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The Antarctic Ice Sheet (AIS) remains the largest uncertainty in projections of future sea level rise. A likely climate-driven vulnerability of the AIS is thinning of floating ice shelves resulting from surface-melt-driven hydrofracture or incursion of relatively warm water into subshelf ocean cavities. The resulting melting, weakening, and potential ice shelf collapse reduces shelf buttressing effects. Upstream ice flow accelerates, causing thinning, grounding-line retreat, and potential ice sheet collapse. While high-resolution projections have been performed for localized Antarctic regions, full-continent simulations have typically been limited to low-resolution models. Here we quantify the vulnerability of the entire present-day AIS to regional ice shelf collapse on millennial timescales treating relevant ice flow dynamics at the necessary similar to 1-km resolution. Collapse of any of the ice shelves dynamically connected to theWest Antarctic Ice Sheet (WAIS) is sufficient to trigger ice sheet collapse in marine-grounded portions of the WAIS. Vulnerability elsewhere appears limited to localized responses.

Plain Language Summary The biggest uncertainty in near-future sea level rise (SLR) comes from the Antarctic Ice Sheet. Antarctic ice flows in relatively fast-moving ice streams. At the ocean, ice flows into enormous floating ice shelves that push back on their feeder ice streams, buttressing them and slowing their flow. Melting and loss of ice shelves due to climate changes can result in faster-flowing, thinning, and retreating ice leading to accelerated rates of global SLR. To learn where Antarctica is vulnerable to ice shelf loss, we divided it into 14 sectors, applied extreme melting to each sector's floating ice shelves in turn, then ran our ice flow model 1,000 years into the future for each case. We found three levels of vulnerability. The greatest vulnerability came from attacking any of the three ice shelves connected to West Antarctica, where much of the ice sits on bedrock lying below sea level. Those dramatic responses contributed around 2 m of SLR. The second level came from four other sectors, each with a contribution between 0.5 and 1 m. The remaining sectors produced little to no contribution. We examined combinations of sectors, determining that sectors behave independently of each other for at least a century.