FIGURE 7.1 Spatial coverage of data from Antarctica. (a) Surface transverses since the 1957-1958 International Geophysical Year. SOURCE: National Snow and Ice Data Center, University of Colorado. (b) Airborne surveys, over snow radio-echo sounding (RES), seismic surveys, gravimetric surveys, and ice-core missions since the 1957-1958 International Geophysical Year. SOURCE: BEDMAP consortium. (c) Satellite coverage. SOURCE: John Crawford, Canadian Space Agency, National Aeronautics and Space Administration, Jet Propulstion Laboratory.

One of the central questions in climate change and cryosphere research is how the warming climate will affect the ice sheets because the amount of continental ice and melt water entering the ocean strongly contributes to the change in sea level. Glaciologists and climatologists have long been debating whether a warming climate would decrease ice mass. However, early research focused on how increased melting would be offset by increased precipitation. The ice mass balance and thus its contribution to sea-level rise was originally thought to be determined by the difference between melting and precipitation.

Satellite observations have revolutionized this thinking by allowing scientists to monitor precise ice sheet elevation, velocity, and overall mass. Satellite images revealed that in fact the overall mass is declining (Luthcke et al. 2006). In addition to observing great variability in the ice stream velocity over time and space, satellite images revealed that the overall velocities of the ice streams in Antarctica and Greenland have increased during the past decade, resulting in more ice flow into the ocean (Bindschadler and Vonberger 1998, Joughin et al. 2001).