Acceleration of the Greenland ice sheet mass loss as observed by GRACE: Confidence and sensitivity

We examine the scale and spatial distribution of the mass change acceleration in Greenland and its statistical significance, using processed gravimetric data from the GRACE mission for the period 2002-2011. Three different data products - the CNES/GRGS, DMT-1b and GGFC GRACE solutions - have been used, all revealing an accelerating mass loss in Greenland, though with significant local differences between the three datasets. Compensating for leakage effects, we obtain acceleration values of -18.6 Gt/yr(2) for CNES/GRGS, -8.8 Gt/yr(2) for DMT-1b, and -14.8 Gt/yr(2) for GGFC. We find considerable mass loss acceleration in the Canadian Arctic Archipelago, some of which will leak into the values for Greenland, depending on the approach used, and for our computations the leakage has been estimated at up to -4.7 Gt/yr(2). The length of the time series of the GRACE data makes a huge difference in establishing an acceleration of the data. For both 10-day and monthly GRACE solutions, an observed acceleration on the order of 10-20 Gt/yr(2) is shown to require more than 5 yrs of data to establish with statistical significance. In order to provide an independent evaluation, ICESat laser altimetry data have been smoothed to match the resolution of the GRACE solutions. This gives us an estimated upper bound for the acceleration of about -29.7 Gt/yr(2) for the period 2003-2009, consistent with the acceleration values and corresponding confidence intervals found with GRACE data. (C) 2012 Elsevier B.V. All rights reserved.