherwise assessed) contributions, namely changes in ocean mass and the steric component (mainly thermal expansion). Misclosure indicates errors in the evaluation of some components or the importance of un-assessed budget elements. ESA's Climate Change Initiative (CCI) projects include Sea Level CCI, Greenland Ice Sheet CCI, Antarctic Ice Sheet CCI, Glaciers CCI and the Sea Surface Temperature CCI, all addressing Essential Climate Variables (ECVs) related to sea level. The cross-ECV project Sea Level Budget Closure CCI used products from the above CCI projects in conjunction with in situ data for ocean thermal expansion (e.g., Argo), GRACE-based assessments of ocean mass change, land water and land ice mass change, and model-based data for glaciers and land hydrology. Involving the authors of the individual data products facilitated consistency in product definition and analysis and a unified treatment of uncertainties and their propagation to the overall budget. We report on the results of the global sea-level budget assessment with a focus on two periods: 1993-2016 (the altimetry period) and 2003-2016 (the GRACE / Argo period). For the long-term trend, the global sea level budget is closed within uncertainties on the order of 0.3 mm/yr (1 sigma). Moreover, the budget is also closed within uncertainties for interannual variations.