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Satellite radar and aircraft laser altimeter data and a volume budget comparison of total snow accumulation with total ice discharge give three independent estimates of the recent mass balance of parts of the Greenland ice sheet above ∼2000 m elevation. Results show the entire region, on average, to be in balance to within 10 mm yr−1, with very low rates of regional thickness change (dH/dt) in the northeast but high rates with large spatial variability in the south. Only the volume budget estimates show significant thinning in the northwest, but thinning in this area is also inferred from local measurements of ice vertical velocities down boreholes. South of latitude 68°N, there has been rapid thickening west of the ice divide, with equally rapid thinning in the southeast, but with large differences between the three estimates of dH/dt throughout this region. The radar data apply to the period 1978–1988, the laser data are for 1993/1994–1998/1999, and the volume budget calculations represent conditions over at least the last few decades. Consequently, many of the differences between results could be caused by temporal changes, particularly in snow accumulation rates, that occurred since the 1970s. However, taken with other information, our results suggest long-term thickening in the southwest and possibly quite recent onset of rapid thinning in the southeast.

Multivariate regression methods are applied toneasurements of accumulation covering much of the interior of the Greenland ice sheet to evaluate the important factors that describe the current distribution of accumulation. Predictor variables considered in the regressions are geographical coordinates and three independent factors describing the geometry of the ice sheet. The results indicate that most of the variance in the data is explained by the combined effect of large-scale atmospheric circulation and ice sheet topographyo This finding implies that climate change scenarios in which changes in accumulation are mostly associated with changes in temperature or some other parameter may only be correct if the pattern of atmospheric circulation remains unaltered. Comparison with values predicted with a precipitation retrieval model is favorable, suggesting that the model captures the most important features of Greenland precipitation. Approximately 80% of the total area of Greenland is ice cov- ered. The main ice sheet reaches thicknesses in excess of 3 km and contains enough water to raise global sea level by 7 m if all ice were to melt. The ice cover is nourished and maintained by snowfall at higher elevations, while mass is lost through surface ablation and subsequent meltwater runoff in the coastal regions, melting underneath floating tidal glaciers, and calving at glacier tmxnini. Redistribution of mass from the accumulation area to the marginal ablation zones is achieved through ice flow. The magnitude of each of these processes determines whether the ice sheet is in balance or whether it is growing or slu-inkingIn as- sessing the state of balance of the Greenland ice sheet, it is thus important to detexnine accurately each term in the mass budget. In this study, the source term of average accumulation in the inte- rior is considered. The interior is defined as the region where surface elevations are in excess of 1100 m above sea level. At these elevations the contributions to net accmnulation of mass as- sociated with evaporation, condensation, surface ablation and runoff, and, perhaps, snowdrift are small (Ohnura et al., 1999). Using observations from automated weather stations, Box and Steffen (this issue) estimate sublimation over the Greenland ice sheet. Their results indicate that annual sublimation loss occurs mostly in the ablation zone at lower elevations (