Palaeoclimate model simulations are an important tool to improve our understanding of the mechanisms of climate change. These simulations also provide tests of the ability of models to simulate climates very different to today. Here we present the results from two brand-new simulations using the latest version of the UK's physical climate model, HadGEM3-GC3.1; they are the mid-Holocene (∼6 ka) and Last Interglacial (∼127 ka) simulations, both conducted under the auspices of CMIP6/PMIP4. This is the first time this version of the UK model has been used to conduct palaeoclimate simulations. These periods are of particular interest to PMIP4 because they represent the two most recent warm periods in Earth history, where atmospheric concentration of greenhouse gases and continental configuration are similar to the pre-industrial period but where there were significant changes to the Earth's orbital configuration, resulting in a very different seasonal cycle of radiative forcing. Results for these simulations are assessed firstly against the same model's pre-industrial control simulation (a simulation comparison, to describe and understand the differences between the pre-industrial – PI – and the two palaeo simulations) and secondly against previous versions of the same model relative to newly available proxy data (a model–data comparison, to compare all available simulations from the same model with proxy data to assess any improvements due to model advances). The introduction of this newly available proxy data adds further novelty to this study. Globally, for metrics such as 1.5 m temperature and surface rainfall, whilst both the recent palaeoclimate simulations are mostly capturing the expected sign and, in some places, magnitude of change relative to the pre-industrial, this is geographically and seasonally dependent. Compared to newly available proxy data (including sea surface temperature – SST – and rainfall) and also incorporating data from previous versions of the model shows that the relative accuracy of the simulations appears to vary according to metric, proxy reconstruction used for comparison and geographical location. In some instances, such as mean rainfall in the mid-Holocene, there is a clear and linear improvement, relative to proxy data, from the oldest to the newest generation of the model. When zooming into northern Africa, a region known to be problematic for models in terms of rainfall enhancement, the behaviour of the West African monsoon in both recent palaeoclimate simulations is consistent with current understanding, suggesting a wetter monsoon during the mid-Holocene and (more so) the Last Interglacial, relative to the pre-industrial era. However, regarding the well-documented “Saharan greening” during the mid-Holocene, results here suggest that the most recent version of the UK's physical model is still unable to reproduce the increases suggested by proxy data, consistent with all other previous models to date.

中文翻译：

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使用HadGEM3对全新世中期和上一次冰期之间的CMIP6 / PMIP4模拟：与工业化前时代，先前模型版本和代理数据的比较

古气候模型模拟是增进我们对气候变化机制的理解的重要工具。这些模拟还提供了对模型模拟与当今截然不同的气候的能力的测试。在这里，我们展示了使用英国物理气候模型的最新版本HadGEM3-GC3.1进行的两个全新模拟的结果；它们是全新世中期（？6？ka）和最后一次冰期（？127）？ka）模拟，均在CMIP6 / PMIP4的主持下进行。这是此版本的UK模型首次用于进行古气候模拟。这两个时段对PMIP4尤其重要，因为它们代表了地球历史上的两个最近的暖期，其中大气中温室气体的浓度和大陆构造与工业化前时期相似，但是地球的轨道构造发生了重大变化，导致辐射强迫的季节周期非常不同。首先，针对同一模型的工业化前控制模拟（模拟比较，描述和理解前工业之间的区别 PI –？和两个古模拟），其次针对相对于新可用代理数据的同一模型的先前版本（模型数据比较，以比较来自同一模型的所有可用模拟与代理数据，以评估由于模型而导致的任何改进进步）。这种新近可用的代理数据的引入为这项研究增加了更多的新颖性。在全球范围内，对于诸如1.5摄氏度的温度和地表降雨等度量标准，而最近的古气候模拟都大多捕获了预期的信号，并且在某些地方，相对于工业化之前的变化幅度，这在地理上和季节性依赖。与新近可用的代理数据（包括海面温度SST和降雨）相比较，并结合了先前版本的数据后得出的结果表明，模拟的相对准确性似乎根据度量而有所不同，用于比较和地理位置的代理重建。在某些情况下，例如全新世中期的平均降雨量，相对于代理数据，模型的最旧到最新一代都有明显且线性的改善。当放大到北部非洲时，该地区的降雨增加在模型方面是有问题的，在最近的古气候模拟中，西非季风的行为与当前的认识是一致的，这表明全新世中期的季风较为湿润。所以）最后的冰河间 相对于工业化之前的时代。但是，关于有据可查的“撒哈拉沙漠绿化”问题？在全新世中期，这里的结果表明，英国物质的最新版本 该模型仍然无法再现代理数据建议的增加量，与迄今为止的所有其他先前模型一致。