True, I was just thinking that 215 km3 is just a small fraction. However I just did this math:

Sea surface area earth: 361,126,221 km2 (source)
Lost of ice on greenland: 215 km3
Average rice in sealevel: 0,69 mm (divide the two)

Synthetic Aperture Radar has been used on a european satellite since 1991: http://en.wikipedia.org/wiki/European_Remote-Sensing_Satellite

That would possibly give one more data point, stil not enough to extrapolate the curve.

Water expands when freezing, did you take that into account?