The mid-Holocene (6000 years ago) is a standard time period for the evaluation of the simulated response of global climate models using palaeoclimate reconstructions. The latest mid-Holocene simulations are a palaeoclimate entry card for the Palaeoclimate Model Intercomparison Project (PMIP4) component of the current phase of the Coupled Model Intercomparison Project (CMIP6) – hereafter referred to as PMIP4-CMIP6. Here we provide an initial analysis and evaluation of the results of the experiment for the mid-Holocene. We show that state-of-the-art models produce climate changes that are broadly consistent with theory and observations, including increased summer warming of the Northern Hemisphere and associated shifts in tropical rainfall. Many features of the PMIP4-CMIP6 simulations were present in the previous generation (PMIP3-CMIP5) of simulations. The PMIP4-CMIP6 ensemble for the mid-Holocene has a global mean temperature change of −0.3 K, which is −0.2 K cooler than the PMIP3-CMIP5 simulations predominantly as a result of the prescription of realistic greenhouse gas concentrations in PMIP4-CMIP6. Biases in the magnitude and the sign of regional responses identified in PMIP3-CMIP5, such as the amplification of the northern African monsoon, precipitation changes over Europe, and simulated aridity in mid-Eurasia, are still present in the PMIP4-CMIP6 simulations. Despite these issues, PMIP4-CMIP6 and the mid-Holocene provide an opportunity both for quantitative evaluation and derivation of emergent constraints on the hydrological cycle, feedback strength, and potentially climate sensitivity.

中文翻译：

---

PMIP4-CMIP6中全新世模拟的大规模功能和评估

全新世中期（6000年前）是使用古气候重建评估全球气候模型模拟响应的标准时间段。最新的全新世中期模拟是耦合模型比较项目（CMIP6）当前阶段的古气候模型比较项目（PMIP4）组件的古气候入门卡，以下简称PMIP4-CMIP6。在这里，我们提供了对全新世中期实验结果的初步分析和评估。我们表明，最新模型产生的气候变化与理论和观察结果大致一致，包括北半球夏季变暖和热带降雨的相关变化。PMIP4-CMIP6仿真的许多功能都存在于上一代仿真（PMIP3-CMIP5）中。全新世中期的PMIP4-CMIP6系综的全球平均温度变化为-0.3  K， 比PMIP3-CMIP5模拟的温度低-0.2 K，这主要是因为对PMIP4-CMIP6中的实际温室气体浓度进行了规定。PMIP4-CMIP6模拟中仍然存在PMIP3-CMIP5中确定的幅度偏差和区域响应的迹象，例如北非季风的放大，欧洲的降水变化以及欧亚大陆中部的模拟干旱。尽管存在这些问题，PMIP4-CMIP6和全新世中期仍为定量评估和推导对水文循环，反馈强度以及潜在的气候敏感性的新限制提供了机会。