Exploring the uncertainty in GRACE estimates of the mass redistributions at the Earth surface: implications for the global water and sea level budgets

Abstract

Observations from the Gravity Recovery and Climate Experiment (GRACE) satellite missionprovide quantitative estimates of the global water budget components. However, these estimatesare uncertain as they show discrepancies when different parameters are used in the processing ofthe GRACE data. We examine trends in ocean mass, ice loss from Antarctica, Greenland, arcticislands and trends in water storage over land and glaciers from GRACE data (2005–2015) andexplore the associated uncertainty. We consider variations in six different GRACE processingparameters, namely the processing centre of the raw GRACE solutions, the geocentre motion,the Earth oblateness, the filtering, the leakage correction and the glacial isostatic adjustment(GIA). Considering all possible combinations of the different processing parameters leads toan ensemble of 1500 post-processed GRACE solutions, which is assumed to cover a significantpart of the uncertainty range of GRACE estimates. The ensemble-mean trend in all globalwater budget components agree within uncertainties with previous estimates based on differentsources of observations. The uncertainty in the global water budget is±0.27 mm yr−1[at the 90per cent confidence level (CL)] over 2005–2015. We find that the uncertainty in the geocentremotion and GIA corrections dominate the uncertainty in GRACE estimate of the globalwater budget. Their contribution to the uncertainty in GRACE estimate is respectively±0.21and±0.12 mm yr−1(90 per cent CL). This uncertainty in GRACE estimate implies anuncertainty in the net warming of the ocean and the Earth energy budget of±0.25 W m−2(90per cent CL) when inferred using the sea level budget approach.