What was done
The authors analyzed a suite of spatially-distributed histories of annual mass accumulation obtained from ice core data collected under the Program for Arctic Regional Climate Assessment (PARCA), including 350-year histories from northwest Greenland and the summit area.

What was learned
Because of the great variability in the results obtained from the different cores, the authors concluded that "climate reconstructions from a single core must be interpreted cautiously."  In addition, the two 350-year histories exhibited significant miltidecadal variability.  Also, regional composites for northwest and central Greenland were determined to be "strongly in and out of phase for decades at a time," and since 1940 have essentially been decoupled.

What it means
Facing up to these realities, the authors indicate that much remains to be done before definitive statements can be made about the current mass balance of the Greenland Ice Sheet.  Specifically, they note that "longer regional annual net accumulation composites from a suite of carefully sited cores, coupled with longer-term altimeter observations, would contribute substantially to future mass balance evaluations."  Until such is done, we will remain pretty much in the dark relative to this important aspect of global climate change.