12 May 2014, it was announced that two teams of scientists said the long-feared collapse of the Ice Sheet had begun, kicking off what they say will be a centuries-long, "unstoppable" process that could raise sea levels by They estimate that rapid drawdown of Thwaites Glacier will begin in 200 – 1000 years. (Scientific source articles: Rignot et al. 2014 and Joughin et al. 2014.) More recent research suggests that a partial collapse of Thwaites Glacier could occur sooner, as the ice shelf that restricts the eastern third of the glacier's flow is now showing instability, as warming waters undermine the grounding zone, where the glacier connects to its floating ice shelf. According to Ted Scambos, a glaciologist at the University of Colorado Boulder and a leader of the International Thwaites Glacier Collaboration, in a 2021 interview from McMurdo Station, "Things are evolving really rapidly here. It's daunting." Later in 2014, the IPCC Fifth Assessment Report discussed the possibility of the collapse of marine-based sectors of the Antarctic ice sheet. It expressed medium confidence that if such an event were to occur, it would not add more than several tenths of a metre to sea level rise during this period. In the absence of a collapse, it estimated that the gradual ice loss would most likely add around 6 cm to sea level rise under the Representative Concentration Pathway 2.6 (a scenario of strong climate change mitigation), and 4 cm under RCP 8.5, a scenario where the greenhouse gas emissions continue to increase at a high rate for the rest of the century. The reason why a scenario of much greater warming sees a lower contribution to sea level rise is because the more intense effects of climate change on the water cycle result in an increased precipitation over the ice sheet, which would freeze on the surface, and this increase in the surface mass balance (SMB) would counteract a larger fraction of the ice loss. The uncertainty in the way different climate change models simulate both ice sheet dynamics and the water cycle means that for RCP 2.6 and RCP 8.5, the 5%-95% confidence interval ranges from a 4 cm decrease in sea levels to a 16 cm rise, and an 8 cm decrease to a 14 cm rise, respectively. In 2016, improved computer modeling revealed that the breakup of glaciers could lead to a steep rise in sea