Abstract. The last deglaciation (∼20–11 ka BP) is a period of a major, long-term climate transition from a glacial to interglacial state that features multiple centennial- to decadal-scale abrupt climate variations whose root cause is still not fully understood. To better understand this time period, the Paleoclimate Modelling Intercomparison Project (PMIP) has provided a framework for an internationally coordinated endeavour in simulating the last deglaciation whilst encompassing a broad range of models. Here, we present a multi-model intercomparison of 17 transient simulations of the early part of the last deglaciation (∼20–15 ka BP) from nine different climate models spanning a range of model complexities and uncertain boundary conditions and forcings. The numerous simulations available provide the opportunity to better understand the chain of events and mechanisms of climate changes between 20 and 15 ka BP and our collective ability to simulate them. We conclude that the amount of freshwater forcing and whether it follows the ice sheet reconstruction or induces an inferred Atlantic meridional overturning circulation (AMOC) history, heavily impacts the deglacial climate evolution for each simulation rather than differences in the model physics. The course of the deglaciation is consistent between simulations except when the freshwater forcing is above 0.1 Sv – at least 70 % of the simulations agree that there is warming by 15 ka BP in most places excluding the location of meltwater input. For simulations with freshwater forcings that exceed 0.1 Sv from 18 ka BP, warming is delayed in the North Atlantic and surface air temperature correlations with AMOC strength are much higher. However, we find that the state of the AMOC coming out of the Last Glacial Maximum (LGM) also plays a key role in the AMOC sensitivity to model forcings. In addition, we show that the response of each model to the chosen meltwater scenario depends largely on the sensitivity of the model to the freshwater forcing and other aspects of the experimental design (e.g. CO2 forcing or ice sheet reconstruction). The results provide insight into the ability of our models to simulate the first part of the deglaciation and how choices between uncertain boundary conditions and forcings, with a focus on freshwater fluxes, can impact model outputs. We can use these findings as helpful insight in the design of future simulations of this time period.

中文翻译：

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末次冰消早期的多模型评估（PMIP4 LDv1）：融水视角

摘要。最后一次冰消期（∼20-11 ka BP）是从冰期到间冰期状态的一个重大、长期的气候转变时期，其特征是多个百年到十年尺度的气候突变，其根本原因尚未完全了解。为了更好地了解这一时期，古气候模拟比对项目（PMIP）为模拟上次冰消期的国际协调努力提供了一个框架，同时涵盖了广泛的模型。在这里，我们对来自九个不同气候模型的末次冰消早期（∼20-15 ka BP）的 17 个瞬态模拟进行了多模型相互比较，涵盖了一系列模型复杂性和不确定的边界条件和强迫。大量可用的模拟提供了更好地了解 20 至 15 ka BP 之间气候变化的事件链和机制以及我们模拟它们的集体能力的机会。我们得出的结论是，淡水强迫的量以及它是否遵循冰盖重建或引起推断的大西洋经向翻转环流（AMOC）历史，严重影响每个模拟的冰消气候演化，而不是模型物理的差异。除了当淡水强迫高于 0.1 Sv 时外，模拟之间的冰消过程是一致的 - 至少 70% 的模拟同意在大多数地方（不包括融水输入的位置）变暖了 15 ka BP。对于 18 ka BP 以来超过 0.1 Sv 的淡水强迫的模拟，北大西洋的变暖被延迟，并且表面气温与 AMOC 强度的相关性要高得多。然而，我们发现末次盛冰期 (LGM) 后 AMOC 的状态在 AMOC 对模型强迫的敏感性中也起着关键作用。此外，我们表明每个模型对所选融水情景的响应很大程度上取决于模型对淡水强迫和实验设计的其他方面（例如二氧化碳强迫或冰盖重建）的敏感性。结果使我们深入了解我们的模型模拟冰消第一部分的能力，以及不确定边界条件和强迫之间的选择（重点关注淡水通量）如何影响模型输出。我们可以利用这些发现作为设计这一时期未来模拟的有用见解。