Antarctica, showing rates of surface-elevation change derived from satellite radar-altimeter measurements

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Antarctica, showing rates of surface-elevation change derived from satellite radar-altimeter measurements

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Antarctica, showing rates of surface-elevation change derived from satellite radar-altimeter measurements. The figure shows rates at which the ice-sheet mass was estimated to be changing based on radar-altimeter data (black), mass-budget calculations (red), and satellite gravity measurements (blue). Rectangles depict the time periods of observations (horizontal) and the upper and lower estimates of mass balance (vertical). Measurements by satellite techniques based on gravity indicate mass loss at a rate of 138 ± 73 billion tonnes per year during 2002–2005, mostly from the West Antarctica Ice Sheet. That is equivalent to a rise in global sea level of 0.4 ± 0.2 mm per year, or 10–30% of the global rate measured since the 1950s, and is in good agreement with recent massbudget estimates. However, two interpretations of satellite radar altimetry pointed to a much smaller loss of about 31 billion tonnes of ice per year or a net gain of about 27 billion tonnes per year. The difference between these estimates from totally independent techniques reflects the uncertainties in these difficult measurements; nevertheless, on balance, they indicate a recent shift to a net loss of Antarctic ice and suggest that losses may be accelerating. Similar conclusions result from studies of Antarctic Peninsula glaciers, indicating that they are melting much faster than previously predicted and are probably already contributing significantly to sea-level rise.

Sources

(corresponding to numbers on rectangles): 1 Rignot and Thomas 2002; 2 Ramillien and others 2006; 3 Velicogna and Wahr 2006; 4 Chen and others 2006; 5 Zwally and others 2005; 6 Wingham and others 2006; 7 Rignot and others 2007 Rignot, E. and Thomas, R. (2002). Mass balance of polar ice sheets. Science, 297(5586), 1502-1506 Ramillien, G., Lombard, A., Cazenave, A., Ivins, E., Remy, F. and Biancale, R. (2006). Interannual variations of the mass balance of the Antarctic and Greenland ice sheets from GRACE. Global and Planetary Change, 53, 198-208 Velicogna, I. and Wahr, J. (2006a). Measurements of time-variable gravity show mass loss in Antarctica. Science, 311(5768), 1754-1756 Chen, J., Wilson, C., Blankenship, D. and Tapley, B. (2006a). Antarctic mass rates from GRACE. Geophysical Research Letters, 33, L11502 Zwally, H.J., Giovinetto, M.B., Li, J., Cornejo, H.G., Beckley, M.A., Brenner, A.C., Saba, J.L. and Yi, D. (2005). Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992-2002. Journal of Glaciology, 51(175), 509-527 Wingham, D., Shepherd, A., Muir, A. and Marshall, G. (2006a). Mass balance of the Antarctic ice sheet. Transactions of the Royal Society of London Series A, 364, 1627-1635 Rignot, E., Arthern, R., Bamber, J., van den Broeke, M., Davis, C., Li, Y., van de Berg, W.J. and van Meijgaard, E. (2007). A net source of ocean mass from coastal thinning of Antarctic glaciers. In print

Link to web-site

http://www.unep.org/geo/ice_snow

Cartographer/
Designer

Hugo Ahlenius, UNEP/GRID-Arendal

Appears in

Global Outlook for Ice and Snow

Published

June 2007

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