Large-scale singularities

Since the Third Assessment, the literature offers more specific guidance on possible thresholds for partial or near-complete deglaciation of Greenland and West Antarctic ice sheets. There is medium confidence that at least partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic ice sheet, would occur over a period of time ranging from centuries to millennia for a global average temperature increase of 1-4ºC (relative to 1990-2000), causing a contribution to sea-level rise of 4-6 m or more [WGI AR4 6.4, 10.7.4.3, 10.7.4.4; 19.3.5.2].