David Vaughan of the British Antarctic Survey, who is leading the year-old project, believes that the IPCC report in 2007 took a brave stance by saying that not enough had been published on ice sheets to know the upper range of their contribution to sea-level rise. "In the next IPCC report I don't think this is going to wash," he said at the European Geosciences Union conference in Vienna, "and we will be under great pressure to give an upper limit." But he admits that the scheduling is difficult.
The question is important as ice-sheet behaviour is the biggest uncertainty in predicting sea-level rise. The contribution of water from melting ice sheets is likely to be at least as large as that from thermal expansion of the oceans.
Firming up this uncertainty is a complex procedure. The first step in the Ice2sea approach is to create emissions scenarios for carbon dioxide and methane, and use them to make global climate projections for the next 200 years. Next the team will adapt this global model to come up with regional climate projections for Antarctica, Greenland and alpine glacier systems. Finally, these regional projections will drive a new suite of ice-sheet and glacier models to predict the ice's contribution to sea-level rise.
But progress has been made. Researchers at the UK's Met Office have already done the global climate models – these are now being passed around the scientific community for comment before the regional climate modelling begins. The Ice2sea project hopes to make its first sea-level-rise projections in 2011 or 2012.