Acceleration of ice sheet mass losses from GRACE: trends and uncertainties

We analyze the spatial trends in ice sheet mass loss in Greenland and Antarctica to determine areas where the mass loss is increasing with time versus areas where the acceleration is not significant and areas where the ice sheet is gaining mass with time using different GRACE gravity solutions and different time periods. We address the statistical significance of these results based on GRACE uncertainties and error sources. Accelerations in mass loss are examined at the ice sheet wide level and at the regional level. At the regional level, we identify the major sources of uncertainty in estimating the acceleration in mass change. To do so, we compare results using GRACE solutions that employ different de-aliasing models, we evaluate the impact of the atmospheric/ocean corrections and of the lower degree variability on the final products and we also compare results obtained using standard spherical harmonics solutions versus the regularized solution and the mascon approach applied to the harmonics. Finally, as an independent mean of evaluation of the results, we compare the GRACE acceleration data with independent observations, namely trends of ice volume acceleration from altimetry in Greenland and over key glaciers in Antarctica, and changes in surface mass balance from regional climate models and in ice velocity from interferometric SAR. We conclude on the key processes that control the estimation of the acceleration in mass loss from the GRACE data and how the results may improve in future missions, e.g. GRACE-FO.