There has been extensive research into the nonlinear responses of the Earth system to astronomical forcing during the last glacial cycle. However, the speed and spatial geometry of ice sheet expansion to its largest extent at the Last Glacial Maximum 21 thousand years ago remains uncertain. Here we use an Earth system model with interactive ice sheets to show that distinct initial North American (Laurentide) ice sheets at 38 thousand years ago converge towards a configuration consistent with the Last Glacial Maximum due to feedbacks between atmospheric circulation and ice sheet geometry. Notably, ice advance speed and spatial pattern in our model are controlled by the amount of summer snowfall, which is dependent on moisture transport pathways from the North Atlantic warm pool linked to ice sheet geometry. The consequence of increased summer snowfall on the surface mass balance of the ice sheet is not only the direct increase in accumulation but the indirect reduction in melt through the snow/ice–albedo feedback. These feedbacks provide an effective mechanism for ice growth for a range of initial ice sheet states and may explain the rapid North American ice volume increase during the last ice age and potentially driving growth during previous glacial periods.

人们对末次冰期期间地球系统对天文强迫的非线性响应进行了广泛的研究。然而，21000年前末次盛冰期时冰盖扩张到最大程度的速度和空间几何形状仍然不确定。在这里，我们使用具有交互式冰盖的地球系统模型来显示，由于大气环流和冰盖几何形状之间的反馈，38000年前独特的初始北美（劳伦泰德）冰盖收敛到与末次盛冰期一致的配置。值得注意的是，我们模型中的冰前进速度和空间模式由夏季降雪量控制，这取决于与冰盖几何形状相关的北大西洋暖池的水分输送路径。夏季降雪增加对冰盖表面质量平衡的影响不仅是直接增加积雪，而且通过雪/冰反照率反馈间接减少融化。这些反馈为一系列初始冰盖状态的冰生长提供了有效的机制，并可以解释上一个冰河时期北美冰量的快速增加，并可能推动先前冰期的增长。