Surface mass balance model intercomparison for the Greenland ice sheet

in Cryosphere (The) (2013), 7

A number of high resolution reconstructions of the surface mass balance (SMB) of the Greenland ice sheet (GrIS) have been produced using global re-analyses data extending back to 1958. These ... [more ▼]

A number of high resolution reconstructions of the surface mass balance (SMB) of the Greenland ice sheet (GrIS) have been produced using global re-analyses data extending back to 1958. These reconstructions have been used in a variety of applications but little is known about their consistency with each other and the impact of the downscaling method on the result. Here, we compare four reconstructions for the period 1960–2008 to assess the consistency in regional, seasonal and integrated SMB components. Total SMB estimates for the GrIS are in agreement within 34% of the four model average when a common ice sheet mask is used. When models' native land/ice/sea masks are used this spread increases to 57%. Variation in the spread of components of SMB from their mean: runoff 42% (29% native masks), precipitation 20% (24% native masks), melt 38% (74% native masks), refreeze 83% (142% native masks) show, with the exception of refreeze, a similar level of agreement once a common mask is used. Previously noted differences in the models' estimates are partially explained by ice sheet mask differences. Regionally there is less agreement, suggesting spatially compensating errors improve the integrated estimates. Modelled SMB estimates are compared with in situ observations from the accumulation and ablation areas. Agreement is higher in the accumulation area than the ablation area suggesting relatively high uncertainty in the estimation of ablation processes. Since the mid-1990s each model estimates a decreasing annual SMB. A similar period of decreasing SMB is also estimated for the period 1960–1972. The earlier decrease is due to reduced precipitation with runoff remaining unchanged, however, the recent decrease is associated with increased precipitation, now more than compensated for by increased melt driven runoff. Additionally, in three of the four models the equilibrium line altitude has risen since the mid-1990s, reducing the accumulation area at a rate of approximately 60 000 km2 per decade due to increased melting. Improving process representation requires further study but the use of a single accurate ice sheet mask is a logical way to reduce uncertainty among models. [less ▲]

Hydrologic response of the Greenland ice sheet: the role of oceanographic warming

in Hydrological Processes (2009), 23(1), 7-30

The response of the Greenland ice sheet to ongoing climate change remains an area of great uncertainty, with most previous studies having concentrated on the contribution of the atmosphere to the ice mass ... [more ▼]

The response of the Greenland ice sheet to ongoing climate change remains an area of great uncertainty, with most previous studies having concentrated on the contribution of the atmosphere to the ice mass-balance signature. Here we systematically assess for the first time the influence of oceanographic changes on the ice sheet. The first part of this assessment involves a statistical analysis and interpretation of the relative changes and variations in sea-surface temperatures (SSTs) and air temperatures around Greenland for the period 1870-2007. This analysis is based on HadISST1 and Reynolds OI.v2 SST analyses, in situ SST and deeper ocean temperature series, surface-air-temperature records for key points located around the Greenland coast, and examination of atmospheric pressure and geopotential height from NCEP/NCAR reanalysis. Second, we carried out a novel sensitivity experiment in which SSTs were perturbed as input to a regional climate model, and document the resulting effects on simulated Greenland climate and surface mass balance. We conclude that sea-surface/ocean temperature forcing is not sufficient to strongly influence precipitation/snow accumulation and melt/runoff of the ice sheet. Additional evidence from meteorological reanalysis suggests that high Greenland melt anomalies of summer 2007 are likely to have been primarily forced by anomalous advection of warm air masses over the ice sheet and to have therefore had a more remote atmospheric origin. However, there is a striking correspondence between ocean warming and dramatic accelerations and retreats of key Greenland outlet glaciers in both southeast and southwest Greenland during the late 1990s and early 2000s. [less ▲]

Estimation of the 1900-2100 Greenland ice sheet surface mass balance

Conference (2008, April)