We present an ensemble of last glacial inception (LGI) simulations for the Northern Hemisphere that captures a significant fraction of inferred ice volume changes within proxy uncertainties. This ensemble was performed with LCice 1.0, a coupled ice sheet and climate model, varying parameters of both climate and ice sheet components, as well as the coupling between them. Certain characteristics of the spatiotemporal pattern of ice growth and subsequent retreat in both North America (NA) and Eurasia (EA) are sensitive to parameter changes while others are not. We find that the initial inception of ice over NA and EA is best characterized by the nucleation of ice at high-latitude and high-elevation sites. Subsequent spreading and merger along with large-scale conversion of snowfields dominate in different sectors. The latter plays an important role in the merging of eastern and western ice regions in NA.The inception peak ice volume in the ensemble occurs approximately at 111 ka and therefore lags the summer 60^∘ N insolation minimum by more than 3 kyr. Ice volumes consistently peak earlier over EA than NA. The inception peak in North America is characterized by a merged Laurentide and Cordilleran ice sheet, with the Davis Strait covered in ice in ∼80 % of simulations. Ice also bridges Greenland and Iceland in all runs by 114 ka and therefore blocks the Denmark Strait. This latter feature would thereby divert the East Greenland Current and Denmark Strait overflow with a potentially significant impact on ocean circulation. The Eurasian ice sheet at its inception peak varies across ensemble runs between a continuous ice sheet and multiple smaller ice caps.In both continents, the colder high latitudes (i.e. Ellesmere and Svalbard) tend to grow ice through the entire simulation (to 102 ka), while lower latitudes lose ice after ∼110 ka. We find temperature decreases over the initial phases of the inception lead to the expansion of NA ice sheet area and that subsequent precipitation increases contribute to its thickening. EA ice sheet area also expands with decreasing temperatures, but sea ice limits any increases in precipitation, leading to an earlier retreat away from the EA maximum ice sheet volume.We also examine the extent to which the capture of both LGI ice growth and retreat constrains the coupled ice–climate model sensitivity to changing atmospheric pCO₂. The 55-member sub-ensemble that meets our criteria for “acceptable” ice growth and retreat has an equilibrium climate sensitivity lower bound that is 0.3 ^∘C higher than that of the full ensemble. This suggests some potential value of fully coupled ice–climate modelling of the last glacial inception to constrain future climate change.

中文翻译：

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结合冰和气候模拟的北半球最后一次冰期起始轨迹

我们提出了北半球的最后一次冰期起始（LGI）模拟的整体，该模拟在代理不确定性范围内捕获了很大一部分推断的冰量变化。使用LCice 1.0，冰盖和气候模型耦合，气候和冰盖组件的变化参数以及它们之间的耦合来执行此合奏。北美（NA）和欧亚大陆（EA）的冰生长时空分布特征和随后的退缩都对参数变化敏感，而对其他参数则不敏感。我们发现，NA和EA上冰的初始始发的最佳特征是在高纬度和高海拔的冰成核。随后的扩散和合并以及雪原的大规模转换在不同部门占主导地位。^∘ 最小日照量超过3 kyr。在EA上，冰量的峰值始终早于NA。北美的初始峰的特征是Laurentide和Cordilleran冰盖融为一体，戴维斯海峡在约80年被冰覆盖 模拟的百分比。冰层还以114 ka的距离在格陵兰岛和冰岛之间架起了桥梁，因此阻塞了丹麦海峡。后一个特征将因此转移东格陵兰洋流和丹麦海峡的溢流，并对海洋环流产生潜在的重大影响。欧亚冰盖在开始时的峰值在整个冰盖和多个较小的冰盖之间的集合运行中有所不同。在这两个大陆上，较冷的高纬度地区（例如Ellesmere和Svalbard）在整个模拟过程中（直至102 ka）都倾向于生长冰，而低纬度地区则在约110度后失冰 K a。我们发现，在开始的初始阶段温度下降导致NA冰盖面积的扩大，而随后的降水增加则有助于其增厚。EA冰盖面积也随着温度的降低而扩大，但海冰限制了降水的增加，导致较早退出EA最大冰盖量的撤退。我们还研究了LGI冰的捕获和撤退受到限制的程度冰-气候耦合模型对大气p CO ₂变化的敏感性。符合我们“可接受的”冰生长和退缩标准的55人小组，具有^0.3∘的平衡气候敏感性下限 C高于完整合奏。这表明对最后一个冰期开始的冰-气候模型进行完全耦合以限制未来的气候变化具有潜在价值。