The Paris Agreement aims to limit global mean warming in the twenty-first century to less than 2 degrees Celsius above preindustrial levels, and to promote further efforts to limit warming to 1.5 degrees Celsius¹. The amount of greenhouse gas emissions in coming decades will be consequential for global mean sea level (GMSL) on century and longer timescales through a combination of ocean thermal expansion and loss of land ice². The Antarctic Ice Sheet (AIS) is Earth’s largest land ice reservoir (equivalent to 57.9 metres of GMSL)³, and its ice loss is accelerating⁴. Extensive regions of the AIS are grounded below sea level and susceptible to dynamical instabilities^5,6,7,8 that are capable of producing very rapid retreat⁸. Yet the potential for the implementation of the Paris Agreement temperature targets to slow or stop the onset of these instabilities has not been directly tested with physics-based models. Here we use an observationally calibrated ice sheet–shelf model to show that with global warming limited to 2 degrees Celsius or less, Antarctic ice loss will continue at a pace similar to today’s throughout the twenty-first century. However, scenarios more consistent with current policies (allowing 3 degrees Celsius of warming) give an abrupt jump in the pace of Antarctic ice loss after around 2060, contributing about 0.5 centimetres GMSL rise per year by 2100—an order of magnitude faster than today⁴. More fossil-fuel-intensive scenarios⁹ result in even greater acceleration. Ice-sheet retreat initiated by the thinning and loss of buttressing ice shelves continues for centuries, regardless of bedrock and sea-level feedback mechanisms^10,11,12 or geoengineered carbon dioxide reduction. These results demonstrate the possibility that rapid and unstoppable sea-level rise from Antarctica will be triggered if Paris Agreement targets are exceeded.

《巴黎协定》旨在将 21 世纪的全球平均升温幅度限制在比工业化前水平高出 2 摄氏度以下，并推动进一步努力将升温幅度限制在 1.5 摄氏度¹。^{未来几十年的温室气体排放量将通过海洋热膨胀和陆地冰的流失2}对世纪和更长时间内的全​​球平均海平面 (GMSL) 产生影响。南极冰盖 (AIS) 是地球上最大的陆地冰库（相当于 57.9 米的 GMSL）³，其冰层流失正在加速⁴。AIS 的广泛区域位于海平面以下，容易受到动态不稳定性的影响^5,6,7,8能够产生非常迅速的撤退⁸。然而，实施《巴黎协定》温度目标以减缓或阻止这些不稳定性发生的潜力尚未通过基于物理的模型进行直接测试。在这里，我们使用经过观测校准的冰盖 - 架模型来表明，在全球变暖限制在 2 摄氏度或更低的情况下，南极冰层流失的速度将在整个 21 世纪以与今天相似的速度继续存在。然而，与当前政策更一致的情景（允许升温 3 摄氏度）在 2060 年左右之后南极冰层流失的速度突然跳跃，到 2100 年每年增加约 0.5 厘米 GMSL - 比今天快一个数量级⁴ . 更多化石燃料密集型情景⁹导致更大的加速度。^{无论基岩和海平面反馈机制10,11,12}或地球工程二氧化碳减少如何，由支撑冰架变薄和丧失引发的冰盖退缩持续了几个世纪。这些结果表明，如果超过《巴黎协定》的目标，南极洲可能会引发海平面快速且不可阻挡的上升。