We can estimate the
potential magnitude of the ice mass biases by
noting that if the average velocity prediction bias of ~ 5 mm / yr evident in Figure 5 is developed over ~ 2 × 10 ^ 6 km2, an area somewhat smaller than that of West Antarctica, this would cause an apparent but spurious ice loss of ~ 33 Gt yr - 1, which is a significant fraction of all published ice mass rates derived from
GRACE [Velicogna and Wahr, 2006; Chen et al., 2006; Ramillien et al., 2006; Sasgen et al., 2007a].