They found that, on average, 13 percent of total ice shelf area is "passive shelf ice:" it's floating ice that provides no further buttressing. That is to say, the loss of such passive shelf ice would not in itself affect the ice sheet, although it would expose a "safety band" of ice behind it.
"Once ice loss through the calving of icebergs goes beyond the passive shelf ice and cuts into the safety band, ice flow toward the ocean will accelerate, which might well entail an elevated contribution to sea-level rise for decades and centuries to come," explained study co-author Dr Johannes Fürst, from the University of Erlangen-Nuremberg's Institute of Geography. Unfortunately, some ice shelves have less passive ice than others.
"The Amundsen and Bellingshausen Seas (in the West Antarctic) have limited or almost no passive ice shelf, which implies that further retreat of current ice-shelf fronts will have serious dynamic consequences," Furst added. "This region is particularly vulnerable as ice shelves have already been thinning at high rates for two decades."