What was done
The authors studied the mass balance of the Greenland and Antarctic ice sheets using two general circulation models (GCMs) developed at the Max Plank Institute for Meteorology, Hamburg, Germany: the older ECHAM3 GCM and its new and improved replacement, the ECHAM4 GCM.  Mass balance calculations were made by each model for both present-day and doubled atmospheric CO2 concentrations.

What was learned
Under the doubled atmospheric CO2 scenario, the mass balance of the Greenland ice sheet was projected to be negative in both models, indicative of a net reduction in the size of the ice sheet.  However, the newer ECHAM4 mass balance results for Greenland were "significantly smaller" (-63 mm per year for the ECHAM4 model vs. -229 mm per year for the ECHAM3 model).  The two models were in close agreement in their mass balance projections for the Antarctic ice sheet, however, where the ECHAM4 and ECHAM3 models projected net increases in ice sheet growth of +22 and +23 mm per year, respectively.  Furthermore, at the time of doubled CO2, the authors state that the ECHAM3 model projects a sea level rise "close to zero" (0.2 mm per year), while the ECHAM4 model projects a sea level fall of 0.6 mm per year.

What it means
With the introduction of the new ECHAM4 GCM, another climate alarmist prediction melts away.  Whereas the older ECHAM3 GCM projected a sea level rise from polar ice sheet wastage under a doubling of atmospheric CO2, the newer ECHAM4 model projects a sea level decline.  This is particularly good news for people living in low-lying coastal regions and on oceanic islands, who have been incessantly bombarded over the past few decades with climate alarmist-inspired stories of widespread flooding as a consequence of CO2-global warming causing sea levels to rise.