The Last Glacial Maximum (LGM, ∼ 21 000 years ago) has been a major focus for evaluating how well state-of-the-art climate models simulate climate changes as large as those expected in the future using paleoclimate reconstructions. A new generation of climate models has been used to generate LGM simulations as part of the Paleoclimate Modelling Intercomparison Project (PMIP) contribution to the Coupled Model Intercomparison Project (CMIP). Here, we provide a preliminary analysis and evaluation of the results of these LGM experiments (PMIP4, most of which are PMIP4-CMIP6) and compare them with the previous generation of simulations (PMIP3, most of which are PMIP3-CMIP5). We show that the global averages of the PMIP4 simulations span a larger range in terms of mean annual surface air temperature and mean annual precipitation compared to the PMIP3-CMIP5 simulations, with some PMIP4 simulations reaching a globally colder and drier state. However, the multi-model global cooling average is similar for the PMIP4 and PMIP3 ensembles, while the multi-model PMIP4 mean annual precipitation average is drier than the PMIP3 one. There are important differences in both atmospheric and oceanic circulations between the two sets of experiments, with the northern and southern jet streams being more poleward and the changes in the Atlantic Meridional Overturning Circulation being less pronounced in the PMIP4-CMIP6 simulations than in the PMIP3-CMIP5 simulations. Changes in simulated precipitation patterns are influenced by both temperature and circulation changes. Differences in simulated climate between individual models remain large. Therefore, although there are differences in the average behaviour across the two ensembles, the new simulation results are not fundamentally different from the PMIP3-CMIP5 results. Evaluation of large-scale climate features, such as land–sea contrast and polar amplification, confirms that the models capture these well and within the uncertainty of the paleoclimate reconstructions. Nevertheless, regional climate changes are less well simulated: the models underestimate extratropical cooling, particularly in winter, and precipitation changes. These results point to the utility of using paleoclimate simulations to understand the mechanisms of climate change and evaluate model performance.

中文翻译：

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PMIP4最后一次冰河最大实验：初步结果并与PMIP3模拟进行比较

最后冰川最大值（LGM，〜 21 000年前）一直是评估最新气候模型模拟气候变化的能力的主要重点，而气候变化将通过古气候重建模拟出与未来预期的气候变化一样大的气候变化。作为对耦合模型比对项目（CMIP）的古气候模拟比对项目（PMIP）的一部分，新一代气候模型已用于生成LGM模拟。在这里，我们对这些LGM实验（PMIP4，其中大多数是PMIP4-CMIP6）的结果进行了初步分析和评估，并将它们与上一代仿真（PMIP3，其中大多数是PMIP3-CMIP5）进行了比较。我们显示，与PMIP3-CMIP5模拟相比，PMIP4模拟的全球平均水平在年平均地表气温和年平均降水量方面具有更大的范围，其中有些PMIP4模拟达到全球较冷和较干燥的状态。但是，PMIP4和PMIP3集合的多模式全球平均降温相似，而PMIP4的多模式全球平均降温要比PMIP3少。这两组实验在大气和海洋环流方面都存在重要差异，其中北部和南部的喷射流更具极向性，而在PMIP4-CMIP6模拟中，大西洋经向翻转环流的变化不如在PMIP3-中那么明显。 CMIP5模拟。模拟降水模式的变化受温度和循环变化的影响。各个模型之间模拟气候的差异仍然很大。因此，尽管两个乐团的平均行为有所不同，新的仿真结果与PMIP3-CMIP5结果没有本质上的不同。对大规模气候特征（如陆海对比和极地放大）的评估证实，这些模型很好地捕获了这些特征，并且在古气候重建的不确定性范围内。然而，对区域气候变化的模拟不太好：这些模型低估了温带降温，尤其是在冬季，以及降水量的变化。这些结果表明使用古气候模拟来了解气候变化的机制并评估模型性能的实用性。证实了这些模型很好地捕获了这些，并且在古气候重建的不确定性范围内。然而，对区域气候变化的模拟不太好：这些模型低估了温带降温，尤其是在冬季，以及降水量的变化。这些结果表明使用古气候模拟来了解气候变化的机制并评估模型性能的实用性。证实了这些模型很好地捕获了这些，并且在古气候重建的不确定性范围内。然而，对区域气候变化的模拟不太好：这些模型低估了温带降温，尤其是在冬季，以及降水量的变化。这些结果表明使用古气候模拟来了解气候变化的机制并评估模型性能的实用性。