Acceleration of the contribution of the Greenland and Antarctic ice

Here, we present a 20‐year record of monthly ice sheet mass balance for Greenland and Antarctica. We examine and reconcile two independent methods for estimating temporal variations in ice sheet mass balance, the mass budget method (MB) and the gravity method, during the last 8 years. The MBM compares the surface mass balance (SMB; i.e., the sum of snowfall minus surface ablation) reconstructed from regional atmospheric models with perimeter loss (D; ice discharge) calculated from a time series of glacier velocity and ice thickness to deduce the rate of mass change, dM/dt [Rignot and Kanagaratnam, 2006; Howat et al., 2007; Rignot et al., 2008a; van den Broeke et al., 2009]. The gravity method employs a monthly time series of time‐variable gravity data from the Gravity Recovery and Climate Experiment (GRACE) to estimate the relative mass as a function of time, M(t) [e.g., Velicogna and Wahr, 2006]. We resolve the differences between the two methods in terms of mass balance, dM(t)/dt, and acceleration of mass loss, d2M/dt2, and conclude by discussing the contribution of the ice sheets to sea level in recent and forthcoming decades.