Greenland ice sheet to melt at lower temperature than anticipated?

I am sitting in the opening session of the science section of the Arctic Frontiers conference gathering scientists and experts from around the world in the Norwegian Arctic town of Tromsö. Leading German climate scientist Stefan Rahmstorf of the Potsdam Institute for Climate Impact research has just quoted an as yet unpublished paper by colleagues, currently being reviewed, indicating that the temperature threshold for a melting of the Greenland ice sheet could be as low as 1.3 to 2.3 degrees C. The IPCC assessment assumes a temperature rise of 1.9 to 4.6 degrees C. as the critical threshold.
The Cancun agreement to limit warming to 2 degrees was based on IPCC figures. There is however an agreement on the need to review the scientific basis for the maximum temperature rise limit.
Given the huge significance of the Greenland ice sheet – a complete melting of the Greenland ice sheet could mean a rise in sea level of 7 metres- this would be a very significant new study, assuming it is reviewed positively. He expects it to be published in a month or two. Rahmstorf does not want to say any more, as it is not his paper and the authors are not present. But he is not the sort of scientist who quotes studies without careful consideration. He says he\’s glad the Cancun conference agreed to keep reviewing the science that provides the basis for setting the temperature limits.