The land ice contribution to global mean sea level rise has not yet been predicted¹ using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models^{2,3,4,5,6,7,8}, but primarily used previous-generation scenarios⁹ and climate models¹⁰, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios^11,12 using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.

尚未使用冰盖和冰川模型来预测陆地冰对全球平均海平面上升的贡献¹用于最新的社会经济情景，也没有使用对所涉及的各种计算机模型产生的不确定性进行协调探索。最近的两个国际项目使用多个模型^{2、3、4、5、6、7、8}生成了大量预测，但主要使用上一代情景⁹和气候模型¹⁰，并且无法充分探索已知的不确定性。在这里，我们估计了新情景下这些预测的概率分布^11,12使用冰盖和冰川模型的统计模拟。我们发现，相对于目前的排放承诺，将全球变暖限制在 1.5 摄氏度将使陆冰对 21 世纪海平面上升的贡献减少一半。到 2100 年，中位数从 25 厘米降低到 13 厘米海平面当量 (SLE)，冰川占海平面贡献的一半。由于气候变暖中冰损失增加和降雪积累的竞争过程存在不确定性，预计的南极贡献并未显示出对排放情景的明确响应。然而，在规避风险（悲观）的假设下，南极冰的流失可能会高出五倍，根据当前的政策和承诺，将陆地冰的贡献中值增加到 42 厘米 SLE，即使在 1.5 摄氏度的升温下，第 95 个百分位的投影也超过半米。这将严重限制减轻未来沿海洪水的可能性。鉴于如此大的范围（在 13 厘米 SLE 之间使用 1.5 摄氏度变暖下的主要预测和 42 厘米 SLE 使用根据当前承诺的风险规避预测），21 世纪海平面上升的适应规划必须考虑一个因素- 在气候政策和南极响应受到进一步限制之前，陆地冰的贡献存在三个不确定性。