The most compelling data for the net change of ice sheets is provided by the gravity satellite mission GRACE, which shows that both Greenland (Chen et al 2006) and Antarctica (Velicogna andWahr 2006) are losing mass at substantial rates.
Those are scary numbers, but a new study published in the September issue of Nature Geoscience suggests that the true melt rate might be much slower than that. (Access a PDF of the study here.) A joint team of American and Dutch scientists took another look at the GRACE data and found that Greenland and West Antarctica may be melting just half as fast the earlier studies estimated. As researcher Bert Vermeersen, a professor at Delft University of Technology in the Netherlands, told the AFP, the earlier estimates failed to account for glacial isostatic adjustment—the rebounding of the Earth’s crust after the end of the last Ice Age:
Success in science depends on objective skepticism. Caution, if not reticence, has its merits.
– James Hansen