2 degrees to go before the Ross Ice Shelf starts to collapse

Warm up the atmosphere by a further 2 degrees, the oceans by 0.5 degrees and the major Antarctic ice shelves will collapse. These are the findings of Nick Golledge from Victoria University of Wellington and colleagues. They ran a three dimensional model of the antarctic ice sheets and found that the only IPCC greenhouse gas scenario that did not lead to ice shelf collapse was if green-house gas emissions peaked this decade. All others led to ice shelf collapse. The scenario where green house gases continue to increase at the current rate leads to the ice-shelves collapsing by the end of this century. The ice shelves currently act as a buttress, holding back glacier flow from within the continent. Without the ice shelves these glaciers will speed up and so will their contribution to sea level rise. This effect will continue for thousands of years. This work was published in Nature

Glacier speed related to liquid water input variability rather than quantity

Laura Kehrl, working with the glaciological team at Victoria University have reported on their precise measurements of the surface velocity of the Franz Josef glacier. They put a whole lot of GPS sensors on the glacier and left them to log their position during March of 2011 and then again over late summer in 2013. They found the glacier sped up and slowed down every day and sped up following rain. The movement propagated from up glacier down to the terminus. When comparing the movement to their best estimates of rainfall and melt water they concluded the glacier speed was related to the change in liquid water, not just the quantity of water. They attribute this to the sub-glacial conduits closing during low flows leading to high pressure when the next high flows occurred. This high water pressure reduced friction between the glacier and the rock beneath it letting the glacier speed up. The research is published the Journal of Glaciology.