Abstract. Here we present the experimental design and results from a new mid-Pliocene simulation using the latest version of the UK’s physical climate model, HadGEM3-GC31-LL, conducted under the auspices of CMIP6/PMIP4/PlioMIP2. Although two other paleoclimate simulations have been recently run using this model, they both focused on more recent periods within the Quaternary and therefore this is the first time this version of the UK model has been run this far back in time. The mid-Pliocene Warm Period, ~3 Ma, is of particular interest because it represents a time period when the Earth was in equilibrium with CO₂ concentrations roughly equivalent to those of today, providing a possible analogue for current and future climate change. The implementation of the Pliocene boundary conditions is firstly described in detail, based on the PRISM4 dataset, including CO₂, ozone, orography, ice mask, lakes, vegetation fractions and vegetation functional types. These were incrementally added into the model, to change from a preindustrial setup to Pliocene conditions. The results of the simulation are then presented, which are firstly compared with the model’s pre-industrial simulation, secondly with previous versions of the same model and with available proxy data, and thirdly with all other models included in PlioMIP2. Firstly, the comparison with preindustrial suggests that the Pliocene simulation is consistent with current understanding and existing work, showing warmer and wetter conditions, and with the greatest warming occurring over high latitude and polar regions. The global mean surface air temperature anomaly at the end of the Pliocene simulation is 5.1 °C, which is the 2^nd highest of all models included in PlioMIP2 and is consistent with the fact that HadGEM3-GC31-LL has one of the highest Effective Climate Sensitivities of all CMIP6 models. Secondly, the comparison with previous generation models and with proxy data suggests a clear increase in global sea surface temperatures as the model has undergone development. Up to a certain level of warming, this results in a better agreement with available proxy data, and the “sweet spot” appears to be the previous CMIP5 generation of the model, HadGEM2-AO. The most recent simulation presented here, however, appears to show poorer agreement with the proxy data compared with HadGEM2, and may be overly sensitive to the Pliocene boundary conditions resulting in a climate that is too warm. Thirdly, the comparison with other models from PlioMIP2 further supports this conclusion, with HadGEM3-GC31-LL being one of the warmest and wettest models in all of PlioMIP2 and, if all the models are ordered according to agreement with proxy data, HadGEM3-GC31-LL ranks approximately halfway among them.

中文翻译：

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HadGEM3模拟上新世中期的暖期：实验设计和模型-模型与模型-数据比较的结果

摘要。在这里，我们介绍了在CMIP6 / PMIP4 / PlioMIP2的主持下，使用最新版的英国物理气候模型HadGEM3-GC31-LL进行的上新世中期模拟的实验设计和结果。尽管最近使用此模型进行了另外两个古气候模拟，但它们都集中在第四纪的较新时期，因此这是该版本的英国模型第一次在如此遥远的时代运行。上新世中期暖期〜3 Ma尤其令人感兴趣，因为它代表了地球与CO ₂处于平衡状态的时间段。浓度大致相当于今天的浓度，为当前和未来的气候变化提供了可能的类似物。首先基于PRISM4数据集（包括CO _2）详细描述上新世边界条件的实现。，臭氧，地形，冰面罩，湖泊，植被分数和植被功能类型。将这些增量添加到模型中，以从工业化前的设置更改为上新世的条件。然后介绍了仿真结果，首先将其与模型的工业仿真进行比较，其次与相同模型的先前版本和可用的代理数据进行比较，其次与PlioMIP2中包含的所有其他模型进行比较。首先，与工业化前的比较表明，上新世模拟与当前的认识和现有工作是一致的，显示出温暖和潮湿的条件，并且在高纬度和极地地区发生的最大变暖。在上新世末期的全球平均地面气温异常为5.1°C，这是^第二次 highest of all models included in PlioMIP2 and is consistent with the fact that HadGEM3-GC31-LL has one of the highest Effective Climate Sensitivities of all CMIP6 models. Secondly, the comparison with previous generation models and with proxy data suggests a clear increase in global sea surface temperatures as the model has undergone development. Up to a certain level of warming, this results in a better agreement with available proxy data, and the “sweet spot” appears to be the previous CMIP5 generation of the model, HadGEM2-AO. The most recent simulation presented here, however, appears to show poorer agreement with the proxy data compared with HadGEM2, and may be overly sensitive to the Pliocene boundary conditions resulting in a climate that is too warm. Thirdly, the comparison with other models from PlioMIP2 further supports this conclusion, with HadGEM3-GC31-LL being one of the warmest and wettest models in all of PlioMIP2 and, if all the models are ordered according to agreement with proxy data, HadGEM3-GC31-LL ranks approximately halfway among them.