Potential Climatic Effects on the Greenland Ice Sheet 
Robert A. Bindschadler 
NASA/Goddard Space Flight Center 
Greenbelt, MD 20771 
The Greenland Ice Sheet covers an area of 1.72 x 106 km? and contains approximately 2.6 x 
106 km3 of ice. Most of the ice sheet receives an excess of snow accumulation over the 
amount of ice lost to wind, meltwater run-off or other ablative processes. The majority of mass 
loss occurs at the margin of the ice sheet as either surface melt, which flows into the sea or 
calving of icebergs from the tongues of outlet glaciers. Many estimates of the magnitude of 
these processes have been published. The following table (from Ambach, 1980) summarizes an 
average of five published estimates: 
Accumulation Surface Melting Calving . Net 
Area (km2) 1.5 x 106 0.25 x 106 
Average Value (mm/a) 333 -1160 
Mass Flux (km3/a) 500 -290 -200 10 
If these estimates are correct, then this fable shows that the Greenland Ice Sheet is in approxi- 
mate equilibrium and contributes 490 km3/a of fresh water to the North Atlantic and Arctic 
Oceans. 
How would these contributions change in a different climate? At present, the altitude of 
the boundary between the accumulation and ablation areas (called the equilibrium line altitude, or 
ELA) is approximately 1,500 meters above sea level. At Camp Century (76.5°N) the increase in 
average surface temperature is 1.12°C per 100 meters of elevation (Benson, 1962), while further 
south along the EGIG line (~70.5°N), this value is 0.6°C/100 meters. Thus, as a rough approxi- 
mation, one can say that a temperature increase from 3 to 5°C would cause the ELA to increase 
about 500 meters in elevation. This scenario also roughly corresponds to the predicted 
atmospheric warming caused by a doubled amount of CO, in the atmosphere. In this case, the 
altered amounts of positive and negative mass flux (assuming no change in the average accumula- 
tion and melting rates) are as follows: 
Accumulation Surface Melting Calving Net 
Change in Area (km?) -0.34 x 106 0.34 x 106 0 0 
Change in Mass Flux (km3/a) -113 -394 0 -507 
New Mass Flux (km3/a) +387 -684 -200 -497 
Thus, the amount of meltwater discharged into the ocean would ne neage by 394 km3/a (or 136%), 
and the flux of fresh water into the seas would increase to 884 km3/a. If this temperature 
change occurred instantaneously, only about half of this increase would reach the oceans; the 
other half would be refrozen in the near-surface layers of snow in the newly created ablation 
regions. Within a decade or so, however, this meltwater contribution could be expected to 
reach the sea. 
How would the flow of the ice sheet be affected? This is difficult to say. The mass defi- 
cit of 497 km%/a would cause a thinning rate averaged over the entire surface of 0.29 m/a. 
Actually, this mass loss would be strongly concentnpted at the margins. To return to balance, 
the ablation area would need to decrease to 0.16 x 106 km? (assuming everything else remained 
constant). The average retreat of the ice edge would be 32 km. These changes in the ice sheet 
profile would lead to a steeper surface profile, which might imply faster flow and increased 
calving rates, but the magnitude of these effects are very difficult to assess. 
How can remote sensing be used to study the ice sheet? In particular, space-based alti- 
metry, passive microwave measurements and high-resolution imaging hold the greatest utility for 
application to the ice sheet. Altimetry surveys can provide measurements of elevation change 
over the entire ice sheet. Repeated every 5 to 10 years, regions of major changes would be 
readily identified. At the margin, where altimeters have a more difficult time tracking the 
steeper slopes, imaging systems can provide the best information on the position of the ice edge 
and its fluctuations. The great difference in microwave emissivity for wet and dry snow provi- 
des an obvious opportunity to monitor the extent and duration of the melt region over the entire 
ice sheet. Some of these studies are presently underway, but more can be done to develop 
these techniques and emphasis must be placed on the need for future remote sensors to provide 
repeated measurements. 
