Description: The HadCM3 AOGCM has been coupled with a dynamic 3D model of the Green-landice sheet that includes a visco-elastic solid Earth model. The AOGCM exchangesinformation with the sheet model once a year. Precipitation and temperature anomalies are passed to the ice sheet model, which calculates ablation (using a degree-day scheme), ice dynamics and basal rebound. The ice sheet model passes back to the GCM an updated orography and freshwater fluxes. Iceberg calving fluxes are applied evenly to the sea region adjacent to Greenland whilst runoff enters the ocean at coastal points. When a GCM grid cell changes from ice-covered to ice-free or vice-versa, the surface characteristics are modified appropriately. A multiple-century experiment is being undertaken, starting from the present-day ice sheet, with four times the pre-industrial atmospheric CO2 concentration, to determine the rate of ice ablation, the effect on oceanic circulation and local climate, and the feedback of orographic and climate change on the ice sheet mass balance. Over the first 200 years, the contribution to global average sea level rise as a result of loss of mass from the ice sheet is about 5 mm/yr.

Description: The HadCM3 AOGCM has been coupled to a 3D dynamic model of the Greenland ice sheet, which includes a visco-elastic solid Earth model. Once every year the AOGCM provides the ice sheet model with precipitation and temperature anomalies which it uses in order to calculate ablation, ice dynamics and basal rebound. A new orography and fresh water fluxes are passed back to the OAGCM to be utilised over the subsequent year. The water from the melting of calved Icebergs is applied evenly to the sea region adjacent to Greenland whilst runoff enters the ocean through 'river' outlets. A multiple century experiment starting from the present day ice sheet with an atmospheric CO2 concentration of four times pre-industrial levels is being undertaken to determine the rate of ice ablation and the impact of ice sheet changes on simulated sea level, and oceanic and atmospheric circulation. The effect of orographic changes in the ice sheet on its own mass balance is also of interest. The results from the first 180 years of the simulation indicate that the modelled surface air temperature over Greenland in the 4xCO2 climate is around 8 degrees warmer than in the pre-industrial control, compared with a global mean difference of 5 degrees. Precipitation is increased by 33% in the 4xCO2 experiment but the rate of ablation rises by 640%, causing a direct sea-level rise of 5mm per year. To understand the mechanisms of change we will examine the spatial patterns of temperature and precipitation anomalies for the model control and 4xCO2 experiments and compare them with data from anomalously warm years determined from in situ (ice core) data.