1. Characterize the inter-annual to decadal variability in ice sheet mass balance and quantify its impact on mass balance uncertainty.


Ice sheets are major contributors to sea level rise. In fact, recent estimates suggest that ice sheets provide the largest water flux into the oceans causing sea level rise, having surpassed mountain glaciers. Three main techniques are available to study ice sheet mass balance: the flux method, the altimetry method and the gravity method. All three techniques offer complementary information about the nature of the changes and about mass balance from regional to continental scale. However, the gravity method provides the only directmeasurement of ice mass change, and it has been available since April 2002 with the GRACE mission. We have pioneered the use of GRACEdata to calculate ice sheet mass changes. Using these data, we have obtained the first modern and precise estimates of ice sheet mass balance, a major achievement compared to prior knowledge. For Antarctica, we provided the first comprehensive mass budget estimate that demonstrated that Antarctica is losing mass (Velicogna and Wahr, 2006). More recently, we showed that the rates of ice sheet mass loss are unequivocally increasing with time (Velicogna, 2009).

These results go well beyond estimating ice sheet mass balance. The gravity data provide an unprecedented record of inter-annual to decadal mass change variability. This information is critical to evaluate atmospheric model outputs, e.g. net precipitation in Antarctica or melt and precipitation in Greenland. It also provides critical information about the spatial and temporal patterns of ice mass loss.

Antarctic & Greenland mass changes relative to average ice mass since 2002 (Velicogna and Wahr, 2013)




2008-2010 NASA ROSES-07 Cryosphere Program.  ‘Interpretation and uncertainties in ice sheet mass balance and seasonal variability from GRACE data’.  P.I..

2009-2012 NASA-NNH08ZDA001N Modeling, Analysis and Prediction (MAP) Program, ‘A three-dimensional, high-resolution flow model of the Greenland ice sheet: validation and prediction’. Co-P.I.

2007-2011 NASA ROSES-05 Cryosphere Program, ‘Mass balance of the polar ice sheets’. Co-P.I. $304K.


2011 –Rignot E. Velicogna I., Van Den Broeke, M, Monaghan A, Lenaerts J., ‘Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise’. Geophys. Res. Lett., VOL. 38, L05503, doi:10.1029/2011GL046583.

2009 –van den Broeke M., Bamber J, Ettema J., Rignot E., Schrama E., van de Berg W., van Meijgaard E., Velicogna I., Wouters B., ‘Partitioning  recent Greenland mass loss’, Science, VOL. 326, 984-986, doi: 10.1126/science.1178176.

2009 –Velicogna I., ‘Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE’, Geophys. Res. Lett., VOL. 36, L19503, doi:10.1029/2009GL040222.

2006 –Velicogna I. and J. Wahr, ‘Acceleration of Greenland Ice Mass Loss in Spring 2004’, Nature, VOL. 443, 329-331, doi:10.1038/nature05168.

2006 –Velicogna I. and J. Wahr, ‘Time variable gravity shows a large mass loss in Antarctica’, Science, VOL. 311, 1754-1756, doi:10.1126/science11237855.

2005 –Velicogna  I. and J. Wahr, ‘Ice Mass Balance in Greenland from GRACE’, Geophys. Res. Lett., VOL. 32, L18505, doi:10.1029/2005GL023955.

2004 –Velicogna I., J. Wahr, E. Hanna, P. Huybrechts, ‘Short term mass variability  in Green- land from GRACE’, Geophys. Res. Lett., VOL. 32, L05501, doi:10.1029/2004GL021948.